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

[Expatriot]

Those are definately unstable bullets. If you increase the range the yaw will get worse. How short an OAL are you loading? Sometimes and excessive jump to the lands can cause keyholing.

[snipecatcher]

I just got my barrel back and went out again today to check for stability. I loaded 240 SMK's over 8.5 grains VVN110. 5 rounds at 2.25", and 5 rounds at 2.17". Velocity was 1000 fps with the longer rounds, and 1040 with the shorter rounds. I still have stability issues. I threaded on an identical barrel, but in 7 twist yesterday. If I can get off work early enough and brave the weather, I'm going to test it today.
-Dan

[snipecatcher]

Braved the 33 degree temps today and took the 1 in 7 twist for a spin.

240 SMK, 8.5 VVN110, OAL: 2.25"

1022
1018
1001
1022

I loaded 5, but the gas port was still in the "Super" position for the first shot, and it didn't even hit paper. The remaining 4 made a 1.25" group, but still are not stable.

220 Sierra Pro-hunters are also not stabilizing, though I loaded them a bit light and ended up with 800 fps velocity. I'll try getting them to 1000 fps and see if it makes a difference.

I also loaded some pulled surplus 175 SMK's to ~1040 fps, and they appear to be stable.

This is driving me crazy! I'm waiting on my local dealer to pick up some AA1680, which I should have by this time next week. Until then, I guess I'll just continue to shoot supersonics in the hope that the barrel just needs to be broken in.
-Dan

[snipecatcher]

Loaded up 20 supersonic and 20 subsonic today with some 2400. It's the only powder besides VVN110 that I have that is suitable. All velocities are the average of 5 shots.

220 Sierra Pro-hunters @ 2.26"

9.5 grains: 1006 fps

10.0 grains: 1060 fps

240 Sierra Matchking @ 2.265"

9.0 grains: 1044 fps

175 Sierra Matchking @ 2.255"

9.8 grains: 1087 fps











I'll try the 1680 next week, but I really don't think that is going to solve the problem. I think it's something else, but don't know what. Any other suggestions? I'm thinking about single loading some 240's out to the lands to eliminate the possibility that it is the extremely long throat of the Blackout chamber. Sound reasonable?