Please help me troubleshoot my ARs FTF issue!

BigMBobbyOP · Jun 7, 2015

Please help me, I'm having FTF issues with my AR.

What I am shooting:

Stock PSA AR-15 carbine except I put in a Tubb Precision AR-15 Performance Spring Pack

The spring pack included the following chrome silicon springs: extractor spring, ejector spring, buffer spring, magazine spring, trigger spring.

I am running 30 round mags with the Tubbs springs in them

I am running Wolf 55 gr FMJ

I am getting about about 2 FTF per 30 round magazine.

Gun was cleaned and lubed before range visit and I am running the gun 'wet'. Trying to follow what Clandestine has been advising for lubing so I'm thinking its not a cleaning / lubing issue.

Here are some pics to show what the FTFs look like:

Here is what the bolt face looks like:

Chamber:

Please let me know what other information would be helpful in
diagnosing this!

Thanks all!!

1time · Jun 7, 2015

Fire a round with an empty mag inserted and see if it locks back. If it doesn't then put the factory buffer spring in it. The tubb spring is a round about way to help with an over gassed gun. If it is not over gassed it may cause it to short stroke.

guthook · Jun 7, 2015

Was it short stroking before you put in the Tubb springs?
Also, try a different mag and ammo.

mopar92 · Jun 7, 2015

Methinks either overgassing or mag issue.
overgassing =bolt cycling too fast and riding over the top round before the mag can push it up.
Looking at the pics again the second pic might be undergassing as the bolt may not have traveled far enough back to allow the mag time to do its thing.
Of course mags could also be suspect. What brand mags and is it a no tilt follower? Does the follower travel smoothly in the magazine body?
What kind of gas system we lookin' at? Clamp on gas block? Set screw? FSB?

BigMBobbyOP · Jun 7, 2015

1time said:
Fire a round with an empty mag inserted and see if it locks back.

it locks back after the last round in a mag

BossmanPJ · Jun 7, 2015

Does it do the same with brass ammo? Also rule out the mag by trying others.

BigMBobbyOP · Jun 7, 2015

guthook said:
Was it short stroking before you put in the Tubb springs?
Also, try a different mag and ammo.

It had done it in the past as well. I want to say less frequently but there are too many variables there. I may just be shooting more now so it could be perception. But yes it had done it before the springs as well.

Same deal with different mag and Herters 55 gr HP ammo.

1time · Jun 7, 2015

BigMBobbyOP said:
it locks back after the last round in a mag

If it locks back in going with mopars answer.

obsolete · Jun 7, 2015

Mopar has some good thoughts. I'd also offer that some PSA receiver extensions are like washboards on the inside. Couple that with a flat wire recoil spring and no grease and you can count on intermittent short stroking with bolt over like in your pictures.

BigMBobbyOP · Jun 7, 2015

mopar92 said:
Methinks either overgassing or mag issue.
overgassing =bolt cycling too fast and riding over the top round before the mag can push it up.
Looking at the pics again the second pic might be undergassing as the bolt may not have traveled far enough back to allow the mag time to do its thing.
Of course mags could also be suspect. What brand mags and is it a no tilt follower? Does the follower travel smoothly in the magazine body?
What kind of gas system we lookin' at? Clamp on gas block? Set screw? FSB?

Mags are PMAGS, follower travels smoothly and is a no tilt follower.

Gas system is mid length with standard FSB.

BigMBobbyOP · Jun 7, 2015

obsolete said:
Mopar has some good thoughts. I'd also offer that some PSA receiver extensions are like washboards on the inside. Couple that with a flat wire recoil spring and no grease and you can count on intermittent short stroking with bolt over like in your pictures.

Sorry, can you explain that?

-What do yo mean about the receiver extension?

- how would the flat wire recoil spring affect things?

why would the combination cause the FTFs..

not calling you out I appreciate the info just trying to understand.

mopar92 · Jun 7, 2015

BossmanPJ said:
Does it do the same with brass ammo? Also rule out the mag by trying others.

