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Thread: AR-15 buffer weight

  1. #1
    Member martentrapper's Avatar
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    Default AR-15 buffer weight

    Bought a 6.8 barrel and built up an AR. Having a heck of a time getting it to fully cycle. It was short stroking. Changed bolt carriers (not bolts) and it now will cycle enough to pick up the next round, but won't quite cycle far enough to lock back after the last shot.
    I see you can remove the plastic end on the buffer and, I assume, remove weights inside, or add. Is that a feasible remedy?
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    Member ak_sierra's Avatar
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    Buy a heavier buffer and that should fix the problem. Check Bravo Company USA, they have them and ship to AK without going crazy on charges.

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    Member Bsj425's Avatar
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    Is it a gas or piston upper ? If it is a piston gun you may have to adjust the regulator. Also in a pinch cutting a few coils off the buffer spring will work only problem is it isn't always a for sure fix and is not reversable. But It has worked for me In the past.

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  5. #5
    Member martentrapper's Avatar
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    Gas upper. If the bolt won't blow back far enough to lock back, how is installing a heavier buffer going to help. I was assuming a lighter buffer would allow more travel of the bolt carrier.
    Have thought about the spring. This is an A2 stock I want to use with the upper I built around the new barrel. How many coils have you tried, Bsj?
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    Member Bsj425's Avatar
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    I started cutting 1 coil at a time until it cycled reliably then cut probably 1/4 of a coil more for good measure. Mind you I had an extra spring on hand but no buffer. So if you booger it up too may you may ruin your spring.

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    Member Bsj425's Avatar
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    Another thing I check first before you do that is to make sure the gas block ( or front site post) or whatever yours has is properly aligned with the gas port on the barrel. I have seen it more than once where they are slightly off blocking some of the gas thus not giving it enough to cycle.

  8. #8
    Member martentrapper's Avatar
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    Have used 2 different lo pro GBs. Made sure they were clean as well as the hole in the barrel. Made sure the GB aligned properly with the hole in the barrel. Before I changed bolt carriers, I couldn't even get any ammo to feed, it was short stroking so bad. Pretty sure trying a different carrier helped. The carrier will lock back when shooting factory SSA ammo w/140 gr. bergers. None of my handloads will lock the bolt back after last round.
    I was trying to get the roll pin out of the buffer tonight so as to remove one of the weights. Don't have a good punch at home. Maybe I'll try the spring shortening and see what that does. I have 4 different lowers and this upper w/ new barrel won't cycle on any of them.
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    Member AKDoug's Avatar
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    I never cut springs. Spring rate on an AR isn't nearly as important as buffer weight. What weight buffer you have now? What are you hand loads? They may simply be too light for this barrel.
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  10. #10
    Member martentrapper's Avatar
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    This is an ARPerformance 20 in. barrel. I also have a stag 20 in. in 6.8. Same handloads work fine in the stag. Handloads also work in a 6.8 PSA upper with 18 in. barrel.
    I don't know what weight the buffer is. It is a buffer that came with this A2 stock, as is the spring.
    The gas hole in the stag barrel is larger than the hole in the ARP barrel.
    Would a lighter buffer work? Looks like I can remove the roll pin in the buffer and removed one weight.
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    Sponsor ADfields's Avatar
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    Iím not a big AR guy, I do work on them and build some parts so here is what Iím getting from your posts here.
     
    You say this new upper wonít run on another proven lower? If so what makes you think itís the buffer, spring, or anything in the lower? Will this new lower run when you put on one of your proven 6.8 uppers? I suspect it will and then youíd know for sure the problem is in the upper not the lower. You may be able to compensate for an upper issue by tweaking the lower but that isnít ďfixingĒ the issue itís working around it and likely to have negative side effects.
     
    My suspicion is that itís an upper problem because it doesnít run on a proven lower. You have a gas port restriction of some sort. Could be that smaller gas port hole is just too small for the pressure curve of your loads. Your gas block may be miss aligned or something drilled slightly off restricting flow. Gas tube may have a restriction of some type, debris, kinked, not well seated on one end, leaking? For some reason you are getting insufficient gas to the bolt is what it sounds like to me.
     
