Subsonic 300 Blackout question

[jimbobborg]

I see all of the barrels for the 300 are at a pretty tight twist rate. I'm assuming this is to stabilize the heavy bullets used for subsonic ammunition. Since these bullets are traveling at less than 1100 fps, how are they expected to expand? It seems to me that you'd want them to tumble after leaving the suppressor. Wouldn't a slower twist rate be better for the supersonic bullets and let the heavy bullets tumble? Maybe I'm missing something.

 

[Pinecone]

You don't want them to tumble before they hit the target. Too slow of a twist will mean they tumble in the suppressor, which is a VERY BAD THING.

When you work up a subsonic load, you shoot at 25 yards and look for evidence of tumbling. If they are tumbling, you need to bump up the velocity or use a lighter bullet.

 

[DaemonAssassin]

Tumbling means the bullet is not stable as soon as it exits the muzzle. If the bullet starts to tumble when it leaves the muzzle, it will cause a baffle strike. Kiss the can good bye.

 

[Speed3]

Not only the baffle strikes but how well do think a tumbling bullet flies?

 

[E.Shell]

I see all of the barrels for the 300 are at a pretty tight twist rate. I'm assuming this is to stabilize the heavy bullets used for subsonic ammunition. Since these bullets are traveling at less than 1100 fps, how are they expected to expand? It seems to me that you'd want them to tumble after leaving the suppressor. Wouldn't a slower twist rate be better for the supersonic bullets and let the heavy bullets tumble? Maybe I'm missing something.

They usually don't expand. It's very hard to get subsonic bullets to expand. Even pure lead .22 LR HP slugs don't reliably open up on small game/varmints at close range. Jacketed rifle bullets are even more difficult to open up. I find BTHPs from 168 to 240 grains that have failed to open up when striking firm clay-based soil at transonic/subsonic velocities and were it not for the 'sandblasted' finish, look like they could be fired again. We've shot several weight Barnes bullets from the .300BO 25 yards into the berm behind my shop and if they are kept subsonic, they look almost unfired upon recovery.

Subsonic ammo is like blackpowder in a way. There is a finite velocity ceiling and if one wishes to impart more energy, then the greater frontal area and weight of larger calibers is called for. Because they aren't traveling fast enough to expand, penetration is usually very deep and your energy transfer isn't in proportion to actual muzzle energy.

If the bullets are marginally stabilized, after the fashion of the early M-16s with their 1:12 twist rate and 55 FMJs, then bullet weight will have to be specific or you will risk the baffle strikes mentioned above.

If you happen to clear the suppressor and the bullet tumbles on the way to the target, the flat spin will cause the bullet to veer off target.

 

[F-Stop]

Lehigh has some interesting subsonic bullets but out of my price range. Maybe if I hunted with suppressed 300blk it be worth it. A hog gun perhaps.

 

[jimbobborg]

They usually don't expand. It's very hard to get subsonic bullets to expand. Even pure lead .22 LR HP slugs don't reliably open up on small game/varmints at close range. Jacketed rifle bullets are even more difficult to open up. I find BTHPs from 168 to 240 grains that have failed to open up when striking firm clay-based soil at transonic/subsonic velocities and were it not for the 'sandblasted' finish, look like they could be fired again. We've shot several weight Barnes bullets from the .300BO 25 yards into the berm behind my shop and if they are kept subsonic, they look almost unfired upon recovery.

So what good is subsonic rounds if they don't dump any energy in the target? You're basically punching .308" holes in someone, and doing little damage to them.

If the bullets are marginally stabilized, after the fashion of the early M-16s with their 1:12 twist rate and 55 FMJs, then bullet weight will have to be specific or you will risk the baffle strikes mentioned above.

For quiet SD ammunition, wouldn't this be optimal? Is MOA ammunition at 100 yards something to really strive for with subsonics?

If you happen to clear the suppressor and the bullet tumbles on the way to the target, the flat spin will cause the bullet to veer off target.

How much distance would that take before it completely misses a human torso? I've seen 7 yard paper targets with keyholes from a 9mm round that was not stabilized.

 

[jimbobborg]

Lehigh has some interesting subsonic bullets but out of my price range. Maybe if I hunted with suppressed 300blk it be worth it. A hog gun perhaps.

From what I'm learning from people running this round, you won't put a pig down with subsonics.

 

[E.Shell]

So what good is subsonic rounds if they don't dump any energy in the target? You're basically punching .308" holes in someone, and doing little damage to them.

If you've ever had a splinter under your fingernail, or a Willy-Zipper Incident, you'll appreciate the potential involved with even a .30" puncture through something important.

For quiet SD ammunition, wouldn't this be optimal? Is MOA ammunition at 100 yards something to really strive for with subsonics?

