Published: November 2025 | Last updated: June 2026
Disclaimer: All load data referenced in this article is drawn from published manufacturer sources. Always consult a current reloading manual before developing any load. Start below published minimums and watch for pressure signs.
Every conventional single-stage press – O-frame, C-frame, regardless of brand – works the same fundamental way: a die is threaded into a fixed position in the press head, a shellholder holds the case on the ram, and the ram travels straight up into the die. The quality of the resulting case dimensions depends on how precisely the die and the shellholder are aligned. If the die axis and the ram axis are slightly off, the case neck is sized unevenly. If the shellholder has a few thousandths of slop relative to the die, the case can rock slightly during the seating stroke and produce runout.
The Forster Co-Ax eliminates this problem at the design level. Rather than holding the die rigidly in a fixed position and hoping everything lines up, the Co-Ax uses a coaxial – floating – die mounting. The die is not threaded into a fixed head. Instead, it floats in the press and self-centers on each case as the stroke begins. Dual guide rods ensure the ram travels in a perfectly straight, consistent line. The case and the die find each other rather than depending on machined tolerances to force alignment. The result – regularly measured at 0.001 inch of runout or less by users – is the most concentric resizing and seating of any single-stage press design on the market.
This design places the Co-Ax in a specific category: the precision reloader’s press. If your loading goal is sub-half-MOA accuracy for long-range rifle work, benchrest, PRS competition, or precision hunting, the Co-Ax’s runout performance is a direct contribution to that goal. If you’re loading 9mm Luger for range practice or hunting rounds to standard industry specs, the floating die’s additional precision is real but not practically meaningful. Knowing which side of that line you’re on determines whether the Co-Ax’s premium price is a worthwhile investment or an over-spec purchase.
What’s in the Box
The Forster Co-Ax ships with:
- Forster Co-Ax press with curved link mechanism and S-jaw set (standard)
- Top-mounted priming device with large and small primer arms
- Spent-primer catcher cup
- Cross-bolt die locking ring
- Printed instructions and parts list
What’s not included: bench mounting hardware, dies, shellholders (the Co-Ax uses jaws instead), or case lube. The S-jaw set included covers the majority of rifle and pistol calibers in common use. For very large case heads – 338 Lapua Magnum, .378 Weatherby Magnum class – an LS (large shell) jaw set is required as a separate purchase. For very small case heads – 22 Hornet, .17 Hornet, .221 Fireball – a BS (small shell) jaw set is needed. Budget for the appropriate jaw size for your primary calibers before ordering.
The cross-bolt die locking ring is unique to the Co-Ax design and deserves a specific mention. Standard reloading dies use a lock ring that threads down against the press head to fix the die position. The Co-Ax’s cross-bolt system uses a horizontal bolt that clamps through the die body to lock it. This means dies can be removed and replaced consistently without the slipping or shifting that standard lock rings sometimes allow. Dies with the cross-bolt ring can also be swapped very quickly, since you’re releasing a bolt rather than threading a ring down. The cross-bolt rings work with standard-thread dies from any manufacturer – you’re not buying Co-Ax-specific dies.
The Coaxial Design: What It Actually Does
Understanding the floating die mechanism is worth spending time on, because it’s the feature that justifies the Co-Ax’s position in the market.
In a traditional single-stage press, the die is threaded into the press head and locked in position. The ram carries the shellholder and case up into the die. For the case to be sized or seated concentrically, the die axis and the ram axis must be perfectly aligned. In practice, they’re close but not perfect – there’s always some minor misalignment from manufacturing tolerances. The case, held rigidly in the shellholder, is sized according to the die’s position rather than its own axis. If the die is even a few thousandths off-center, every case sized in that die comes out with that same offset – and the sized case has runout relative to its own axis.
The Co-Ax’s floating mechanism allows the die to move laterally by a small amount within the press head. When the case enters the die on the upstroke, the die’s self-centering forces – the chamfered die mouth and the case body contact – push the die to align with the case rather than the case being forced to align with the die. The result is that each case is sized or seated along its own axis rather than the press’s mechanical axis. The dual guide rods keep the ram traveling in a perfectly consistent straight line during this process, so the die’s floating is a controlled, repeatable self-centering rather than random movement.
