Strange accuracy patterns.

[M&POwner88]

Hello, I have had my M&P 10 for about two years and had many ups and downs when it comes to accuracy. My rifle is the 811308. What I would call a standard M&P10. I have made a few upgrades, elftman ar10 drop in trigger, Odin works adjustable low profile gas block and a MI free floated hand guard. I also have a Burris M-tac 4.5x14 scope on a Burris Pepr mount. First time I shot the rifle I was able to group 150gr. Hornady American whitetail about an inch to two inches at 200 yds. The next time I took it to the range I used freedom munitions 150gr. Fmj. They shot pretty bad about 3 inches at 100 yds (also had some case head separation.) a few range trips go by and I start using federal 150gr. Soft points they shot ok. Then I used Remington 150 gr. Soft points,shot 1/2-5/8 inch groups at 100 yds. consistently. but in the same range outing the same Hornady load as I previously used shot all over the place ranging from 1"-4" groups. And my last outing at the range I shot Remington 180gr. Soft points they wouldn't group at all maybe at best 4-5 inches between shots. I have done some reading on this forum and saw that the m&p 10 can be very ammunition specific. But I find it very strange that Hornady would shoot so well one day and then poorly on another. That makes me think that I'm not cleaning it correctly or something also I'm not a world class shooter but I feel pretty confident with my trigger pulls and shooting technique. I use a 30 cal. Bore snake and butler creek clenzoil for the barrel every range outing and I also clean my bolt and carrier every time I shoot and re-lube with Lucas green heavy duty grease. Also I saw that the barrel seemed like it had grit in it today as I shot the heavier loads possibly un burnt powder since the rifle only has an 18" barrel. I don't do any re-loading I'm basically a casual shooter about once a month. I realistically need it to shoot at best minute of groundhog or worst minute of black bear/whitetail deer so maybe I should just stick to 150gr. Remington and hope that it stays consistent. Hopefully some of the forum sages can either come up with a possible solution or reaffirm that a semi-auto rifle only has the capability of shooting on average 1-3" groups depending on the ammo since I've read an even amount of those conclusions. Any advise would be appreciated. I apologize for the length I wanted to be through.

 

[bergermeister]

That rifle likes 168gr bullets

If you can handload, Hornady or Sierra match HP's are excellent choices. If you cannot, these IMI 168gr HPBT SMK cartridges 20 Round Box - 7.62x51 NATO 168 Grain HPBT SMK OTM RazorCore Semi-Auto Match Ammo by IMI | SGAmmo.com are quite capable of under a MOA if you do your job.
Remember 'garbage in garbage out' when it comes to ammunition and accuracy expectations. Keep the lesser offerings for spraying and praying...

 

[NJM15]

Hornadyfor me

If you can handload, Hornady or Sierra match HP's are excellent choices. If you cannot, these IMI 168gr HPBT SMK cartridges 20 Round Box - 7.62x51 NATO 168 Grain HPBT SMK OTM RazorCore Semi-Auto Match Ammo by IMI | SGAmmo.com are quite capable of under a MOA if you do your job.
Remember 'garbage in garbage out' when it comes to ammunition and accuracy expectations. Keep the lesser offerings for spraying and praying...

I have been using the Hornady150 gr FMJ/BT never had any reason to change, they are consistent well made reasonable, price wise "why fix it if it is not broken "

 

[bergermeister]

"Different strokes for different weapons"

Not suggesting anyone "fix it if it is not broken" NJM15.
Your postings indicate you obviously know that any given weapon is unique in itself ballistically and have their individual nuances. We both speak from our individual first-hand experiences.

Most here would think I am 'curious' at best in what I am saying but I have shot MANY hundreds of precision rounds from bench rest rifles, ALL handloads lovingly constructed with greatest care and (get this) Moly coated target grade projectiles. CRAZY? Maybe, but I like these black beauties for many reasons... MY personal liking.

This quirk carries over to the specific M&P10 to which I refer. IT likes the 168 HPBT match BLACK bullets and screws them down real tight at the 120 yard concrete bench range that I have access to. Unlike many of you, this is the longest range I shoot currently but I would expect the 168's would perform better at extended ranges than would 150's.

Not trying to 'sell' anything to anyone just speaking fact as I know it

 

[Dennis]

What is the twist-rate? it might matter.
Try purchasing a good cleaning rod instead of just using the bore-snake. Accuracy may improve with a good, proper cleaning.

 

[lrrifleman]

@OP,

First, you need to give your rifle a good cleaning with a 1 piece rod. Try using Shooter's Choice or some other cleaner with a copper dissolving ingredient, then put a light coat of oil in the bore.

You have a number of variables to contend with. First, you need to identify the barrel twist and match the bullet to the twist. Smith says that your rifle has 1:10 twist, so you should be good with 147 to 180gr bullets, give or take. I would shy away from bullets with exposed lead tips, they can get deformed in the transition from magazine to the feeding ramp.

