Ha. If only we all shot 20 inch rifle length gas. This from an M4:
http://www.dtic.mil/ndia/2006smallarms/taylor.pdf
Page 44:
"Most Bolts Subjected to Harsh Firing Schedules Will Show Initial Cracking Around 3,000 to 6,000 Rounds"
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Ha. If only we all shot 20 inch rifle length gas. This from an M4:
http://www.dtic.mil/ndia/2006smallarms/taylor.pdf
Page 44:
"Most Bolts Subjected to Harsh Firing Schedules Will Show Initial Cracking Around 3,000 to 6,000 Rounds"
Last edited by rsilvers; 12-04-11 at 03:47.
Sorry, I posted in the wrong thread.
Last edited by rsilvers; 12-04-11 at 04:07.
Anyone can look up the tensile and yield of the 2 materials as you can see they are very close in strength. Less than 2% difference in tensile and less than 5% in yield.
As far as 556 bolts, they will not be avail after about a week. We're busy running 6.8, 7.62x39 and 6BR bolts that can use the extra strength at the lugs.
9310-
http://www.latrobesteel.com/assets/d...heets/9310.pdf
Carp 158-
http://cartech.ides.com/datasheet.aspx?i=101&E=100
Last edited by constructor; 03-01-12 at 01:43.
AR15performance
TRUMP 2020
The 6.8 is the best choice for hunting deer and hogs with an AR15.
I had an extractor pin fail in a Bushmaster bolt a few years ago. It never quit working but was deforming from the exrtactor tension (had a D-ring) and a high round count.
It was found during a routine tear down for cleaning and replaced before it ever caused a malfunction but it certainly could have been an issue had it been left in much longer.
Advanced techniques are the basics mastered.
Excellence is an art won by training and habit. We are what we repeatedly do. -- Aristotle
Pistol/Shotgun/Rifle Instructor
Sig/Remington/RRA/Sabre Armorer
I've tried bolts out of the 3 materials referenced, Carpenter is basically just an old callout, it is very good and by only a small margin the best, but it was made a standard by a contract and it was only available to Colt. They made a deal where they would be the only company that could use the material from Carpenter.
8620 should never ever be used in a bolt, 9310 is an awesome material that is a good machineable alloy, it is used everywhere in other industries. Nearly the same for one piece piston carriers.
The only bolts I have seen fail are either lugs, or cam pin area elongating and developing a crack.
*This is what the shot peening fixes, I have no idea if the shot peening does anything anywhere else but that area is too thin and shot peening helps it, I wouldn't try increasing the bolt o.d. I would rather seem the cam pin od decreased and(.03") its material strength increased to match its current strength(its not a tough material currently).
High Rate shorter guns and it seems piston guns are harder on bolts. I had a magic bolt on a DI gun that had about 15k of machine gun mode, it was old and it could have died any second but I had to use its bolt to replace a bolt in a piston setup with a pretty loose carrier that was tilting badly and it ripped the top lug or two off the bolt in just a few rounds.
It would seem that many folks into variants prefer your bolts due to their belief that the bolt is stronger and will hold up better to the heavier calibers, particularly when a larger bolt face is used.
On the other hand, those that use 5.56 for duty weapons prefer the time tested version because it is a known quantity in a rifle that your life may depend on.
I see both points. My question to you would be, is your 9310 bolt something you would personally recommend for a duty weapon? Also, you mentioned that the 5.56 bolts will only be available for another week or so. Is that a permanent change, or just temporary while you run more of the variant bolts?
Advanced techniques are the basics mastered.
Excellence is an art won by training and habit. We are what we repeatedly do. -- Aristotle
Pistol/Shotgun/Rifle Instructor
Sig/Remington/RRA/Sabre Armorer
The only bolts in over 20 years I have had fail were Y/M, they broke at the cam pin hole. I've seen a few bolts from the largest producer of civilian ARs in this country that looked like the lugs were compressing, further inspection showed they were very soft. I know someone who built a grendel using a 7.62x39 bolt from the same company, after several stiff rounds the cases started taking the shape of a belted magnum, he checked and found the lugs were .008 shorter. I believe those bolts to be 8620 and not heat treated properly.
I checked into Carp 158 4 years ago, found out that all of the material was allocated to 2 companies that had DOD contracts to supply Colt and FN.
I ran shear tests on the carp bolts and ours, for all out strength our lugs are stronger. Fatigue test depending on the heat treat process also showed an improvement over the 158 bolts. I designed the bolts with a large radius on 3 sides of the lugs for a reason. There are other factors that are important other than just looking at the specs of the material. Some 9310 bolts on the market are or were too hard and brittle, the surface will develop cracks.
I've only made about 15000 bolts in the last 3 years, don't really need to push the sales, it's more to supply the rifles we build. There has not been 1 single bolt broken in 556,6.8 or 7.62x39.
There are some Fed teams using our 6.8s I have no doubt our bolts will last longer than any other 6.8 bolt on the market.
Something is going on with the 7.62x39, a couple of companies are testing heavily and asking for quotes on tens of thousands of bolts. It seems ours held up under full auto fire better than the rest.
As for the 556s it's too easy for us to buy Carp 158 bolts complete from a DOD contractor for less than it cost us to machine our bolts. I need our machine time for other projects, and I am dialing in our machining process on a new alloy that is apx 40% stronger than Carp 158 and 9310. It takes time to figure out the correct carbide grade, coating and chip breaker to turn out parts quickly.
I don't plan on making 556 bolts again unless we can't buy enough to supply our own builds just like what happened with the 6.8s, time will tell.
AR15performance
TRUMP 2020
The 6.8 is the best choice for hunting deer and hogs with an AR15.
A decent amount of time has gone by since you posted this, if you are still paying attention to this thread do you have any updates?
The rounded lugs on the E3 bolt are what the AR should have had in the first place IMO.
The biggest thing that surprises me is that Remington retained the 90 degree angles on their bolts lugs in the SCAR instead of using a radius on the lugs.
Just FYI - 9310 seems to get bashed a bit for not being tried and true like C158, yet KAC makes their E3 bolts out of it. My guess is it has more to do with the heat treat and post machining processes than just material selection alone. KAC's also has bolts made of Aermet 100, how about them apples?
Last edited by E-man930; 03-11-12 at 21:09.
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