The practical consequence – 0.001 inch of runout or less on sized and seated cases – is meaningful for precision rifle loading because runout is a direct variable in bullet flight. A case with 0.005 inch of neck runout presents the bullet at a slight angle to the bore when chambered, which is one of several variables that widen groups. Eliminating that variable contributes to ES reduction alongside case weight sorting, primer consistency, and powder charge uniformity. The Co-Ax addresses the press-related portion of the runout budget more thoroughly than any traditional fixed-die design.
The Snap-In Jaw System
Traditional single-stage presses use shellholders to position the case on the ram. Each shellholder is machined to fit a specific case head dimension, and the case head rim fits into a groove in the shellholder. This works reliably and universally, but adds the shellholder’s own tolerance to the case positioning stack.
The Co-Ax replaces shellholders with spring-loaded jaws that grip the case head directly. The jaws snap in and out of the press head without tools – press them in until they click, and they’re locked. Remove them by squeezing the release and pulling. A full jaw change for a different case head size takes about 15 seconds.
The jaw system removes the shellholder-to-case-head tolerance from the positioning equation, which is one more variable eliminated in the pursuit of consistent case positioning. Practically, it also means you don’t need to buy and track shellholders for every caliber – the S-jaw set covers most calibers in the standard size range.
Three jaw sets cover the full caliber range:
- S jaws (standard) – included. Covers 9mm Luger, 45 ACP, 223 Remington, 308 Winchester, 6.5 Creedmoor, 30-06 Springfield, 6mm BR, 6mm Dasher, 270 Winchester, and the majority of standard rifle and pistol calibers.
- LS jaws (large shell) – separate purchase. Required for 338 Lapua Magnum, 300 Winchester Magnum, 7mm Remington Magnum, and other large rebated or belted magnum case heads.
- BS jaws (small shell) – separate purchase. Required for 22 Hornet, .17 Hornet, .221 Fireball, and similar small-base cases.
The Top-Mounted Priming System
The Co-Ax’s priming system is mounted at the top of the press – above the die head rather than at the side of the ram as most presses design it. This is another feature unique to Forster’s design, and it produces a different priming experience than conventional on-press priming.
Top-mounted priming seats the primer from above, traveling straight down into the primer pocket as the ram holds the case stationary at the top of its travel. The travel path is directly in line with the ram’s vertical movement. Conventional on-press priming typically has the primer approach the pocket from a slight angle or from a lever arm at the side, which can introduce lateral force on the primer cup during seating. The Co-Ax’s top-mounted design eliminates that lateral force and produces straight, consistent seating depth.
The tactile feedback through the top-mounted device is generally rated as better than on-press side-arm primer feeds – you’re feeling the primer seat directly through the priming arm’s travel rather than through a linkage that transmits the force indirectly. Some reloaders, particularly for benchrest and long-range precision loading, still prefer a dedicated hand tool like the RCBS Universal Hand Priming Tool or the Forster Co-Ax Bench Priming Tool for volume priming. For a reloader doing 50-100 precision rifle cases in a session, the Co-Ax’s integrated top-priming system handles the task without needing a separate tool.
Key Specs and Compatibility
| Feature | Specification |
|---|---|
| Frame Material | Cast alloy, red powder coat |
| Design | Coaxial floating die with dual guide rods |
| Guide Rods | Dual floating steel rods |
| Case Holding | Snap-in jaw system (no shellholders) |
| Jaw Sets | S (included), LS (separate), BS (separate) |
| Die Thread | Standard 7/8-14 |
| Die Locking | Cross-bolt locking ring |
| Priming | Top-mounted device, large and small arms |
| Stroke | Handles cases up to 3.5 inches |
| Mechanical Advantage | 3x |
| Caliber Range | 17 Hornet to 338 Lapua |
| Spent Primer | Bottom catcher cup |
| Mounting | Three-hole base |
| Runout | 0.001 inch or less (documented by users) |
| Warranty | Limited lifetime against defects |
| Origin | Forster Products, USA |
The 3.5-inch case handling capacity covers every standard rifle and pistol caliber without length constraints, including 338 Lapua Magnum and 300 Winchester Magnum with the LS jaw set. The 3x mechanical advantage makes heavy sizing of large-capacity magnum cases – which require significant force on cold or work-hardened brass – manageable without excessive operator effort.
