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Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
Posted: 4/19/2015 3:42:20 AM EDT
First post.  I am sched for a 3gun match next Weds and Thurs & I'm in a bind.

I have an A2 bushmaster, 20" HBAR. Ran flawlessly til I put on a 16" Elysium Arms barrel, 1:8 w/Wylde chamber. The gas tube is 8" long.

It stovepipes 2-6 rounds per 30 shooting fast pairs. Brass is caught & new round is always partially fed. The new round ends up with a big ding where it strikes and binds on the stovepiped brass. Empty brass is always pointed outward when stuck.

I've tried:

1. Scrub & decopper barrel.

2. Blow out gas tube. I get a strong stream of air from the muzzle. I’ve not checked the gas block for tightness, because,

3. I've fired single round mags 19 times, string of 10 one day, 9 the next. The bcg has locked back 19 times.  Means no gas problem, right?

4. #60 o-ring under the ejector.  Shot Freedom 55gr reloads, Federal Match 69gr, XM193.  No difference with o-ring or type of ammo.

5. Changed the A2 buffer & spring for spring & buffer from new collapsible stock.  The A2 buffer is 6" long w/ a shoulder 1 9/16" from the end, spring is 12 3/8" long of .072 wire.  The collapsible butt stock buffer is 3 1/4", spring is 10 3/8" long, same diameter wire. Neither buffer has any ID.  Made no difference.

6.  Shoot 30 rounds slow fire w/original bcg.  All brass ejected except #30, roughly 1 o'clock path, landed around my feet out to a couple cases at about 7'.  No real pile anywhere, #30 ended up lying on the mag in the chamber.  Don't know if that signifies anything.

7. Swap in a different bolt.  I couldn't feel any difference in the fit of the gas rings, or the spring tension of the ejector or extractor. Only used the A2 buffer set up when I tried this. Didn't make any difference.

Suggestions greatly appreciated! I really, really could use some help


Link Posted: 4/19/2015 7:40:17 AM EDT
[#1]
Quoted:
First post.  I am sched for a 3gun match next Weds and Thurs & I'm in a bind.

I have an A2 bushmaster, 20" HBAR. Ran flawlessly til I put on a 16" Elysium Arms barrel, 1:8 w/Wylde chamber. The gas tube is 8" long.
View Quote

Is this a typo, 8 inches for a CAR length tube?  Don't think so, a correct CAR length tube should be about 9 ¾ inches long.  The tube should be sticking into the upper about a half inch.  Pull back your BC and lock it back, drop the mag and look inside.  If you do not see about a half inch of gas tube then theres the problem and and I strongly suspect it is locking the bolt back properly when it is fired.

It stovepipes 2-6 rounds per 30 shooting fast pairs. Brass is caught & new round is always partially fed. The new round ends up with a big ding where it strikes and binds on the stovepiped brass. Empty brass is always pointed outward when stuck.

I've tried:

1. Scrub & decopper barrel.

2. Blow out gas tube. I get a strong stream of air from the muzzle. I’ve not checked the gas block for tightness, because,

3. I've fired single round mags 19 times, string of 10 one day, 9 the next. The bcg has locked back 19 times.  Means no gas problem, right?
View Quote


Does the bolt lock back on the face of the bolt or on the front of the bolt carrier?  If it is locking back on the bolt carrier instead of the bolt then it is short stroking, which is what your symptoms sound like.  If it is locking back on the bolt face like it should be, then all is well gas wise.  If it is locking back on the front of the carrier, then pull your gas block and do some measurements to make sure it is positioned correctly.  Make sure it is not slam up against the barrel shoulder unless your gas block was specifically cut to do so.  Most are not and need to be spaced off the shoulder and I have seen them vary in the amount from slam up against it to as much as .055 off, so measure to make sure and do not assume anything.


4. #60 o-ring under the ejector.  Shot Freedom 55gr reloads, Federal Match 69gr, XM193.  No difference with o-ring or type of ammo.

5. Changed the A2 buffer & spring for spring & buffer from new collapsible stock.  The A2 buffer is 6" long w/ a shoulder 1 9/16" from the end, spring is 12 3/8" long of .072 wire.  The collapsible butt stock buffer is 3 1/4", spring is 10 3/8" long, same diameter wire. Neither buffer has any ID.  Made no difference.
View Quote

No. 5 has be big time worried.  You CANNOT use a CAR length buffer and spring in a rifle buffer tube or you are going to cause damage to your lower from the carrier key slamming into the rear of the lower.  This is a BIG mistake unless you are using a spacer to take up the difference in length of the buffer.  It is not the cause of your problem but a huge muck-up by you trying to fix it.

Either use a rifle length buffer tube with rifle length buffer and spring or a CAR length buffer tube with CAR spring and CAR buffer, never mix the two unless using the spacer designed to take up the difference.

6.  Shoot 30 rounds slow fire w/original bcg.  All brass ejected except #30, roughly 1 o'clock path, landed around my feet out to a couple cases at about 7'.  No real pile anywhere, #30 ended up lying on the mag in the chamber.  Don't know if that signifies anything.

7. Swap in a different bolt.  I couldn't feel any difference in the fit of the gas rings, or the spring tension of the ejector or extractor. Only used the A2 buffer set up when I tried this. Didn't make any difference.

Suggestions greatly appreciated! I really, really could use some help


View Quote



Link Posted: 4/19/2015 3:56:51 PM EDT
[#2]
Big-Bore,

On the gas tube, you're right.  It extends into the chamber as you say.

On locking back, you may well be right.  The bolt catch has been barely holding the bcg.  I can test that today.  I will check the gas block if it is locking on the carrier.

I appreciate the warning on the CAR buffer and spring, won't do it again.

If it is short stroking and catching the bolt carrier, but the gas block is on right, what would I do next?  

Thank you for responding.

Link Posted: 4/19/2015 6:30:37 PM EDT
[#3]
Link Posted: 4/20/2015 10:40:19 AM EDT
[#4]
Yesterday I just reconfirmed one thing.  The  bolt catch, on an empty magazine, is catching the bolt face and not the bolt carrier.  

Dano532, thanks for the tips! I will check today.

Also, is it possible for magazines to cause this?  I have been using them indiscriminately so far, not thinking they might be the culprit.

Off to the workbench.

Link Posted: 4/20/2015 5:28:13 PM EDT
[#5]
Link Posted: 4/21/2015 9:36:43 AM EDT
[#6]
I checked the bolt travel.  It was able to move maybe 1/16" past the rear of the ejection port.  Played with quarters, settled on two.  Put the bolt about 3/16" in front of the rear port, also about the same behind the bolt catch.

Took it to the range.  Ran 6 different mags, 10-20 rounds each.  Ran perfect.  No FTEs of any type.  Woo hoo!

Best 50 cents I've invested in anything, ever!

I can't tell you how grateful I am for the help.  The match starts tomorrow, USPSA Mulitgun Nats in LV.   I'll just check my zero today and then get my stuff ready.

Another question:  since I limited the bolt travel with solid metal (the quarters), does that mean the bcg is slamming steel against steel at the rear of its travel?  Would some kind of a rubber/elastic shim be better?

Courses avec trois canons!

Thank you!
Link Posted: 4/21/2015 4:03:20 PM EDT
[#7]
Link Posted: 4/22/2015 9:46:03 AM EDT
[#8]
Ok and thanks.

I shoot for 2 days straight, fingers crossed.

Thanks again for the help.
Page AR-15 » Troubleshooting
AR Sponsor: bravocompany
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