Who has broken a bolt with a mid-length gas system?

[Disciple]

lysander, do you believe the LMT enhanced carrier helps with bolt life in carbine gas systems?

[lysander]

I have no data one way or another.

All I can say is their claims are based on good engineering principles.

[MShaw]

Broken cheap bolt after about 50 rounds cycling in a 10-in carbine gas system was the last time I used 10 inch barrel and last time I used cheap parts. What about 14.5 midi is my new favorite

Sent from my moto g power (2021) using Tapatalk

[Pasta123]

I have no data one way or another.

All I can say is their claims are based on good engineering principles.

I wonder what’s the original goal when Stoner designed the AR-15. I doubt he wanted the bolt to only lasts about 20k at best, even on a rifle gas system.

Is there any data to show how long the A1 lasts?

[lysander]

I wonder what’s the original goal when Stoner designed the AR-15. I doubt he wanted the bolt to only lasts about 20k at best, even on a rifle gas system.

Is there any data to show how long the A1 lasts?

I seriously doubt that there was any "designing" of the AR bolt back in the 1950s. There was no stress model analysis, or anything like that. They probably, just calculated the shear load based on the proof load and made sure the shear stress was 2-1/2 less than the strength of the steel*. Then they just used best practices to figure the fillet radii and such. Remember the AR-10 bolt started life with the same geometry as the AR-15 bolt, it wasn't until after a few years of development in the various AR-10 "models" do we get the trapezoid profile lug. The Stoner 63 has a slightly beefier bolt to.

_ _ _ _ _ _
* The shear strength of Carpenter 158 is around 101,000 psi, the total shear area of the seven lugs is .198 493 sq in, and a conservative proof load is 8,000 pounds, which gives a shear stress of 40,303 psi, multiply that time 2.5 gives . . . any guesses?

[HKGuns]

I seriously doubt that there was any "designing" of the AR bolt back in the 1950s. There was no stress model analysis, or anything like that. They probably, just calculated the shear load based on the proof load and made sure the shear stress was 2-1/2 less than the strength of the steel*. Then they just used best practices to figure the fillet radii and such. Remember the AR-10 bolt started life with the same geometry as the AR-15 bolt, it wasn't until after a few years of development in the various AR-10 "models" do we get the trapezoid profile lug. The Stoner 63 has a slightly beefier bolt to.

_ _ _ _ _ _
* The shear strength of Carpenter 158 is around 101,000 psi, the total shear area of the seven lugs is .198 493 sq in, and a conservative proof load is 8,000 pounds, which gives a shear stress of 40,303 psi, multiply that time 2.5 gives . . . any guesses?

There have been a lot of new steels developed since the 60’s.

Is C158 still the best steel for use in AR bolts?

[Pasta123]

I seriously doubt that there was any "designing" of the AR bolt back in the 1950s. There was no stress model analysis, or anything like that. They probably, just calculated the shear load based on the proof load and made sure the shear stress was 2-1/2 less than the strength of the steel*. Then they just used best practices to figure the fillet radii and such. Remember the AR-10 bolt started life with the same geometry as the AR-15 bolt, it wasn't until after a few years of development in the various AR-10 "models" do we get the trapezoid profile lug. The Stoner 63 has a slightly beefier bolt to.

_ _ _ _ _ _
* The shear strength of Carpenter 158 is around 101,000 psi, the total shear area of the seven lugs is .198 493 sq in, and a conservative proof load is 8,000 pounds, which gives a shear stress of 40,303 psi, multiply that time 2.5 gives . . . any guesses?

40,303 x 2.5 = 100757.5, pretty near to what C158 can handle.

I wonder if we could just improve it simply by using even stronger material, along with some slight modifications. Sounds like what LMT is doing. I do think there's a practical limit (say, 100K) where further enhancement only makes a diminishing return.

Redesign the bolt is the best solution, except we'll running into compatibility issues and might not be worth it. I did find this, though.


That said, I kept hearing how the bolt on old M16s can survive several rebarrel, with one claimed to be at ~50K. I'll ask him to see.

[Pasta123]

There have been a lot of new steels developed since the 60’s.

Is C158 still the best steel for use in AR bolts?

There are, and we have quite a few bolts were made from them. The only problem is to buy 100K ammo and test it out...

[lysander]

Throwing stronger (and more expensive) material at a problem is an "iffy" way of finding a solution. Especially if the problem is fatigue related.

The thing about an AR be bolt is it's so small there just isn't a whole lot of room to work with before you start to get into compatibility issues.

[Pasta123]

Throwing stronger (and more expensive) material at a problem is an "iffy" way of finding a solution. Especially if the problem is fatigue related.

The thing about an AR be bolt is it's so small there just isn't a whole lot of room to work with before you start to get into compatibility issues.

We could try, then most would thought the improvement is “pointless” because 99% of them never wears out their milspec bolt…

Didn’t the URG-I got two bolts survived after 34000k of rounds? Will that means something?