The cast alloy frame is lighter than a heavy cast-iron O-frame, which suits the Co-Ax’s compact physical footprint. The dual guide rods carry more of the alignment burden than the frame mass itself, which is the correct engineering tradeoff for a press designed around the coaxial floating mechanism rather than brute structural weight.
Where the Co-Ax Excels
Precision rifle loading for long-range and competition. The 0.001-inch runout target is achievable on 308 Winchester with Hodgdon Varget or IMR 4064, 6.5 Creedmoor with Hodgdon H4350, and 6.5 PRC with Alliant Reloder 26 at a consistency level that conventional presses with their fixed-die tolerance stacks cannot match. For PRS competitors, F-class and F-Open shooters, and hunters building loads for cartridges at ranges where ES drives group size, the Co-Ax’s floating die system directly addresses the press-related contribution to runout.
Benchrest cartridges. 6mm BR, 6mm PPC, and 6mm Dasher loading at the precision end of the benchrest community uses the Co-Ax paired with Forster Bench Rest Die Sets and Forster Bushing Bump Die Kits – Forster’s own die line designed around the Co-Ax’s design philosophy. These die sets are optimized to work with the floating die mechanism and produce the tightest possible case neck concentricity for benchrest applications. The Forster Ultra Micrometer Seater Bushing Full Length Sizer Die Set is the flagship die combination for this workflow.
Large magnum rifle resizing. 338 Lapua Magnum and 300 Winchester Magnum cases are large, the brass is thick, and full-length sizing requires significant force – particularly on once-fired brass that hasn’t yet been annealed. The Co-Ax’s 3x mechanical advantage and the floating die design together make this work manageable and accurate. For 338 Lapua with Vihtavuori N160 or Hodgdon H1000 hunting loads, the Co-Ax produces sized cases with consistent neck tension case after case.
Multi-caliber bench setups with quick jaw changes. The jaw snap-in system makes the Co-Ax practical for a reloader who loads multiple precision calibers and values caliber-change speed at the press. A jaw swap for 223 Remington to 308 Winchester takes 15 seconds. Adding the cross-bolt die quick-release, the full press reconfiguration for a new caliber is the fastest available on any single-stage press without a bushing-based die system.
Case forming and wildcat loading. The floating die’s self-centering behavior is particularly valuable when forming cases – pushing brass from one case head into a different die configuration where the case dimensions don’t yet match the die precisely. The Co-Ax’s floating mechanism accommodates the case-die interaction more forgivingly than a fixed-die press, producing more consistent formed cases. For the 6mm Dasher case forming workflow covered in the how to form Dasher brass guide, the Co-Ax is one of the preferred press choices.
Realistic Limitations
Premium price for precision features. The Co-Ax costs more than the RCBS Rock Chucker Supreme and competes in price with the Redding Big Boss II. For a reloader whose accuracy goals are met by a conventional press – which describes most hunters, casual competitors, and beginning reloaders – the Co-Ax’s runout advantage over those alternatives doesn’t translate into measurable improvement in field performance. The floating die’s precision benefit is real but matters primarily at extreme ranges and benchrest distances where 0.001-inch runout differences contribute to measurable group size differences.
No on-press powder measure option. The Co-Ax does not accommodate a powder measure mounted to the press head in the conventional way. Powder charging is done as a separate step – with a standalone measure like the Forster Bench Rest Powder Measure on a separate stand, or an automated dispenser like the RCBS Chargemaster Supreme or Frankford Arsenal Intellidropper 2.0. For a precision reloader, this is actually the preferred workflow – charging is a separate, verified step rather than integrated into the production cycle – but it does mean the bench setup requires more space and more equipment.
