Load is suddenly hotter than usual??

[canezach]

My load using the Hornady 140 BTHP is 42.0 grains of Reloder 16, CCI BR2 primer, 3x Hornady brass, seated 20 thou off the lands. It's been the same load for almost two years. Initially, my load gave me 2832 fps, low SD and ES, routinely gave me respectable groups at 100 yards and at distance. I've chronoed my rounds several times and I'm usually around the same velocity, give or take a few fps. Last outing, velocity jumps by 30 fps. SD was still in the single digits (3.5 to be exact) and my spread was below 15, so what gives??

Rifle is a DTA SRS with 26" factory barrel and SilencerTech suppressor. Factory barrel has just over 2100 rounds. Chronograph is a MagnetoSpeed V3. My brass processing hasn't changed. I'm still full length sizing, same Redding Type S match dies, same bushing, same everything. Same Chargemaster throwing the charges and checked on a GemPro or RCBS beam scale. Same lot of powder as the last time I chronoed a couple of weeks earlier and primers were from the same box of 1000. The temps weren't drastically different, maybe 5° difference. It's literally like I changed absolutely nothing, yet gained velocity.

 

[waveslayer]

Did you switch lots of powder? I have H1000 that I load for a Warbird at 93 grains. This new lot is 91.8 grains... that could be your trouble or temperature

My wife thinks I only have 3 guns

 

[canezach]

No, it's not lot-to-lot variance. Like I said, the powder is from the same lot as a previous time I chronoed. I bought 24 pounds at the same time and all 3 jugs were from the same lot. That's what makes this so odd. There's literally nothing different about this load than other loads that were all roughly the same velocity.

 

[Fursniper]

No, it's not lot-to-lot variance. Like I said, the prefer is from the same lot as a previous time I chronoed. That's what makes this so odd. There's literally nothing different about this load than other loads that were all roughly the same velocity.

I'm going to venture a guess that your barrel is starting to feel the mileage.....

 

[canezach]

I'm going to venture a guess that your barrel is starting to feel the mileage.....

It's certainly possible, but gaining velocity? I've had barrels lose accuracy and velocity, but speed up?

 

[Fursniper]

It's certainly possible, but gaining velocity? I've had barrels lose accuracy and velocity, but speed up?

Yeah, I know the usual signs are the opposite for velocity (combined with degrading accuracy) but I ventured a guess just due to an almost exact experience with a rifle some years ago that gave me increases in velocity for no good reason that i could figure out. I just couldn't figure it out. I had about 2500 rounds on it. After scratching my head & having alot of WTF moments, after about 100 rounds of that accuracy degraded and velocity actually fell off, very weird. It was like the barrel was going through death throes but trying to "hang on" lol. I haven't burned through that many barrels in my life on any specific rifle so didn't know what to think but after rebarreling all was well. You seemed to have covered all the bases in documenting consistancy in the your reloading process as well as the individual components (except for your bullets, thats a possibility) unless you just happened to have your loads that day sitting in the sun & just didn't notice. Anyway, as I said, just a guess based on a one time experience. Maybe mic & compare the bullets you're using?

 

[Milo 2.5]

I'd almost bet the barrel is getting slugged with shit. Clean it, both carbon and copper remover, if you run an eye hook with a big enough patch, when you think it is clean, you will feel a pinch point about 6" long beginning at your rifling. 6mm's noted for this, I use a cleaner called witches brew form Hollands guns, work the area over.

 

[Fursniper]

I'd almost bet the barrel is getting slugged with shit. Clean it, both carbon and copper remover, if you run an eye hook with a big enough patch, when you think it is clean, you will feel a pinch point about 6" long beginning at your rifling. 6mm's noted for this, I use a cleaner called witches brew form Hollands guns, work the area over.

That was going to be my next suggestion that's more likely the issue. Good insight there.

 

[Milo 2.5]

Another product to clean this would be JB bore paste, may be able to find locally, but be careful, you're basically hand lapping your barrel to some degree, know when to quit, lol
Use this with a jag, work the pinch spot.

 

[canezach]

Thank you, guys. I'll give it a good cleaning and see what happens. I have a replacement barrel on had, so if this one gives up the ghost, I'll be covered.

 

[Milo 2.5]

Thank you, guys. I'll give it a good cleaning and see what happens. I have a replacement barrel on had, so if this one gives up the ghost, I'll be covered.

Clean it good, if it tones down, should get some more accurate rds down it. My experience lately is coming from small primer Lapua brass in 6 creed, I feel we're not getting complete burns with slower powders, and if you're not ready for this it really kicks a guys ass.

 

[jsthntn247]

Like others have said probably a dirty barrel. I'd have it borescoped and check for a carbon ring in the throat, that will spike pressure.

 

[JePhyllis]

It seems the velocity increment is systematic and repeatable. One possible explanation is the over-build of copper fouling. It will reduce the cross-section of your bore and produce a slightly higher pressure for the bullets, which ends up with higher velocities. So you may need to remove some copper fouling and check the result.

 

[BLKWLFK9]

Carbon build up. Use injector or brake cleaner to break it up.

 

[canezach]

It wasn't a carbon ring. I took the barrel to my smith and took a look through a borescope. No ring, but I had erosion almost two-thirds down the barrel. Sure enough, accuracy degraded within the next 50 rounds in the middle of a match. It wasn't even gradual degradation either. It went from precision rifle to shotgun. Thankfully I ordered a backup barrel since I knew it was only a matter of time.

 

[Fursniper]

Like I said, you're barrel was feeling the mileage....