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View Full Version : AR experts - what is up with my rifle?


Paradiddle
02-11-2009, 3:46 PM
Took my OLL to the range. DPMS upper, not sure who makes the bolt, but it is essentially unfired (I got it used).

I tried several mags (all worked fine in buddy's SU) and 3 types of ammo (cheap Norinco, Black Hills, and Remington).

The bolt just isn't cycling hard enough to feed the next round. That round in the picture is the fresh one from the mag - NOT the empty case. I stripped the bolt down and cleaned it - reassembled and had the same issue. It will fire one at a time.

Any ideas?

http://i275.photobucket.com/albums/jj289/Paradiddle11/IMG00025.jpg

http://i275.photobucket.com/albums/jj289/Paradiddle11/IMG00026.jpg

PS - my friends SU ran all day long - not a single hiccup.

SuperSet
02-11-2009, 3:49 PM
1. Is the previous case being extracted correctly?

2. If extraction is fine, are you saying that the bolt won't fully close on a new round? If yes, what type of chamber do you have on your rifle? .223 match, .223 Wylde or 5.56?

djleisure
02-11-2009, 3:51 PM
Could be something wrong with the gas system - maybe it is misaligned?

Jicko
02-11-2009, 3:52 PM
Lube heavy.... run the bolt, BCG "wet"....

Now, where does the tip of the round getting caught on?

Paradiddle
02-11-2009, 3:55 PM
1. Is the previous case being extracted correctly?

2. If extraction is fine, are you saying that the bolt won't fully close on a new round? If yes, what type of chamber do you have on your rifle? .223 match, .223 Wylde or 5.56?

It is extracting.

Not sure on teh chamber - the bbl is marked DPMS - 223 1/8 twist - it's stainless.

It ran perfect for about 20 rounds - then this started. Chamber was cleaned prior to shooting - again the rifle was unshot by the previous, and original owner.

Jeff

Paradiddle
02-11-2009, 3:57 PM
Lube heavy.... run the bolt, BCG "wet"....

Now, where does the tip of the round getting caught on?

I tried it pretty damn wet and then a little drier. Round is just sitting there - in limbo. Bolt won't close. If you pull the bolt all the way back - clear out the unfired round - and let the bolt fly home it will shoot once - then same issue.

It has a U15 on it as an FYI.

dieselpower
02-11-2009, 3:58 PM
What type / kind of Buffer , buffer spring and tube do you have?

Something could be "braking" the bolts forward movement...could even be a broken FA paw, but I think you would see scrapes on the FA cuts.

If you have a heavy buffer and poor gas issue, you wouldnt extract properly, (shotstroke) and the buffer would just bearly clear the next round, but all the energy is wasted..the buffer spring SHOULD shove the bolt into battery though.

Is the bolt release hanging up the bolt? Take the bolt out and look for any signs of scraping or wear that shouldnt be there.

dieselpower
02-11-2009, 3:59 PM
Ok U15...but what buffer spring / type buffer and size tube?

Paradiddle
02-11-2009, 4:05 PM
Ok U15...but what buffer spring / type buffer and size tube?

I believe it's a CAR buffer - I think that's what comes with the U15 because a standard buffer won't work - it hits the back of the stock.

I didn't recall seeing any marks on the bolt at the range - I'll break it down tonight and look for drag marks.

Wonder if it's the short buffer - can you run a "stock" length buffer spring in a CAR sized buffer - or will it fail to eject?

Jeff

Paradiddle
02-11-2009, 4:08 PM
Just measure the buffer tube - it's 7" long (the length exposed so not including the threads).

Jeff

dieselpower
02-11-2009, 4:09 PM
can you run a "stock" length buffer spring in a CAR sized buffer - or will it fail to eject?

dont know...I think it would still eject, but fail to feed. You are feeding, but failing to go into battery.

SuperSet
02-11-2009, 4:12 PM
Do you have another OLL complete lower? I'd slap it on there and see if it has the same problems. So, it'll help isolate the issue.

dieselpower
02-11-2009, 4:12 PM
7 is a car tube. heavy buffers slow the bolt (and cyclic rate) so look at the buffer and see if it has an "H" on the face....I think heavys are marked with an H.

aplinker
02-11-2009, 4:15 PM
1.) lube the carrier generously. Spray it down liberally with CLP, shake off excess, reinstall.

2.) load 1rd in the mag and fire. Check to see the bolt locks back. Repeat 5X's, if it doesn't lock back each time, then you're short stroking.

2a.) try someone else's mags. Your rifle may not like these.

3.) check your feed ramps and show us a pic. It's possible someone built a rifle barrel into a M4 feed ramp upper.

4.) check your carrier key bolts - tighten them down VERY well, then stake.

5.) check your gas tube to carrier key lock-up.

6.) check for leakage (fouling) around the gas block.

Casual Observer
02-11-2009, 4:19 PM
1.) lube the carrier generously. Spray it down liberally with CLP, shake off excess, reinstall.

2.) load 1rd in the mag and fire. Check to see the bolt locks back. Repeat 5X's, if it doesn't lock back each time, then you're short stroking.

2a.) try someone else's mags. Your rifle may not like these.

3.) check your feed ramps and show us a pic. It's possible someone built a rifle barrel into a M4 feed ramp upper.

4.) check your carrier key bolts - tighten them down VERY well, then stake.

5.) check your gas tube to carrier key lock-up.

6.) check for leakage (fouling) around the gas block.