Single-stage throughput. This is inherent to the design category, not the Co-Ax specifically. The floating die mechanism and the top-mounted priming system are precision-first features, not production-speed features. Loading 9mm Luger or 45 ACP in volume on this press is technically possible but not the application it’s designed for. The Dillon RL 550C or Dillon XL 750 are the right tools for high-volume pistol production.
Die compatibility caveats. The Co-Ax works with standard 7/8-14 dies, but the floating die mechanism requires the die’s exterior to be able to move laterally within the press head. Dies with unusually large or irregular exterior geometry can interact with the Co-Ax’s floating mechanism differently than expected. Forster’s own die line is optimized for the Co-Ax; standard dies from RCBS, Redding, Hornady, and Lyman work well. Dies with very large-diameter lock rings or non-standard exterior configurations may need individual verification.
Setup and Mounting
Bench requirements. 2-inch or thicker hardwood, Grade 8 bolts through all three base holes with large washers. While the Co-Ax’s cast alloy frame is lighter than heavy iron presses, the three-hole base needs a solid mount for the dual guide rods to deliver their alignment benefit – a press that rocks or shifts during the stroke introduces variability that the floating die mechanism was designed to eliminate.
Jaw installation. Snap the S-jaw set into the press head until the click confirms seating. Test the release by squeezing the jaw release before installing a case – a jaw that’s not fully seated can release during a stroke, which drops the case. If you’re changing to LS or BS jaws for a different caliber class, swap before mounting the die. The jaw and die change together should take under a minute.
Die setup with cross-bolt ring. Install the cross-bolt ring on the die body at the correct position for your operation – the ring position sets the die’s height in the press. Use the how to tune a sizing die guide as the reference for full-length sizing die setup, including confirming proper shoulder bump before running a batch. For seating, use the seating die tuning guide and verify OAL on 3-5 test cases before running production. The cross-bolt ring holds position reliably when tightened correctly – check it after the first 10 cases on a new setup.
Floating die verification. After installing a new die, cycle an empty case through the press and feel whether the die centers on the case smoothly or hangs up. A die that doesn’t float freely may have a cross-bolt ring that’s binding against the press head. Verify the ring is correctly positioned and not creating friction against the Co-Ax’s die guide surface.
Guide rod lubrication. Light oil on the guide rods at the start of each session. The dual guide rods are the mechanical foundation of the consistent ram travel – keeping them clean and lightly lubed ensures smooth operation and prevents the binding that would affect the floating die’s self-centering behavior. Wipe down after each session to prevent powder residue from building up in the rod channels.
Priming device setup. Install the appropriate primer arm – large for Federal 210, Federal GM210M, CCI 200, CCI BR-2 large rifle primers; small for Federal 205, CCI 400, CCI BR-4, Remington 7-1/2 small rifle primers. Verify the primer depth adjustment seats primers 0.003-0.005 inch below flush on the first 5 cases before running the batch. The top-mounted design gives clear visual and tactile confirmation of each primer seating without the awkward viewing angle that side-arm systems require.
Case lube. 223 Remington, 308 Winchester, 338 Lapua Magnum, and all bottleneck rifle cases require case lube before full-length sizing. The floating die’s self-centering benefit depends on the case entering the die smoothly – a dry case in a tight die can bind before the die has a chance to center, reducing the floating mechanism’s effectiveness and risking a stuck case. Apply lube evenly to the case body and neck. The case prep essentials guide covers the systematic case preparation workflow that complements precision press work.
Competitors – Four Direct Comparisons
RCBS Rock Chucker Supreme
The RCBS Rock Chucker Supreme is the most common alternative evaluation for a reloader considering the Co-Ax. The Rock Chucker is a cast-iron O-frame press with a proven decades-long track record, excellent priming feel, robust construction, and RCBS’s lifetime warranty at a notably lower price than the Co-Ax. What it cannot do is match the Co-Ax’s runout performance – the Rock Chucker uses conventional fixed-die mounting with standard shellholders, so runout is determined by machining tolerance alignment rather than by the case-centering mechanism. For most reloading applications – hunting ammo, competition loading where 0.003-inch runout is acceptable, batch production of rifle ammunition to hunting specs – the Rock Chucker delivers excellent results. For benchrest and extreme precision work where 0.001-inch runout is a goal rather than a ceiling, the Co-Ax’s floating die design provides a measurable advantage.
