Published: January 2026 | Last updated: June 2026
Disclaimer: All primer seating data referenced in this article follows published manufacturer guidelines. Always seat primers flush to 0.003-0.005 inches below the case head and inspect every primer before chambering. Never exceed published load data.
Primer seating is the step in reloading that most reloaders learn to overlook – and most precision reloaders learn to stop overlooking. A primer seated at 0.003-0.005 inches below flush fires with the full, consistent strike energy the firing pin delivers. A primer seated proud of the case head fires with variable strike energy that changes based on how far the firing pin has to push the primer down before it contacts the anvil. Over 20 rounds at 500 yards, that variation shows up as vertical stringing that no powder charge precision will correct.
The Forster Co-Ax Bench Priming Tool is the bench-mounted priming solution for reloaders who treat primer seating as a critical variable rather than a workflow step to complete as fast as possible. Its defining feature is the E-Z Just universal jaw system – an adjustable three-jaw chuck that holds cases by their rim without requiring shellholders for any caliber. No 223 Remington shellholder, no 308 Winchester shellholder, no 300 Winchester Magnum shellholder – one jaw adjustment covers any case from 9mm Luger through 338 Lapua Magnum within that rim range. The tool was originally developed under the Bonanza brand before Forster acquired the line, and benchrest shooters have used it for decades as the priming tool that provides the tactile feedback no other bench-mounted system matches at this price.
What’s in the Box
The Forster Co-Ax Bench Priming Tool ships with:
- Co-Ax Bench Priming Tool – machined aluminum base, hardened tool steel jaw assembly
- Large primer seating post assembly
- Small primer seating post assembly
- Large primer feed tube (holds 52 primers)
- Small primer feed tube (holds 41 primers)
- Integrated primer flip tray (built into the base)
- Mounting hardware
- Allen keys for jaw adjustment
- Printed instructions
Both primer size assemblies are included. Switching from large to small primers – from Federal GM210M large rifle to CCI BR-4 small rifle, for example – requires swapping the seating post assembly, which takes under two minutes.
What’s not included: shellholders (not needed), and bench mounting hardware beyond what ships with the tool. For users who want to mount the tool to an Inline Fabrication quick-change system, Inline Fabrication makes specific adapter plates for the Forster Co-Ax Bench Priming Tool.
The E-Z Just Universal Jaw System: No Shellholders Required
Traditional bench-mounted priming tools hold cases with shellholders – caliber-specific inserts matched to the case head rim diameter. An RCBS Automatic Bench Priming Tool uses RCBS shellholders. A Lee Auto Bench Priming Tool uses Lee shellholders. For a reloader who loads 9mm Luger, 45 ACP, 38 Special, 357 Magnum, 40 S&W, 308 Winchester, and 30-06 Springfield, those are six or more different shellholders, tracked and swapped with each caliber change. Over years of multi-caliber reloading, this adds up in both cost and workflow interruption.
The Forster Co-Ax Bench Priming Tool eliminates this entirely. The E-Z Just jaw system uses three adjustable steel jaws arranged around a central axis. To configure for a new caliber:
- Loosen the three socket head cap screws in the jaw housing
- Insert a deprimed, resized case from your current caliber into the center of the tool
- Depress the handle slightly to raise the primer seating post into the case primer pocket
- Snug the three jaws around the case head rim – firm enough to hold square, loose enough to allow easy case insertion and removal
- Tighten the three screws to lock the jaw position
That jaw setting now works for any cartridge sharing the same rim diameter. 308 Winchester, 30-06 Springfield, 6.5 Creedmoor, 6.5 PRC, 7mm Remington Magnum, 300 Winchester Magnum – all share a .473-inch rim and use the same jaw setting. The jaw adjustment for 223 Remington covers 22-250 Remington, 243 Winchester, and other calibers on the same .378-inch rim.
For a reloader who loads five or more calibers regularly, eliminating shellholder purchases and tracking has real value. The tool costs more than competitors that require shellholders, but the total cost of ownership across a multi-caliber bench is lower than the tool price suggests when shellholder expenses are removed.
The Sideways Tube: Safety by Design
The Forster Co-Ax Bench Priming Tool’s primer feed tubes are a safety-first design rather than a convenience feature.
