The bolt failure issue is less significant these days... now that we, for the most part, know to run our BCGs well lubed.
The bolt failure issue was primarily linked to pitting.
Printable View
The bolt failure issue is less significant these days... now that we, for the most part, know to run our BCGs well lubed.
The bolt failure issue was primarily linked to pitting.
Two of the main factors in high cycle fatigue are peak and average stress values.
To extend the life of a typical AR bolt, you're probably going to have to lower those two values. That entails either increasing material cross sectional area or lowering the applied force, neither of which is likely to be easy given the constraint of working within the remainder of the platform.
You could try some more exotic things like maybe switching from shot peening to laser peening to further improve the surface quality or maybe some process to reduce the grain size of Carpenter 158 steel but I imagine the ROI on either of those is going to be small.
I think gassing the gun correctly and not running a bunch of over powered XM193 is the way to make a bolt last for a friggin long time.
Look at the weak points the bolt lugs they are small and where the cam pin goes through the bolt, really thins out the metal. That is why the bolt has to be made from the C 158 steel and go through the hpt and shot peened to last. If the parts were thicker they would last longer.
Actually, high pressure testing doesn't increase bolt life. It reduces it
From a military stand point....Drop in is a must for good reason. When, not if a part breaks you cannot have half the guys using bolt design 1 with barrel extension 1 and the other half using bolt design 2 with barrel extension 2, it would make it difficult to have to keep 2 bolts in stock until all barrels/bolts are replaced.
With a drop in bolt that fits the standard barrel extension phasing them in is easier because even though some will have older bolts they will still be comparable with each other.
Also, generally a good bolt will shear lugs before breaking at the cam pin area.
If you haven't seen a broken bolt, this is what they look like.
Thanks for the replies. Lots of good info. I have a bit more research to do and then I plan to mock up my designs in an autocad program I have and hopefully find someone to machine a working physical model (not likely out of spec materials, just something 3D and functional). I'm still looking into patents and trying to figure out the best time to apply for one... not sure if I need a full spec part built, or just a model, or if I can apply for a patent simply based on a design sketch. Either way, I need to figure that out before I go public.
Can anyone point me in the direction of a spec sheet detailing the all dimensions of a milspec M16 bolt carrier group and a standard barrel extension? Thanks.
So it looks like specs or blueprints for the bolt have not been made public... All my searching turned up was multiple people saying they are the property of Colt, released only under licensing, yada yada... and that companies that manufacture them have either reverse engineered the specs or apparently purchased a license... looks like I'll be spending some time with a pair of calipers.
Sort of a side note, has anyone ever heard of a bolt carrier breaking? (other than the gas key coming loose)
What is the service life of the bolt carrier?