Choose the Co-Ax if: runout below 0.001 inch is a genuine accuracy goal for your application, and the premium price is justified by that precision requirement. Choose the Rock Chucker Supreme if: conventional fixed-die precision is adequate for your accuracy goals, the lower price is meaningful, and RCBS’s proven service ecosystem is preferred.
Redding Big Boss II
The Redding Big Boss II is machined steel construction with the tightest tolerances of any conventional O-frame press, designed for match-grade and benchrest loading. It competes with the Co-Ax in price and in precision intent. The Big Boss II delivers exceptional results through precision machining of conventional geometry – tight shellholder fit, minimal ram slop, and a seating die contact area that produces consistent bullet seating depth. The Co-Ax achieves its runout advantage through a fundamentally different mechanism – the floating die design rather than the tolerance-stacking approach of even the best machined fixed-die presses. Which approach produces better runout in practice depends on the specific caliber, die quality, and brass being used. In head-to-head testing by precision reloaders, the Co-Ax’s 0.001-inch average is typically slightly better than the Big Boss II’s 0.002-inch average on the same caliber. The Big Boss II’s steel construction is heavier and more mass-stable than the Co-Ax’s cast alloy. For a benchrest reloader committed to the Redding die ecosystem, the Big Boss II is a natural press choice. For a reloader who wants the best achievable runout from a single-stage press design, the Co-Ax’s floating mechanism is the stronger engineering argument.
Choose the Co-Ax if: minimizing runout through the floating die mechanism is the priority, or you’re building a Forster-centric bench around the Forster Bench Rest Die Sets and the Co-Ax’s integrated design philosophy. Choose the Big Boss II if: you’re committed to the Redding die ecosystem, prefer machined steel construction, and the Big Boss II’s tolerance-stacking approach to precision meets your runout targets.
Redding Ultramag
The Redding Ultramag is Redding’s heavy-duty O-frame single-stage press designed specifically for large-capacity magnum cases where maximum frame rigidity under heavy sizing loads is the priority. The Ultramag’s massive frame and extended linkage handle 338 Lapua Magnum, .50 BMG, and extreme wildcat forming with a mechanical advantage that makes the heaviest sizing tasks feel manageable. It doesn’t attempt the Co-Ax’s runout minimization – it uses conventional shellholder-and-fixed-die geometry. The comparison is relevant for reloaders specifically loading large magnums: if runout precision at the Co-Ax level is the goal, the Co-Ax with LS jaws handles 338 Lapua Magnum and 300 Winchester Magnum well. If maximum mechanical leverage for the most extreme case forming operations is the priority, the Ultramag is the tool.
Choose the Co-Ax if: precision runout management in magnum calibers is the goal, and the cases involved are within the Co-Ax’s LS-jaw caliber range. Choose the Redding Ultramag if: maximum mechanical advantage for the heaviest possible case forming tasks – extreme magnums, .50 BMG, wildcat forming – is the application, and runout precision is secondary to forming force.
Lee Classic Cast
The Lee Classic Cast represents the value alternative – cast-iron O-frame strength, the longest stroke in class, a fully adjustable handle, and 50 BMG capability at a fraction of the Co-Ax’s price. The Classic Cast’s cast-iron construction resists frame flex under heavy loads better than the Co-Ax’s cast alloy. What it doesn’t offer is the coaxial floating die alignment, the snap-in jaw system, or the top-mounted priming. For a budget-conscious reloader who loads heavy magnums and needs frame rigidity above all else, the Classic Cast is the right tool at the right price. For a precision reloader who loads precision rifle calibers and wants the Co-Ax’s runout performance, the Classic Cast’s lower price doesn’t deliver the same dimensional consistency.