Most tube-fed priming systems stack primers vertically – one on top of the next in a vertical column. If a primer detonates in the tube, the energy from that detonation can initiate the next primer in the column, which initiates the next, causing a chain detonation. The Forster’s tubes orient primers sideways – stacked on their sides with a slot running the length of the tube. If a primer fires in the tube, the energy exits through the side slot rather than compressing against the next primer in the column. The chain-fire mechanism requires primer-to-primer face contact under confinement – the sideways slot eliminates both conditions.
In practice, primer detonations in priming tools are rare but not unknown, particularly when using dirty or moisture-damaged primers. The sideways tube means a detonation event is startling rather than dangerous. The large tube holds 52 primers; the small tube holds 41. For a session priming 100-200 cases of 308 Winchester or 6mm Dasher precision loads, the tube holds enough primers to work through the session with 2-4 refills.
The Lever Length: Why Shorter Is More Precise
The Forster Co-Ax Bench Priming Tool’s lever is noticeably shorter than a reloading press handle. This is a deliberate engineering decision that affects the tool’s use case.
Mechanical advantage scales with lever length. A longer lever requires less force to seat a primer but provides less feedback about what’s happening at the seating post. With sufficient mechanical advantage, a reloader can seat a primer well past the bottom of the pocket – crushing the primer pellet – without feeling the resistance that signals over-seating. The Forster’s shorter lever provides lower mechanical advantage intentionally. The operator feels the full primer seating resistance – the moment the primer contacts the bottom of the pocket, the resistance increases noticeably. That tactile signal is the tool’s primary feedback: when you feel the stop, the primer is seated.
For CCI BR-2 large rifle benchrest primers, Federal GM210M for 6.5 Creedmoor and 308 Winchester match loading, CCI BR-4 small rifle for 6mm BR and 6mm Dasher benchrest, and Federal GM205M small rifle match for 223 Remington precision bolt-gun loads – the primers where seating depth consistency matters most for ES reduction – the Forster’s tactile feedback is the feature that precision reloaders cite most often.
Key Specs
| Feature | Specification |
|---|---|
| Design | Bench-mounted, lever-actuated |
| Jaw System | E-Z Just universal three-jaw chuck |
| Primer Feed | Sideways-stacking tubes (large and small included) |
| Large Tube Capacity | 52 primers |
| Small Tube Capacity | 41 primers |
| Materials | Machined aluminum base; hardened tool steel jaws and seating posts |
| Weight | 1.54 lbs (0.7 kg) |
| Seating Depth Target | 0.003-0.005 inches below flush |
| Caliber Range | 25 ACP through large magnum rifle (NOT 50 BMG) |
| MPN | 011521 |
| MSRP | $187 |
| Street Price | $124-143 |
| Warranty | Lifetime limited against defects under normal use |
| Made | USA, Forster Products |
The lifetime limited warranty covers defects in materials and workmanship under normal use. Verify current warranty terms with Forster Products directly.
The 50 BMG limitation is firm: the jaw system is sized for standard rim diameters. 50 BMG cases require specialized heavy-duty priming equipment.
Where the Co-Ax Bench Priming Tool Excels
Precision rifle loading where seating depth consistency matters. For 6.5 Creedmoor and 308 Winchester competition loads, 6mm Dasher and 6mm BR benchrest, 338 Lapua Magnum for long-range hunting – any application where ignition consistency is a tracked variable rather than an assumption. Federal GM210M and CCI BR-2 large rifle match primers consistently seated 0.003-0.005 below flush, case after case through a 100-round batch, produce more uniform ES than the same primers seated at varying depths on an on-press arm or less-refined hand tool.
Multi-caliber benches where shellholder management is the friction point. For a reloader loading 9mm Luger, 45 ACP, 40 S&W, 44 Magnum, 223 Remington, 308 Winchester, and 300 Winchester Magnum – the E-Z Just jaws’ rim-diameter coverage without shellholder purchases and swaps reduces the per-caliber setup work significantly.
