Rechambered barrels.. Questions

OK I rechambered my 6BRX barrel that had 1700 rounds on it.. It was 30 inch and cut it back to 28 inch.. Chamber was 005 shorter than my old one so had to bump cases back more and I mixed 2 bottles I had laying around of 2208/varget. Now I worked my load back up and finished with 31.6gr with 105gr hybrids at 2965fps and shot like this for 300 rounds.. I then put my new firing pin spring in as it finally turned up.
Then on sunday I put 90 rounds on it (Mrs shot her match and I used it to) .. Got home and cleaned and isso paste barrel barrel has done 400 rounds now.
Today I used same load as I wanted to do a quick load test to see if firing pin had made a difference and I had found i lost speed, was only getting 2930fps with 31.6gr.. I had a few other loads and 31.8gr only got me 2945fps and groups started to shrink again (looking at 31.9gr or 32gr to get it back to 2965fps) .. Question is as this is my 1st rechambered barrel do they slow down so quick or would the firing pin spring make a speed difference . Barrel had done 1700 then rechambered and its now done 425 rounds
Cheers
Stu

 

I had a 6.5-284 barrel set back at 800 rounds, it was already shooting 1 moa again by 1200 rounds. I was shooting hot loads with H4350 back then and didn't know about barrel throat wear.

Had my 6x47l barrel set back at 400 rounds, 2" as well, barrel slowed 77 fps in the last few months at 1600 rounds. From past experience with other barrels in 6x47L they only lasted/stayed reasonably accurate, a few hundred more rounds once they slowed down, so I pulled it.

IMO, in the hotter chamberings, at the higher round counts, it's not worth doing a set back. Of course it was for me with the 6x47l.

Since I have to pay for barrel work I just buy a new barrel but if I was doing the labor myself I'd consider doing a set back at half life.

 

at 1700 it was toast. no rechambering will save that

 

I had my PPC barrel set back a thread after about 2000 rounds and it grouped a .217 at 200 last target at my last short range comp I was in. That was after 2 full matches. Hope it holds up for another few matches! I just went with a slower reliable load and didn't try to set velocity targets.

 

nah it wasn't toast it was still putting down 1 to 2 inch groups at 500m

 

righto so what vibe i'm getting is don't bother rechambering ..got ya ..just shoot the barrel out and be done with it

cheers

 

Has your throat moved in the last 400 rounds ?
Are/were you jamming bullets when you last chronographed?

Effectively the barrel has 2100 rounds through it. I think theres a point where the barrel starts getting rougher, and you start losing some of your velocity. But of it still shoots, keep shooting it!

If you still have your old spring, you may put it in and shoot your old load, see if theres a correlation.

Have you looked down it with a bore scope ?

 

Borescope would be my best bet also before a rechamber. If the throat is all cracked and lands are definitely worn then it might be best to toss it or turn it into a fireformer or practice barrel.
I’ve noticed on most setbacks we’ve done it’ll give you roughly 1/5 of the life even if you set it back 2” or .200”.

Sometimes it’s just best to buy a new barrel

 

my lands only moved from 1st firing of rechamber to 250 rounds .005 but all of that was in the 1st 50 rounds and hadn't moved since .. i haven't had a chance to recheck after shooting the last 150 rounds on the weekend.. but its on my list
i found the hybrids liked .012 jump on this chamber
yeah we bore scoped before we rechambered and only the 1st inch was cracked and gunsmith said we will cut off 2 inches and chamber
i will look down it with bore scope and recheck lands
it still shot this 0.810 inch group at 300yards in windy conditions at a fun shoot on weekend, just need to read the wind better haha
i just ordered a new barrel for it tonight, might just put my 6BRA barrel back on and finish tuning it

 

Barrels are a disposable item"

 

Cant be unhappy with that target. Look down the entire barrel, look for rough/build up. Could be your velocity drop. Then, Just keep putting the powder to it until it wont shoot anymore. They say they shoot best right before they fall apart, so just dont be upset when it does! Living above 2000 accurate rounds out of a 6 is something to be proud of. Should probably hang that one on the wall!

 

I'm assuming Rushty would prefer you keep that barrel running a bit longer.

 

I’m confident he’d get another 2k rnds out of it!!

Yes I wish that barrel would just give up already,it’s been hard to beat...

 

+1. I’d guess it was likely fire cracked a good 3-4” from the neck,if not more.

 

Nope tim.. was only cracked 1 inch down it

 

I dont know why you guys are so worried about the round count. If the barrel still shoots, I'd shoot it. I may not take it to places I want to agg well. Because it may just have its last good group one day. But local "club" level matches wouldn't be any issue for me. And the day it blows up you just laugh and gell everyone " well apparently trying for 2860 rounds of accurate barrel life was just asking a little too much"

 

Comagutsa,
Your loss in velocity happened after using iosso and I am positive that is the cause. Even more so since you used it after 400 rds.

I have also experienced this issue. With the abrasives (JB/Iosso), I think it’s best to use every 150-200 rds or sooner since it cleans all fouling and deposits down to bare metal. Once down to bare metal, velocities decrease until the barrel fouls again.
My most recent example is my 284 Shehane which was cleaned with Iosso after approx 450rds.
I was aware of this decrease in velocity so my next shooting session I figured 10 foulers would be sufficient. I proceeded to develop a load w a different powder and settled on a charge that at the time yielded an AVG velocity of 2830FPS. After that session the barrel had 40rds down the tube. I then put another 30rds down the barrel for seating depth testing and my AVG was still 2830.
My next session was all at 1000 yards to proof my load. I noticed my poi was creeping up so I used the chrono and my rounds now had an AVG of 2870-2880 FPS. This was with the exact same charge. I figured it was the temp that day or somehow I dropped more powder. I went back out and shot over the chrono and it was steady at 2870FPS. Luckily my ES/SD was still good and accuracy at 1000 was also good.
Based on this experience I believe it is best to use the abrasives in shorter intervals such any 150-200 rds. Otherwise you are in for a treat and it may take the barrel a while to settle back in to the pre-abrasive cleaning state.

When I clean with just solvent/patch, it will usually take my barrel 3-7 rds before velocities stabilize and get back into the 2870 range.