Strange grouping, any ideas?


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hq
November 26, 2012, 07:33 PM
I got back from the range a while ago, sighting in my Remington R-25 because it has acted strangely. And it did, again.

Normal five shot 100yd groups were about .75", with Magtech 150gr factory ammo. They open up to about 1" average with cheap, old german surplus ammo and at worst they're 1.5" with south african suplus stuff. No problem there.

However, every now and then the groups open up considerably, no matter what ammo I'm using. Up to 5" and I mean they're consistently all over the place. It happens both hot and cold, after just a few rounds or after half an hour of almost continuous shooting.

Barrel crown is pristine, so is the bore as far as I can tell. I though it might be copper fouling and cleaned the bore with foam, three times. Didn't help. Free float tube isn't binding, neither is the gas tube. I shoot from a sandbag rest, current scope is Meopta 4-12x50 which keeps zero flawlessly on another rifle, I've also tried Zeiss Conquest 3-9x40 which didn't help. The barrel isn't worn out, I've only shot about 300-400 rounds through it and I'm running out of explanations for what's going on.

Any ideas what to check next are very welcome. I really like this rifle, it's been very accurate so far and unexplainable sudden loss of accuracy sounds very strange.

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plouffedaddy
November 26, 2012, 07:36 PM
Do you sometimes drink a lot of coffee before shooting? I've seen that impact shooter accuracy...

You didn't mention it but I'm assuming you're taking wind into account.

Sheepdog1968
November 26, 2012, 07:44 PM
A group opening up can indicate that you are not focusing on the front sight before the bullet leaves the barrel. In the case of a scope (which is what I'm assuming you have) are you transition from looking at the reticle to the target impact. Have you changed target types recently so you can now see impact through your scope?

Revoliver
November 26, 2012, 07:59 PM
Where are you shooting and are you alone or near other people? If near other people, are any of them using muzzle brakes? I can account for some pretty piss poor shooting after trying to time my shots between shooters in lanes on either side of me using muzzle brakes. Not many mind you, I'm still no where near as good as I used to be, but there are definately a few groups I've shot with piss poor flinching going on due to the surroundings.

hq
November 26, 2012, 08:04 PM
Thanks for the ideas. I'm fairly confident that the human factor can be excluded, this is the only rifle I'm experiencing this problem with and this time I even took my son to the range to shoot the gun and verify that it's not just me. The results were identical, loss of accuracy is truly random and very puzzling. 5"@100yd isn't totally unacceptable for a deer gun, but that's a bit worse than I'm comfortable with.

I've thought about taking the whole upper receiver apart, cleaning, deburring and polishing everything, if I can't find an explanation otherwise.

hq
November 26, 2012, 08:05 PM
And, I'm shooting practically alone. No-one else at that particular range at the same time.

Revoliver
November 26, 2012, 08:07 PM
Is the ammo being used always the same?

hq
November 26, 2012, 08:20 PM
Same ammo. I buy it in cases of 200-500, often several cases with the same batch code. I reload, too, but haven't really had time to develop a custom handload for this rifle yet.

VAPOPO
November 26, 2012, 08:28 PM
How is the trigger? does it break consistantly? If the accuracy changes but comes back it has to be something you are doing. When a rifles accuracy goes to pot it just doesnt come back intermittantly. Try using a plastic bore brush with sweets 7.62 on it let it sit an hour then do it again followed with a good CLP to neutralise the amonia and dry patches untill they come out clean and dry. I've had poor luck with the foaming cleaners.

hq
November 27, 2012, 08:37 PM
Thanks VAPOPO, the trigger question is a very valid one. The rifle currently has a stock trigger, only polished slightly, which means about 5-6lbs. I'll drop in a JP or Geissele from another rifle and see what happens. Actually, now that you mentioned it, I got a flashback - the only time I've experienced anything like this before was about 20 years ago, with an AK that not only had a horrible, gritty trigger pull, but also world-class trigger slap which occasionally made me twitch without even consciously realizing it.

I'll pick up a bottle of liquid copper remover, clean the bore one more time and see how the rifle works with a proper trigger.

chaser_2332
November 27, 2012, 08:44 PM
quit cleaning the barrel so much, let it foul up. most rifles shoot better fouled up. The barrel on my match rifle now has around 1000rds of 260 thru it and not once has it been cleaned.

hq
November 27, 2012, 09:05 PM
I left the barrel alone at first, cleaned it twice with a boresnake during first ~200 rounds and only after the problem first surfaced, I cleaned it properly and tried to remove copper fouling.

