New 10" barrel, bullet stability problems

[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?

[snipecatcher]

Results of today's shooting using VVN110 powder again:

240 Matchkings loaded long, just off the lands @ 2.29" OAL


155 Sierra PALMA @ 2.135" OAL:


Closeup showing slight offcenter hole from 155:



The only place to set up the chronograph this evening was in the shade, and I didn't get any readings, but I can extrapolate the data I already have and all of these loads should have been between 1000 and 1100 fps. I say "should have" because the 240's had a pretty significant thump when seated out to the lands compared to seating them at 2.26 mag lenth. Still no pressure signs on the brass. I also shot some more 220 Pro-hunters with a stiffer charge of powder that should have put them near 1100 fps. Still not hitting straight. As of today, I have 100 rounds through this barrel.
-Dan

[TCCrewchief76]

I'm wondering what kind of target backing you're using. It is possible that the noses are encountering enough resistance that it's causing the bullets to tumble before the shank exits it target. Try shooting the rounds through just the target, no backer. See if that changes things.

Kevin

[snipecatcher]

Yeah, I was thinking the same thing. Its the 3/4" thick paper type backer common at shooting ranges. Seems like I would have noticed it before with my 30/221 though. I'll make a target frame and take that to the range tomorrow. I'm also going to try shooting at 50 yards and see what it looks like. I'm willing to try about anything at this point.

[mavrick]

It might be worth a shot I have had good luck with lil gun powder in my bolt gun and my AR .

Dustin

[i8asquirrel]

what distance are yoiu firing at?
I was having trouble with 200 nosler BT. full Keyholes at 100yds. I tried 190 gr Hornady SPBT and had wonderfull luck. ( lenght of bullet ,center of gravity?) anyway you might try some different OGive style bullets , Good luck

[snipecatcher]

I've tried a fairly exhaustive list of bullets/speeds mostly at 100 yards, a couple at 50 yards. I get the same results with both barrels. There is something wrong here. If I didn't have a bolt-action before this that ran well, I would probably be turned off by the whole idea of the 300 BLK and give up. But I KNOW that it can and does run fine when everything is right, so I'm going to stick with it. The machinist I'm going to tomorrow suggested that there may be a tight spot in the bore that is swaging the bullets down just enough to give them problems as they leave the muzzle. We shall see.