Reloaders who experience hand fatigue with hand priming tools. The bench-mounted design transfers lever force to the bench structure rather than the operator’s palm and fingers. At 200+ primer seatings per session, this is a meaningful ergonomic improvement over the RCBS Universal Hand Priming Tool or Frankford Arsenal Perfect Seat Hand Priming Tool for extended sessions.
Complement to the Forster Co-Ax Press. The Forster Co-Ax Press‘s integrated single-feed primer system is precise but slow for volume priming. The Co-Ax Bench Priming Tool handles batch priming efficiently while reserving the press for sizing and bullet seating. The same precision philosophy extends from the press to the dedicated priming station. Forster Bench Rest Die Sets complete the Forster-centric precision workflow.
Revolver and pistol loading where primer consistency affects ES. For 38 Special, 357 Magnum, and 44 Magnum loading where the primer directly affects burn consistency and velocity uniformity, the Co-Ax Bench Priming Tool’s consistent seating depth is a real contribution to tightening ES in precision revolver loading.
Realistic Limitations
Price premium over shellholder-based tools. The street price of $124-143 is significantly more than the Lee Auto Bench Priming Tool and more than the RCBS Automatic Bench Priming Tool. The shellholder cost savings materialize over time and caliber count, not on first purchase.
Jaw adjustment learning curve. The E-Z Just jaw setup is not difficult, but it requires understanding the three-jaw chuck concept. First-time users sometimes under-tighten (case rocks during seating) or over-tighten (difficult to insert and remove cases). Follow the calibration procedure completely.
Slower tube capacity than large-tray systems. The tube holds 41-52 primers and refills in 20-30 seconds with the built-in flip tray. The RCBS Automatic Bench Priming Tool‘s larger primer tray suits higher-volume production runs with fewer loading interruptions. For reloaders priming 500+ rounds per session regularly, the RCBS’s production efficiency is a real advantage.
Not for 50 BMG. The jaw system is sized for standard rim diameters only.
Setup and Operation
Bench mounting: Bolt the Co-Ax Bench Priming Tool securely to the bench surface. The priming force is lower than sizing force but the stable surface ensures consistent case presentation. For portable use, an Inline Fabrication quick-change adapter plate allows the tool to mount and dismount without re-bolting.
Jaw adjustment for your caliber:
- Loosen all three socket head cap screws in the jaw housing
- Insert a deprimed, resized case – deprimed is required so the seating post can rise into the pocket
- Depress the handle slightly to raise the seating post up into the primer pocket
- Snug the three jaws evenly around the case head rim – no play when seated, no binding when removed
- Tighten the three screws firmly
Primer tube loading: Use the integrated flip tray. Place primers on the tray, shake gently with the circular motion the tray assists, and primers orient anvil-up within 20-30 seconds. Slide the oriented primers into the tube. A straightened paper clip holds primers in the tube during transfer to prevent sliding back out through the slot.
Primer size changeover: Swap the seating post assembly. Center the jaws before moving the assembly forward after the swap – this ensures the new post aligns correctly with the case head center. Takes 1-2 minutes.
Which primers seat best: Federal GM210M large rifle match, Federal 210 large rifle standard, CCI 200 large rifle, CCI BR-2 large rifle benchrest for rifle; CCI 300 large pistol, Federal 150 large pistol for pistol. For small primer: Federal GM205M small rifle match, Federal 205 small rifle, CCI 400 small rifle, CCI BR-4 small rifle benchrest, CCI 500 small pistol, CCI No. 41 military small rifle for AR-15. Magnum rifle: CCI 250 large rifle magnum, Winchester WLRM large rifle magnum. Small rifle benchrest: Remington 7-1/2 small rifle bench rest.
Seating depth verification: On the first 5 cases of each session, verify primers are 0.003-0.005 inches below flush with a priming depth gauge. The Forster’s tactile stop makes gross over-seating detectable by feel, but a gauge confirms you’re within the precision tolerance window. See the case prep essentials guide for the systematic pre-loading brass preparation workflow.