Choose the Co-Ax if: precision runout minimization is the core requirement and the Classic Cast’s conventional fixed-die geometry isn’t the right tool for the accuracy goal. Choose the Lee Classic Cast if: heavy-duty frame rigidity for magnum sizing, the longest stroke in class, and maximum value at the budget price point are the priorities over precision runout management.
Comparison Table
| Feature | Forster Co-Ax | RCBS Rock Chucker Supreme | Redding Big Boss II | Redding Ultramag | Lee Classic Cast |
|---|---|---|---|---|---|
| Frame Type | Floating die, cast alloy | O-frame, cast iron | O-frame, machined steel | O-frame, cast iron | O-frame, cast iron |
| Alignment Method | Coaxial floating die | Fixed die, shellholder | Fixed die, shellholder | Fixed die, shellholder | Fixed die, shellholder |
| Case Holding | Snap-in jaws | Standard shellholders | Standard shellholders | Standard shellholders | Standard shellholders |
| Typical Runout | 0.001 in. or less | 0.002-0.004 in. | 0.002-0.003 in. | 0.003-0.005 in. | 0.003-0.005 in. |
| Priming | Top-mounted device | On-press arm | On-press arm | On-press arm | On-press arm |
| Stroke | 3.5 in. | 3.75 in. | 4 in. | 4.5 in. | 4 in. |
| Max Caliber | 338 Lapua (LS jaws) | 50 BMG capable | 50 BMG capable | 50 BMG+ | 50 BMG |
| Die System | Cross-bolt + 7/8-14 | Standard 7/8-14 | Standard 7/8-14 | Standard 7/8-14 | Breech Lock + 7/8-14 |
| Best Die Match | Forster dies | RCBS dies | Redding dies | Redding dies | Lee Breech Lock |
| Price Range | $$$ | $$ | $$$ | $$$ | $ |
| Best For | Precision/benchrest | General precision | Match grade | Extreme forming | Heavy-duty, value |
Real-World Use Notes
The precision reloading community’s experience with the Co-Ax consistently confirms the runout figures. 6mm Dasher and 6mm BR reloaders – calibers where the entire case is optimized for minimum variation – regularly report 0.001-inch or less runout on Berger VLD Hunting and Berger Hybrid Target bullets seated in Forster-resized cases, using match primers like CCI BR-4 small rifle or Federal GM205M and top-quality powders like Hodgdon H4350 or Alliant Reloder 17.
For 308 Winchester long-range competition loading with Lapua Scenar or Sierra MatchKing bullets and Hodgdon Varget or IMR 4064, the Co-Ax consistently produces the runout numbers that underpin the precision loading process. Combined with case weight sorting, primer uniformity using Federal GM210M or CCI BR-2 large rifle match primers, and charge weight verification on an automated dispenser, the Co-Ax’s press-related contribution to ES is minimized to the point where other variables dominate.
One note on the Co-Ax’s top-mounted priming system that doesn’t always appear in reviews: the primer arm selection (large vs. small) matters not just for primer size but for primer height in the arm. A primer that doesn’t sit properly in the arm can be presented at a slight angle to the pocket, defeating the top-mounting advantage. Verify each arm seats your specific primer brand correctly before committing to a batch. CCI and Federal primers are well-dimensioned and seat consistently in both arms. Some overseas manufacturers’ primers have cup diameter variation that requires arm position verification.
Troubleshooting
Die not floating freely in the press head. The most common cause is a cross-bolt ring that’s too tight against the press head’s die guide surface, or foreign material in the guide channel. Back off the cross-bolt ring slightly and check the channel for debris. The die should be able to move laterally by a small amount when no case is present – that’s the floating mechanism working as intended.
Cases coming out with more runout than expected. First verify the jaw set is correct for your case head size – a case that’s slightly loose in the jaws because you’re using S jaws on a case head that should use LS jaws will rock during the stroke. Second, check that the die is actually floating – a die that’s been inadvertently locked against the guide surface (from a cross-bolt ring position issue) won’t center on the case. Third, verify the guide rods are clean and lightly lubed – binding guide rods introduce ram travel deviation that the floating die can’t compensate for.