I've thought about hand-lapping the barrel, it has helped me many times and sometimes the results have been nothing short of spectacular, but that's the last resort (and most likely unnecessary) because the rifle already has a history of being quite accurate. I'll have to see what happens with a better trigger, I really hope this is a case of an unconscious operator error.

kingcheese
November 27, 2012, 10:57 PM
What's your stance? Change location of shooting? Anyone as a backup shooter to verify accuracy, if the rifle is scoped check your rings, my guess is that its the muzzle, or the handgaurd, i have seen ars group horribly because of a poorly installed muzzle break

Andrew Leigh
November 28, 2012, 01:20 AM
How tight are your actions screws?

It would be nice to see a photo of the group in question as shot patterns can be very diagnostic.

VAPOPO
November 28, 2012, 05:04 AM
Andrew this is a AR 10 based semi auto rifle. There are no action screws.

urbaneruralite
November 28, 2012, 07:34 AM
Are you closing the action the same way each time? If you're going to hunt deer with it you may need to settle on a fairly quiet way to consistently get the bolt all the way home. With my AR15s I use the forward assist while pushing in on the bolt with my thumb, then I bear down on the button after it's all the way in. Keeping them wet seems to help.

Andrew Leigh
November 28, 2012, 08:31 AM
Andrew this is a AR 10 based semi auto rifle. There are no action screws.
I ought to read slower next time.

hq
November 28, 2012, 08:37 AM
"Bad" 10-shot groups look like a buckshot shotgun blast, which makes them difficult to analyze. Hits are uniformly all over the place and wander randomly; one hit may be 3" off at 11 o clock, next one 2" at 3 o clock the next one 2" at 7 o clock and so on.

I let the gun feed from the magazine, chambering the first round with bolt release button. That hasn't affected accuracy before, with the same ammo. All screws are tight; scope rings, mount base and I even made sure the float tube is too, with an oil filter strap tool. Scope rings are lapped straight on the mount so there should be no torsion there. I only use one range for testing. If all groups were bad, this would be much easier to diagnose, but accuracy varies from group to group. Approximately two out of three are nice and tight.

One thing that I just realized is that a while ago I bought new magazines. They feed reliably and they don't seem to damage the brass, but now I'll have to double check their lips and follower for the feed angle. It doesn't take much to unseat the bullet and we all know what that does to accuracy.

helotaxi
November 28, 2012, 09:10 AM
I have an AR that acts similarly. I've torn it down twice and found various things that were not as I wanted them. I finally narrowed it down though to a burr in the feed ramps that is gouging the bullets as they feed from the left side of the magazine causing those bullets to go rogue.

Number your magazines and see if it happens with a certain mag or with all of them. If it is with a certain mag only...if they weren't so expensive for the .308 based rifles I'd saw set it downrange as a target.

Ramone
November 28, 2012, 09:11 AM
I had an AR15 mag that sat just a little low, so the tips of the bullet were getting dinged when feeding from it.

acted just like you are describing- took me a while to figure it out, even though my mags are marked, as it didn't occur to me that a mag might be an accuracy issue.

hq
November 28, 2012, 03:18 PM
Ok. Dry testing for function. I chambered rounds from all magazines and with the exception of slight scratch marks from the barrel extension / lugs, they all seemed fine. Not truncated our out of shape in any way. Curiously, the new magazines sit 2mm (.08") higher than OEM, but that didn't make a difference in function or scratch marks on the brass/bullets. Feed ramps look fairly smooth, the only sharper edges being near the lugs. Nothing out of the ordinary compared to AR15:s.

