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Weird AR mag issue
llama
Member Posts: 2,637 ✭✭
When prices bottomed out after Trump got elected, I decided to get an AR. Ended up with 3, but that is a different thread...
Anyway, the first AR I wanted for accuracy from the bench. 20" heavy barrel, A2 stock, total flat top, got a 2lb trigger in there and at 20x scope. Goal is golf balls at 200...
But I need to get a decent group at 50 yards first, and that is becoming impossible. Heck, doing any kind of "what kind of ammo does this thing like for accuracy" testing is impossible...
Bench gun, so I wanted a short mag for it. Picked up a 10 round P-Mag, but it is weird. First shot is always waaay out of the group (6-8 inches high, 4 inches left at 50 yards), and successive shots move closer to POA, with the 4th and 5th shots actually being next to each other and at POA. Cold bore? Nope. Reload mag, do it again, and again first shot is way off, and each shot gets closer to POA. Cold bore, warm bore, hot bore doesn't seem to matter. Weird huh?
I insert mag with bolt open, tap mag bottom to be sure it is fully seated, and then hit the bolt release button so the bolt will slam forward (no babying it!), so I don't think it is my loading technique. If I load 10 rounds in the mag, same symptoms, but I can at least get a workable group to determine zero from the last half of the mag.
I would try testing with one of my 30 round mags, but they are too long and end up acting as a monopod on my bench when I use my front rest and bag at the rear, so a real accuracy comparison - even for that first round - isn't really possible.
Suggestions on cause or fix? Failing that, suggestions on a quality, metal (I *hate* plastic on guns!) 5 round mag (might end up going hunting with this thing one day) that is as flush as possible with a standard AR mag well are appreciated.
NOTE - answering questions by editing, so to not waste posts against the 10 limit...
quote:Originally posted by charliemeyer007
Interesting. What does it do if you drop the rounds into the chamber, by passing the magazine and perhaps damage to bullet alignment feeding.
Haven't tried that, was under the impression that there is the potential for extractor damage. However, if it were damage I'd expect all the rounds to be effected, or possibly just the first (due to not quite same experience as a gas driven cycling of the action).
quote:Originally posted by rufe-snow
Something has to be moving, from your description. Kind of doubt, that it's the mag.
I would check the scope first. Make sure all screws and mounts are tight. If everything appears OK. Take it off, and shoot it with irons, to see what happens.
If the rifles a home build. Could be anything? From the gas block, barrel, hand guards, etc. At the very least check everything for tightness.
Everybody and their BIL's are building AR's nowadays. All that gingerbread that's on yours, don't mean squat. If they don't know what there doing.
Yup, scope is on proper, mounts are secure. Scope is known-good. No irons to test with. Rifle built by PSA - my only mod has been the replacement trigger and adding the scope mount (Burris PEPR) and scope.
Not sure about a decent trigger and a scope being gingerbread, but I ain't got no tacticrap hanging off all over it.... [:D]
quote:Originally posted by Mobuck
I don't think it's the magazine. If it was something about loading the first round from bolt lock, I might think it was mag related but not a consistent moving POI.
Have you tried just loading 4-6 rounds and do you have another 10 round mag to try?
I run 10 round P-mags w/o any issue.
Have tried everything from a full 10 rounds down to 3 in the mag.
Gotta say, this is reminding me why I've not wanted an ar for the past 25 years.... (Had one when Bush I was in office, sold it during the Clinton AWB panic)
Anyway, the first AR I wanted for accuracy from the bench. 20" heavy barrel, A2 stock, total flat top, got a 2lb trigger in there and at 20x scope. Goal is golf balls at 200...
But I need to get a decent group at 50 yards first, and that is becoming impossible. Heck, doing any kind of "what kind of ammo does this thing like for accuracy" testing is impossible...
Bench gun, so I wanted a short mag for it. Picked up a 10 round P-Mag, but it is weird. First shot is always waaay out of the group (6-8 inches high, 4 inches left at 50 yards), and successive shots move closer to POA, with the 4th and 5th shots actually being next to each other and at POA. Cold bore? Nope. Reload mag, do it again, and again first shot is way off, and each shot gets closer to POA. Cold bore, warm bore, hot bore doesn't seem to matter. Weird huh?
