PDA

View Full Version : AR-15 Accuracy Problems???


Z.1
05-05-2011, 4:26 PM
So I've been wondering about this for a while, thought I'd ask people more knowledgeable than me.

I built my first AR about a year and a half ago. CMMG lower, DD LPK, Spikes complete upper: 16" midlength, 1:7 chrome lined.

When I first shot it, I wasn't a pro but I didn't notice any problems. As I'm sure other can relate, I had a specific idea in mind for my AR, so I quickly added a Troy drop-in battle rail (MRF-DI). It is NOT free-float

When I installed the rail, I had some difficulty getting it to seat right. I noticed that my FSB seemed to be a little crooked - it cants slightly to the right when you look down the sights.

My problem is, I cant get a tight group with it. At 100 yds from a bench my shots are scattered all over the paper. Like I said before, I'm not a pro, so i'm sure my shooting technique can be improved, but I'm not bad with other guns, and others that have shot my rifle aren't getting tight groups either - kinda sprayed around the paper.

So my question is this - could the Troy rail be putting enough stress on the barrel because of the FSB that its affecting accuracy? I know this isn't a target rifle, but I should be at least groups within a few inches, no?

I've looked at the rifling - clean and no burrs as far as I can tell
I've looked at the crown - no problems that I can see
I've used some different types of ammo, and nothing seems to group real tight

Any suggestions or explanations would be much appreciated.

MasterYong
05-05-2011, 4:33 PM
So I've been wondering about this for a while, thought I'd ask people more knowledgeable than me.

I built my first AR about a year and a half ago. CMMG lower, DD LPK, Spikes complete upper: 16" midlength, 1:7 chrome lined.

When I first shot it, I wasn't a pro but I didn't notice any problems. As I'm sure other can relate, I had a specific idea in mind for my AR, so I quickly added a Troy drop-in battle rail (MRF-DI). It is NOT free-float

When I installed the rail, I had some difficulty getting it to seat right. I noticed that my FSB seemed to be a little crooked - it cants slightly to the right when you look down the sights.

My problem is, I cant get a tight group with it. At 100 yds from a bench my shots are scattered all over the paper. Like I said before, I'm not a pro, so i'm sure my shooting technique can be improved, but I'm not bad with other guns, and others that have shot my rifle aren't getting tight groups either - kinda sprayed around the paper.

So my question is this - could the Troy rail be putting enough stress on the barrel because of the FSB that its affecting accuracy? I know this isn't a target rifle, but I should be at least groups within a few inches, no?

I've looked at the rifling - clean and no burrs as far as I can tell
I've looked at the crown - no problems that I can see
I've used some different types of ammo, and nothing seems to group real tight

Any suggestions or explanations would be much appreciated.

Those other people that shot it: are they generally good shots?

I ask because I had a buddy that kept insisting his pistol shot to the right. I tried it and had the same problem. Several weeks later we had a rangemaster shoot it that did marksman comps in the military and had an extensive shooting background. He was able to hit the bullseye every single time with no issues.

His opinion was that the grip had an odd shape (wish I could remember the make/model of the pistol) so we were having issues with it beause we just weren't experienced enough. He was right. Eventually, my buddy could hold decent groups with it without compensating for windage.

I have an AR that I can't hit the broad side of a barn door with when I'm using the iron sights- but I have buddies that can shoot it all day long. I can hit the 6" gong at my local range 10 out of 10 shots no problem at 100 yds, but I can't keep it in much better than a 5" group on paper. My eyes must just not like the irons it has much, because I can do much, much better with other rifles using irons.

Z.1
05-05-2011, 4:47 PM
At least one of them is pretty good - used to shoot competitively. I'm thinking next time I head out to the range, I'll put the original handguards back on and see if this helps? The Troys seem to have a real tight fit

SuperSet
05-05-2011, 4:49 PM
Your non-free floated rail will not have enough influence on your group size at that range with that barrel.
Forget about 100y for now. You should be able to shoot with bullets touching at 50y.

killshot44
05-05-2011, 5:01 PM
What weight bullets? I've seen a fair number of 1/7s that didn't group with 55s.

Does it group at 25 or 50? Aside from different point of impact they should be touching at 25/50.

Contrary to popular belief, there aren't a lot of factory ARs that will shoot group after group of 1MOA.

Z.1
05-05-2011, 5:10 PM
Yeah, mostly 55gr. Some 40 gr too. I've never been clear on the twist vs. bullet weight thing. Would heavier bullets be a potential fix?

