Gunsmithing AR-10?

[tansinator]

I was shooting my AR-10 today. First few rounds were fine (single fed). All of the sudden the bolt would not stay locked back. I remove the magazine and a piece of the bolt stop catch fell out. It was sheared off.
A. What could cause this?
B. Where can I get a new one in a hurry? as I have a match next weekend.

Thanks

Eddie

 

[SpotcheckBilly]

Re: AR-10?

Not really unusual in the AR10.

Commonly, using a powder with too slow of a burning rate will cause it in one of these. The idea is that it causes excess gas port pressure, not chamber pressure which is a different thing. The slow burning powder causes the pressure in the barrel to peak further down (nearer the gas port) and causes an over-active gas system. You have to reduce the hit from the gas system to get the bolt latch to survive.

Some fixes -
Go to a faster burning powder . Hint- H4895 works in an AR10 .308 really well, as an example.
Increasing the carrier weight is a good way to do it. Use a Tubbs CWS. It slows down the carrier to ease the hit on the bolt stop.
An adjustable gas manifold might do the trick.
Many custom builders locate the gas port farther ahead if the shooter is going to use a slow powder.

Just a few ideas. Best of luck with it.

ps - I have no idea where you might get a new boltstop this quickly

 

[chas1759]

Re: AR-10?

I was going to recommend 762SASS.com but I checked and he's out. Great guy and fast shipping. Otherwise I'd call Armalite Monday and see if they can hook you up.

 

[RedMan*]

Re: AR-10?

Armalite won't answer their phones.
I had to send an Email with what I was looking for along with contact info and a couple of days later they called me back.

Have yet to receive product nor has my C.C. been charged so the waiting game is on. They did tell me it would take about a month so no biggie.

FWIW,
Stu

 

[dmg308]

Re: AR-10?

As stated not uncommon in ar10s I should have one PM me if needed.

 

[tansinator]

Re: AR-10?

Would IMR 4064 be considered too slow of a powder?

 

[Queequeg]

Re: AR-10?

SpotCheck,

Any types of factory ammo to be avoided? I bought 400 rounds of Winchester 180 grain soft points just after the coup last November. I've gone through 40 rounds with out any noticeable issues but I understand it is a cummulative thing.

 

[tansinator]

Re: AR-10?

This was also the second time running with a suppressor. Could this cause some of the excess pressure?

 

[SpotcheckBilly]

Re: AR-10?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: queequeg</div><div class="ubbcode-body">SpotCheck,

Any types of factory ammo to be avoided? I bought 400 rounds of Winchester 180 grain soft points just after the coup last November. I've gone through 40 rounds with out any noticeable issues but I understand it is a cummulative thing.</div></div>

The only factory ammo I've ever used in my AR10(T) was Federal GMM and it had no problems, so I can't tell you about anything else from personal experience. Now I strictly use handloads with H4895.

Glen Zediker mentioned that the AR10 shooter should probably stay away from much of the factory hunting ammo in .308 because it's probably intended for use in bolt guns and might be loaded with a slower powder than what's optimum for a gas gun like an AR10. He's got a lot of experience with these things, so his opinions should be considered.

 

[border_reiver]

Re: AR-10?

Hey Spotcheck,

Ha, how've you been. I'm probably going to be playing with gas guns a bit more on a personal level than in the past, for obvious reasons, but devils advocate here, what prevents a guy from customising the barrel/gas port/block to suit the ammunition he wants to use? I could have 3-4 barrels for different ammo/pressures per se..

JR

 

[81STFACP]

Re: AR-10?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tansinator</div><div class="ubbcode-body">Would IMR 4064 be considered too slow of a powd </div></div>

I've shot 4064 in both AR10 and M1A with no problem.

 

[our gang]

Re: AR-10?

Assume it's a 308? VARGET is the best powder.

 

[trilogymac]

Re: AR-10?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tansinator</div><div class="ubbcode-body">This was also the second time running with a suppressor. Could this cause some of the excess pressure?

</div></div>

Oh yea. Could very well be the problem. It was with mine. Bought a adj gas block from Tuppo Jutsu {SP} and the problem went away.

Mine was cycling so fast with the suppressor it wouldn't pickup rounds out of the mag.

