Short-stroking 260 AR10(T)

[Rancid Coolaid]

I am the proud owner of a new Armalite AR10(T) upper chambered in 260 Rem. It is a very nice upper, it groups quite nicely with 139s and 142s, and it short-strokes everything.

No problems extracting or ejecting, but it will not strip off a fresh round from the mag and it will not lock the bolt on an empty mag.

In looking around online, I see multiple complaints from 260 AR owners, and it seems to be happening with multiple platforms.

Anyone have this problem and solve it?

The rifle previously ran a 308 upper with no problems.

 

[BOLTRIPPER]

Re: Short-stroking 260 AR10(T)

savvy the magazine springs or magazine lock-up to the upper......and or the magazine lips

 

[Rancid Coolaid]

Re: Short-stroking 260 AR10(T)

The mag has been in use for a year+ with a 308 upper, never a hiccup.

 

[ranger1183]

Re: Short-stroking 260 AR10(T)

I had a similar problem with a DPMS 260. It turned out that mine was not short stroking but actually way over gassing. The bolt carrier group was actually going <span style="font-weight: bold"><span style="font-style: italic">much to fast</span></span> for the rifle to operate correctly.

My gunsmith had to go over the rifle from head to toe to get it operating correctly. One thing in particular, he had to build a custom adjustable gas block. It ended up that a lot of gas had to be restricted to <span style="font-weight: bold"><span style="font-style: italic">slow down</span></span> the bolt carrier group. There were a lot of other things that ended up being checked as well.

Out of curiousity, what type of ammo are you firing? Is it pretty "hot" stuff so to speak? If it is, I'd try as a test either some less powerful handloads or if I didn't reload, some of Remingtons "Reduced Recoil" ammo.

Basically, see if your rifle is not going to slow but actually to fast.

Good luck with that.

 

[ChadTRG42]

Re: Short-stroking 260 AR10(T)

+1 for what was stated above. What load(s) are you running?
I've also seen this on another AR in 260. The powder they were loading with was H4831, which is very slow burning. This powder prolongs the peak pressure, which causes increased pressure on the BCG. We solved the problem with going to a lighter load of H4350. If you had an adjustable gas block, you could choke it down to help reduce the gas flow into the BCG. When trying to run max loads for a bolt gun in an AR, you can get pressure problems in your AR.

 

[overkill]

Re: Short-stroking 260 AR10(T)

did you go throug the std checks?
gas key tight
gas rings tight
gas block alined
.308 buffer and spring(insert empty mag, try to lock bolt all the way back by hand. bolt catch should end up infront of the bolt face)
over lube the weapon. BRAND new guns generaly need extra lube when breaking in. for the first couple hundred rounds, that BCG should be dripping.
slowly cycle the weapon by hand with live ammo in mag. feel for any abnormal resistance, make sure the new round gets picked up and feeds correcty.
check BCG and reciver for marks that would indicate drag.
AFTER checking all that, switch up ammo(powder if reloading)
my .260 did not like the 4831. ran best with IMR 4350.

 

[T-Hoe]

Re: Short-stroking 260 AR10(T)

I agree that you gun is over gassed, I had the same problem with a custom .243 upper when I was shooting heavy bullets. My gun guy made a adjustable gas block, choked it down a little and it ran perfect.

 

[STI_1911_Guy]

Re: Short-stroking 260 AR10(T)