After shooting competitive high power rifles for almost 30 years, my first guess is that you have a significant amount of fouling in your rifle's leade, which is causing your accuracy problems. A bore snake is good for a quick clearing of residue, but it is inadequate for a thorough cleaning. My second guess is that your rifle has an excessive leade which is causing a high degree of bullet jump. This can be confirmed by measuring the leade. In order to do this, you need a Stoney Point/Hornady C.O.L. Guage. Ideally, you want the bullet to have no more than 0.010" bullet jump from the chamber to the rifling. Unfortunately, I am seeing too many rifles leaving the factories with excessive leade. Since you are most likely looking at feeding via the magazine, you are not only limited in your options, but also magazine length. You may need to use a bulbous nose heavy bullet to minimize jump, or have the barrel cut back to salvage the barrel, but this can be very expensive.

Short of investing in the time and tools, I would suggest the following approach.
1. Scrub the bore down from the breach and do a thorough cleaning, making sure to use a chamber brush to clean the chamber of build up.
2. Purchase a box of 150gr, 168gr, 175gr, and 180gr factory ammo, and test it for groups (noting vertical dispersion more than horizontal dispersion) at 200 yards, cleaning the bore and chamber thoroughly between bullets. [200 yards allows the bullet to stabilize.] The smallest vertical dispersion should be your most accurate load. Don't worry about horizontal dispersion, since that will be the wind variable.
3. Between the above 4 bullet weights, you should see a marked difference in grouping, since each bullet weight has a slightly different bullet profile, changing the leade/jump.
4. Once you find a match bullet that groups acceptably, look at and test a hunting hollow point closest to the match bullet that groups the best.

Good luck in your quest.

 

[rct269]

A (considerably) less sophisticated experience-----------------

At the point in time when Slick Willie et al were fussing and fuming about "Assault Rifles", I decided if Slick was against them, I was for them-----never mind I didn't really know what they were talking about. Off I go to my favorite LGS----"Tell me about these assault rifles." They did. I left with a Colt Sporter (AR-15). Given our wont to not leave well enough alone, it wasn't long before it had a Trijicon ACOG up top, and whatever the trigger du jour was down below. Other than that, it's as stock as a stove. I still have it. It works fine.

Works fine means it shoots 1/2-1" groups at 100 yards. It does this with pretty much whatever ammunition I stick in it------which is to say it's never been fed anything it didn't like.

Here's how that works: This performance starts off from one of those "portable" bench rests-----portable if you're really strong. There's the fancy front and rear rests on top---pretty much any and everything to make it easy to be a good shot.

All of it works. That is, if I do my job. My job, made remarkably easy by all these fancy accessories, amounts to this: Shoot slow---slow shooting makes those 1/2-1" groups. Shoot other than slow----still very carefully, but other than slow, and the groups change---for the worse---and the faster you shoot, the worse they get.

So what's the difference between slow and not so slow? Heat---at least that's the only only thing that comes to mind---my mind because I know next to nothing about fancy rifle shooting. And not enough heat to really feel, much less talk about---but my rifle knows it when it feels it.

I mention this because no one else has---and because I know the accuracy of my rifle goes all to hell if/when I shoot anything other than slow.

Ralph Tremaine

It occurs to me it might be worthwhile to try to define "slow". Here's the best I've got: I reckon "slow" means the rate of fire one would achieve if he was loading one round at a time into a bolt action rifle, getting all hunkered down again, sending the round, ejecting it, picking it up and putting it in the shell holder, fetching another round, sticking it in the gun, chambering it and closing the bolt, getting all hunkered down again----------shooing away some bugs---getting all hunkered down again---and sending the round. Do otherwise with my rifle at the peril of your group size. And, of course, given an auto-loading rifle, that's not real world----unless you're after those tiny, little groups. You pay for your thrills!

 

[M&P10 owner]

Check your barrel

A few inches behind the flash suppressor is a stamping of the 308 caliper on your thin barrel. Check inside the barrel to see that the stamping has not transferred to the bore. If you can see a dimple there send the rifle back to S&W. Barrel is no good and will never shoot accurate when it deforms the bullet because of this problem. There is another post on this subject with pictures.
S&W needs to make a recall on this problem. The suggestions by folks on this thread indicate very few folks seem to be aware of this problem.

 

[bergermeister]

TOO BIG TO FAIL..

A few inches behind the flash suppressor is a stamping of the 308 caliper on your thin barrel. Check inside the barrel to see that the stamping has not transferred to the bore. If you can see a dimple there send the rifle back to S&W. Barrel is no good and will never shoot accurate when it deforms the bullet because of this problem. There is another post on this subject with pictures.
S&W needs to make a recall on this problem. The suggestions by folks on this thread indicate very few folks seem to be aware of this problem.

S&W is ignoring a problem that they were most probably aware of from the get-go and buyers are still beating their door down. That will never happen!