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Bolt Carrier Group Parts
Bolts, pins and kits for a carrier group you already own. Every cam pin we sell carries the SOT arrow index mark — the arrow point faces toward the bolt face.
// What these are for
Most of these exist because a part broke, went missing, or went back in the wrong way round.
A bolt is the part asked to do the most and given the least room to do it in. A firing pin stops the rifle completely when it fails. A retaining pin lives on the workshop floor. And a cam pin — small, dark and symmetrical to the eye — goes back in whichever way it happened to be facing, which quietly passes wear into the bolt.
So the parts on this page do two things. The HMB™ bolts answer the geometry: the pass-through cam pin hole becomes a socket run with a radiused cam pin, retaining material where a drill removes it. Everything else answers the human problem — having the right spare, and being able to tell at a glance that it went back in correctly.
01 Bolt face first
Mil-spec .378 covers 5.56, 6mm MAX, .300 BLK and .350 Legend. 6mm ARC is a 6.5 Grendel-derived case head and is a different part entirely.
02 Then the finish
Hard chrome is slicker and wipes carbon off easiest. Black nitride is a conversion rather than a plating, with nothing to chip at an edge.
03 The mark is the point
A witness mark says “as it was last time”. An arrowhead states a direction, so a pin with unknown history can still be checked against a rule.
// Bolts
Four HMB™ · one standard geometry
Four carry the HMB™ cam pin socket, licensed from HM Defense. The fifth is standard geometry — a bored cam pin hole, as the platform has had since the 1950s — and ships with our marked cam pin and a firing pin. All five run in any mil-spec bolt carrier.
HM Defense · 6mm ARC
HMB™ Bolt — 6mm ARC, Black Nitride
Cam pin socket in place of a pass-through hole, so material is retained where a drill removes it. The 6.5 Grendel-derived bolt face.
- 6.5 Grendel derived face
- Black nitride
- SOT cam pin included
$109.00BLT-HMB-6ARC-NIT
General-duty pick
HM Defense · 5.56 / 6mm MAX
HMB™ Bolt — 5.56 / 6mm MAX, Black Nitride
The general-duty pick. A surface conversion rather than a plating, so there is no coating to chip at an edge.
- Mil-spec .378 face
- Black nitride
- SOT cam pin included
$135.00BLT-HMB-556-NIT
HM Defense · 5.56 / 6mm MAX
HMB™ Bolt — 5.56 / 6mm MAX, Hard Chrome
Chromed after heat treatment, so the finish sits on a fully hardened bolt. The easier one to wipe carbon off.
- Mil-spec .378 face
- Hard chrome
- SOT cam pin included
$159.00BLT-HMB-556-CHR
HM Defense · 6mm ARC
HMB™ Bolt — 6mm ARC, Hard Chrome
The 6mm ARC bolt in hard chrome — the pick for high round counts and suppressed use.
- 6.5 Grendel derived face
- Hard chrome
- SOT cam pin included
$159.00BLT-HMB-6ARC-CHR
Standard geometry
Microbest · 5.56
SOT Enhanced Chrome Bolt
Standard geometry — the cam pin passes through a bored hole. C158, shot peened, HPT and MPI, and it ships with the SOT arrow-indexed cam pin and a firing pin.
- C158, HPT & MPI
- Cam pin & firing pin included
$89.00BLT-MBEST-C158-CHR-E
Want it finished?
Complete bolt carrier groups
Eight complete groups, grouped by bolt geometry — including the SOT Enhanced HMB™ 5.56 group with both SOT marks.
// Pins and kits
Four items
The small parts, and the two kits that bundle them. The kit is $5 more than the cam pin alone and adds a firing pin and a retaining pin — for most people that is the sensible buy. The standalone pin is there for anyone who only needs the pin.
Small parts
AR15 Firing Pin, Chrome Plated
8740 steel, machined to the mil-spec print, precision ground and chrome plated. Buy the spare before you need it.
