Bulletproof AR15 bolt

If one were to build a bulletproof AR 15 bolt, meaning no cracking of lug shearing with automatic use and slow wear , what material would you make it out of? What treatment processes would you do attain this strength?

trg-s338

Reply to
trg-s338
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K*********ium Heat treat by *************** *** ********** ***** ** ************ ***

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I***

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Reply to
I***

obviously unobtanium is the correct material

Reply to
DH

Personally..Id buy one. They are cheap, and properly head treated and made of the proper materials.

Im considering building a California AR, but will be using a commercial bolt.

Gunner

Reply to
Gunner Asch

I apologise for failing to be more specific in the application. No need for better than what's available for the 223 but I've been considering a California AR15 in the 6.5mm Grendel. This round exerting higher preasure on the bolt has been reported to crack bolts of commercial origin or shear lugs. Even the developers of this round have had occassional failure in their bolts. The commercial rounds are downloaded to limit preasure development because of this weak link in the system. Just wondering if one could be built without the business considerations commercial manufacturers are subject to or limited by. Materials like any of the various tool steels or exotic metals like Inconel or other such materials able to handle the stresses of an AR bolt in this application, are any of these appropriate?

trg-s338

Reply to
trg-s338

Do you know the material and heat treatment of the original? If you want something better, you have to know what you're starting with.

(When I was at Wasino we were facing those bolts in a trial run for Colt, but I don't remember the material. Sorry.)

-- Ed Huntress

Reply to
Ed Huntress

Ed is certainly right. You could waste a lot of time and money by trying to reinvent the wheel.

Off the cuff response: S-class tool steels are make for severe shock environments Things like blanking and cold-heading, where less rugged tool steels will shatter.

You can also investigate powered-metallurgy tool steels. Bloody tough to machine (not for amateurs) and very expensive, but if you're able to build your part, it will likely be about as strong as can be made.

You should discuss the application with a tool steel apps engineer. You'll also get information on proper heat-treat (likely impossible at home - will need to be farmed out).

(this advise is worth exactly what you paid for it)

Regards,

Robin

Reply to
Robin S.

Thanks for at least attempting to answer my post. For my personal edification and learning, I will look up the materials you mentioned. Yes most heat treat processes are beyond my realm.

Reply to
trg-s338

There is another caution, the one about a chain not being any stronger than its weakest link. A super-stong bolt may cause the receiver to fail. If there is any group that cn shed some light on this it would be this one.

Unka' George [George McDuffee] ============ Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.

Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.

Reply to
F. George McDuffee

If you want to re-design the bolt of an AR15 then the first step is to determine what material and tensile strength, i.e., heat treatment, was used for the original bolt. As I believe the original bolt was chrome plated you will need to advise the testing lab of this fact. In addition chrome plating is known to be a source of hydrogen enbrittlement so the lab should also test for that.

Once you have a lab report as to material and strength in hand you need to consult a competent engineer with experience in designing high strength steel components who can advise you of the feasibility of re-manufacturing the bolt. It may even be that given the pressures developed by the new cartridge that the present bolt design cannot be made to successfully withstand the pressures in which case you will need to redesign the locking system for these higher forces.

This is probably not what you want to hear but the empirical method of "suck it and see" is going to bust a lot of receivers before you get it right.

Bruce in Bangkok (brucepaigeATgmailDOTcom)

Reply to
brucedpaige

Hey Gunner,

What comprises a California AR? What comes to mind is a single shot manual bolt with a 5' barrel, a flashing red warning light and GPS locator?

Jay Cups, an exKalifornian now liv> >

Reply to
JayCups

Ha, don't forget the plugged barrel, and required permit only illegals can get.

Reply to
Cydrome Leader

If you call Colt and persist, they'll probably tell you what it's made of. Just don't tell them you want to improve it.

-- Ed Huntress

Reply to
Ed Huntress

so what is the difference between the California bolt and stock standard bolt? what about the gas hole size for the barrel, since this will effect cycle rate? how different is this size than the 6.8 that is available now?

Reply to
jay s

One big difference in AR bolts is how they are treated & tested after manufacturing. Real Colt bolts are shot-peened (stress releaved?), magnetic particle tested for cracks, and supposedly proof tested somehow. I'm not sure if this is done separate from proof testing of the rifles or not.

There are a few 3rd party bolts that are shot peened & MP tested, but I don't know of anyone else who proof tests their bolts. This is why Colt bolts are extra pricey, aside from the usual markup for just being Colt.

Doug White

Reply to
Doug White

FWIW, shot-peening actually work-hardens and compresses the surface, making the bolt much more resistant to initiating stress cracks and adding just a bit of strength overall. I've never heard about it in relation to stress-relieving but I suppose it's possible.

Shot-peening often is used on steel connecting rods for racing engines for the same purpose.

-- Ed Huntress

Reply to
Ed Huntress

You are probably correct in that the bolt as designed was not meant to handle the increased preasure of a bigger cartridge, and that to successfully get the bolt reliable, a major redesign of the lockup system needs to be addressed. All that is of course beyond the tinkering/hobby realm of mine. Busting a lot of receivers through bolt lug shearing, lockup failure and the resultant explosion is not my cup of tea either. Thanks for the response.

PS--

Reply to
trg-s338

It is my understanding that on the AR15, the bolt and barrel extension lockup take up all the stress. The receiver is there essentially just to give the bolt carrier something to ride in, assuming the gas system is tuned properly. Perhaps I'm missing something with reguards to the point of what significantly stresses the receiver in the AR15 system?

Reply to
trg-s338

The California AR is basically a rifle with a permanently mounted 10 round magazine, or a removeable magazine but no handle on the rifle. To load the fixed magazine, you would have to break open the upper from the lower receiver and use stripper clips or manually load. There is no difference between CA AR bolt and standard commercial bolt but using other cartridges of course requires specific sizing of the bolt face.

Reply to
trg-s338

You know, I've been thinking about your problem and it seems funny to me that bolt lugs are cracking. Years ago P.O. Ackley did some tests on the actual thrust exerted on the bolt when the gun is fired and if I remember correctly because of the cartridge expanding as the powder burns it grips the sides of the chamber and actual thrust forces, against the bolt were far lower then chamber pressure would have one believe.

Another point, many bolt guns are converted to higher power cartridges then originally intended, witness some of the chamberings for the poor old '98 Mauser, military, that has a relatively weak (compared to modern actions) bolt and receiver.

How much higher chamber pressure is this new round developing and what is the cartridge head size compared to the normal AR-15?

Another point, if you are firing a higher powered cartridge then unless you either limit the amount of gas vented to the action, increase the weight of the bolt and carrier or increase the strength of the recoil spring the bolt is going to slam back against the stops with considerable more force then normal. Might this have any effect on bolt cracking?

If chamber pressure is higher then gas pressure is higher - is the bolt starting to unlock earlier in the cycle so that higher pressure is exerted against a partially opened lock?

These are just random thoughts but it might be interesting to see what happens if, say a gas port is plugged or a very heavy recoil spring fitted.

Bruce in Bangkok (brucepaigeATgmailDOTcom)

Reply to
brucedpaige

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