AR10 bolt material

[mark5pt56]

While we are on the topic of lug loads and stress(same thing?) is the chamfered area on the lugs to assist in relieving that as it unlocks or to aid in locking?

[lysander]

While we are on the topic of lug loads and stress(same thing?) is the chamfered area on the lugs to assist in relieving that as it unlocks or to aid in locking?

Load and stress are closely related but not the same. Load is measured in pounds (at least in the imperial system), and stress is load divided by the area supporting that load or lbs/square inch.

As the to the second part - Are you referring to the small angled cuts on the counter-clockwise, rear corner of the bolts locking lugs? Those are there just to ensure when the bolt rotates is does not hang up on the barrel extension lugs and allows the bolt to cam itself into locked position.

If you are referring to another feature of the bolt, you're going to have to be more precise in its location, a picture perhaps?

The AR design really does not need "help" during unlocking. In the AR specifically, because the bolt is the gas piston and the bolt carrier the gas cylinder, the load on the locking lugs is very close to zero during the actual act of unlocking, provided the gas system is properly timed. Because there is a time delay between the maximum chamber pressure, the gas port being uncovered, and the time it takes the gas to flow down the gas tube a fill the carrier cavity, the chamber pressure has dropped considerably. The force pushing the carrier backwards (gas pressure in the carrier cavity times the area of the bolt tail flange) also pushes the bolt forward, and this force is very close to the remaining chamber pressure times the area of the case head.

[RobertTheTexan]

The difference between my LMT MWS BCG and my BA 308 BCG is very noticeable , in hand and in the rifle. VERYnoticeable. According to LMT the 308 BCG is made from the same material as the LMT Enhanced 5.56 BCG with some secret squirrel coating, and even more importantly the same principles of design as the E-BCG. That’s just good news for everyone. (Who has one) I think the bolt is chromed or something. I recall reading it somewhere. (Probably an internet lie.)What I can tell you is that I’ve run my LMT MWS upper hard. Good ammo - cheap crap ammo and it just cycles and cycles with a can without a can. Like an energizer bunny. It cleans up better than any NiB BCG I’ve cleaned by a million miles.

If I build another AR-10. I would without question invest in the LMT BCG. As it stands one of the reasons I bought an MWS Upper was so when I could swap barrels and give me another purpose/better capability.


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[mark5pt56]

Lysander, great, thank you. Yes the locking phase, explains it well.

[constructor]

C158 and 9310 are close in strength but 9310 has a better charpy value(stronger at the notch). More important than material is proper heat treat. Years ago a company made bolts using 9310 but made the mistake of heat treating them so hard they were brittle. Same thing has been going on for over 15 years with one company using C158.
Compressive strength of the bolt is figured by area of the bottom of the lug x7(number of lugs)x the yield strength of the material. Figuring the strength of the lugs really takes a program. It isn't as easy as a simple compression or tensile formula.

The original AR10 bolts were 8620, later changed to c158. I made ours from 9310 after the results we had from the AR15 bolts. AR10 bolts made from any of the 3 materials above when properly heat treated are plenty strong enough to handle the thrust from a 308.