New 10" barrel, bullet stability problems

[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.

[Titleiiredneck]

Originally Posted by 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.

This may have been asked before, but whats the thread pitch on the muzzle?

[snipecatcher]

It's threaded 1/2x28, the same as the Shilen barrel I had before it. The first time out, I shot it with a Noveske pig to ensure it would cycle, but I took it off after that to eliminate it as a variable. I went to the range again today and shot at 50 yards for the first time. I shot at a posterboard with no backer. Same thing. Still getting off center holes.
-Dan

[snipecatcher]

Well I've finally found a bullet that will stabilize at subsonic velocities: the 110 V-Max. I loaded some from 1400 down to 950 fps and all are making round holes. They have a calculated stability factor of 5.2 at 1000 fps. I also loaded some 175 matchkings in the 1400 fps range. These also made round holes. They have a stability factor of 4.2 at 1400 fps. It appears that I need a calculated stability factor of at least 4 in order to shoot the 300 BLK at subsonic velocities. As of right now, things aren't looking good.
-Dan

[Hoser]

Im thinking it isnt an 8 twist or maybe something along those lines...

Do you know anyone with a borescope? Might be a good idea to take a look in there and check things out.

[TCCrewchief76]

Originally Posted by Hoser

Im thinking it isnt an 8 twist or maybe something along those lines...

Do you know anyone with a borescope? Might be a good idea to take a look in there and check things out.

I was just gonna recommend that. Take a cleaning rod with a line marked down the center line. Mark the rod just as it starts to turn, and when the centerline rotates back to the top again, remark. Measure the distance between the marks, and this is your twist rate.

Kevin

[mavrick]

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

Dustin

[Titleiiredneck]

Originally Posted by snipecatcher

It's threaded 1/2x28, the same as the Shilen barrel I had before it. -Dan

Quick question, ya think it could be because the muzzle walls are so thin with the .308 bore vs the 1/2 od? Why I ask is had having a simmilar problem with one of my sbr uppers in 9mm. Thin walls can cause warpage when threaded, in which case it may cause the bullet to wobble when leaving the muzzle, just a thought.