I don't think MOA groups at 100 yards are possible with .300 BO subsonics, handloaded or not. We have struggled to get handloads to meet both subsonic requirements and low SD numbers at the same time. Getting decent performance with supersonic is no problem.

With the .300BO subsonics, velocity variation alone kills any chance of acceptable accuracy and vertical stringing with Remington factory subsonics in on the order of 4" at 100. The slower the bullet, the greater a percentage of the whole standard deviation becomes. A 25 fps extreme spread at 3,000 fps is 0.83% of the velocity, while the same number at 1,000 fps becomes 2.5% of the velocity and this percentage only gets larger as the bullets lose velocity while the deviation remains unchanged.

How much distance would that take before it completely misses a human torso? I've seen 7 yard paper targets with keyholes from a 9mm round that was not stabilized.

Good question and I do not know the answer. I occasionally see keyholed bullets on paper at 100 yards, but I don't know how far they got before they destabilized. I have seen Sierra 168s from a .308 shoot 8" groups at 800 yards, then move out to 950 and can't hit a car hood.

 

[F-Stop]

From what I'm learning from people running this round, you won't put a pig down with subsonics.

With the average open tip or fmj bullet I agree. They just pass through. That's why I specified LeHigh. Probably the only one I would try for hunting at this point. Check out the LeHigh maximum expansion 194 bullet. They are very expensive complete rounds but, also impressive at subsonic speeds.

 

[teratos]

So what good is subsonic rounds if they don't dump any energy in the target?

They can still do some damage. .45 ACP is a subsonic round. You do not want to be on the receiving end of that.

As for .300 BLK subs, I'm not sure why anyone would want to shoot them if they weren't using a suppressor. If shooting suppressed it is a trade off between energy and noise.

 

[DanGuy48]

I haven't read this whole thread so maybe it was already mentioned. Just to be correct, it's not the weight of a given caliber bullet, but the length, that is important when calculating twist rates for bullet stability. Granted, most longer bullets are heavier but this is not always the case , for example larger caliber solids weigh less than shorter lead core bullets of the same caliber. If you want to see the actual numbers, plug in some values here to play around. Also note that BC has very little influence on bullet stability also.

http://www.bergerbullets.com/twist-rate-calculator/

 

[Praeger]

From what I'm learning from people running this round, you won't put a pig down with subsonics.

Go to 7:15, 7:37, or 13:55.

 

[Klunatic]

I don't think MOA groups at 100 yards are possible with .300 BO subsonics, handloaded or not.

Its definitely possible. Using hand loaded Lehigh ME 300blk projectiles, Accurate 1680 in my 16" SOTA arms barrel have shot sub MOA groups at 100 yards. I weighed cases, bullets before loading and then matched groups of cases, bullets and then loaded ammo and weighed the final loads and did a final grouping. The bottom left 3 shot group is what I shot first. Was only seeing a single hole in the target. I was sighting in a new optic and then shifted my point of aim to zero the scope which resulted in the 2 flyers on the top.


Head or neck shot on hog with the Lehigh Subsonic ME round will put down a hog no problem. Heart lung shot can be effective as well but it will run a bit before it dies.

 

[E.Shell]

Its definitely possible. Using hand loaded Lehigh ME 300blk projectiles, Accurate 1680 in my 16" SOTA arms barrel have shot sub MOA groups at 100 yards. I weighed cases, bullets before loading and then matched groups of cases, bullets and then loaded ammo and weighed the final loads and did a final grouping. The bottom left 3 shot group is what I shot first. Was only seeing a single hole in the target. I was sighting in a new optic and then shifted my point of aim to zero the scope which resulted in the 2 flyers on the top.
View attachment 161363

Head or neck shot on hog with the Lehigh Subsonic ME round will put down a hog no problem. Heart lung shot can be effective as well but it will run a bit before it dies.

Nice groups, what is your standard deviation?

 

[lee2]

308 holes make invisible souls

 

[friendlyhippo]

lehigh defense makes some fantastic projectiles intended for subsonic expansion from a .300 blackout. they're rather cost-prohibitive for most casual shooters, but if you want reliable expansion at subsonic velocities, odds are you're more than just a casual shooter. it's a 194-grain all-copper design that is absolutely devastating on both whatever it hits....and whatever buys it. $77 for 50 projectiles. loaded ammo is even worse.

here is a link to the bullet in question.

 

[jimbobborg]

$50 for a box of 20. That's African dangerous game money.

 

[teratos]

$50 for a box of 20. That's African dangerous game money.

Lol. I have a .458 Win Mag. My son wants to shoot it. >$5 a round.

 

[rsideout]

Lol. I have a .458 Win Mag. My son wants to shoot it. >$5 a round.

Why did you buy that rifle?