Hope this helps.

Trilogymac

 

[okiefired]

Re: AR-10?

just get Tubb's CWS or adj gas block and burn what you want. think its good to tame the cycling a bit on these things anyway.

okie

 

[SpotcheckBilly]

Re: AR-10?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: __JR__</div><div class="ubbcode-body">Hey Spotcheck,

Ha, how've you been. I'm probably going to be playing with gas guns a bit more on a personal level than in the past, for obvious reasons, but devils advocate here, what prevents a guy from customising the barrel/gas port/block to suit the ammunition he wants to use? I could have 3-4 barrels for different ammo/pressures per se..

JR </div></div>

Hi JR,
I've been fine, just kinda laying low for a little while. Glad to hear from ya, and a much belated welcome back to this side of the pond

I suppose that you could swap barrels until you get tired of it (they're so easy to change), especially if you're someone that posesses the talent, equipment, and skills that allows you to make your own ...HA!

I've settled on a single load for my AR10(T) that suits me just fine for the forseeable future, but I would think that if a guy had a barrel that was a real hummer and wanted to stick with it, but experiment with a multitude of different powders and bullets he could do very well with a Tubb CWS (includes interchangeable weights) and an adjustable gas block. At least if it's a .308 that you're thinking of.

Now if it's a .243 or .260 you're talking about, especially using a slow powder, moving the gas port out four to six inches is not uncommon. Playing with the diameter of the gas port is fine as long as you remember that the name of the game is to decrease the pressure (at the gas port) so that you slow down the carrier so it doesn't hit so hard. Making the bolt carrier effectively longer so it reduces the distance the bolt will travel before it hits the bolt stop also will help. You can do this real easy by lengthening the buffer itself with one (or two) of those stick on buffer pads. This will also help with the bolt stop problem. Keep in mind that you're limited by a 2.800" magazine length in these rifles, so you won't be able to take the utmost advantage of the high BC long bullets. One barrel specifically for a 123gr. 6.5 bullet, another tailored for the 107's would be interesting, for example. But I lack the practical experience to get involved that heavily .........

PM me when you get a chance and let me know what you've been up to since you've gotten back.

 

[Sc0]

Re: AR-10?

If the bolt catch broke I assume it's the nature of the beast being that the bolt carrier group is so freaking heavy. Armalite did have a bad batch awhile back though, how old is your AR10? Also if the sear is accidentally tripped when the rifles upper was separated the hammer hits the bolt stop with authority...

 

[SpotcheckBilly]

Re: AR-10?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sc0</div><div class="ubbcode-body">If the bolt catch broke I assume it's the nature of the beast being that the bolt carrier group is so freaking heavy. Armalite did have a bad batch awhile back though, how old is your AR10? Also if the sear is accidentally tripped when the rifles upper was separated the hammer hits the bolt stop with authority...</div></div>

I think that it's more along the lines that the carrier is coming back too fast and has to be slowed down, although I'll certainly agree that ArmaLite did supply some bad bolt stops in the past.

Yes, the bolt carrier is awfully heavy, but even if you can lighten it up, without making any other changes it's gonna come back even faster and still hit really hard. I've done a little experimentation along these lines and believe that the best way out of the dilemma (while keeping the original barrel) is first to use a powder that provides the proper amount of pressure at the gas port to begin with, then add a CWS system, if more mods are needed, to do two things - first to delay the unlocking of the bolt and then to reduce the overrun at the bolt stop (the CWS adds some length to the carrier). The shooter can then play with the CWS inserts until he finds a combination that works with the load he's using (running the insert hollow is a workable option) and can fine tune it even further by going to an adjustable gas block if more adjustability is needed. All band-aids, but they work. Going to a custom barrel with its gas port moved forward and of a proper diameter is probably the best solution in any case.

Just my considered opinions, but I want to stress that I'm not trying to argue that the heavy out-of-the-box AR10 bolt carrier isn't a large part of the problem. I'm just suggesting ways to get around that fact.

 

[tansinator]

Re: AR-10?

I've put in several calls to GA Precision today, but I have not heard back from George. I'll try again tomorrow. I would like to get his opinion since it came from his shop.

Thanks again for your responses

Eddie