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Posted: 5/11/2025 8:55:13 AM EDT
| I noticed at the range the other day that many of my .300 Blackout rounds were "keyholing" the paper targets, even at about 35-50 yards! My Palmetto State Armory 8" .300 AAC upper/PSA multi-caliber lower with Silencerco Omega 300 suppressor functioned perfectly and was very accurate, but I could tell that some of the bullets were tumbling. I was shooting factory Remington UMC 220 gr. subsonic rounds. Even though the rounds were tumbling, they still hit to POA. Any ideas for why this was happening? |
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Take the can off and see if they're still keyholing. If not, well, there's your answer. If they are, the the barrel doesn't like those bullets, probably too heavy for the velocity. The 8" barrel may be too short to get the velocity needed to stabilize that bullet. Either way, DON'T SHOOT THOSE THROUGH YOUR CAN until you get it figured out. |
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Bullets are too long and too slow for the rifling twist. Probably on the edge if only some bullets tumble. Just one failing of pistol length barrels chambered for rifle cartridges. |
Keep your powder dry, and watch your back trail.
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I'm watching my back trail.
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^ So far what everyone else has already. This post caught my attention because I have a 8-inch (can't remember my twist...?) .300 BO built with a dedicated SF 300 SOCOM can/WarComp that I'm currently running 220-grain subs through. No issues so far but I'd shit a chicken if I was keyholing with a can on. ETA: It's an Aero (or BA) barrel that's 1:7... |
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The Remington ammo is designed to develop 940 fps out of a 16” barrel, and a 1:7” twist is recommended. The velocity the OP is getting out of his pistol will be somewhat less, clearly below what that long bullet needs to be stable. Hitting the POA at 35 yards is not a great feat, try it again at 100. He needs to get faster ammo, or handload to a higher velocity. I’m not certain why Remington loads that bullet to such a minimum velocity when anything below 1100 fps will be subsonic - unless perhaps you’re shooting on top of Mount Everest. . |
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| Thanks for all of the useful feedback. I'll check out those UMC 220 gr rounds without the suppressor to see what happens, but also look at getting some lighter ammo (190-200 gr). Unfortunately I do not reload, and most manufacturers (except for Hornady and Magtech) only make subsonic in 220 gr. It'll be a real bummer if I can't get subsonic ammo to work properly in my 8" pistol since I built this for home defense. |
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A few options with lighter bullets at subsonic velocities listed as faster than the Remingtons. All are listed on Midway’s site. Hornady 190 WW 200 Hornady 208 Underwood 194 S&B 200 Some marginally stable bullets will be more effective in their terminal effects as they will tumble in flesh. Those bullets which are designed to expand may be less effective. My concern with the OP’s pistol is damaging his can with those non-expanding bullets. . |
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| Thanks again. I went head a bought a couple of boxes of Hornady 190 gr. Subsonic ammo. I'll shoot some of the UMC 220gr without my suppressor and see if that fixes the tumbling. Then I'll try the 190gr with the suppressor. The PSA Upper with 8" bbl. is designed to handle subsonic ammo with a suppressor, so I'm a little confused. But hopefully a lighter weight bullet is the answer. |
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Originally Posted By MojoJim: Thanks again. I went head a bought a couple of boxes of Hornady 190 gr. Subsonic ammo. I'll shoot some of the UMC 220gr without my suppressor and see if that fixes the tumbling. Then I'll try the 190gr with the suppressor. The PSA Upper with 8" bbl. is designed to handle subsonic ammo with a suppressor, so I'm a little confused. But hopefully a lighter weight bullet is the answer. If you would like us to take a look at the upper, feel free to PM me. Thank you, Josiah |
Palmetto State Armory
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3760 Fernandina Rd
Columbia, SC 29210
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The bullet in that ammo is advertised with a BC of .680 and a length 1.127 inches. Even as slow as 600 FPS, it is more than stable at 1:8 twist. Physical length of the bullet is the primary deciding factor for twist and stability (yes, other factors affect it, but physical bullet length is the main factor). Barrel length only matters for velocity for any given load. A 2 inch barrel will still spin the bullet at the same rate as a 16 inch barrel (assuming muzzle velocity is the same). I would remove the suppressor and see what kind of results you get. |
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Originally Posted By EDL: Barrel length only matters for velocity for any given load. A 2 inch barrel will still spin the bullet at the same rate as a 16 inch barrel (assuming muzzle velocity is the same). I had to re-read that a couple times. What you say is absolutely technically correct, but I think it's worth pointing out that your statement lives in "happy physics land", where certain inconvenient realities are ignored. "Assuming muzzle velocity is the same" -- how often is this a true statement when going from a 2" to an 16" barrel in the same caliber? And how often with the same load? Almost never and never? For many calibers, it's possible to work up two different loads in the same caliber to accomplish this, but they'd be drastically different loads, and it would require some effort. I mean, if you have ammo that shoots the same velocity out of 2" and 16" barrels, I want to know what ammo you're buying. Muzzle velocity changes with cartridge (projectile weight and powder load) and barrel length. So if you don't also alter the projectile weight & powder load to compensate for the change barrel length, the muzzle velocity will change with barrel length. But, yes, if you keep muzzle velocity and twist rate the same, RPMs at the muzzle will also be the same. Absolutely true. |
