For Future Reference

[Spook]

http://www.ar15performance.com/home

Scroll down to " I.T.S. Superbolts "

Without inferring anything,You might want to think about bookmarking this...just sayin'
Really well made products and nice people to deal with.

[BWE Firearms]

Thanks for the tip. I bookmarked it as suggested.

[alorton]

I've been thinking about those for some time.

I had some correspondence with AR Performance after reading a long thread on M4carbine.net about the 9310 alloy bolts. The consensus on M4 was that the 9310 alloy was not as strong as Carpenter 158 (standard bolt steel) but that the design of the super bolt (more material around the cam pin hole, radius at the base of the lugs) was superior.

When I asked AR Performance about it they said that the tempering process they use to harden the 9310 makes it stronger than Carpenter 158 and that Harrison has really pounded on several of the super bolts without having any breakage issues. I haven't been able to locate any direct comparisons, most likely because the ammo cost to test two of them heads up would be too much for most folks (myself included).

[Spook]

Originally Posted by alorton

I've been thinking about those for some time.

I had some correspondence with AR Performance after reading a long thread on M4carbine.net about the 9310 alloy bolts. The consensus on M4 was that the 9310 alloy was not as strong as Carpenter 158 (standard bolt steel) but that the design of the super bolt (more material around the cam pin hole, radius at the base of the lugs) was superior.

When I asked AR Performance about it they said that the tempering process they use to harden the 9310 makes it stronger than Carpenter 158 and that Harris has really pounded on several of the super bolts without having any breakage issues. I haven't been able to locate any direct comparisons, most likely because the ammo cost to test two of them heads up would be too much for most folks (myself included).

Not being a metallurgist, ( but having stayed at several Holiday Inn Expresses ) I would conclude that you could reduce the cost of the comparison by reloading less ammo to higher pressure
Here's a hint, rather than test to failure, test for wear and or distortion.

I've really hammered a few of the .473 bolts/extensions (6 BRX,6.5 BRX and 30 BRX) and couldnt get anything to break.... attempting a 338 BR next.

[rsilvers]

9310 may be stronger than C158, but the bolts do not fail from not being strong - they fail from fatigue, cracking, etc.

So the question is - what material is BETTER for a bolt?

Answer: C158.

So why does not everyone use it? It is MUCH more expensive due to a minimum order quantity that smaller makers cannot swing.

[Spook]

Originally Posted by rsilvers

but the bolts do not fail from not being strong - they fail from fatigue, cracking, etc.

WTF? So they crapout beacause they are strong enough?

Sorta defies logic dont it?

[JFettig]

He may be correct, however the number of cycles that the bolts see is usually sub 100,000 so it is hard to say. - it depends on the stresses

C158 is some super hard stuff in the case but softer in the inside, if it does crack the case, the crack will stop when it gets through it.

9310 will likely be hard thru and thru giving the cracks a place to continue propogating.

This is however considering LOTS of cycles.

Its hard to say exactly which one will last longer without getting an engineer to do some serious math and testing.

Many loaded objects fail by fatigue and are way under-loaded, I've seen some examples of rotating shafts with light loads that eventually fail, they crack almost all the way through and no one notices until finally they snap.

I'd love to see some high resolution photos of bolts that have broken to see what the failure mode was.

Jon

[Spook]

Hi Jon,
They break due to the case hardening not being done uniformly. I read a report a few years back that the government had done by an engineering firm with a four or five name title.

The conclusion went something like that the hardness levels werent consistent from one area of the bolt to the next which allowed a wear pattern to occur, which led to fracture.
The photos you want were part of the report along with graphs and round count..the entire shebang.

rsilvers
The point being that if you hold one of Harrisons bolts in your hand, you immediately realize how much weight difference there is from a "standard" bolt.
The fact that 9310 costs less doesnt account for much when you consider how much more steel there is, and that the steel is tempered as opposed to Case hardened... to say nothing of where on the bolt he's put the extra mass.
Apparently C152 "mil spec" bolts dont realize how expensive they are as they've been failing with regularity all along and will likely continue to do so in instances where higher pressure's are a factor.

[LouBoyd]

I've been shooting AR-15s since 1968 and have never had a bolt or barrel extension break, nor personally seen one that did. It certainly can happen with overpressure loads. but I'm not going to change out the bolts in any of my AR's nor buy these bolts for future builds. I have no doubt these are stronger bolts, but in the case of a random over-pressure cartridge I'd prefer the bolt to fail rather than the barrel extension. A bolt is easy to replace.

[alorton]

From the information I've found I think these Superbolts are more durable than the standard Mil-Spec bolts if for no other reason than the physical design features. The problem for me, however, is from an armorer's perspective I can't recommend them for duty use because they represent somewhat of an unknown compared to the standard.

I know what to expect in terms of service life from a standard bolt and I know that they are reliable enough within those constraints to trust for duty use. Until these have been used and abused in documented high volume testing I couldn't use them in our duty rifles.

Having said that, since I think they are stronger I am seriously considering a couple for my wildcat AR's. Since I tinker with different loads in those guns, most of which are higher energy and possibly higher pressure than standard 5.56, a stronger bolt has appeal and if my belief is wrong it won't be during a firefight when the bolt fails.

Just my take on it.