Need Help - Subsonic Rounds Tumbling

[dellet]

Very first thing to do is verify the twist, make sure it’s 1/7. You can use a cleaning rod with a tight patch. Index the rod and barrel so you can tell one revolution. An 8.5” barrel will have almost exactly 1 full twist.

Thanks, dellet. That’s something that I can easily try. I have to clean up after running 100 rounds through tonight, so I’ll check the twist tomorrow.

Well, that didn’t work. I tried to determine the barrel twist...but all that happened was the brush kept twisting loose of the cleaning rod. I couldn’t get that rod to turn no matter how tight I made the connections...yet I can easily rotate the rod in my fingertips. I don’t have a 30 cal cleaning jag, so I put a patch on a new, 30 cal bronze brush. Patch or no patch, the brush head just unscrews itself.
Will need to pickup an actual cleaning jag and try again. Well, at least my barrel is super clean.

I never realized how tiny the land and grooves are in a rifle (pistol length) barrel...or at least my barrel. All of my handguns have massive lands compared to my 8.5” and 10.5” .300AAC Blackout barrels.

If the cleaning rod won’t twist freely in the handle while pushing a brush through, it might be time for a new cleaning rod. Maybe something with a bearing.

Groves should be .004” deep which is pretty standard. 300” bore, .308” grooves.

[markr6754]

I had a response on another site stating that "boat tail bullets do not stabilize well out of short barrels". Has anyone else observed that, or heard that? I haven't pulled any rounds, but the Armscor Subs and Sellior & Bellot subs all performed the same way as my handloads. My sub loads were 220 gr Lapua Scenar L, beautiful bullets, same projectile DanielDefense uses for their $50/box (30) FirstChoice 300 BLK ammo https://danieldefense.com/daniel-defens ... ition.html

My supers were the Hornady Interlock SP 150gr. These are a flat base bullet, and produced beautiful pukas...but of course, they were supers. They had a much lower recoil than the 147gr Armscor factory loads. But without a chrony, I have no idea how fast they went downrange.

Something else, I can try to load the Lapuas a bit hotter, and perhaps a bit deeper (less than 2.250"). At this point, accuracy is more important than slow speed. I will also try a light crimp, though each change needs to stand alone. I noticed the factory subs had a pretty noticeable roll crimp. They're all shot up so I don't have pics. But I haven't applied any crimp at all to the 20 rounds I've loaded. Since my subs tumbled and factory subs tumbled I didn't think it an issue.

Lastly, I have 2 boxes of Hornady 190 gr Sub-X Subsonics that I can test. These are quite pricey, at $1 per round, so I didn't jump right out to test these. At this point...why not? Interesting, in view of my first sentence, the Hornady Sub-X is a boat tailed, flat point, polymer filled bullet.

[markr6754]

If the cleaning rod won’t twist freely in the handle while pushing a brush through, it might be time for a new cleaning rod. Maybe something with a bearing.

Groves should be .004” deep which is pretty standard. 300” bore, .308” grooves.

It's a strange case. This rod twists quite easily by hand, or pushing through a handgun barrel. But, I wanted to get something different, anyway. Any suggestions? What's your opinion on fiberglass rods?

[thisguysguns]

I've got a 9" barrel with a 1 in 8" twist and I've shot heavy boat tail projectiles just fine out of my gun as subs. I haven't experienced any issues with yawing, tumbling, or key holing out to at least 50 yards.

Projectiles I've used:

220gr Sierra BTHP
210 Berger VLD
Hornady 220gr BTHP
Hornady 208gr A-Max
230gr Hard Cast BT solid

I've also shot the Sig factory subs and Remington Factory subs. Both shot fine. I wonder if you have a barrel issue? Maybe the rifling is too shallow or the crown has been damaged? This is an interesting predicament.

[markr6754]

I've got a 9" barrel with a 1 in 8" twist and I've shot heavy boat tail projectiles just fine out of my gun as subs. I haven't experienced any issues with yawing, tumbling, or key holing out to at least 50 yards.

Projectiles I've used:

220gr Sierra BTHP
210 Berger VLD
Hornady 220gr BTHP
Hornady 208gr A-Max
230gr Hard Cast BT solid

I've also shot the Sig factory subs and Remington Factory subs. Both shot fine. I wonder if you have a barrel issue? Maybe the rifling is too shallow or the crown has been damaged? This is an interesting predicament.

What barrel do you have? You're certainly experiencing what I was hoping for...but to be certain I went for 1:7 vs the lower cost 1:8. That said....Palmetto State Armory is known for okay, but not great products. I have no prior experience...this is my first AR. If I built the upper I'd be blaming myself.

The crown is perfect...can't speak to the rifling...it sure looks tiny to me. But again...no prior experience, and not a lot of equipment for inspecting/testing. At least there IS rifling, and it's enough to twist the brush off of a cleaning rod. Beyond that...still just speculating. If it was just my handloads, I'd be blaming them...but it's all subs I've shot so far. Naturally, I picked a bullet that no one else is loading, so pretty much alone in that regard. Thanks for the feedback.