Z.1
05-05-2011, 5:13 PM
At 50 its still pretty scattered. Definitely not touching. I'll have to go check @ 25... I know I can hit beer cans from roughly that distance :D

gemini1
05-05-2011, 5:35 PM
Try 62 and higher grains. I was having the same issues, I get consistent groupings at 25 yards using 55 and 45 grains but at 100 yards the 55 grns goes all over, the 45 is even worst, the 62 grn green tip solved my issues.

killshot44
05-05-2011, 5:35 PM
The heavier bullets have a longer bearing surface which works better with the faster twists.
Observe the huge difference between a 55 and a 75.
http://i878.photobucket.com/albums/ab348/Killshot44_bucket/bullets2.jpg

See if you can get your hands on some 75 or 77s to try. Shoot from a rest or sandbags. If it won't group at 50 yards with those I'd be talking to the seller about a refund. I'm not surprised that 50/55s are all over the place given your twist rate, but it should do better.

Z.1
05-05-2011, 5:42 PM
Alright, when it's explained like that - more contact area for the faster twist - it makes more sense. I'll see about picking up some heavier weight bullets and see if that makes a difference. Thank you all for the help.

Bigtwin
05-05-2011, 8:21 PM
My Father in laws AR has a similar problem. He put it together early on and it is now a RAW. The problem is he has shot it maybe 5 times since then. We went out a couple months ago and my AK had better grouping and accuracy than his AR(not normal), I realized that he was using the wrong ammo for his 1 in 9 twist 20" barrel. After he went and bought different ammo for it, the rifle worked much better. I will have to ask him what he had and what he changed up to.
I just know he had too much of the ammo that did not work well with his rifle( to the tune of 500 rounds.....ouch).

Gts408
05-06-2011, 12:49 AM
I was having the same problem with my 16" 1/7twist chrome line upper at a 100 yards. It's the barrel. Chrome line is more for plinking than shooting groups. If you want something to shoot tighter groups get a stainless steel barrel maybe 18 or 20 inch. After I switch to stainless steel 18" my groups were a lil bigger than a quarter but I'm not that good of a shot.

17+1
05-06-2011, 7:49 AM
I was having the same problem with my 16" 1/7twist chrome line upper at a 100 yards. It's the barrel. Chrome line is more for plinking than shooting groups. If you want something to shoot tighter groups get a stainless steel barrel maybe 18 or 20 inch. After I switch to stainless steel 18" my groups were a lil bigger than a quarter but I'm not that good of a shot.

Funny you say that because I saw a chrome lined AR (A4) win iron sights at the chabot offhand match last weekend.

OP: Is the rifle clean? Excessive fouling will cause the group to shotgun. Patch the bore with hoppes and let it sit. Brush the piss out of it and patch it again. I wouldn't be surprised if this is the issue. Canted FSB isn't as big a deal as it's made out to be, especially if you're shooting at 100 only.

FeuerFrei
05-06-2011, 8:51 AM
Don't over think this.
Problem started when you added 2 piece rail?
Remove rail and shoot it w/naked barrel.
Is it a clamp on front sight? Fix the front sight.
Pinned front sight? Still cycles okay? Check barrel index pin by removing barrel.
Could be sheared off and moved a tad during rail install.
Undue pressure on the barrel can change the POI.

Gts408
05-07-2011, 3:00 AM
Funny you say that because I saw a chrome lined AR (A4) win iron sights at the chabot offhand match last weekend.

OP: Is the rifle clean? Excessive fouling will cause the group to shotgun. Patch the bore with hoppes and let it sit. Brush the piss out of it and patch it again. I wouldn't be surprised if this is the issue. Canted FSB isn't as big a deal as it's made out to be, especially if you're shooting at 100 only.

I didn't say chrome line was bad. But I still think stainless is better. Maybe the people with stainless barrels weren't any good that day. That's the thing about shooting matches there can be many reasons why somebody wins. But good for them that they won with the set up they had.

But If you think it's because of a dirty barrel I would recommend using copper solvent too. It could be from copper build up.

Another thing is, what kind of optics are you using? Makes sure your scope rings are tight or check your sights if there loose. I had that problem I thought it was tight enough but after a few weekends of shooting it came loose.

But I would go with what was said above if everything was fine before the rail remove the rail and go back to the range.

Z.1
05-07-2011, 7:24 AM
Thanks for the input guys. Yeah, the rifle is clean. I'm going to be as scientific as possible on this. I bought some 62gr (heaviest they had at the local gs) and next time I go to the range I'm going to switch between that and the 55gr and see if that makes any difference. If not, I'll switch the handguards out and see if that helps before getting more invasive and removing the barrel, etc.