JP trigger went in. I'll try to get to the range later this week and see what happens.

adelbridge
November 28, 2012, 05:13 PM
From your original post I gather it shoots .75 and opens up to 5" groups- does it randomly go back to normal tight groups? I have the same gun and best I get with good ammo is 1.5" groups. I tore that stock trigger out the first week and replaced with a G-Trigg. I notice my chambered rounds are gouged up pretty good when I remove a live one but it doesnt seem to bother 100 yard accuracy. The one thing that puzzles me is the camo dip can't possibly be a uniform thickness and it covers the picatinny rail. I scraped off the camo on the rail as it would certainly flake off under scope mounts.

hq
November 28, 2012, 07:28 PM
adelbridge,

It does exactly that. One group can be (and usually is) well under an inch, the next one five and the following one again under an inch. Mine seems to like Magtech 150gr and Lapua Mega 180gr. I have high hopes for Hornady Superformance, I'm about to try it as soon as I get this random accuracy problem sorted out.
Having some personal experience with water transfer printing, I'm not sure if paint + dip + clearcoat affect the rail that much, especially when the scope base is tightened as tight as mine. The rings themselves are mounted on a 7/8" spacer.

Bullets definitely get a beating when chambered, but that doesn't seem to affect accuracy most of the time. Brass doesn't and it looks perfectly reloadable.

1 old 0311-1
November 28, 2012, 09:12 PM
Broken mechanical things STAY broken. Using the same ammo that leaves something loose, changing point of impact, or operator issue.
I would start by checking ALL screws, and pins. That removes any mechanical issues.
From there I would have someone else try and see if they get same results.
I am betting something loose.

chris in va
November 28, 2012, 10:54 PM
Check your rings. Saw a similar issue at the range, guy was getting intermittent grouping issues and we found the rings weren't screwed down properly.

3twelves
November 28, 2012, 11:04 PM
Glitch in the matrix?

fishshocker
November 28, 2012, 11:32 PM
Maybe loose scope mounts.

murf
November 28, 2012, 11:40 PM
change the scope and try again. especially if your group center changes.

murf

Fatelvis
November 29, 2012, 12:56 PM
I agree to check your scope base screws (if possible), ring screws, and action screws, to make sure they are all torqued properly.

hq
November 30, 2012, 10:42 AM
Back from the range again. Good news: I couldn't duplicate the problem this time. All groups were nice and tight, averaging about 1", both with Magtech and german surplus ammo.

The only changes this time:
o Trigger group
o Thoroughly cleaned barrel

Even surplus ammo grouped better than usual and POI of different ammo was closer to each other than ever before, which leads me to believe there has been something wrong with the barrel for some time. Most likely copper fouling foam couldn't remove. The rifle was accurate earlier with the stock trigger, it's going back in for now; the competition trigger is way too light for hunting anyway. I'll try to find time for a final sighting in before hunting trip next week, and to confirm that the intermittent accuracy problem doesn't return.

Thanks to everyone who posted. Almost everything you mentioned has now been checked and double checked and if everything goes smoothly on the next range session, my confidence in the rifle is pretty much restored.

I'll probably have to try out Superformance ammo at the same time, there has been sightings of a 20+ point moose in the area where I'll be hunting next week... ;)

ms6852
November 30, 2012, 01:16 PM
The scope you have mounted may be the culprit. Exchange the scope and put that scope on another rifle. Shoot it several times for for several periods just to see if the cross hairs are floating intermittently. If this is not check the gas tube make sure it is not loose or has a dent or bent incorrectly.

hq
November 30, 2012, 01:42 PM
Thanks, ms6852.

I've tried three quality scopes on the rifle, Zeiss, Meopta and Nikon Monarch, which didn't help. They all were on different mounts and lapped rings, so I think scope and mount can be ruled out. I cleaned the rifle again a while ago and noticed that the barrel seems to stay much cleaner than it did before I got all copper fouling removed.

Mr. T
November 30, 2012, 06:18 PM
I watched a similar issue going on with a gentleman at the range roughly a year ago....turned out that the mount had some loose screws. The owner overlooked it because he was certain that those screws were torqued down properly. The problem was that they loosened up from the recoil of the weapon. As the screws loosened up they went through various stages of tightness, holding the optic in the necessary position to obtain accuracy....then after a number of shots were fired loosened up again to create just enough looseness to open up the groups. This young man was ready to give up on a Browning X-bolt in .270 Win that was spotless; I believe I could have offered him a $100 dollar bill for that weapon at the range that day and he would have taken it. We went through the weapon top to bottom and started with the simplest things first again....and guess what it was the scope mount's screws. I'm not saying that's your issue for sure, but don't overlook something just because you checked it before or you are sooooo sure that it's right because you did it....**** happens and it happens all the time. Good luck!

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