Primer arm presenting primer at an angle. Check that the primer is fully seated in the arm’s holder before seating stroke. A primer that’s tilted in the arm seats tilted in the pocket. Also verify the arm is the correct size – using a large arm for a small primer allows the primer to move within the arm holder before contact with the pocket.
Stuck case in the die. Even with the floating die design, a stuck case from insufficient lube or an oversized case requires extraction. The Co-Ax doesn’t have the same geometry as conventional presses for stuck-case removal tools. Contact Forster directly for the correct procedure for the Co-Ax’s specific floating die design before attempting any extraction that might damage the mechanism.
Jaw not releasing cleanly. Check for primer compound or brass shavings fouling the jaw release mechanism. Clean with solvent and a small brush. The spring-loaded jaw release should click cleanly both in and out – a jaw that requires force to release indicates debris fouling or worn spring tension.
What to Buy with It
LS or BS jaws for additional calibers. If you load 338 Lapua Magnum, 300 Winchester Magnum, or 7mm Remington Magnum class calibers, order the LS jaw set before the press arrives. If you load 22 Hornet or sub-standard case head calibers, order the BS jaws.
Forster die sets. The Forster Bench Rest Die Sets and Forster Bushing Bump Die Kits are engineered to work with the Co-Ax’s floating die design and cross-bolt ring system. The Forster Ultra Micrometer Seater Bushing Full Length Sizer Die Set is the precision rifle die set that takes full advantage of the Co-Ax’s design for benchrest-level work. Standard dies from Redding Deluxe Rifle Die Sets and RCBS Competition Die Sets are also compatible.
Powder charging equipment. Since no powder measure mounts to the Co-Ax, a standalone precision dispenser is the appropriate pairing. The RCBS Chargemaster Supreme or Frankford Arsenal Intellidropper 2.0 dispenses charges automatically. The Forster Bench Rest Powder Measure is the standalone mechanical measure from the same manufacturer.
Concentricity gauge. The Co-Ax’s 0.001-inch runout capability is only useful if you’re measuring it. A runout gauge verifies that the floating die is delivering its design benefit on your specific caliber and die combination, and identifies any setup issues before they affect the whole batch.
Match primers. For 6.5 Creedmoor and 308 Winchester precision loading, Federal GM210M large rifle match primers, CCI BR-2 for large rifle, Federal GM205M for small rifle applications, and CCI BR-4 for small rifle benchrest calibers are the natural companion primers. The top-mounted priming system seats them straight and consistently.
Digital scale and calipers. The RCBS Rangemaster 2000 for charge verification. Digital calipers for OAL and case length measurement. A micrometer for case head thickness measurement if you’re doing comprehensive brass sorting for precision work.
FAQ
Is the Forster Co-Ax worth the price over the RCBS Rock Chucker Supreme? For precision rifle loading where runout is a tracked variable – 6mm BR, 6mm Dasher, 308 Winchester at 600+ yards, 338 Lapua for long-range hunting – yes. The Co-Ax’s 0.001-inch runout versus the Rock Chucker’s 0.003-0.004 inch typical runout is a real difference at extreme ranges where every variable contributes to group size. For hunting ammo at 300 yards or competition at standard distances where runout below 0.003 inch doesn’t produce measurable group improvement, the Rock Chucker delivers excellent results at a lower price.
Can I use my existing standard 7/8-14 dies in the Co-Ax? Yes, with cross-bolt rings in place of your existing lock rings. The Co-Ax’s cross-bolt system works with any standard 7/8-14 die body. Forster sells cross-bolt rings separately for use with non-Forster dies. The floating die mechanism works with dies from RCBS, Redding, Hornady, Lee, and all other standard 7/8-14 manufacturers – you’re not locked into Forster dies, though Forster’s die line is optimized for this press.