    Could also have a sticky bolt lock-up or a lot of excess drag on the carrier taking more force to move it. But I think you would feel that when you cycle it by hand so Iím more inclined to think gas issue.
    Andy
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    Member AKDoug's Avatar
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    I didn't know you had an A2. That makes it a rifle buffer and there really is only one rifle buffer weight. Looks like you might need a lighter spring now. I'll keep doing some research for you. All of my experience is with carbine length stocks.
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  14. #14
    Member AKDoug's Avatar
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    BTW. Buffers can be disassembled. Drive out the pin and carefully work out the plastic end. Unfortunately you need all the weights in place or it will pound itself to death. There should be a slight space (you can hear it when you shake the buffer) but that's about it. The weights are a combination of steel and tungsten in a carbine buffer. I don't know what's inside a rifle buffer, but I'm going to find out for you.

    ARP does warn us that some ammo won't work in their barrels. I think your other barrel is over gassed and that's why your reloads work in it.
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  15. #15
    Member AKDoug's Avatar
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    After a bit of research, it looks like you might want to start with a reduced power spring. Wolf sells one http://www.gunsprings.com/index.cfm?...2&mID=1&dID=79 You want the 16505.

    I
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  16. #16
    Member AKDoug's Avatar
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    Inside the rifle buffer should be three steel weights and an aluminum one. You'll need another rifle buffer to steal an aluminum weight out of it and replace two of your steel weights with them.
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  17. #17
    Member AKDoug's Avatar
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    That should have said five, not three. It was getting late last night. Anyhow here is a picture. Remember that you CANNOT use a carbine buffer in a rifle length A2 tube. Length of the buffer is critical. You can modify your rifle buffer, though. There also is nothing wrong with making your own weights if you are technically savvy enough to do so.

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  18. #18
    Member Scorpion8's Avatar
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    Sheesh, LONG before I started fiddling with the buffer, I'd look at the gas rings on the bolt. Make sure the 3 rings haven't lined up. If that's not it, and swapping bolt carriers hasn't worked (as above) then try the one-piece gas rings and clean/lube the carrier. Make sure there's no crimp in the gas tube. Try a different upper and see if it cycles fine there, then you know the problem is "inside" your upper.

  19. #19
    Member AKDoug's Avatar
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    Rings lining up is a wive's tale. It has no effect on function. We've tested it repeatedly, an AR will run on ONE ring. Not for long, but it will run.
    Lube I agree with. Run it wet and see if it helps.
    Using another upper will not test a buffer in the lower unless it's the exact same spec upper he is testing, which they aren't. His other barrels have larger gas ports so they will run on a heavier buffer than one with a smaller gas port.
    The other option is to open up the gas port on his ARP barrel to the port size of his other barrels, but I would do that as an absolute last resort.
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  20. #20
    Member martentrapper's Avatar
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    Thanks for all your time Doug. And thanks to the other commenters. I think AD is right. The problem is the upper. I have shot this ARP barrel upper on other lowers with 6 pos. stocks and it doesn't fully cycle with them either.
    I'm confused on the reload aspect. This is the 4th 6.8 upper I have owned. Any loads I made up worked in the other 3. Why would ARP use a gas hole size that only runs the highest pressure ammo? Being in Alaska, there's no point in owning a barrel that will only shoot factory ammo........it's too hard to get here. Some of the reloads I have shot in this upper show flat primers. That means high pressure, yet they won't blow the BCG back far enough to lock the bolt.
    I have one other avenue to try. I have an adjustable GB. I could try it. However, it is a clamp on type by JP enterprises. Might be difficult to get perfectly lined up with the hole in the barrel. Won't get to the range until sunday. I'll have some more ammo loaded up. I have H335, AA2200, R10x, and AA2230. Have several size bullets. 120s, 130s, 110s, 85s and 90s. Wasn't planning on trying any 85s or 90s.
    I can't help being a lazy, dumb, weekend warrior.......I have a JOB!
    I have less friends now!!

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