Increasing Bolt and Barrel Extension Strength

[Vynz]

When I look at the MCX Spear I can see the bolt lugs and barrel extension lugs are longer than typical AR-10 lugs. But I can’t really see much else different: the barrel isn’t thicker than a standard heavy barrel, the barrel extension doesn’t seem thicker than an AR-10 barrel extension.

If one was to make custom AR bolt and barrel extensions with longer locking lugs similar to the Spear would this basically back port the ability to handle the cool-kid high-pressure cartridges to the AR-15 and AR-10?

 

[45-90]

When I look at the MCX Spear I can see the bolt lugs and barrel extension lugs are longer than typical AR-10 lugs. But I can’t really see much else different: the barrel isn’t thicker than a standard heavy barrel, the barrel extension doesn’t seem thicker than an AR-10 barrel extension.

If one was to make custom AR bolt and barrel extensions with longer locking lugs similar to the Spear would this basically back port the ability to handle the cool-kid high-pressure cartridges to the AR-15 and AR-10?

The brass is the weak link, and continues to be so regardless of the length or thickness of the bolt / barrel extension lugs...the primers will blow out of the brass before there would be a need for more bolt lug and extension strength...which will handle more than the brass will contain, by design. But any added strength would be positive even if it is not needed, for extra safety. Now if ya go to hybrid SS head cases for a caliber 80,000 psi max instead of standard 60,000 psi max area the extra material in the bolt and barrel extension would not only be desirable but probably necessary, to give a safety margin for the high pressure loads...but this is for a special SS case, and no advantage for standard brass cases, by engineering design of firearms manufacturers.

 

[ElvisUSMC]

The brass is the weak link, and continues to be so regardless of the length or thickness of the bolt / barrel extension lugs...the primers will blow out of the brass before there would be a need for more bolt lug and extension strength...which will handle more than the brass will contain, by design. But any added strength would be positive even if it is not needed, for extra safety. Now if ya go to hybrid SS head cases for a caliber 80,000 psi max instead of standard 60,000 psi max area the extra material in the bolt and barrel extension would not only be desirable but probably necessary, to give a safety margin for the high pressure loads...but this is for a special SS case, and no advantage for standard brass cases, by engineering design of firearms manufacturers.

45-90 you are proving to be quite the SME on the Hybrid cases! You always have good detailed answers.

I’ve been searching the internet for anything on max chamber pressure of an AR-10, just the max safe tolerance. But everything I can find is relative to .308 SAMMI pressure, which isn’t what I’m looking for. I need to go through the .277 Fury safe action thread again.

 

[45-90]

45-90 you are proving to be quite the SME on the Hybrid cases! You always have good detailed answers.

I’ve been searching the internet for anything on max chamber pressure of an AR-10, just the max safe tolerance. But everything I can find is relative to .308 SAMMI pressure, which isn’t what I’m looking for. I need to go through the .277 Fury safe action thread again.

I have some old military data where "all 30 caliber weapons" are tested with a proof load of 67,500 psi max ave...including the M60. Old data...Most 30 cal mil spec loads were 50,000 psi, noticed one load at 52,000 psi, and Armor piercing was 54,000 psi.
9mm was proof tested at 50,000 psi in military weapons.
I've ran some zippy loads through an AR 10 with brass cases and adjustable gas block...2673 fps 200 gr SMK .715 BC, in an 18" AR10. So they will take 65,000 psi loads. Turn the SA gas block down 7 clicks and shoot the same high pressure loads as the bolt guns ..brass cases only, 65,000 psi area... I use high pressure bolts in AR 10s with .062" dia firing pin.
The Hybrid SS cases fired in tbe AR 10 are normal pressure loads.
The Only 80,000 PSI loads in hybrid cases were fired in bolt actions only...the 2 lug Remington 700 308, and 3 lug Ruger Precision rifle 6.5 Creedmoor reformed from 277 hybrid cases...
Need accurate pressure testing equipment and a donor AR 10.