- 8740 steel
- Mil-spec print
$7.50FPN-SOT-CHR
SOT arrow index
Small parts
SOT Nitride Arrow Index Marked Cam Pin
The mark states a direction rather than only a memory: the arrow point faces toward the bolt face, checkable with the bolt out of the rifle.
- Salt bath nitride
- SOT arrowhead
$20.00CAM-SOT-NIT
The sensible buy
Kit
Carrier Completion Kit — Full Chrome Cam Pin
Firing pin, retaining pin and a full chrome cam pin carrying the SOT arrow index mark. Five dollars more than the cam pin alone.
- Three parts
- Full chrome cam pin
$25.00KIT-SOT-CCK-CHR
The sensible buy
Kit
Carrier Completion Kit — Nitride Cam Pin
The same three parts with a black nitride cam pin — the finish that matches a nitride or phosphate carrier group.
- Three parts
- Nitride cam pin
$25.00KIT-SOT-CCK-NIT
Not sure?
Compare every part side by side
Bolt face, cam pin geometry, finish and price in one table — read the bolt face column first.
// Compare
Side by side
Read the bolt face column first on the bolts. It is not a preference — get it wrong and the part will not work, and no finish or geometry makes up for it.
Bolts
| Bolt | Bolt face | Cam pin location | Finish | Ships with | Price |
|---|---|---|---|---|---|
| SOT Enhanced Chrome Bolt | Mil-spec .378 | Pass-through hole | Chrome | SOT cam pin & firing pin | $89.00 |
| HMB™ 6mm ARC Nitride | 6.5 Grendel derived | Socket, radiused pin | Black nitride | SOT cam pin | $109.00 |
| HMB™ 5.56 / 6mm MAX Nitride | Mil-spec .378 | Socket, radiused pin | Black nitride | SOT cam pin | $135.00 |
| HMB™ 5.56 / 6mm MAX Hard Chrome | Mil-spec .378 | Socket, radiused pin | Hard chrome | SOT cam pin | $159.00 |
| HMB™ 6mm ARC Hard Chrome | 6.5 Grendel derived | Socket, radiused pin | Hard chrome | SOT cam pin | $159.00 |
Pins and kits
| Item | Contents | Cam pin finish | SOT arrow mark | Price |
|---|---|---|---|---|
| AR15 Firing Pin | Firing pin | — | n/a | $7.50 |
| SOT Cam Pin | Cam pin | Salt bath nitride | Yes | $20.00 |
| Carrier Completion Kit — Chrome | Firing pin · retaining pin · cam pin | Full chrome | Yes | $25.00 |
| Carrier Completion Kit — Nitride | Firing pin · retaining pin · cam pin | Black nitride | Yes | $25.00 |
// Before you order
Bolt face compatibility. The mil-spec .378 face and the 6.5 Grendel-derived 6mm ARC face are not interchangeable. The ARC case head is larger. Fitting the wrong bolt is a headspace and safety problem, not an inconvenience. If there is any doubt about what your barrel is chambered for, tell us the barrel and we will tell you the bolt.
Cam pin orientation. Install with the arrow point facing toward the bolt face. The reference holds with the bolt out of the rifle and out of the carrier — which is exactly when the mistake gets made.
Headspace. Where SOT fits a bolt, headspace is gauged against the barrel it will run behind. Sold bare, headspacing is the purchaser’s responsibility and should be done by a qualified armourer before firing.
Carrier compatibility. Every bolt here is compatible with any mil-spec bolt carrier. No proprietary carrier is required and no external dimension changes.
WARNING: This product can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.
// Ordering
Talk to us about bolts and parts
Tell us the barrel and we will tell you the bolt — or order any part here by its SKU.
HMB™ is a mark of HM Defense, LLC, used under license. Microbest and Young Manufacturing are the property of their respective owners, used for identification only. School of the American Rifle and SOTAR are the property of their respective owners; these products are not affiliated with, endorsed by or produced in conjunction with the School of the American Rifle. Bombproof by Design™ and Gundaddy® are marks of Second of Ten LLC.
Bombproof by Design™
Precision // Purpose // Performance