Competitors – Four Direct Comparisons
RCBS Automatic Bench Priming Tool
The RCBS Automatic Bench Priming Tool is the direct category competitor at a lower price. It uses RCBS shellholders (separate purchase per caliber), a vertical primer tube, and cast iron and steel construction. The RCBS’s larger primer tray capacity makes high-volume production runs more fluid between refills. The Forster’s advantages: the universal jaw system eliminates shellholder purchases, the sideways tube reduces chain-fire risk, and the shorter lever preserves tactile precision. For a reloader loading one or two calibers at high volume, the RCBS’s production efficiency and lower price are genuine advantages. For a multi-caliber precision reloader, the Forster covers more ground with better tactile feedback.
Choose the Forster Co-Ax if: multi-caliber loading without shellholder management, sideways tube safety, and precision tactile feedback for match loading are priorities. Choose the RCBS Automatic Bench Priming Tool if: one or two calibers at high production volume, lower price, and large tray capacity for fewer refills are the requirements.
Hornady Versa-Prime Bench Priming Tool
The Hornady Versa-Prime Bench Priming Tool uses standard shellholders and a tray-feed system at a mid-range price. The alloy and plastic construction is lighter but less durable than the Forster’s all-metal design for sustained production use. The Hornady Versa-Prime is the natural choice for reloaders in the Hornady ecosystem who already own Hornady shellholders. For a multi-caliber precision reloader building from scratch, the Forster’s no-shellholder design offers better total value over years of use.
Choose the Forster Co-Ax if: all-metal construction, universal jaws, and sideways tube safety are the priorities. Choose the Hornady Versa-Prime if: you already have Hornady shellholders and prefer Hornady’s tray-feed system.
Hand Priming Tools
The RCBS Universal Hand Priming Tool, K-M Primer Deluxe Hand Priming Tool, Hornady Hand Priming Tool, and Lyman E-Zee Prime Universal Hand Priming Tool provide excellent tactile feedback through direct finger contact with the primer during seating. Many precision benchrest reloaders prefer hand priming over bench-mounted tools precisely because the feedback pathway is shorter. The Forster Co-Ax Bench Priming Tool’s argument over hand primers is sustained session ergonomics: 200-300 primers per session without hand fatigue, at comparable precision. For moderate session volumes without fatigue concerns, a quality hand primer delivers equivalent precision at a lower price.
Choose the Forster Co-Ax if: session volumes are high enough that hand fatigue is a real concern, or you prefer bench-mounted operation for workflow reasons. Choose a hand priming tool if: session volumes are moderate, hand fatigue isn’t a concern, and you want maximum direct tactile feedback at a lower price.
Lee Auto Bench Priming Tool and Lyman Bench Primers
The Lee Auto Bench Priming Tool is the budget bench-mounted alternative with Lee’s triangular tray and Lee-specific shellholders. Functional and affordable for reloaders loading one caliber who want bench-mounted priming without the Forster’s investment. The Lyman Accu-Prime Auto Load Bench Priming Tool and Lyman Accu-Prime Manual Bench Priming Tool are the Lyman-ecosystem alternatives in the mid-range budget tier. All three use shellholders and have less refined tactile feedback than the Forster.
Choose the Forster Co-Ax if: build quality for long-term sustained use, universal jaw coverage, and sideways tube safety are the requirements. Choose the Lee or Lyman alternatives if: budget is the priority, one-caliber use is the primary application, and adequate bench-mounted priming at a lower investment level is the right fit.
Comparison Table
| Feature | Forster Co-Ax Bench Priming | RCBS Auto Bench Priming | Hornady Versa-Prime | Lee Auto Bench Priming |
|---|---|---|---|---|
| Case Holding | Universal E-Z Just jaws | RCBS shellholders | Standard shellholders | Lee shellholders |
| Shellholders Required | No | Yes | Yes | Yes |
| Feed System | Sideways tube (41/52 capacity) | Vertical tube | Tray feed | Triangular tray |
| Primer Safety | Sideways slot design | Standard vertical | Standard | Standard |
| Frame Materials | Machined aluminum + steel | Cast iron + steel | Alloy + plastic | Zinc + plastic |
| Lever Feel | Excellent tactile feedback | Good | Moderate | Moderate |
| Caliber Change | Jaw re-set (no shellholder swap) | Shellholder swap | Shellholder swap | Shellholder swap |
| Warranty | Lifetime limited | Lifetime limited | Lifetime limited | Limited lifetime |
| Street Price | $124-143 | $85-100 | $70-85 | $35-45 |
| Best For | Precision multi-caliber | High-volume single/two-caliber | Hornady ecosystem | Budget bench-mounted |
What to Buy with It
Precision match primers. For 308 Winchester competition: Federal GM210M or CCI BR-2. For 6.5 Creedmoor: Federal GM210M or CCI 200. For 223 Remington bolt-gun precision: Federal GM205M or Remington 7-1/2. For 223 Remington AR-15 semi-auto: CCI No. 41. For 338 Lapua Magnum: Federal GM210M or CCI 250 large rifle magnum. For 6mm Dasher and 6mm BR benchrest: CCI BR-4 small rifle benchrest.
