Groups Opening Up Recently?

[JW74]

I noticed recently that my groups have been opening up at 100 yards with my .308. I haven't changed anything with my loads and even loaded up another batch and was very careful to make sure everything was consistent with before. The riffle is a Remington 700 with varmint barrel and bedded B&C stock. The load it likes the best is 178gr Hornady A-max with 44.1gn of Varget @ 2701 fps. This until recently would average 0.25-0.5 MOA and is now shooting 1-1.5" groups at 100 yards! The first time I saw the groups open up I went home and cleaned the barrel thoroughly thinking that was the issue and when I went back to the range I still had opened up groups.

When I put my MagnetoSpeed chrono on it today I noticed the average velocity was at 2660 fps when the same load consitently would produce 2700fps before. Possibly temp is effecting the load? (indoor range)

Should I try cleaning the barrel again in case there is still too much copper fouling?

I can't imagine the barrel is shot out at 1000 rounds even though it got hot a couple of times while shooting it this fall?

Thanks for any help.

 

[Laelkhunter]

It seems that it started all of a sudden, not gradually getting worse according to what I read in your post. Try checking the scope mounting screws, and check the action screws to make sure they haven't worked loose.
Then if they are tight, check your scope. Change to a different one if you have an extra. Could be the scope crapped out.
I'm not sure 40 fps should make that much of a difference in accuracy.

 

[new shooter]

If you went to a different lot of powder it will shot different.

 

[JW74]

If you went to a different lot of powder it will shot different.

I have loaded this same load in the past with different lots of powder and didn't have any issues at the time. Really scratching my head today. I am going to check all the screws in the morning.

 

[WildRose]

You shoot one hot and then keep shooting it's possible to burn out the throat even in a .308 if you do it often enough.

Most likely though something is loose, busted, or out of adjustment.

Check your scope mounts and trigger guard screws and make sure it's still floated properly.

Since it's an indoor range it's doubtful temps are the problem. On a .308 I would not expect to see much of a problem with even a 30 deg (F) temp variation.

 

[AZShooter]

Several good suggestions so far. Action screws was my first thought.

What cleaning products are you using?

Crown could have gotten damaged.

Without a bore scope it is hard to tell the condition of crown or bore.

 

[geo4061]

This happened to me a couple of weeks ago. I thought I would try the new school of thought and not clean until my groups opened up. I cleaned the rifle with no improvement. I pulled the scope, rings, and mount. Cleaned with acetone, used loctite, and torqued to specs. No improvement. What I thought was clean was not clean. Upon barrel inspection with a very bright light I could see traces of copper. Scrubbed it with Bore Tech. It's back to it's old self .25 at 100.

 

[ShootnMathews]

This happened to me a couple of weeks ago. I thought I would try the new school of thought and not clean until my groups opened up. I cleaned the rifle with no improvement. I pulled the scope, rings, and mount. Cleaned with acetone, used loctite, and torqued to specs. No improvement. What I thought was clean was not clean. Upon barrel inspection with a very bright light I could see traces of copper. Scrubbed it with Bore Tech. It's back to it's old self .25 at 100.

Plus one on that. I've a firm believer in the bore tech. A couple friends of mine scrubbed all day on and off on two guns trying to remove copper fouling with only a minor improvement in accuracy and in 10 minutes I used my boretech to clean a ton of copper out and both guns went back to 1/2 MOA.

It is possible that if you shot it hot a couple of times that you've damaged the throat or the throat is eroded a little and you need to measure and adjust your bullet length to the correct jump again.

 

[JW74]

Thanks for all of the info everyone! I am going to go over all the screws on the rifle today as well as clean the barrel again with Bore Tech.

For cleaning products I used Gunslick foaming bore cleaner and Hoppe's 9 then ran a nylon brush through the barrel 10 times. Got blue patches and assumed a lot of the copper came out but possibly not. I haven't checked the crown but with the rifle having a muzzle break I am thinking it hasn't been damaged or banged?

 

[geo4061]

That is exactly the cleaners I used. They just do not do a great jog on copper.

 

[geo4061]

job. Hope it helps.

 

[JW74]

I went over the entire rifle and everything was tight. I took off the brake and the crown was in good shape, no damage that I could see. I then gave the rifle a thorough cleaning. I started with wipe-out and got "a lot of blue" on the patches. I then dried the bore and did 3 cleaning cycles with Montana Extreme Copper Killer as the directions stated. Took until the third time to see no more copper on the patch after letting it soak for 15 minutes. Then dried the bore and did one more wet patch with wipe-out before running a series of dry patches to finish. I will shoot this week and see if that fixed the problem. If that fails I will swap out my scope and see if that was the problem.

 

[jaybo]

If all else fails try a different scope if you have one. I have had similar problems in the past and just recently and it was a scope problem. I just sent in a Leupold because it was a sub MOA rifle that went to a 5 inch spread. It is the second Leupold I have had to send in and one was a Ziess. I will never buy another Leupold. I know some swear by them but I swear at them. I have a family member that is an FBI agent and he told me they are looking at Night Force because they have to send in about 1/3 of the Leupolds for repair. He told me this some time ago so they may have already converted. You know politics and contracts...

 

[ATH]

At this point I vote copper or carbon buildup or scope. Let us know how it shoots this weekend.

Last year I had a 358 wildcat, built by a nationally known smith, which just would not group the way I expected it to. Made me feel bad, a guy with that reputation building a barreled action which would not shoot better than MOA no matter what I did. I missed a couple shots on deer around 500 yards for no reason, subsequently cutting my range I would take shots at. Later in the season I moved the scope to my smokeless ML, and while things looked good at the range in the field when I dialed up for a longer shot it went bad.

That was more bad shots than in the prior 20 years of hunting, in one season.

This year back on the 358 I had the same issues, but they seemed worse. The evening before the season I got a "group" at 100, dialed up for 300, and it hit 3 MOA higher than it should have. Out of desperation, I pulled my new Burris XTR from my 300WM (thank God for QR rings and Picatinny rails) and put it on the 358.

Bam, .3-.4 MOA groups! It had been the scope all along.