I insert mag with bolt open, tap mag bottom to be sure it is fully seated, and then hit the bolt release button so the bolt will slam forward (no babying it!), so I don't think it is my loading technique. If I load 10 rounds in the mag, same symptoms, but I can at least get a workable group to determine zero from the last half of the mag.
I would try testing with one of my 30 round mags, but they are too long and end up acting as a monopod on my bench when I use my front rest and bag at the rear, so a real accuracy comparison - even for that first round - isn't really possible.
Suggestions on cause or fix? Failing that, suggestions on a quality, metal (I *hate* plastic on guns!) 5 round mag (might end up going hunting with this thing one day) that is as flush as possible with a standard AR mag well are appreciated.
NOTE - answering questions by editing, so to not waste posts against the 10 limit...
quote:Originally posted by charliemeyer007
Interesting. What does it do if you drop the rounds into the chamber, by passing the magazine and perhaps damage to bullet alignment feeding.
Haven't tried that, was under the impression that there is the potential for extractor damage. However, if it were damage I'd expect all the rounds to be effected, or possibly just the first (due to not quite same experience as a gas driven cycling of the action).
quote:Originally posted by rufe-snow
Something has to be moving, from your description. Kind of doubt, that it's the mag.
I would check the scope first. Make sure all screws and mounts are tight. If everything appears OK. Take it off, and shoot it with irons, to see what happens.
If the rifles a home build. Could be anything? From the gas block, barrel, hand guards, etc. At the very least check everything for tightness.
Everybody and their BIL's are building AR's nowadays. All that gingerbread that's on yours, don't mean squat. If they don't know what there doing.
Yup, scope is on proper, mounts are secure. Scope is known-good. No irons to test with. Rifle built by PSA - my only mod has been the replacement trigger and adding the scope mount (Burris PEPR) and scope.
Not sure about a decent trigger and a scope being gingerbread, but I ain't got no tacticrap hanging off all over it.... [:D]
quote:Originally posted by Mobuck
I don't think it's the magazine. If it was something about loading the first round from bolt lock, I might think it was mag related but not a consistent moving POI.
Have you tried just loading 4-6 rounds and do you have another 10 round mag to try?
I run 10 round P-mags w/o any issue.
Have tried everything from a full 10 rounds down to 3 in the mag.
Gotta say, this is reminding me why I've not wanted an ar for the past 25 years.... (Had one when Bush I was in office, sold it during the Clinton AWB panic)
Comments
added Take the magazine apart and deburr the follower and inside the body. Make sure there aren't any dents. How good a fit to the well is there.
I would check the scope first. Make sure all screws and mounts are tight. If everything appears OK. Take it off, and shoot it with irons, to see what happens.
If the rifles a home build. Could be anything? From the gas block, barrel, hand guards, etc. At the very least check everything for tightness.
Everybody and their BIL's are building AR's nowadays. All that gingerbread that's on yours, don't mean squat. If they don't know what there doing.
Have you tried just loading 4-6 rounds and do you have another 10 round mag to try?
I run 10 round P-mags w/o any issue.
1. For battered bullets when feeding - Clean barrel & chamber and very carefully load and eject a few live rounds and inspect the ejected cartridges for damage. If there is damage, it could be due to the M4 feed ramps.
2. Scope problem - switch out scopes - hopefully you have another AR configured with a scope which makes the switch easy.
3. Muzzle crown - inspect the muzzle crown - sometimes this is hard to inspect because the muzzle is recessed in the AR gas block.
4. To me it sounds more like as one person replied "AR not returning to same battery after each shot" - must be something loose or something interfering with the AR's return to battery.
Let us know what you find out and how you resolved the accuracy problem with your AR.
The barrel could be very slightly loose, I have seen receivers that had a very tight barrel fit, so much so that the barrel could not be seated properly, it seemed ok, but close but not perfect. With every shot moving it slightly till it settled itself at a certain spot and then started all over again.
I have also seen a total slick slide in barrel that could not be properly tightened do to bad tolerances, it also seemed properly tightened , never figured out if it was the barrel or upper, or barrel nut, but it was just a little off and that was enough to have flyers.
I used these same barrels on different uppers and they fit perfect and the problems went away.
So almost anything not tight enough or the least bit out of spec, or stacked minimum/maximum
tolerances ranges could be a factor.