New 10" barrel, bullet stability problems
 

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

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.

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

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:
http://i47.photobucket.com/albums/f1...5/DSC03314.jpg


Closeup of a different shot, 208 Amax velocity unknown:
http://i47.photobucket.com/albums/f1...5/DSC03315.jpg


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

http://i47.photobucket.com/albums/f1...5/DSC03316.jpg

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.

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

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.

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

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

more progress
 

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


http://i47.photobucket.com/albums/f1...5/DSC03342.jpg

http://i47.photobucket.com/albums/f1...5/DSC03343.jpg

http://i47.photobucket.com/albums/f1...5/DSC03344.jpg

http://i47.photobucket.com/albums/f1...5/DSC03345.jpg


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?

Results of today's shooting using VVN110 powder again:

240 Matchkings loaded long, just off the lands @ 2.29" OAL
http://i47.photobucket.com/albums/f1...5/DSC03346.jpg

155 Sierra PALMA @ 2.135" OAL:
http://i47.photobucket.com/albums/f1...5/DSC03349.jpg

Closeup showing slight offcenter hole from 155:
http://i47.photobucket.com/albums/f1...5/DSC03350.jpg


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

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

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?

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

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

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

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

Dustin

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.

Interesting. That thought has crossed my mind too. I know 1/2x28 generally isn't recommended for a 30 caliber bore, but people still do it, and even on 9mm. The problem with that is that my 30 caliber RIFLE suppressor is threaded 1/2x28. That's just what the manufacturer uses so it can be put on a standard AR. It does bother me how thin it is, but I've been told it is fine by the suppressor manufacturer. As for the twist rate, the barrel maker measured it down to the 1/4", so I trust his word that it is a 7 twist.
-Dan

I don't think the thread diameter and pitch are causing the issue. This thread is in use on many other .308's with no problems at all. 9MM is a larger bore and is getting much closer to the thread root so in a high pressure rifle I could see a possible issue there but not in the .308. In reality the 1/2-28 works very well in 9mm for the most part so the smaller .30 cal should have no issues whatsoever. I think there is either a problem with the barrel or the twist rate and the simplest solution is to do as others have noted and check the twist. If he's down to 110gr bullets to get a straight hole than something is seriously wrong....its not just a muzzle thread issue.


Frank

I did try measuring the twist rate, but it is pretty tough to do when you only have about 7" of rifling to work with. I ended up with something close to 9", but I'm not sure if the measurement I got is accurate.
-Dan

OK, I'm confused. How is there only 7" of rifling in a 10" barrel? Maybe this is your problem...:grin: Just kidding! Perhaps mark the cleaning rod on the top and bottom, and double the twist rate when you measure the rod at half-rotation.

Kevin

Good idea. I did it that way, five times in a row, and all 5 measurements were really close. I took the average of those and ended up with about 8". Still, there has got to be something else. Even a 9 twist should stabilize a 175 Matchking at 1000 fps.

Are you shooting it with the threads bare? If you have a thread protector, shoot 3 shots with it on tight and 3 shots with it off. It's important that it's a protector and not a brake or something else that will put downward pressure on the threads. Just a little experiment.

I don't think the thread protector will make any difference at all. I've fired a number of threaded rifles with no protector or suppressor and never seen any difference between doing that and having something threaded on. I've never seen any wobblies caused by having no thread protector or can either. I have seen some problems when the crown isn't square to the bore or even though.

Frank

I don't have a thread protector. Like I said, when I got the first barrel (8 twist), I shot with a Noveske pig because I didn't know if the rifle would function. I then took it off and got the same results. I then put on the 7 twist barrel and have been using it ever since. I have not used any type of muzzle device on this barrel. I may take "the pig" with me to the range next time with the 'blast baffle' removed just to see if there is any difference. Anybody want to try the 8 twist barrel and see if you can do any better? I don't have a gas block for it, but I'd be willing to send it to one of the members on here who has a good bit of experience with this type of thing to experiment with if I can't get something to work with the 1680 powder.
-Dan

did you ever borescope the barrel? Perhaps there's a burr somewhere, a warped barrel, or manufacturing mistake at the gas port. Your loads should all be working fine.