^ what he said.

Feeding problems are usually because of a faulty magazine but your weapon isn't cycling right. I'd guess it's a gas tube/ key problem, but the others might be the culprit as well.

(good thinking on the feed ramps btw. It's unlikely, but possible.)

Corbin Dallas
02-11-2009, 4:31 PM
1.) lube the carrier generously. Spray it down liberally with CLP, shake off excess, reinstall.

2.) load 1rd in the mag and fire. Check to see the bolt locks back. Repeat 5X's, if it doesn't lock back each time, then you're short stroking.

2a.) try someone else's mags. Your rifle may not like these.

3.) check your feed ramps and show us a pic. It's possible someone built a rifle barrel into a M4 feed ramp upper.

4.) check your carrier key bolts - tighten them down VERY well, then stake.

5.) check your gas tube to carrier key lock-up.

6.) check for leakage (fouling) around the gas block.


UCLA is spot on and I'll add this:

If you are chambered for .223 and you're using 5.56 ammo you WILL have problems with chambering rounds.

Make sure to use LOTS of lube on the BCG.

BroncoBob
02-11-2009, 4:42 PM
I had that problem and it was caused by loose carrier key bolts. Piss poor staking done at the factory.

series8217
02-11-2009, 5:39 PM
I have a brand new Armalite/Eagle Arms upper which had a similar problem.
The gas block was leaking. Too much clearance or something. I removed it, put some black nailpolish on the front sight seating area, and reinstalled it.
I also put some oil through the gas ejection ports on the bolt carrier, and around the bolt cam key, and pushed the bolt back and forth in the carrier a few times to get the rings and bore lubed up.
Works perfectly now.

Rust
02-11-2009, 5:53 PM
Another possible contact point is the lips of the magazine if its seated to high, the lips are to tight, or the grove cut into the bottom of the bolt is out of spec. Also in addition to checking the gas key check the end of the gas tube to make sure its straight in there and not binding on the inside the of the key. Try pulling the recoil spring out, and possibly the bolt head as well and move the parts back and forth by hand feeling for any hangups.

rayra
02-11-2009, 7:06 PM
My quatloos are on a gas system obstruction. Either a misalignment at the barrel port / gas block, or possibly something like a qtip head jammed in the BCG gas assembly.

MonsterMan
02-11-2009, 7:08 PM
Check the rings on your bolt and make sure the little gaps aren't lined up. That can mess things up a bit.

Paradiddle
02-11-2009, 7:26 PM
Awesome response. I will do everything listed and report back in - thanks guys.

pedro_c111
02-11-2009, 7:27 PM
Could be something wrong with the gas system - maybe it is misaligned?

Thats the problem I had with my first build, I used a YHM gas block front sight and the hole was off by just a little so it would not cycle properly.

niko454
02-11-2009, 7:40 PM
UCLA is spot on and I'll add this:

If you are chambered for .223 and you're using 5.56 ammo you WILL have problems with chambering rounds.

Make sure to use LOTS of lube on the BCG.

+ 1 on the lube unless you're in a sandy environment. but as far as the 5.56 in a .223 chamber please explain this, because i shoot 5.56 out of mine all day long without a single problem

jfuller429
02-11-2009, 7:44 PM
+2 on running that sucker wet, just lubing the bcg makes it run great. I just used CLP. Makes it all shiney and nice too !

Experimentalist
02-11-2009, 7:52 PM
It appears that the bolt is moving back far enough, since the bolt face is pressing against the cartridge head. It's hard to tell from the pictures, but I think if the round is oriented the way it appears, then the bolt has gone back far enough to pick up the case head like it should. A faulty gas system might be the problem, but I would guess it's not.

If my observations above are correct, then one of two things are happening: 1) excess friction on the bolt carrier, or 2) insufficient force on the bolt carrier.

If your using the correct spring for the rifle, then there's excess friction somewhere. You say everything is properly lubed, and I assume you've checked that the round isn't hanging up on anything. With an unloaded gun slowly cycle the bolt back and forth, and try to see if it's hanging up anywhere.

freshdriver
02-11-2009, 7:52 PM
+ 1 on the lube unless you're in a sandy environment. but as far as the 5.56 in a .223 chamber please explain this, because i shoot 5.56 out of mine all day long without a single problem

http://en.wikipedia.org/wiki/.223_Remington

Paradiddle
02-11-2009, 7:59 PM
Thats the problem I had with my first build, I used a YHM gas block front sight and the hole was off by just a little so it would not cycle properly.

That is the same front sight that's on my build - a YHM foldable.

I see a little discoloration around the front gas tube - so perhaps that's the leak. It's hard to tell if the gas piece on the bolt is leaking - it doesn't seems excessively dirty.

I will do some more experimenting tomorrow.

Jeff

Lateralus
02-11-2009, 8:09 PM
Where are you located? Im sure an AR Doctor could make a house call.

bobbyblank
02-11-2009, 8:21 PM
+ 1 on the lube unless you're in a sandy environment. but as far as the 5.56 in a .223 chamber please explain this, because i shoot 5.56 out of mine all day long without a single problem

Read his post again,

He said .223 in a 5.56 chamber, not the other way around....

J_Rock
02-11-2009, 8:58 PM
Check the rings on your bolt and make sure the little gaps aren't lined up. That can mess things up a bit.

Nah, this is a myth. The AR can run on one gas ring so it doesnt matter of theyre lined up or not.