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Posted: 4/7/2011 4:58:09 AM EDT
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hey all,
i have a dpms lr-308 with a 24" s.s. fluted barrel that i've been working with. after several powders and bullet's, i've settled on 45.5 grains of imr4064 behind a sierra 168 grain bthp. i have been single loading it, and am amazed at the accuracy of this rifle. here is a pic of yesterday's target. i cleaned the barrel the night before, so i am thinking it takes 5 shots to foul the barrel and to get it to settle in. the bottom group about dead center is 5 shots, then shot 6 went straight up about an inch. i fired 9 more just to make sure this is where it was shooting. yeah guy's, that's a 10 shot group. now my problem starts. i loaded 3 in a 5 round mag, charged the rifle, by tripping the bolt release. first shot went 1.5 inches high, and the next 2 strung down vertical for a 1.5 inch group. i single loaded it, and it went in the center dot. without going into great detail, when single loaded it's ragged hole shooter, but when mag fed, it strings vertically. why ? what do i need to do to stop the stringing ? i have many other 223 ar's, and have not experienced this problem to this degree. all factors remained the same, bipod, rear bag, same everything, except feeding from a mag. it's not me, as attested by the groups.http://img.photobucket.com/albums/v631/splattermatic/6c937e28.jpg |
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Quoted:
hey all, i have a dpms lr-308 with a 24" s.s. fluted barrel that i've been working with. after several powders and bullet's, i've settled on 45.5 grains of imr4064 behind a sierra 168 grain bthp. i have been single loading it, and am amazed at the accuracy of this rifle. here is a pic of yesterday's target. i cleaned the barrel the night before, so i am thinking it takes 5 shots to foul the barrel and to get it to settle in. the bottom group about dead center is 5 shots, then shot 6 went straight up about an inch. i fired 9 more just to make sure this is where it was shooting. yeah guy's, that's a 10 shot group. now my problem starts. i loaded 3 in a 5 round mag, charged the rifle, by tripping the bolt release. first shot went 1.5 inches high, and the next 2 strung down vertical for a 1.5 inch group. i single loaded it, and it went in the center dot. without going into great detail, when single loaded it's ragged hole shooter, but when mag fed, it strings vertically. why ? what do i need to do to stop the stringing ? i have many other 223 ar's, and have not experienced this problem to this degree. all factors remained the same, bipod, rear bag, same everything, except feeding from a mag. it's not me, as attested by the groups.http://img.photobucket.com/albums/v631/splattermatic/6c937e28.jpg Feeding OTMs from mags scratches/dings the bullets sometimes... And by vertical stringing, how badly in a ten shot group? |
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1. Are you seating the bullets out as far as you can and still have them fit the mag?
2. Are you using a good crimp or no crimp? My guess is that you are doing #1 and not doing #2, and during recoil the bullet is banging into the front of the mag causing the bullet to seat deeper. Seat the bullet deeper and pressures raise. Pressures raising will generally yield more velocity and more recoil (negligible but an increase none the less). And that results in bullets striking higher on the target. OR: Are you resting the butt stock on something hard? Is the pistol grip touching the bench? Is the magazine touching the bench? Any or all of these can result in vertical stringing. OR: Is your barrel free floated? If it is not, then as you shoot the firearm may be walking on the rest, with the rest moving further out on the forend for each shot, putting more and more upwards pressure on the forend. That can cause vertical stringing. |
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oh boy.
2.795 to 2.80 oal. tips vary ... no crimp. rifle is a dpms s.s. 24" fluted, free float tube. now is did shoot some aussie surplus and it did a horizontal 1 1/4" group. 1st shot right, 2nd 1 1/4" left, then 3rd bout in the same hole as 1, then 4th shot bout in the same hole as shot 2, 5th shot was just left of shots 1 and 3. so it seems it's this load with 168 gr sierra bthp's. i am messing with it right now. i loaded 2 dummies. the c products 5 round mag, leakes a long scratch along the casing sides, and yep, sharp edge's. solution, drewel/files smoother. the bulets are also getting a good scracth from tip to about half way down. guess the extension needs smoothed out on the leading edges. other than that, the apears to be no run out issues, so maybe i need to crimp. the bullets are a bit away from the front inside of the mags. i want the 5 rounder for legal hunting. oh, and i'm shooting off a bipod, and rear bag. same as when single loading it. maybe the nasty scratches on the bullets are effecting, as well as needing a crimp ?? |
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Another thing to consider in a DI AR, LR, LAR is there is an incrimination of heat build-up/soak in the mag area as the rounds get exposed to progressively more and more heat as more and more rounds are fired....cartridges exposed to heat generally see a rise in velocity...
Try shooting five or six rounds at a 15 or 20 second cadence, eject the mag and look at the copper on the next up-coming round for any discoloration, usually rose colored... Most of the guys I know that shoot ARs for groups single feed to avoid heat soak in the mag, but then you have to contend with heat soak in the camber... |
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i did a lil tinkering on it, and switched out to a pmag.
here's todays 10 shot mag fed group. i got it running right now ! http://img.photobucket.com/albums/v631/splattermatic/d23b4ea3.jpg |
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