New AR not feeding..not short cycling

LS6TT

LS6TT

Sergeant
Full Member
Minuteman
Feb 28, 2009
437
0
DFW, Texas
#1
New AR, just finished building, went shooting today. Two or three rounds would be fine then it wouldnt pick up the next round. Id pull the charging handle and it would feed.

There were a few times that even when I pulled the charging handle to cycle it wouldnt grab one.

I tried the mags (P-Mags) in a buddies AR, no issues. Tried his mags in mine, same issue.

Ideas?
 
#2
Re: New AR not feeding..not short cycling

bolt carrier group not fully cycling?
ammo issues?
magazine lip, follower or spring adjustments needed?
buffer spring to stiff?
gas block adjustable? too restrictive, or leaking?
bcg improperly lubricated?
 
#3
Re: New AR not feeding..not short cycling

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Casey Simpson</div><div class="ubbcode-body">bolt carrier group not fully cycling?
ammo issues?
magazine lip, follower or spring adjustments needed?
buffer spring to stiff?
gas block adjustable? too restrictive, or leaking?
bcg improperly lubricated? </div></div>

im almost thinking its the last, when i soaked the BCG and I mean soaked it, i was able to rattle off 10-11 rounds before it did it again.

brand new pmags, how would I adjust?
not adjustable gas block, a2 sight factory installed
brand new buffer spring so its possible it just needs to be worked out
 
#4
Re: New AR not feeding..not short cycling

How is the fit between the upper and lower?

What parts kit? What brand lower?

It could be the way the mag sits in relation to the bcg, but there could be several things effecting that.
 
#5
Re: New AR not feeding..not short cycling

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RADcustom</div><div class="ubbcode-body">How is the fit between the upper and lower?

What parts kit? What brand lower?

It could be the way the mag sits in relation to the bcg, but there could be several things effecting that. </div></div>

very tight fit

dpms lpk, rra lower (and BCG)

think its something that will go away once all the parts are broke in?
 
#6
Re: New AR not feeding..not short cycling

Try firing while pushing up on the mag.

It sounds like the loaded round is riding a little low for the bolt to catch it, you just need to figure out why.
 
#10
Re: New AR not feeding..not short cycling

I think that RADcustom and vmpgsc are right on here about this being a mag catch issue.

I am betting that pushing up on your mag may fix your issue. You can apply pressure to the bottom of the mag while shooting or rest the rifle on the mag while shooting. If it stops your FTFeed issues, you should look to your mag catch as the culprit. First, determine if it is installed properly, fits properly, and isn't loose, etc. If all that seems ok...try replacing your mag catch. It is possible that you got a bad one and it is not letting your mags seat properly, thus causing your FTFeed issues. This would be the most likely culprit since your mags worked in another AR, but not yours.
 
#11
Re: New AR not feeding..not short cycling

Okay good, ill check that out tonight. do cycling to see if that squares me away.

I appreciate the quick help guys.

just for your viewing pleasure, the AR in question

IMG_0984.jpg
 
#12
Re: New AR not feeding..not short cycling

Are you shooting handloads or factory ammo?

#1...If handloads, what is your OAL, they MUST be under 2.26" for aluminum mags, maybe shorter for some P-mags. Sounds like noses of your bullets dragging the front of the mag.

#2...Possibly a mag catch out of spec, change it with your buddies gun and try.

#3...Possible gas issue (irratic pressure in handloads or gas port size borderline for ammo used...), to check...

Load ONE round, fire, does the bolt lock back?

Do this 6 times, it should lock back every time.
 
#18
Re: New AR not feeding..not short cycling

key prop staked and tight, mag catch wasnt too tight (followed the directions on AR15.com) but went ahead and loosened it one turn.

ill try and get some range time next weekend to test it out.

if it is a gas issue i cant think of any way to fix it...
 
#19
Re: New AR not feeding..not short cycling

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scottmilk9</div><div class="ubbcode-body">its a gas issue, either underpressured ammo or gas block needs to be adjusted slightly.</div></div>

I agree with Scott. I built a AR a few years ago from the ground up and screwed up the gas tube. The screw up resulted in exactly what you are seeing.... The other reason I agree with Scott is he is one of the most knowledgeable AR builders I know.
 
#21
Re: New AR not feeding..not short cycling

Did you make SURE the gas block port is exactly lined up with the barrel port? Not too far forward or back or slightly turned?