Does the Co-Ax work for pistol calibers? Yes, the S-jaw set handles 9mm Luger, 45 ACP, 38 Special, 357 Magnum, and comparable pistol cases without additional jaw purchases. The floating die’s runout improvement is less practically significant for pistol calibers where tolerances are broader, but the snap-in jaw convenience and top-mounted priming work for pistol loading as well. That said, loading 200 rounds of 9mm Luger on a single-stage press at single-stage speed is the wrong application for an instrument of this precision level – a progressive press handles that work better.
What’s the correct jaw size for 338 Lapua Magnum? 338 Lapua Magnum requires the LS (large shell) jaw set, sold separately. The S-jaw included with the press does not accommodate the .588-inch case head diameter of the 338 Lapua. Order the LS jaws before your first session with this caliber.
How does the top-mounted priming compare to a dedicated hand priming tool? The top-mounted priming device is better than conventional on-press side-arm priming for tactile feedback and seating consistency. It’s comparable to quality hand priming tools for most reloaders. Benchrest competitors and extreme precision reloaders sometimes prefer the RCBS Universal Hand Priming Tool for volume precision priming because they’ve developed specific feel reference for that tool. For the typical precision reloader using the Co-Ax, the integrated top-priming is the correct solution – adding a hand tool is optional, not required.
Does the floating die help with case forming? Yes, significantly. Case forming involves pushing brass into a die that it doesn’t yet conform to – the case walls are being reshaped rather than just springing back from a sizing operation. The floating die’s self-centering is more forgiving during this forming process than a fixed die, because the case can shift slightly during the stroke without binding. The how to form Dasher brass guide specifically mentions the Co-Ax as a preferred press for this reason.
Conclusion
The Forster Co-Ax earns its position as the precision reloader’s single-stage press by addressing runout at the design level rather than through tight-tolerance conventional geometry. The coaxial floating die mechanism, the snap-in jaw system, the top-mounted priming device, and the cross-bolt die locking ring are all engineering decisions that serve the same goal: eliminating every preventable source of dimensional inconsistency in the loading process. The result – 0.001-inch runout or less – is the best achievable from a single-stage press design.
That precision capability is worth its price premium for a specific reloading application: precision rifle loading for benchrest, long-range competition, PRS, or hunting at distances where ES and runout are measurable contributors to group size. For a reloader loading 6mm BR or 6mm Dasher for benchrest, 308 Winchester or 6.5 Creedmoor for PRS competition, or 338 Lapua Magnum for long-range hunting where each round is built to the same standard, the Co-Ax is the press that the application justifies.
For a reloader loading hunting ammunition to standard accuracy specs, or pistol ammunition for practice, the Co-Ax’s precision is genuine but exceeds what the application demands. The RCBS Rock Chucker Supreme or Lee Classic Cast delivers excellent results for those applications at a lower price.
Choose the Forster Co-Ax if you load precision rifle calibers for benchrest, long-range competition, or demanding hunting applications where 0.001-inch runout is a meaningful accuracy variable, and you want the best achievable press-related dimensional consistency available from a single-stage design.
Choose the RCBS Rock Chucker Supreme instead if conventional O-frame precision meets your accuracy goals, the lower price is meaningful, and RCBS’s proven service ecosystem is preferred over the Co-Ax’s premium precision approach.
Choose the Redding Big Boss II instead if machined steel construction and Redding’s tolerance-stacking approach to precision meet your runout targets, and you prefer the Redding die ecosystem for your precision loading.
Choose the Lee Classic Cast instead if heavy-duty magnum capability, the longest stroke available, and cast-iron O-frame strength are the priorities at a significantly lower price point than the Co-Ax.
Editorial note: Originally published November 2025, revised June 2026. The revision expanded all sections from list-format to full prose, added dedicated explanations of the coaxial floating die mechanism and how it differs mechanically from conventional fixed-die presses, explained the snap-in jaw system in practical terms including all three jaw sizes and their appropriate caliber ranges, expanded the top-mounted priming section with the mechanical rationale for straight seating, rewrote the competitor comparisons with four head-to-head analyses and specific “Choose X if” guidance, and added full internal linking throughout including powder pages, primer pages, caliber guides, Forster die sets, and related equipment.
