Accuracy opening up after 15 rounds

[TroyMN]

Rem sps tact 20" 175SMK, Lapua, 46.0 RL 15, FGMM primer. This gun can shoot about .7 MOA at 100. More resently I have been doing less load development and more just practice shooting so my rates of fire are a little faster. The barrel is not hot by any means I am shooting 10 to 40° weather so the barrel gets barely warm to the touch. My five round groups can go from .6 to 1.5 in groups 11-15 vs 16-20??...... Does anyone have a experience with this? I have shot F class in the summer (90 degrees) that's 22 rounds in 20 minutes, barrel gets so hot you can barely touch without getting burned. Barrel has about 1000 rounds through it. Normally during load testing 40 rounds can last me couple hours. Have I just never shot groups this fast before at 100 yards?
Thanks
Troy

 

[jbell]

Did you shoot the rifle in question in the F class match you talked about? Does the accuracy of the rifle in question come back after the barrel cools? Have you noticed a POI shift while shooting it, is it stringing the rounds or do they just open up to more or less round groups. Do you have to clean the bore to get the accuracy back (it could be a fouling problem if so, but highly unlikely with the caliber)?

I would verify everything is tight: action screws, scope base, scope rings...

I had a 6.5X284 with a hart barrel that started doing this after 800 rounds or so, but I was pushing a 140 class bullet as fast as I could. I had to clean it to get the accuracy back, but the throat was getting pretty bad on that barrel.

 

[zfastmalibu]

Warm to the touch in 0 degree weather is a 60-70 degree temp change. So it is getting alot warmer than you think. If you let the case sit in the chamber and get warm before the shot you could be talking 50 fps or more with a 60 degree change in temps. I shoot rl15 in my dasher and go up or down about .1 grain per 10 degrees to stay in tune. Also, factory barrels can have a lot of stress in them and temp changes can cause them to walk.
I would tell you first, get a good barrel if your serious about competing, second switch to something less sensitive like Varget. It is still temp. sensitive but not as bad.
Alex

 

[Jkob60]

I agree, if you are shooting a factory barrel you will do yourself a favor by putting a GOOD barrel on and getting it trued, it will help with cosistency.

Jim

 

[TroyMN]

It is the same rifle I shot in F class last year 200+ rounds ago
The accuracy comes back when it cools
I hope it is a cleaning issue
I have noticed a larger cold bore POI change than before??
Not so much stringing. My friend used the term shotgun
When I spend money on a better barrel it might be in a better gun? For sure a 6.5 caliber.
I have/ had a varget load but had to switch to rl15 when I could find no Varget. Yes I also change the load I use 45.5 if temps are above 60 degrees (46.0 gr at 90 degrees left in a hot chamber to COOK, kills the brass)

 

[agbm]

Rem sps tact 20" 175SMK, Lapua, 46.0 RL 15, FGMM primer. This gun can shoot about .7 MOA at 100. More resently I have been doing less load development and more just practice shooting so my rates of fire are a little faster. The barrel is not hot by any means I am shooting 10 to 40° weather so the barrel gets barely warm to the touch. My five round groups can go from .6 to 1.5 in groups 11-15 vs 16-20??...... Does anyone have a experience with this? I have shot F class in the summer (90 degrees) that's 22 rounds in 20 minutes, barrel gets so hot you can barely touch without getting burned. Barrel has about 1000 rounds through it. Normally during load testing 40 rounds can last me couple hours. Have I just never shot groups this fast before at 100 yards?
Thanks
Troy

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[TexasMade]

I would suggest scrubbing the barrel like crazy with Shooters choice or sweets copper solvent. Then JB polish it. That should keep it from fouling. Sounds like it goes to fouling bad after a few rounds

 

[M40_A1]

Sounds like it goes to fouling bad after a few rounds

Not if this....

The accuracy comes back when it cools

 

[Barikade]

I'll throw this out there for what it's worth (you didn't list your glass, and this occurrence varies with glass) I also assume 10 to 40 degrees F not C. Anyways, when I shoot strings in that cold of weather, depending on light and a few other atmospherics, I get significant heat shimmer off the barrel which if unaccounted for, will cause me to consistently shoot higher than what I think. I notice this much more at 100 yards than I do at distance, and much more when I shoot high contrast targets like bulls-eyes on paper targets. As the barrel cools and heats back up it can cause the paper targets bulls eye to change apparent shape and position. This is not a game-changer, but it can easily account for a 1 MOA open-up if its happening.

 

[nashlaw]

For me, factory and button rifled barrels "walk" much more than cut rifled barrels. First thing I would have thought was fouling as factory tube take a while to clean up the bore. Had a Douglas that fouled like a mutt for about 200 rounds and accuracy was mediocre at best. After some shooting, it is a hammer.

The return of accuracy after cooling might be because of the barrel/recoil lug hitting the barrel channel or lug mortise when it heats. Might try bedding.