Thread: Throat Erosion - New Barrel

First time I've taken the time to re-measure this but it certainly affects accuracy (group size) more than I thought, and ultimately down range kill shots.
So last December I upgraded to a carbon wrapped barrel. As part of the whole load development exercize, I obtained the OAL measurement and CBTO. From here I proceeded to trial seating depths until I got what I wanted - so standard procedure really.
Ended up with a .4 inch group at 100 so understandably pretty happy with the investment and result.
Last Sunday sees me up at the range with a couple of mates, and up I get to put a few rounds into a target just to reinforce the .4 inch group. Well .4 grew to just over an inchand a bit when absolutely nothing had changed with my components or process. This is after 200 rounds, a few of which were a bit hot but mostly pretty reasonable
Bit of head scratching had me re-measure my OAL and CBTO, and of course that wont change, but the jump to the lands certainly had. Where I was using a 40 thou jump, now its a 50 thou jump and the groups are shit.
Hopefully now that Ive fixed the problem.

May I ask which barrel manufacturer have you used

A lot of barrels get faster after about 200 rounds ...

are you running a suppressor? can get carbon build up which will cause shite groups. Cu build up too for that matter.

Originally Posted by 7mmsaum

May I ask which barrel manufacturer have you used

Hardy

Originally Posted by chainsaw

are you running a suppressor? can get carbon build up which will cause shite groups. Cu build up too for that matter.

Yea I am, but after 200 rounds?? Copper was a problem initially but pretty good now

yep, carbon build up especially when running a suppressor can happen pretty quick. Really thorough clean and plenty of bronze brush should deal to it. Or else some of the more aggressive cleaning solvents like KG or Boretech will help. A polish of bore with autosol might do the trick too

I would invest in some JB's or auto solve and give it a real heavy duty clean. You would be surprised at what you think is clean and what isnt. But in saying that 10 thou loss is a fair bit for 200 rounds, are you running a high stepping round?

Not really, There were a few loads that were a bit fast and showed pressure signs for sure, but I backed off a fair bit and now would only have what I consider moderate loads. Ill try the HD clean and see what happens, but that still doesnt explain why I now need to seat the projectiles further out.

What cartridge is it chambered for?

You don't say what the calibre is but some seriously over bore jobbies like the 22/243 and 300 RUM burn them out pretty quick

Originally Posted by GWH

What cartridge is it chambered for?

6.5-06

Originally Posted by Bos

Ended up with a .4 inch group at 100

how many shots were in the group . . . and how many .4 groups did you shoot ?

Going from .4 inch to 4 inch after 200 rounds, id also suggest its a carbon problem, as ive experienced similar big change in grouping, and after trying everything else to no avail, polishing out the carbon got me back to .5 moa.

Get some autosol on a patch and polish it back and forth, focus on one third of the barrel length at a time, just be careful you dont pull it back thru the muzzle.

You could change the patch for each third and add more autosol polish on each one.

Then after polishing give it a normal clean with your normal chemical to flush out the polish and carbon residue.

Id try this first and test shoot.

He said it has worsened to an inch group, not 4".

There is probably some sampling error in all of this as has been alluded to.