New 10" barrel, bullet stability problems

[snipecatcher]

UPDATE WITH NEW BARREL ON PAGE 8




I just got my 10" barrel in 300 BLK, and I've taken it to the range yesterday and today. It's an 8 twist with TP555's adjustable gas block, which is very well made, by the way. Day 1, I loaded up some supersonic rounds and subsonic. The subsonics were loaded with 208 A-max's and VV-N110 powder.

10 grains = 1200 fps
9.0 grains = 1100 fps
8.5 grains = 1000 fps

None of these loads were stable at 100 yards. They weren't completely key-holing, but groups were in the 5" range and the holes were oblong.

Today, I took out some new loads. These consisted of supersonics once again, and some subsonics loaded with 240 SMK's and VV-N110.

9.4 grains = 1120 fps
9.0 grains = 1080 fps
8.6 grains = 1050 fps

Once again, none of these loads were stable. Slightly oblong holes, groups in the 4" range.

I had an 18" Shilen 8 twist before this and it shot the 208's and 240's just fine, no stability problems. I'm not sure where to go from here, does anyone have any suggestions?
Regards,
-Dan

[Hoser]

Verify that is actually an 8 twist barrel. Try the cleaning rod trick.

If it isnt an 8 twist you might be stuck shooting lighter bullets.

[amafrank]

First thing is to check the crown and make sure its clean, even and centered. Any deviation can cause problems.
Next try setting targets at 50 and 150yds and see what your groups look like. That will give you some idea whether or not the bullets are settling down or getting more wobbly.
Lastly try some different bullets. Some barrels and bullets don't mix well. Change your load as well. It seems that some powders will give you identical velocity but less stability.

Good luck
Frank

[snipecatcher]

I verified that it was an 8 twist. Took it out again and shot some 155 V-max's at 900 fps. The holes were much better. Am I just crazy? I snapped a few pics of targets from the 208s and the 240s. Is it possible that they could be starting to yaw just from hitting the backerboard of the target? Maybe I just never noticed this with the last rifle.

3 shots, 208 Amax, velocity ~1000:



Closeup of a different shot, 208 Amax velocity unknown:



5 shots, 240 SMK, 1050 fps (2 in same hole, 1/2" up and to the right of target):

[N310toN170]

I'd move to a slower powder like IMR4227 or AA1680, see if that helps. Then after more rounds have been shot come back and try the VihtN110 again.

If it's a newer barrel and the powder is completely burning prior to the bullet reaching the muzzle it may cause erratic behavior.

[snipecatcher]

I'm sending it off to have the crown checked out, and I'm going to try to get some 1680 while the barrel is away. I'll give an update in a couple of weeks when I get it back and shooting again. Thanks for all the advice so far.
Regards,
-Dan

[alorton]

I'm looking forward to seeing what you find out. I've read through the thread and I'm stumped, especially since there are problems with two different barrels.