AR-15 Help Needed: Failure to Feed

[Duster_360]

I shot a re-worked, but leg legal Colt in high power for several years and it developed a ftf and hold open problem but only offhand. Prob was eventually solved by running the BCG wet - few drops of Break-Free CLP and it never had the problem again.


I have a Colt based space gun and all 3 variants of AR-X's 6mm AR rifles and they are run wet as well with no feeding probs.

 

[Jet]

Lots of great advice. The advice from rcw3 and Racesnake would be the likely suspects. Also, does your upper receiver have mil spec feed ramps? If not and depending on the barrel you've installed, that could interefere/be the cause. Good luck getting it sorted out.

Jet

 

[jscandale]

Phil,

I would be curious to know what gas port size your barrel has. Robert is absolutely correct about the powder that you are using and it's pressure cure as it relates to the bullet weight.
If you try RL15 or Varget, you will likely never have any pressure problems even if you fill the case to max capacity with the 52-69 gr bullet weight. I would take a stab in the dark and guess that your gas port is about .089" from the sounds of it, but it's only a wild guess.

JS

 

[Phil3]

JS,

A .092" diameter drill bit fits, a bit loosely, but no larger bit fits. I am going to try the Reloder15 and Varget and see how those perform. Hodgdon H335 is supposed to work very well in ARs, so may try that, but open to other options.

Phil

 

[Phil3]

Lots of great advice. The advice from rcw3 and Racesnake would be the likely suspects. Also, does your upper receiver have mil speck feed ramps? If not and depending on the barrel you've installed, that could interefere/be the cause. Good luck getting it sorted out.

Jet

Jet,

I do not think the gun has mil spec (M4?) feed ramps. The barrel and barrel extension came from Krieger.

Phil

 

[Phil3]

Is the barrel torque ok,in another words does the barrel have any play if you try to move it and looking at the barrel nut. I have seen a few loosen slightly and cause problems that is the barrel extension.

I pulled the hand guard off, and barrel nut is tight as ever. The hand guard and barrel nut is from JP Rifles.

Phil

 

[jscandale]

Phil,

I produce several AR barrels a month. Many of them are 20" NM service rifle barrels. With barrels varying in length of 20-24", my standard gas port is .094" and are usually geared towards end users who are using heavy bullets and RL15, Varget speed powders. The 24" guns are mainly used by varmint guys who are using lighter bullets, but experience slightly more dwell time due to longer barrel length. All function very well. You would be very suprized, as I was, to learn what just .002" of gas port size will do to the cycling of an AR.
If you use the slower powders, I'm sure that you will have a good experience with a .092" gas port.

One tip; from the looks of some of the pics, it seems as though you fuse a lot of lube on the bolt/bolt carrier. Cut back on that and you will find that your cleaning process will go easier and you will have much less carbon and gunk build up due to the hot gases frying the oil every time the trigger is pulled. For many years, I have run my guns dry with just a drop of oil on the bolt cam pin. I have done this for tens of thousands of rounds over many years with almost no function issues or excessive wear.
Hope this info helps you out.

JS

 

[Phil3]

JS,

Yes, your info does help me out. Your comment on dwell time and powders makes good sense. My port size may be .094, but did not have a drill bit in that size to test. The .092 size fits loosely, and it is possible a .094 pin would fit. Still, an increase from .092 to .094 increases the area of the port by only 4.4%, which is not much, but from what you say, enough to make a difference. I am going to try a slower powder and have confidence it will be OK.

Yes, will cut back on the lube, substantially. Heard people say over and over, run them dripping wet, but not buying that.

Thanks again.

Phil

 

[johnu]

You've already received a number of good suggestions, but I'll add a couple of ideas. Failure to feed combined with failure of the hammer to reset indicates short stroking. Factory ammo is generally loaded pretty hot, I imagine with slower burning powders than N133. I've had good luck with N135 and N140. You have a rifle-length gas system, which can cause the action to run a bit softer - that's why they are preferred by three-gun shooters. "Full auto" bolt carriers (if that;s what you have) are a bit heavier which can slow things down, as can a heavy buffer. If you want to continue to use N133, consider swapping in a lighter buffer.

John

 

[Phil3]

John,

You raise something I wanted to ask about. When there was a FTF, and I pulled the trigger, there was a light click, seemingly lighter than if I dry fired the gun. Is that even possible, or am I just imagining things? I also have a Young Manufacturing National Match bolt carrier group, which is 1/2 oz heavier than a normal parkerized bolt carrier. That could contribute to the problem, even if 1/2 oz is not much.

See here for more info.

http://www.ar15.com/forums/t_3_4/552333_Review_How_to__Young_Manufacturing_Inc__Chrome_National_Match_Bolt_Carrier.html

Phil

 

[johnu]

Just a guess, but the click may be binding in the trigger pin, trigger spring or the disconnector/spring assembly. (Or you could have imagined it!) A slightly heavier bolt carrier combined with a rifle length gas system and light loads could cause your problem. As I mentioned, a heavy buffer could contribute, as well as a buffer spring that is stiff or binding a bit.

Probably not a problem on yours as you have run it some, but I had a bolt that was causing me trouble - the lugs were not mating with the lugs on the barrel extension, causing it to bind up. Kept applying JB compound on the bolt lugs and operating it manually until the lugs were lapped. Took a while but eventually it ran smoothly.

John

 

[Hal]

Clean your rifle and see if it helps the feeding. If not try a smaller resizing die, made for AR's.

-Hal-

 

[MLC81654]

Carrier key loose.
Take it off, clean, torque, stake.

 

[Beau]

When there was a FTF, and I pulled the trigger, there was a light click, seemingly lighter than if I dry fired the gun. Is that even possible, or am I just imagining things?

Probably what happened is the locking lugs were not fully seated. The hammer may have seated the lugs without firing the cartridge.

I also have a Young Manufacturing National Match bolt carrier group, which is 1/2 oz heavier than a normal parkerized bolt carrier. That could contribute to the problem, even if 1/2 oz is not much.

Yes, but N133 is still too fast. I don't even like N135 much in an AR.

 

[Phil3]

It is interesting that a friend of mine shoots a 20" AR-15, using 52 grain bullets, and N133 powder, and it runs reliably all day long. I even used his 10 round P-Mag which works fine in his gun, but again gave me FTF problems in mine. The 20" barrel would be even worse for short-stroking than my 22", yet it runs fine. My friend was running 23.4 grains of N133 in Lapua brass, and I 23.6 in Winchester brass, and even my hotter loads were still unreliable.

If it turns out to be powder, it just goes to show no two guns are identical and can behave in unexpected ways. We will see as soon as I get to the range. By the way, the 23.6 grains of N133 behind a 53 grain flat based bullet was delivering 3150 fps or so, so not a light load.

Phil

 

[Beau]

That why populations are studied using statistics, not anecdotes.