Frankford Arsenal Vibra-Prime for faster primer tube loading. The Vibra-Prime orients primers automatically into the correct position for tube loading without the manual flip-tray method. For reloaders priming 200+ cases per session, the Vibra-Prime’s automated orientation reduces tube-loading time significantly.
Forster Co-Ax Press for the complete Forster precision bench. The press’s floating die design achieves 0.001-inch runout on sized and seated cases. The Co-Ax Bench Priming Tool handles batch priming at the same precision standard. Forster Bench Rest Die Sets complete the Forster-centric precision workflow.
RCBS Rock Chucker Supreme as a single-stage companion for reloaders who don’t own the Forster press. The RCBS Rock Chucker Supreme and the Forster Co-Ax Bench Priming Tool are common pairings – Rock Chucker for sizing and seating, Co-Ax Bench Priming Tool for dedicated batch priming. Many Rock Chucker owners add the Forster for consistent depth and no-shellholder convenience across multiple calibers.
Priming depth gauge. Verifies 0.003-0.005 inches below flush during initial setup and when changing brass lots. The Forster’s tactile stop makes gross seating errors detectable by feel; a gauge confirms you’re within the precision tolerance window.
RCBS Universal Hand Priming Tool or Frankford Arsenal Perfect Seat as a backup for low-volume sessions where setting up the bench tool isn’t worth the setup time, or for field use when the Forster isn’t available.
Troubleshooting
Gritty feel during seating. Brass shavings or primer pocket residue accumulate in the jaw housing and seating post channel. Disassemble the jaw housing by removing the three cap screws and clean with a small brush and light solvent. Clean the seating post of brass residue. Reassemble and verify jaw alignment before the next session.
Primers not feeding from the tube. Most primer feed failures trace to oil contamination of the tube interior. Even a trace of case lube on the tube causes primers to stick. Wipe the tube interior with a dry cotton swab. Keep spray case lube away from the priming area. CCI 500 small pistol and CCI 300 large pistol are among the most dimensionally consistent and feed most reliably. For small rifle: CCI 400 and Federal 205.
Primers seating proud. Either the primer is not entering the pocket squarely (jaw not holding the case centered), or the seating post is the wrong size for the primer type. Verify the seating post assembly matches your primer size (small or large). Verify jaw adjustment is snug without play.
Difficulty inserting cases (jaw too tight). Loosen the three cap screws slightly, insert and remove a few cases to find the correct jaw tension, and re-tighten. The correct feel: the case seats with light positive pressure and removes cleanly without requiring force.
Case rocking during seating (jaw too loose). Tighten the jaw screws and re-test. The case must be held square to the seating post axis – any case rocking during the seating stroke produces primers seated at a slight angle.
FAQ
Do I need to buy shellholders for different calibers?
No. The E-Z Just three-jaw chuck adjusts to hold any rim diameter from 25 ACP through large magnum rifle. The same jaw setting covers all cartridges with the same rim diameter – adjusting the jaws when you change rim diameter groups, not for every individual caliber.
How many primers do the tubes hold?
The small primer tube holds 41 primers; the large holds 52. The integrated flip tray makes refilling fast – 20-30 seconds per tube with practice.
Can it handle small-pocket 45 ACP brass?
Yes. Install the small primer seating post assembly and adjust the jaws to the 45 ACP rim diameter. The tool handles small primer pockets in large-caliber cases cleanly.
How does the tactile feedback compare to a hand priming tool?
