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Palmetto AR- upper to lower fit?

Discussion in 'Rifle Country' started by jimbombo, Mar 3, 2012.

  1. jimbombo

    jimbombo Well-Known Member

    I just recently built a PSA m4 carbine parts kit with PSA stripped lower. Everything used was Palmetto state armory. After the build noticed there was a little bit of slop between the upper and lower! The rifle functions perfectly, however the rattle kind of has me worried it may get worse.

    Looking at a Rock River video there was no apparent gap in fit of a Rock River upper to a Rock River lower, I know that Rock River is more money ( I prefer Palmetto over rock river anyway) But If I mate my next Palmetto Upper (mid length 16" Classic upper) to a different lower will i get a better fit??

    What kind of gap have you guys noticed with your Palmetto upper's and lowers??

  2. courtgreene

    courtgreene Well-Known Member

    There is no gap in mine, I mean no noticeable one. Fit perfectly... I really think it's luck of the draw though. You can always get an accuwedge.
    Mine is a palmettostate stamped aero precision lower with a palmetto state 14.5 m4-like upper.
  3. KansasPaul

    KansasPaul Well-Known Member

    Don't worry about the rattle - it's perfectly normal and does not effect accuracy. If the rattle just bothers you you have a few options:

    1) Purchase an "Accu-wedge" for about $7 - it fits in the back of your lower receiver and will tighten up the fit.
    2) Buy a .29 cent rubber o-ring and place it over the front lug of your upper - it will take away all the slop (5/8x1/2x1/16)
    3) Try a JP Tension spring (jprifles.com?) as it should accomplish the same thing.

    I have a "Frankengun" that is based on an Aero Precision upper and lower (bought from different suppliers) that fits like the parts were machined together. I've also got a Colt 6940 upper on a Noveske lower (both top shelf parts) that rattles but functions flawlessly.
  4. jimbombo

    jimbombo Well-Known Member

    Now which upper??!!!

    Thanks Guys this helps!
    Now I just have to decide between Palmetto's CHF( FN barrel) or the CMV lead lapped barrel (Wilson Arms) ??? Been banging my head against the wall on this one!!!

    For occasional shooter taking the rifle out 4-5 times a year and running 300 rds through it or so, will I notice any advantage of the cold hammer forged barrel??

  5. madcratebuilder

    madcratebuilder Well-Known Member

    My preference would be the FN barrel, but either well be GTG.

    The spec on the upper/lower fit is up to a .020" gap is acceptable. You can drill and tap the lower for a tensioning Screw that contacts the take down lug of the upper. This is adjusted for a near zero clearance fit, then loc-tite in place. A few manufacturers have this screw on their lowers, like AXTS. IMHO the AXTS A-DAC-F lower with the 45* selector option is the best you can buy for a dead serious carbine.
  6. highpower

    highpower Well-Known Member

    Like courtgreen I have a PSA M4 W/14.5 barrel. There is absolutely no play between the upper and the lower. When held up to the light you can't see any light (gap) between the receiver halves. On another AR I have (PWA lower, surplus upper) you can see light from front to rear and there is some play in it. I have had that rifle for over 20 years and it still shoots sub MOA with the right load.

    What you probably have is what is known in manufacturing as a stack up of tolerances. What happens is a manufacture will spec a part at X dimension + or - .001 in. If you get two parts where both are at the upper limit (-.001) and put them together, you will have .002 clearance. This could have the effect of seeming loose or in machinery causing a noisy condition. When it happens with the parts at the other end of the limit you will have a situation where they will seen too tight.

    Most times the random fitting of mass produced parts will cause no issues, but on occasion it does create situations like yours. In certain circumstances like gear fitment, manufactures will measure gears and assign them a code of some kind and set up a chart to show which gears will work together.

    On an AR, slight clearance between the receiver halves will not create any problems.
    Last edited: Mar 4, 2012
  7. Liberty1776

    Liberty1776 Well-Known Member

    KansasPaul, thanks. That's a great tip about the O-ring
  8. Captains1911

    Captains1911 Well-Known Member

    Upper and lower play is completely normal, and preferred by many over a rifle that fits so tightly together you need tools to pop the pins. There is nothing wrong with your rifle.
  9. Sergeant Sabre

    Sergeant Sabre Well-Known Member

    No advantage at all.

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