You can check and see if it's a gas problem by doing the lock back test I mentioned earlier.


Also, looking at your pic, have you modified your stock length with an adapter for flush cups? Did you change the screw that holds the stock to the buffer tube?

When you pull your charging handle back all the way, does your bolt come back past the bolt catch by about 1/8", or is it very close?
 
#22
Re: New AR not feeding..not short cycling

ill check the gas block but it was installed when ordered from dsg and i assume installed by armalite. ill do the same on the gas tube and make sure there is no bends or isnt turned slightly

no modification to the length (i think your seeing my quick sling detach, it mounts over the a2 stock)

yes the bolt comes back past the catch about that far
 
#23
Re: New AR not feeding..not short cycling

my brother just build an ar and the buffer was a little to big (long) so it wouldnt always chamber a new round after a shot it would bounce back to fast
 
#24
Re: New AR not feeding..not short cycling

so i may have had a gas leak. pulled the handguards noticed residue on the tube. i pulled the pin noticed residue around the hole on the tube as well. block is lined up with the hole. tube isnt bent.

i put the tube back in and we shall see

i did loosen the mag catch as well
 
#26
Re: New AR not feeding..not short cycling

thats kind of what I thought.

ill test it out hopefully this weekend and see if those two did the trick. if not, dont know where to go now
 
#27
Re: New AR not feeding..not short cycling

Alex

I'm in the aerospace business and I can tell you, even when you spend big $$, quality escapes happen all the time. It's just part of manufacturing. The mark of a good company is how they treat you when you are the lucky recipient of said defect. I had a similar problem with my POF 415. With more than 1 round in the mag the BCG would jam on the next round in the magazine and would stop before the bolt face was fully seated in the chamber. It didn't matter if I changed mags, same issue no matter what. Spoke with Darrell @ POF at length and he said it sounded like the feed ramp needed to be polished (there was a small but noticeable burr upon visual inspection). He had me send in the upper, at POF expense, and they polished the feed ramp and put a new bolt in for me free of charge. Upper came back this week with no burr and a letter stating it had been tested with no issues. I have not had time to go back to range, but I do not anticipate any other issues. BTW, ammo in question was Remington UMC 55grn FMJ. Can't say enough good things about the customer service, Darrell and John @ POF were both very helpful and went out of their way to make sure I was satisfied. The only downside to the whole thing was nobody told me the new roller cam pins were in and I'd have gladly paid for one to be put in at the factory while it was being worked on. Gonna rectify that next week though!

Overall great job Team POF!
 
#29
Re: New AR not feeding..not short cycling

thanks for the help guys. as soon as I get some range time Im going to do the one round at a time and make sure the bolt is locking back.

we shall see
 
#31
Re: New AR not feeding..not short cycling

Does the end of your gas tube bind any at all in the bolt carrier key?

If it's not in-line, drag can use up some of the energy that's supposed to be kicking your bolt carrier group to the rear over the friction of any new coating inside the upper and from the top round in the magazine.
 
#33
Re: New AR not feeding..not short cycling

i was having a similar problem with my new ar. but mine wouldnt fire semi at all. i ended up cutting about a half inch off my buffer spring. now it works great. the spring was 13" before I cut it. might consider it takes only a min with a pair of good snips.
 
#35
Re: New AR not feeding..not short cycling

i guess there is a very long spring length spec. something like 11.25" to 13.00" Thats what i was told but would recommend looking it up yourself if youre questioning.
 
#36
Re: New AR not feeding..not short cycling

LS6TT- have you cracked the action, and with the muzzle pointing 45 degrees down, pulled the bolt carrier group to the rear, then let it go? It should fall forward and lock the bolt up under its own weight. If it doesn't-check to see if the gas tube is dragging in the gas key.
 
#38
Re: New AR not feeding..not short cycling

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">LS6TT- have you cracked the action, and with the muzzle pointing 45 degrees down, pulled the bolt carrier group to the rear, then let it go? It should fall forward and lock the bolt up under its own weight. If it doesn't-check to see if the gas tube is dragging in the gas key. </div></div>

just tried it, locks in place everytime.
 
#39
Re: New AR not feeding..not short cycling

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">Does your bolt have standard gas rings or a one-piece McFarland? You may have more friction there, too. </div></div>

neg, standard rings
 
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