Before anyone idiotic jumps on this. Steel cased ammo is great IF the rifle is DESIGNED for it (AK, SKS, Mosin etc). If the rifle is NOT designed for it, it can cause issues.
The primary issue with AR's and steel cased ammo is that steel is not as malleable as brass and some very important gas leaks around the chamber walls leading to undergassing issues. This is designed into the round so that extraction is easier as steel (ammo) + steel (chamber walls) + steel (BCG) creates a lot of friction for the round to overcome.

But, this has been posted before and will likely be posted again.

IF YOUR RIFLE DOES NOT FUNCTION ON SAAMI SPEC AMMO, THE PROBLEM IS YOUR RIFLE NOT THE AMMO.

mopar92 · Jun 7, 2015

BigMBobbyOP said:
Sorry, can you explain that?

-What do yo mean about the receiver extension?

- how would the flat wire recoil spring affect things?

why would the combination cause the FTFs..

not calling you out I appreciate the info just trying to understand.

PSA is typically low cost but functional. That said its not finished as well. The rough finish on the inside of the reciever extension can lead to increased drag on the action spring and BCG.

Theoretically speaking the combo of rough interior finish and flat wire action spring could lead to energy losses as the spring "jumps" over each surface imperfection.

outrider58 · Jun 7, 2015

It could be over or under gassed. Any marring or damage to the rear end of the slot of the charging handle(where the gas key might be contacting it from over gassing) or at the mouth of the buffer tube?

It could be the buffer(too heavy or too light) since the change in B/spring.

It could be the steel cased ammo.

It could be the mag. Is it a steel mag? Have you tried other mags?

BigMBobbyOP · Jun 7, 2015

outrider58 said:
It could be over or under gassed. Any marring or damage to the rear end of the slot of the charging handle(where the gas key might be contacting it from over gassing) or at the mouth of the buffer tube?

just checked, didnt notice any damage

outrider58 said:
It could be the buffer(too heavy or too light) since the change in B/spring.

I assumed I could use the same buffer but maybe I need a heavier one with the new springs? Maybe I'll try the old spring and see if that is the issue here

outrider58 said:
It could be the steel cased ammo.

It could be the mag. Is it a steel mag? Have you tried other mags?

tried multiple mags

MKR03 · Jun 7, 2015

If the bolt consistently locks to the rear on an empty mag, (and the OP has ruled out mags/ammo as the issue) wouldn't this mean the gun is more likely overgassed than under? I would throw a heavier buffer in and see if that makes a difference.

ETA: OP - Where does the ejected brass usually land? Are the casings dented?

clandestine · Jun 7, 2015

Extra power extractor springs can cause issues, but I doubt this is related.

What other ammo have you fired and seen this issue with the gun? I only ask because PMC and Steel Cased ammo are generally the worst offenders with AR reliability.

Others have brought up good points, but it is hard to say what it the actual issue, it could be undergassing or overgassing. The Gas Key could be loose or have broken Bolts, or the Gas Rings could be the cause. Are you using 1 piece rings?

clandestine · Jun 7, 2015

BTW, if its a NiB Carrier, it could be the cause in relation to my Gas Key comment. When these companies NiB the assembly they do it AFTER the Gas Key is installed, torqued, and staked. The NiB just does not hold as well on the Gas Key Screws.

mopar92 · Jun 7, 2015

MKR03 said:
If the bolt consistently locks to the rear on an empty mag, (and the OP has ruled out mags/ammo as the issue) wouldn't this mean the gun is more likely overgassed than under? I would throw a heavier buffer in and see if that makes a difference.

ETA: OP - Where does the ejected brass usually land? Are the casings dented?

Not necessarily. With steel cased ammo additional friction from the magazine full of steel ammo and spring pressure can cause the bolt to slow down enough to cause issues.

Oldcarjunkie · Jun 7, 2015

I had a rifle that would do something similar, it was short stroking. it would eject the round but then not come back far enough to pick up the next round. I first cut the spring which then allowed me to shoot brass 556, but still had issues with .223. I posted on here and was told by Chad and a few others that it was bad to cut the spring like that, i bought a new spring and kept playing with it. I then measured the gas hole and found it to be approx .070 I believe, I found out that colt uses like a .093 on their carbines so i bought a few drill bits to open up to a max of .086, which is what i ended up doing, now it runs everything with a good full size spring in there.

Please help me troubleshoot my ARs FTF issue!

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