Okay so i just had this same problem with my dpms 260. Basically i would try cycling the action and make sure it feels smooth by hand. If you changed the stock check the bolt that screws into the buffer tube and see if its hitting the buffer and shortstroking it. Check all the normals like the gas block/key/tube for blockage/gas rings on bolt. Now mine would cycle remington 140's just fine but nothing else. But after sending it to DPMS they polished the chamber and replaced the extractor and sent it back. Now that was all that was done and really all i had to was lube the shit out of it and run it. It now works with federal 120's but no other 120's and i do have an adjustable gas block and no i was not overgassed on them it still wont work with anything 120 beside federal including 20 different handloads. I talked with a few locale smiths and 1 from dpms and they said that to be able to run 120's you would have to open the port. Now if it wont function with anything including 140's or anything you tried after soaking in lube and checking all the normal checklists then something is wrong with the firearm like gas port size or who knows what. If you run some 140 grainers and H4350 42gr charge and it dont work i would get in contact with armalite. I was never "overgassed" or "magazine problems" like alot of people were sure of. Check out my posts on "DPMS 260 Remington Cycling issues....Please Help"

 

[Rancid Coolaid]

Re: Short-stroking 260 AR10(T)

Update.

I talked to my local smith (who is exceptional), he said he doubted it was overgased. I talked to Armalite, they said probably not overgased. Both said soak the BCG in lube (actually, they said put on enough so you think it is too much, then it is almost enough.)

Took it to the range today, lube almost dripping from the BCG, ran like a champ, shot through 120s and 140s, no problems, no failures to extract, eject, or load a fresh round from the mag.

I wasn't,t running it dry, but didn't have it dripping lube,

2 ways to learn: experience and instruction.

 

[sobrbiker883]

Re: Short-stroking 260 AR10(T)

Seen my buddy's SASS need to be wet like that too.

I would have been in the excessive bolt speed camp for an internet diagnosis, but as usual a little sluething and ingenuity by the guy with the rifle trumps online pondering

 

[bowslngr]

Re: Short-stroking 260 AR10(T)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: STI_1911_Guy</div><div class="ubbcode-body">Okay so i just had this same problem with my dpms 260. Basically i would try cycling the action and make sure it feels smooth by hand. If you changed the stock check the bolt that screws into the buffer tube and see if its hitting the buffer and shortstroking it. Check all the normals like the gas block/key/tube for blockage/gas rings on bolt. Now mine would cycle remington 140's just fine but nothing else. But after sending it to DPMS they polished the chamber and replaced the extractor and sent it back. Now that was all that was done and really all i had to was lube the shit out of it and run it. It now works with federal 120's but no other 120's and i do have an adjustable gas block and no i was not overgassed on them it still wont work with anything 120 beside federal including 20 different handloads. I talked with a few locale smiths and 1 from dpms and they said that to be able to run 120's you would have to open the port. Now if it wont function with anything including 140's or anything you tried after soaking in lube and checking all the normal checklists then something is wrong with the firearm like gas port size or who knows what. If you run some 140 grainers and H4350 42gr charge and it dont work i would get in contact with armalite. I was never "overgassed" or "magazine problems" like alot of people were sure of. Check out my posts on "DPMS 260 Remington Cycling issues....Please Help" </div></div>

I know you have continued to work on this. Just curious how you came to the conclusion that your rifle is not overgassed with the 120 loads you have tried. If you would like, we can go off-line and I will share with you what I have continued to learn about my rifle and its dislike for most 120 grain factory loads (and a whole lot of 120 grain handloads). Based on the experiments I ran, I can say with certainty that too much pressure at the time the bullet passes the gas port is the problem with mine. Whether you call that "overgassed" or something else, that is the problem. What it causes is short stroking. Perhaps a better description of the problem is that the rifle is undergassed for over pressure. I now have mine running like a top with a very wide range of loads.

 

[Rancid Coolaid]

Re: Short-stroking 260 AR10(T)

Not trying to light fires or cause problems, just pointing out that there were 2 schools of thought leading to 2 solutions. The one I tried (the first I tried) seems to have solved the problem.

My purpose in posting was not to generalize but to solve my problem. that mine was under-lubed does not in any way mean someone else's isn't overgased.

Problem solved - for now at least.

once the barrel is threaded and the can is run, things might change, but for now it runs great.

 

[rpk762]

Re: Short-stroking 260 AR10(T)

As stated above I would look at powder. It looks like way too much or not enough. You could also try a carier weight system.