AR cycling trouble

[dobarker]

I took my newly built M4 setup out to the range today and to my disappointment, it had trouble firing through the 55 gr. fmj factory loads that I had but chewed straight through the 62 grain ss109 loads.

The problems I noticed were short strokes, the bolt wasn't going far enough back to grab the next round from the magazine. Even with the 62 grain bullets it would only have enough throw to lock the bolt back after the magazine was empty part of the time.

I'm running a 1/7 twist 16" barrel with a auto bcg and heavy buffer with standard buffer spring.

I believe the rifle is getting plenty of gas but could be wrong.

What would be the thing to do to resolve the problem?

I'm more than likely only going to be shooting 62 grain bullets out of this rifle but would like it to function with whatever I throw in it.

 

[The_Hunter]

did you fit the gas block?

 

[codygjohnson]

Is the carrier key staked? If not, check it. It's probably coming loose. When I first started building ARs I didn't realize how important staking them was until I had several come loose and stop cycling correctly.

 

[Joat]

What length gas tube are you running? you may not need the heavy buffer. Short stroking is also caused by having too heavy a mix in there.
Also check that the gas block is aligned with the gas port. (Front to back as well as side to side)
If you went with a free float hand guard, did you leave the gap between the back of the gas block and the front of the barrel shoulder? Remember that the gas block doesn't fit tight to the shoulder. If its pushed tight, you may be occluding part of the gas port.

Joat

 

[tweek]

I don't know anything, but how well lubed up was the rifle? So far I've had no trouble out of mine but I lube the piss out of it after each visit to the range.

Again, I really don't know very much, but this article seems accurate: http://www.ar15.com/content/swat/keepitrunning.pdf
Just about the opposite of what I was taught. But before worrying about all of that other stuff I'd soak it and see if the problem goes away. If it doesnt then it's time to call tech support.

 

[dobarker]

It's a carbine length tube.
I removed the gas block to check it for alignment and it was perfectly aligned while I was firing it. There was a perfect little o of carbon around the barrels gas port where the block was on it.
The gas key was the first thing I checked, removed the bcg and gave the key a jiggle, it's still tight and was bought pre-fabbed by BCM.

and tweek, I'm not the most experienced with ar's, it was well lubed by my standards, I know there's some that don't run unless they're dripping oil.

I've got a picture of the rifle here http://www.texasguntalk.com/forums/...works/17745-primary-arms-m4-clone-review.html
I honestly believe now after spending no time at all removing the gas block and an hour getting it re-aligned that it is indeed an overweight buffer or a stiff buffer spring.

On a side note though, when I removed the handguards I noticed a bit of carbon buildup at the gas block/gas tube mating, is this normal or is this point supposed to be sealed tighter than a frogs butt?

I appreciate all the help, keep the ideas coming, i'll keep stripping and rebuilding it till things go right.

 

[dobarker]

Alright high-cap, I measured the port and it's 5.5 hundredths of an inch or 0.055 of an inch.
What is the right measure of what it should be? And yes it is a daniel defense.

As well what would be the best route to go about opening it up?

 

[dobarker]

Alright, upon using the famed google device i've learned that average port hole size is between .085 and .093 which means i'm getting a little less than half the gas I should be getting to the bolt so now the question is... What way to go about opening it up? I don't have direct access to a drill press but over time can get to one. Ideas? I don't think a hand drill would be the best way to go about it but maybe a tap drill with a proper sized bit?

 

[The_Hunter]

it is not airtight, and carbon will seal it after a while.

measure the gas port in the barrel, if it is a daniel defense barrel, odds are it needs to be opened up - several including me have had that problem.

On a side note I asked a DD rep about this, the reply was that it was done intentionally so you could adjust it as needed. Much easier to take materiel out then add it back

 

[30+GSXR]

I was having trouble with my AR after replacing the single point sling attachment which required the removal of the buffer tube. I had screwed the buffer tube in too tight. Once I back the buffer tube back out 1 turn - the son of a gun started to cycle and locked the bolt back normally again.

 

[dobarker]

Thanks for the help everyone. Last night I opened up the gas port to .062 with a 1/16 bit and a variable speed drimel. We'll see how it rolls from here. I'll let y'all know how it turns out when I take her back out to the range.

 

[AusTex]

I would drop that heavy buffer keep shooting the hot stuff and do the break in process... Then go back to the comm ammo. If you can get it running with the smaller hole by all means use that. Less gas, less heat, less stress on the system. If you have to open it open it very slowly. I had this problem on a 24" bull bbl but that is the rifle system and it was also undersized b/c they make a lot of the 20"+ barrels for the hot heavy military loads. I opened it up and my problem was solved.

 

[lilricky2]

First, put the standard buffer back in. It is the easiest solution to try. Gas ports vary in dimension, even from the same manufacturer but yours MAY be on the small side. If you drill it out don't go crazy as you are probably only a few thousandths on the small side. Try changing the buffer first though.

Rick