Barrel changes requiring load changes

[bsumoba]

As some of you are aware, barrel characteristics changes and as a result, some loads need to be tweaked every so often.

With that said, I just wanted to share my results.

Initially, my rifle was shooting sub-1" groups no problem (more like 3/4" groups @ 2650 fps using 43.5 gr of Varget at 2.800" OAL and 175gr SMKs shooting out of my LR-308.



Then, all of a sudden, it started shooting 1"-2" groups!!!



I decided to do another load workup and found out that now I have to push 43.8gr of Varget and its now at an ave of 2616 fps, so in 400-500 rounds, I lost some velocity and I actually picked up some accuracy, shooting under 3/4" consistently now



So, the moral of the story for some of the newer reloaders or people trying to eek out more accuracy and precision out of their rifles or noticed a load going to crap, it could just be your loads needing some tweaking to match the changing barrel characteristics. it seems like you have to do this every so often, especially if you're slinging bullets all the time and getting high round counts on your barrel.

[highpower790]

How many rds have been fired since the barrel was new?, maybe the throat is a little long now and the copper has all of it been removed?

[bsumoba]

according to my databook, 524 rounds.

i did a full bore cleanup (copper and carbon) around 350 rounds and after that it was just carbon cleaning. after the cleanup, it took about 22 rounds to get to steady state and was still shooting 3/4" groups.

then, all of a sudden at about 450, it started to shoot 1-2" groups. im guessing my throat is probably getting a little longer.

i almost gave up on it and thought i might have done something to it like damage the crown. i checked all the screws and everything was tight and i consider myself a decent shooter so I couldnt just all of sudden be shooting 1-2" groups.

[highpower790]

Yep I too think the throat is growing.I check my 600yd ammo every 400rds or so and there is always a minor change,and your groups that show using less powder proves that more is not always better...good shooting to you!

[highpower790]

What brand of barrel do you have?

[J-cat]

Same lot of Varget? Checked your gas block? You are going to have an insignificant amount of throat wear after 500 rounds and it will certainly not cause such a drastic change in accuracy.

[FLIGHT762]

I have a 1993 vintage SR-25. It shot well @1MOA with FGGM 168 for years. After about 1700 rds. down the tube, the groups opened up. I cleaned every bit of Copper out, but it still shot over 1 MOA.

I switched ammo to some Winchester Supreme Match 168 ammo. The ammo shot consistently back to 1 MOA. All I could figure is the throat had worn and for whatever reason, the Winchester ammo worked better with the barrel in it's current condition.

[bsumoba]

What brand of barrel do you have?

JP Supermatch SS barrel 20", thermal dissipator, JP Large Comp

Same lot of Varget? Checked your gas block? You are going to have an insignificant amount of throat wear after 500 rounds and it will certainly not cause such a drastic change in accuracy.

Come to think of it, I am not sure on the lot. I currently have 2 lots of powder and havent been paying attention. ive been finishing up my 1 pounders before getting to the 8 lb jugs. gas block is fine.

could be that the 43.5 load was developed around late fall/early winter of last year?

ive heard of people having to adjust their loads after the barrel "breaks" in. it seems like its stabilizing now though.

i've also adopted a rather minimal cleaning regimen and dont clean the barrel nearly as much or frequent as I used to.

[J-cat]

Powder burning rates change from lot to lot. For years people have complained about Varget's lot to lot burning rate variability. The accepted tolerance is 5%. If you had QuickLoad you'd see what 5% can do to your pet load.

I am currently on my third lot of 4064. I developed my first load and settled on 41.5grs. My second lot gave me fits until I realized my stupidity and adjusted the load to 41.1grs. My third lot calls for 41.4grs. How did I determine this? By finding the optimum charge weight that also gives me the optimum barrel time with ES in the low teens.