[dellet]

I had a response on another site stating that "boat tail bullets do not stabilize well out of short barrels". Has anyone else observed that, or heard that? I haven't pulled any rounds, but the Armscor Subs and Sellior & Bellot subs all performed the same way as my handloads.

Without seeing the exact wording of what you were told, I will be polite and tell you that whoever said that is either inexperienced or a complete idiot. They might be talking about barrels shorter than 3.5", so I will cut them some slack.

An incorrect twist is the most common thing that would cause your problem, then probably a bad bore or maybe crown.

Since the shorter bullets, spinning faster seem to work it probably comes down to twist or bore. Twist would be spin rate. Bore would be a pressure problem where the bullet does not seal the gasses behind the bullet and the base is deformed from gas cutting.

Easiest thing to check is twist rate. The bore you would have to push a bullet or lead slug though and measure it. sometimes you can feel a loose spot in the barrel when doing that also.

Unless someone drove over your box of bullets or beat them with a hammer before you loaded them, they are not the problem.

As for cleaning rods, I am partial to coated steel. They are less likely to flex and rub the bore. The imortant thing to me is that they have an actual bearing that the rod spins on.

[markr6754]

Thanks dellet. I agree that the bullets are not the problem. I just entered the data into the Berger Bullets "Twist Rate Stability Calculator". No matter how I manipulated the data, this should be a stable bullet. Even down to 800 FPS and 1:10 twist, at sea level, and 48 degrees, this bullet should still be "comfortable stable". It doesn't drop to marginal stability until I get the temp below 45.
Since I'm at 741 feet, shoot in a 68 degree range, with a (supposed) 1:7 twist, and surely greater than 900 FPS, this should be a tack driver round.

I'll stop at Cabela's tonight and see what they have for quality cleaning rods. Otherwise, internet order time.

[dellet]

I was going to hold off on this until you knew the twist was correct, but here's what I would do if it is. Or anything faster than 1/10.

More thoughts on this that concerns the bullet.

Look closely at any you have loaded and look for a ring on it that is not there on ones that you have not seated. It's possible at that charge weight you are compressing the powder and deforming the bullet.

What you can do is to take a fired case that the bullet will sip in and out of, then put in your powder charge and lightly seat the bullet on the powder. Then measure the length. If it's more than 2.250" bullet deformation is possible.

Next thing is to make sure you're not loading it too long for the chamber.

With a round made up, (live is ok, but without primer and powder is best) pull the upper and then the carrier group out. you should be able to insert the round into the chamber with finger pressure and have it fall out with gravity. If not, then the bullet may be hitting the lands and becoming off center when fired.

Last, if either of these two things happen, I would drop the charge to 10.5 grains and seat the bullet as above and load some rounds at that length and check the holes again.

[rebel]

Check out J.Dewey rods. I like and use them.

[thisguysguns]

I've got a 9" barrel with a 1 in 8" twist and I've shot heavy boat tail projectiles just fine out of my gun as subs. I haven't experienced any issues with yawing, tumbling, or key holing out to at least 50 yards.

Projectiles I've used:

220gr Sierra BTHP
210 Berger VLD
Hornady 220gr BTHP
Hornady 208gr A-Max
230gr Hard Cast BT solid

I've also shot the Sig factory subs and Remington Factory subs. Both shot fine. I wonder if you have a barrel issue? Maybe the rifling is too shallow or the crown has been damaged? This is an interesting predicament.

What barrel do you have? You're certainly experiencing what I was hoping for...but to be certain I went for 1:7 vs the lower cost 1:8. That said....Palmetto State Armory is known for okay, but not great products. I have no prior experience...this is my first AR. If I built the upper I'd be blaming myself.

The crown is perfect...can't speak to the rifling...it sure looks tiny to me. But again...no prior experience, and not a lot of equipment for inspecting/testing. At least there IS rifling, and it's enough to twist the brush off of a cleaning rod. Beyond that...still just speculating. If it was just my handloads, I'd be blaming them...but it's all subs I've shot so far. Naturally, I picked a bullet that no one else is loading, so pretty much alone in that regard. Thanks for the feedback.

I have a McGowen stainless fluted barrel... Made before Mr. McGowen passed away. Palmetto is usually ok, but they are no stranger to quality control issues.

I think your first order of business is to invest in a .30 caliber jag and figure out your rate of twist. Next, if your barrel is, in fact a 1 in 7" twist, check your muzzle device for bullet matter or signs of contact. If the bore of the muzzle brake or the barrel threads are not concentric, your projectiles might be making contact and causing them to yaw. Longer projectiles are going to have a greater presence on paper than the shorter projectiles. I actually have had this happen with a 9mm handgun using thread converters. While the bore of the converters was larger than .355, the bore was just enough off center to tap the projectile slightly and send it sideways (luckily) just after they exited the suppressor. That might be part of your problem. If there doesn't seem to be anything awry after all of that, you might consider contacting PSA for a return/exchange.