Any chance of getting a couple < 150 Grains loaded?

I usually load up a bunch of 150 FMJ BT's with cannelure and lightly crimp into the cannelure. This allows the brass to be fully fire formed at the shoulder as opposed to the soft squeeze put on by the 300/221 die when converting .223 brass. While the brass is being formed by higher pressure loads, I've seen some really strange behavior.

Once you're using fire formed brass that has been full length sized (and optimally checked for neck thickness), if your barrel won't stabilize 110-150 hypersonic then you know its a manufacturing issue that may or may not get better with use. If they do stabilize try progressively increasing bullet weight, while decreasing powder charge.

The current barrel has 155 rounds through it, and this has all been with A) 20 pieces of FC brass formed by Hoser, or B) 15 pieces of virgin LC brass formed by me. I just recently chunked the FC brass as the primer pockets were getting inconsistent. I picked up the 1680 today and I'm going to try some loads with it either tomorrow or Thursday. If that doesn't work, I'm taking the barrel to a local machinist who is going to borescope and pin-gauge the barrel. If there is nothing wrong there, I'm going to have him cut off the threaded portion and put a target crown on one of the barrels to determine if there is something wrong with the crown/thin walled threaded portion. By the end of this week, I should know what the problem is.

As to the question about the 150's, I've put some 155 Matchkings through it and they are not stable. 110 V-max's are. I haven't tried 125's, but don't think it will matter because there is definitely something wrong here. It SHOULD be stabilizing at least the 220 round nose bullets and the 175 Matchkings without a problem. I'll keep the thread updated as I find out more.

-Dan

With the problems you are having with both Subs and Supers, I'd say it's time to slug the barrel. I honestly cannot think of anything else besides an oversized barrel at this point. An oversized barrel will cause tumbling with both Subs and Supers. Slugging will also let you feel the consistency of the rifling as the slug is pushed down the bore.

Kevin

I had an SSK upper that was shooting the same way. I tried multiple loads with multiple powders at various speeds. 240gr SMKs and 220gr SMKs were not stable and were all over the target. 190gr SMKs appeared stable but would not group better than about 2" at 100 yards.

I never tried any lighter bullets because I was not interested in shooting them. Never tried supersonic loads for the same reason.

I tried Corbon and SSK ammo with the same results.

The barrel was 10" long threaded 5/8 - 24 with a 3 position gas block. It was a 1 in 8 twist that I verified.

I talked to JD about it several times to no satisfaction and finally decided to send it to someone else for a new barrel. I considered sending it back to SSK and trying to make them fix it but was not confident that it would be worth the trouble and that it would be better in the end.

I really don't know what the problem was.

Good luck with your rifle. I am hoping to have my upper back soon with a new barrel.

Joe

My last bit of hope was 1680 powder. I tried it this morning and I'm still getting understabilized bullets, of course. It's also too slow for my rifle. I had a couple cases that were covered in soot all the way to the case-head, which I attribute to them being yanked out of the chamber too early. I don't have a problem at all with this, because the faster powders that it runs best with will be quieter, if I can ever shoot the rifle with a suppressor. I'll be taking both barrels to my machinist friend on Saturday morning to try and find what's wrong with them. I've never looked through a bore-scope, and I'm looking forward to it!
-Dan

Powder will make zero difference in bullet stability. Bullet speed/RPM is stabilizes a bullet.

The longer/heavier a bullet is and the slower you drive it, the faster the twist you have to have. What powder you use to get it to that magic RPM does not matter.

The borescope results should be interesting.

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

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.

What does the resistance feel like when you run a patch down the bore?

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.

By any chance were both these barrels made from the same blank?