I’ve been researching alternative AR-15 chambering, and the differences between them all. Most folks are aware of the standard AR-15 bolt face, but may not know the actual size and what alternative cartridges will work with it.
.378″ – The Standard Bolt Face
- .223 Remington
- 5.56x45mm NATO
- .300 BLK
Where can I get these bolts from?
Stag Arms – Mil-Spec shot peened Carpenter 158 steel
.420″ Bolt Face
- 6.8 SPC
- .224 Valkyrie
Who Makes These?
Stag Arms – Mil-Spec shot peened Carpenter 158 steel
.440″ Bolt Face
- 6.5 Grendel – Type 2 with .136″ Head Space
- 7.62x39mm – Type 1 with .125″ Head Space
- 6mm ARC – Type 2 with .136″ Head Space
Who Makes these?
Maxim Firearms – 9310 Steel
Stag Arms – Material not listed
Underground Tactical – 9310 AQ Steel
.473″ Bolt Face
- .358 SCOCOM
- .375 SCOCOM
- 450 Bushmaster
- .458 SOCOM
- .50 Beowulf
Who makes these?
Tromix – Included in Builders kit or BCG Kit