Please help me troubleshoot my ARs FTF issue!

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  • BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    Just by switching uppers, lowers, and BCGs would really help to narrow things down. What say you, BigM?

    Working on it. I'm getting a new mag first off just to be sure it wasn't the mags (I only had 2 and both caused problems).

    I have a friend with a carrier I can get after that if its not the mags.

    I'll probably inspect the gas tube after that which I'll have to get tools for to take off the fsb. The whole thing is turning into a nice learning experience.

    I WILL get this resolved!! Goon as I get back from the Beach that is ;)

    Thanks everyone!
     

    photoracer

    Competition Shooter
    Oct 22, 2010
    3,318
    West Virginia
    One question is this a real PSA or their PTAC off brand. Real PSA is fairly decent but PTAC is a cheap brand not from them they took on during the "crisis" in 2012. The only problem I had with any PSA stuff was my 6.8mm upper. Could not get the round to feed cleanly and would not occasionally pick a round off the mag successfully. Tried a lot of stuff and even asked on the 68forum but ended up fixing it by taking a Dremel sanding drum and slightly expanding the M4 feed lips on the barrel and then polishing them. Now it runs as well as my 3-gun AR. The larger 6.8 rounds were hitting the feed lips and sometimes got stuck which cause the bolt to slip off the round and pass over it or to jam slightly on feeding. Tried a lot of springs and such but none of that worked. The edges of the M4 feed lips felt like they has some flash and were a little rougher than I liked. Once cleaned up it was good to go.
    Anyone who says they make a better spring for the PMag is just trying to sell you something. I never had one fail and the only reason I switched to Lancer L5s was for the steel lips and the see thru cases.
     

    Boss94

    Ultimate Member
    Feb 15, 2013
    6,945
    I have seen the same problem with some ar10s out there. The problem with the ar10s is the center line of the bore in the upper is .025 to .03 to high. A way to see if this is your issue is to push up on your mag as you are firing it or while trying to chamber a round and see if it gets any better. The mag to center line is to low and the bolt isn't able to grab the back of the round. But instead hits it about in the middle and try to push the round forward from there.
     

    BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    UPDATE:

    Well, looks like this is definitely NOT a magazine or lubrication issue.

    I lubricated according to Chad's video on youtube. Received a brand new Brownells 30 rnd magazine w/ chrome silicon spring and magpul follower.

    I still got a bunch of malfunctions with the Tul ammo. Pretty much same as before.. pictures below.

    A couple strange things happened - first when I tried to drop the bolt on a full magazine i got a FTF which looked like one of the pictures below.

    Second I got a FTF on I think the 3rd round out of the mag and I went to look at the action by tilting the rifle, it was jammed up as per below but when i returned it to vertical it loaded the round. Very weird.

    I also double checked whether it locked back on the last round in a magazine and it consistently did lock back without issue.

    It seems like there is a problem with the bolt grabbing the round from the magazine and pushing it in the chamber correctly but I have no idea how to diagnose that..

    2kq6ns.jpg




    here is what the rounds look like after taking them out:



    ww1d7k.jpg


    9rrudy.jpg



    Here is a picture of the ramps/chamber:

    52i3gg.jpg











    I have seen the same problem with some ar10s out there. The problem with the ar10s is the center line of the bore in the upper is .025 to .03 to high. A way to see if this is your issue is to push up on your mag as you are firing it or while trying to chamber a round and see if it gets any better. The mag to center line is to low and the bolt isn't able to grab the back of the round. But instead hits it about in the middle and try to push the round forward from there.

    Thanks, I'll have to check that next time.
     

    drkeg

    Member
    Jan 14, 2011
    77
    Catonsville
    On one of my uppers I had a problem where certain rounds (77gr GMM) wouldn't feed reliably. It turned out that the edges of the lugs in the barrel extension were so sharp that they would snag the round on the way in the chamber. The round would literally be wedged between two lugs at the top of the feed ramp. One of your pictures looks like that. Maybe the coating on steel cased ammo is soft enough to get snagged similarly. Very slightly smoothing that edge fixed it.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    I'd try some decent brass case ammo first, Tula and Herter's aren't exactly known for generating high or stable gas-pressures.
     

    BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    On one of my uppers I had a problem where certain rounds (77gr GMM) wouldn't feed reliably. It turned out that the edges of the lugs in the barrel extension were so sharp that they would snag the round on the way in the chamber. The round would literally be wedged between two lugs at the top of the feed ramp. One of your pictures looks like that. Maybe the coating on steel cased ammo is soft enough to get snagged similarly. Very slightly smoothing that edge fixed it.

    How did you do that?
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Maybe it's the light but it looks like those upper receiver ramps were dremeled.

    The Barrel extension can cause ammo to not feed. A cratex bit on a dremel works great to fix that.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    Maybe it's the light but it looks like those upper receiver ramps were dremeled.

    The Barrel extension can cause ammo to not feed. A cratex bit on a dremel works great to fix that.

    Page 1, the ramps in those pics don't appear to have any of the anodizing removed, but in the page 3 pics they do look a bit steeper/deeper than normal - but I'm willing to bet that's just the lighting and angle.
     

    BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    Maybe it's the light but it looks like those upper receiver ramps were dremeled.

    The Barrel extension can cause ammo to not feed. A cratex bit on a dremel works great to fix that.

    Definitely the light. I'm finding it a pain to get a good picture of that area..

    Thanks for the tip on the cratex bits, maybe I'll try that. Got nothing to lose at this point.

    Any tips on that procedure? I'm assuming the barrel needs to come off?
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    A) the feed ramps appear misaligned (thought I saw that in first pic but thought it an illusion). Looks like ramps on the bbl. extension could need some refining. Do not do this with the bbl. mounted. You don't want to grind off the anodising on the upper. The problem rests in the bbl. feed ramps. Also, BEFORE you go through all that trouble, make damned sure your gas tube is 100% in line with your BCG. The reason I say that...the up righting of the rifle/loading of the round. Take the upper, stand it upright with muzzle pointing down, drop the bolt down into it. If the bolt doesn't fully lock...gas tube is mid aligned. Solution, bend it till it is or check bbl. nut line up. I'm staying at the Hilton but, I am a graduate of the School of the American Rifle.:brows:
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    Get it functioning (reliably) first, then worry about tweaks.

    Yes, barrel comes out for the ramp work. It's a short procedure to do the ramps, and going from memory (watching Chad do one of my 300BLK barrels), the angle is relatively shallow - although that could be more for the 300BLK subs, so refer to Chad's input there.
     

    BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    Thanks Guys.

    Does it look like there is some kind of misalighment here? Is it just me?

    I scored some better pictures:

    ramps2.jpg



    20150612_193137.jpg
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    Sounds like the rifle may only need "tweeking". Fix the little problems before tackling the big ones.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    Looks like it could be a 'clicker' - bit of a uneven transition from receiver cut to barrel extension ramps.

    Take a ball-point pen and run it up and down the feed ramp/cuts, if you feel a spot in the transition where it hangs up, then it could stand some ramp work at a later point.
     

    BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    Sounds like the rifle may only need "tweeking". Fix the little problems before tackling the big ones.

    I've tried proper lubrication and new mags. Trying to tackle the small things first.. I'll check if the bolt falls into the gas tube without hitch...

    What's next , polish the ramps?
     

    BigMBobbyOP

    Ultimate Member
    Sep 30, 2011
    1,021
    PA
    Looks like it could be a 'clicker' - bit of a uneven transition from receiver cut to barrel extension ramps.

    Take a ball-point pen and run it up and down the feed ramp/cuts, if you feel a spot in the transition where it hangs up, then it could stand some ramp work at a later point.

    Just tried it. I didt feel anything. I'll try that again more thoroughly later, my wife is complaining I've been in the garage too long lol.

    Do you suggest anything further before the ramp work?
     

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