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Posted: 4/19/2009 9:16:56 PM EDT
| I just finished putting together a new to me weapon. I have a DPMS lower, Adj carbine stock, and DPMS parts kit. I mated it to a slighly used 14.5 " (w/ 1.5" muzzle brake) Bushmaster upper that I bought complete with BCG. Everything passes function checks fine. I took it out and shot it but the groups were 3-5" @ 100 yds and I was getting flyers left, right, up and down. I happened to pull the mag and eject the live round to find it had severe scratches and gouges in the bullet and case neck. I inspected the rest of my spent cases and they too had gouges in the neck area, long scratches on the body and small dents 1/3 the way down the body from the shoulder. These were fired from several different mags. It seems to me that the feed ramp/ bolt lug grooves correspond to the dimentions of the gouges, but I can feel no burrs or the like. It doesn't have M4 feedramps in either the barrel or reciever. I have done extensive work with accurized turnbolts for benchrest and long range shooting, but I am new to AR's Any insight would be greatly appreciated. |
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Welcome to ar15.com and to the troubleshooting forum. You did not mention the ammo. Some shoots better than others as far as accuracy. Sorry about no extended feed ramps. BM was the last mfg. on the planet to offer those. Those gouges and dings are often caused in the extraction part of the cycle rather than the feed part of the cycle. Slices in the bullet gilding is usually caused by banging around the lugs during the trip to the chamber.
See if you can find some 69 grain HPBT or Plastic Tip ammo that has an O.A.L. just under the 2.260 magazine limit. That might improve your accuracy somewhat. Are you shooting off bags, or bipod or what? [edit]PS: If you are concerned about loss of accuracy caused by the autoloader, you can manually and gently insert some rounds and see if there is an effect. |
| I have been using 55 gr Hornady V-max rounds. They have the polymer tip and are very consistent in other rifles I have. My friend had a Bushmaster and he said that he never saw any bullet damage in his and it would regularly shoot 1 MOA groups no problem. I'm barely getting 3 MOA with flyers out to 5 MOA. I bought this with coyote hunting in mind, but didn't expect more than 200 - 250 yd usage (I have other weapons that can reach 500 + yds). I am somewhat disconcerted with the performance when I have read about other AR's that hold 1 - 1.5 MOA on similar configurations. Would a different upper, barrel or extension be better?? |
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Go here: http://www.ar15.com/content/manuals/m4milspec.pdf [edit]figure 1, page 10, for MilSpec on 100 yd accuracy requirements for the M4 carbine configuration. If you are running outside those maximum allowables, then you have reason for concern.
I mentioned the 69 grain because it has a better BC and less effected by wind. As a Turn Bolt BR shooter, I am surprised you did not mention the crappy trigger feel. Most people who want good accuracy off-hand or on the bipod spend the $200-$300 for a trigger upgrade on the lower first. Yes, a wylde chambered, longer bull barrel, 1:8 twist, protected crown, no FH, upper would probably be a good choice for more accuracy 100yds and beyond. As to critical assessments about AR performance on the arfcom network here, there may be some "faith based" influences creeping in from time to time. With usage and time, often the sharp edges of the lugs on the bbl extension wear smooth and the bullet torture abates. |
| I didn't think the trigger was all that bad. A football field worth of creep, but a fair break. Although, I have shot a 1.36" 5 shot string with a Ruger M77 MkII and its lawyer-proof 9 lb trigger though. But I can see your point on a better trigger would help. I figured for a fairly short barreled weapon there would need to be some room for interpretation on accuracy. I read the Mil-Spec you listed and the only mention of accuracy is a 16 x 22 target at 100 yds and a ten shot group. I have an XD 45 that can do that. What in most peoples opinions is the average 100yd accuracy of an M4? Can bolt lug mortices be smoothed without danger to structural integrity? I'm not trying to be cynical, but I chose an AR because of all the good things I've heard lately and overpassed a Mini 14 with better accuracy at half the price. Where do the AR's really shine that justifies the cost? Or do I need to drop another 2 G's to find out?..... |
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Quoted:
I mated it to a slightly used 14.5 " (w/ 1.5" muzzle brake) Bushmaster upper that I bought complete with BCG. Could the barrel have been shot a bit more than advertised? 
Test your ammo in another upper if possible. As far as bullet scratches go... http://www.ar15.com/forums/topic.html?b=3&f=118&t=408777 |
| That last link was more than invaluable. I appreciate all the good advice. I need to make another trip to the range and check the accuracy while single loaded vs. mag fed. I was told that the previous owner only fired 80 to 100 rounds before selling. Maybe this weapon needs more break-in to aleviate some of my problems. Only time will tell. Does anyone have suggestions on aftermarket triggers, ie. Timney, Jewel, etc.?? |
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Quoted:
That last link was more than invaluable. I appreciate all the good advice. I need to make another trip to the range and check the accuracy while single loaded vs. mag fed. I was told that the previous owner only fired 80 to 100 rounds before selling. Maybe this weapon needs more break-in to aleviate some of my problems. Only time will tell. Does anyone have suggestions on aftermarket triggers, ie. Timney, Jewel, etc.?? Geissele DMR. Love it. |
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I am sorry if I misled you on the MilSpec. [edit]Acceptance at the factory is allowed a 5" group at 100 yards for 10 rounds, with 3 rounds allowed for warm-up. The large dimension is to assure the iron sight adjustments are effective to bring it back on zero. If the group is falling outside the large area, the sights are off, the front sight base is twisted, etc. The ammo for test is M855 or approved equivalent. This is for new equip. After break-in there should be some improvement.
One thing you might want to do with that 80-100 rd. upper is use some agressive copper solvent to assure the hard chrome liner is not laced with copper from the bullet gilding. Regular CLP for cleaning will not get it out. You can tell if the solvent takes on a blue tint. Then make sure (and this is not easy) that the crown and flash hider are free of copper deposits. As the barrel breaks in you will find less and less copper. Hard chrome does not really "break-in" like your CMS or SST BR stuff does. But, the bbl lasts alot longer. |
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