Hand priming tools like the RCBS Universal Hand Priming Tool and K-M Primer Deluxe provide feedback through direct finger contact – some reloaders find this marginally more sensitive. The Forster’s bench-mounted tactile feedback through the lever is excellent for any bench tool and equivalent to hand priming for most reloaders. The bench-mounted design’s advantage is sustained session operation without hand fatigue over 200-300 primings.
Is it compatible with magnum primers?
Yes. CCI 250 large rifle magnum and Winchester WLRM large rifle magnum seat correctly with the large seating post assembly. The jaw adjustment for 300 Winchester Magnum and 7mm Remington Magnum cases covers these magnum calibers without additional accessories.
Can I mount it to an Inline Fabrication quick-change system?
Yes. Inline Fabrication makes specific adapter plates for the Forster Co-Ax Bench Priming Tool, allowing it to integrate with Inline Fabrication’s quick-change bench mounting system.
What’s the recommended seating depth target?
0.003-0.005 inches below flush with the case head for all applications. A primer seated flush or proud can affect ignition consistency and, in semi-automatic firearms, can cause a slam-fire if the primer protrudes enough to contact the bolt face during chambering.
How does it compare to the RCBS Automatic Bench Priming Tool for a two-caliber bench?
For a two-caliber bench loading 9mm Luger and 308 Winchester, the RCBS Automatic Bench Priming Tool requires two shellholders (one per caliber). The Forster requires one jaw re-adjustment when changing between these rim diameters. Over years of loading these two calibers, the Forster’s no-shellholder approach saves minor time at each caliber change. For a reloader loading more than two or three calibers regularly, the Forster’s advantage is more significant.
Conclusion
The Forster Co-Ax Bench Priming Tool is the bench-mounted priming tool for a reloader who loads multiple calibers, values primer seating depth consistency as a precision variable, and wants sustained session ergonomics. The E-Z Just universal jaw system eliminates shellholder purchases and management across all calibers. The sideways tube design reduces chain-fire risk compared to vertical stacking systems. The shorter lever preserves the tactile feedback that makes each primer seating a confirmed operation rather than an assumed one.
Its limitations are honest: the price premium over shellholder-based tools is significant and only offsets fully for multi-caliber users over time; the jaw adjustment has a learning curve; and the tube capacity means more refills per session than large-tray alternatives at the highest production volumes.
For a precision rifle reloader who treats primer seating as seriously as powder charge weight – loading 6.5 Creedmoor, 308 Winchester, 6mm Dasher, and similar calibers where ignition consistency contributes measurably to ES – the Forster Co-Ax Bench Priming Tool is the tool that the precision community has converged on for good reason.
Choose the Forster Co-Ax Bench Priming Tool if you load multiple calibers requiring different rim diameter settings, value bench-mounted ergonomics for sustained sessions without hand fatigue, want the sideways tube safety design, and treat primer seating depth as a precision variable worth optimizing.
Choose the RCBS Automatic Bench Priming Tool instead if your loading is concentrated in one or two calibers, production volume is high enough that tube refills are a meaningful interruption, and the lower price with RCBS shellholders is the right fit.
Choose the RCBS Universal Hand Priming Tool or K-M Primer Deluxe instead if session volumes are moderate, hand fatigue isn’t a concern, and maximum direct tactile feedback at a lower price is the priority.
Choose the Hornady Versa-Prime instead if you’re in the Hornady ecosystem with existing Hornady shellholders and prefer Hornady’s tray-feed system.
Choose the Lee Auto Bench Priming Tool or Lyman Accu-Prime Manual instead if budget is the priority, one-caliber use is the primary application, and adequate bench-mounted priming at a lower investment level is the right fit.
Editorial note: Originally published January 2026, revised June 2026. The revision expanded all sections from list-format to full prose, added dedicated explanations of the E-Z Just universal jaw system and its practical caliber coverage, the sideways tube safety mechanism, and the deliberately shorter lever’s precision tradeoff. Added hand priming tools as a fourth competitor category. Added a comprehensive primer reference section covering which specific primers work for which calibers. Added full internal linking to approximately 50 destinations including caliber guides, primer pages, competing priming tools, and related equipment articles.