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Originally Posted By PreacherOfGadget: I had to re-read that a couple times. What you say is absolutely technically correct, but I think it's worth pointing out that your statement lives in "happy physics land", where certain inconvenient realities are ignored. "Assuming muzzle velocity is the same" -- how often is this a true statement when going from a 2" to an 16" barrel in the same caliber? And how often with the same load? Almost never and never? For many calibers, it's possible to work up two different loads in the same caliber to accomplish this, but they'd be drastically different loads, and it would require some effort. I mean, if you have ammo that shoots the same velocity out of 2" and 16" barrels, I want to know what ammo you're buying. Muzzle velocity changes with cartridge (projectile weight and powder load) and barrel length. So if you don't also alter the projectile weight & powder load to compensate for the change barrel length, the muzzle velocity will change with barrel length. But, yes, if you keep muzzle velocity and twist rate the same, RPMs at the muzzle will also be the same. Absolutely true. Help me understand that. How does the bullet RPM change if the twist is the same in two different length barrels? Muzzle velocity I get... Is it because (for example with an 8" twist) the bullet gets a full revolution in an 8" barrel, but would only make 1/2 revolution in a 4" barrel? |
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Originally Posted By eracer: Help me understand that. How does the bullet RPM change if the twist is the same in two different length barrels? Muzzle velocity I get... Is it because (for example with an 8" twist) the bullet gets a full revolution in an 8" barrel, but would only make 1/2 revolution in a 4" barrel? It has nothing to do with the number of revolutions it goes through before leaving the barrel, but, rather, that muzzle velocity directly determines the rotation rate at muzzle. Longer barrel means higher muzzle velocity with the same cartridge, which also means higher rotational rate. I'm gonna go simple on these terms to avoid complicated math that misses the basic concept. Muzzle Velocity x Twist Rate = Rotation Rate So how does that equation work? Lets look at the unit types to see what cancels out. Rotation Rate= rotations/time Muzzle velocity = distance/time Twist rate = rotations/distance Now to substitute values
Distance cancels out Now, to wrap around to the earlier scenario: if you change your barrel length from 2" to 16", your muzzle velocity will change and this necessarily changes the rotational rate at muzzle, too. And in the real world, with most cartridges, with most realistic barrel length increases, the bullet will increase in velocity and thus increase rotation rate. The change in speed & rotation rate is non-linear, and there's points where rates change, etc., but at a basic level, the longer the barrel, the more energy transferred to the bullet from the powder, and the faster the bullet goes and the faster it spins. Edits: to clarify, tried pare down redundancy |
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...It has nothing to do with the number of revolutions it goes through before leaving the barrel. It's the rate at which it is going through those rotations at the point it leaves the barrel, which is determined by the speed it's going at the point it leaves the muzzle. Longer barrel means higher muzzle velocity with the same cartridge.... A great explanation, but not necessary. From the OP's post you quoted: ...How does the bullet RPM change if the twist is the same in two different length barrels? Muzzle velocity I get... . |
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Originally Posted By PreacherOfGadget: I had to re-read that a couple times. What you say is absolutely technically correct, but I think it's worth pointing out that your statement lives in "happy physics land", where certain inconvenient realities are ignored. "Assuming muzzle velocity is the same" -- how often is this a true statement when going from a 2" to an 16" barrel in the same caliber? And how often with the same load? Almost never and never? For many calibers, it's possible to work up two different loads in the same caliber to accomplish this, but they'd be drastically different loads, and it would require some effort. I mean, if you have ammo that shoots the same velocity out of 2" and 16" barrels, I want to know what ammo you're buying. Muzzle velocity changes with cartridge (projectile weight and powder load) and barrel length. So if you don't also alter the projectile weight & powder load to compensate for the change barrel length, the muzzle velocity will change with barrel length. But, yes, if you keep muzzle velocity and twist rate the same, RPMs at the muzzle will also be the same. Absolutely true. I should have prefaced it more, and I only added that part because I frequently see people telling someone they need a faster twist with a shorter barrel (implying that a shorter barrel won't spin the bullet enough). Of course I know there are velocity differences for the same load out of different length barrels, that wasn't the point. I also get that not everyone reloads in order to tailor their ammo to their barrel. Sorry if I wasn't clear enough. |
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Originally Posted By eracer: Help me understand that. How does the bullet RPM change if the twist is the same in two different length barrels? Muzzle velocity I get... Is it because (for example with an 8" twist) the bullet gets a full revolution in an 8" barrel, but would only make 1/2 revolution in a 4" barrel? Full turn, or half turn, or even quarter turn, doesn't matter. The only time the bullet won't spin at RPM regardless of barrel length and twist is if the bullet "strips" in the rifling. |
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Originally Posted By EDL: Not true. I have a 7.5" PSA barrel in 300 Blk that's 1:7. Originally Posted By EDL: Originally Posted By EdgecrusherXES: PSA barrels are 1/8 twist. Not true. I have a 7.5" PSA barrel in 300 Blk that's 1:7. Well, it depends on what you mean by PSA. Both of the following are “PSA” uppers, one is 1:8” and the other is 1:7”. Attached File |
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I have a similar problem, PSA 300ACC 8.5" 1-8 upper with a YHM Phantom QD brake shoots great with S&B 124gr supers and Win 200gr subs. Starts keyholing with the 200gr subs thru a YHM Resonator R2. Is this an ammo problem, a barrel problem or "I'm doing it wrong" problem? Edit. I was doing it wrong. I used a crush washer to time the Phantom muzzle device and that was a mistake. Removed the crush washer and properly shimmed the brake for the right timing and then fired a 80 rounds supers and subs without observing any keyholes. I hope sharing my dumbness helps someone 
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