.300 BLK subsonic vs. 10 mm subsonic

[bearcreek]

A couple of recent threads got me to thinking about this subject. Suppose a person wanted to build an AR platform rifle, pistol or SBR that was designed and intended primarily to be used suppressed with subsonic ammo. For something like that does .300 BLK have any real advantage over a 10 mm or even a .40S&W? The bullet weights and velocities are basically the same, there's just a slight difference in diameter. Seems like the pistol calibers would have the advantage of more compact magazines and cheaper practice ammo.

 

[pdsmith505]

.30 caliber bullets have better ballistic coefficients than 10mm or .45 caliber bullets. Driven to the same muzzle velocity, the .30 cal bullet will retain energy longer and have a flatter trajectory.

Aside from the CMMG Guard series rifles, the .300 BLK has the advantage of not using blowback actions.

With the advent of .30 cal bullets designed to expand at subsonic velocities, the pistol calibers lose the advantage of expansion.

 

[jdh]

300 uses a standard AR magazine. That removes the necessity of special lowers or mag well adapters.

 

[Elkins45]

If you were starting from scratch I can see how a carbine in 40 S&W would make sense as a close range hunting gun vs the others. The bullets are designed to expand at subsonic velocities.

The down side is that most 40 caliber cans are designed for pistols, and there aren't that many of them on the market. There are a gazillion in 30 caliber. Of course this means nothing if you were going to Form 1 your can.

 

[mjsdwash]

ubiquitous rifle parts, and components, much cheaper, none blowback, and better super performance.

 

[mcb]

No reason a 40S&W/10mm pistol suppressor will not work fine on a carbine chambered in the same cartridge. It should worked better since exit pressures will be lower.

 

[CraigC]

It would be a fine choice, if any were available. The 10mm would be great in a good carbine but for strictly subsonic use, the .40S&W would work better with factory ammo. I'd like to see something like the Ruger PC or CZ Scorpion in 10mm. Subsonic handloads with 220gr cast bullets would make for a nice, quiet mid-bore thumper.

 

[bearcreek]

.30 caliber bullets have better ballistic coefficients than 10mm or .45 caliber bullets. Driven to the same muzzle velocity, the .30 cal bullet will retain energy longer and have a flatter trajectory.

True, although, with a weapon zero'ed at 100 yards, if my calculations are correct, at 200 yards, you're only looking at a difference of about 2 inches in elevation and 40 ft. lbs. of energy

 

[bearcreek]

300 uses a standard AR magazine. That removes the necessity of special lowers or mag well adapters.

I suppose if the plan was to use the same lower for multiple uppers that would be a factor. I know myself well enough to know that even if I got just an upper I'd eventually end up with a dedicated lower anyway.

 

[bearcreek]

Aside from the CMMG Guard series rifles, the .300 BLK has the advantage of not using blowback actions.

Why is a blowback action a disadvantage for that sort of weapon?

ubiquitous rifle parts, and components, much cheaper, none blowback, and better super performance.

What's much cheaper? The gun itself?

 

[pdsmith505]

Why is a blowback action a disadvantage for that sort of weapon?

1) Straight blowback will have a more pronounced recoil than a locked action as more reciprocating mass is required to keep the case in the chamber until pressure has dropped

2) More mass is a disadvantage in itself. Ounces make pounds. Pounds make pain.

3) Especially in suppressed weapons, straight blowback weapons put more gas in the shooters face.

True, although, with a weapon zero'ed at 100 yards, if my calculations are correct, at 200 yards, you're only looking at a difference of about 2 inches in elevation and 40 ft. lbs. of energy

Back of the envelope SWAGs would tell you that a slender, pointy, boat tailed shape will have significantly less drag than a fat, blunt, flat based shape.

But, since ballistics is a funny animal...

Hornandy's free calculator, with given BC's for Hornandy bullets gives:

10mm, 1000fps, 200gr, .199 BC - drop of 40 inches at 200 yards when sighted at 100 yds, velocity of 846 fps, energy of 318 ftlbs

.30 cal, 1000fps, 200gr, .597 BC - drop of 36 inches, velocity 939, energy 391

The 10mm has 20% less energy than the BLK at that point... which is concerning since you are already limiting yourself to subsonic velocity and wont see much damage due to shock.

Even at 100 yds, the 10mm has 10% less energy (416 vs 370 ft lbs).

The above was chosen to highlight the effect of BC ONLY on the ballistics. Going to hornandy's expanding subsonic 300 blk ammo (https://www.hornady.com/ammunition/rifle/300-blackout-190-gr-sub-x-subsonic#!/), we see numbers in the same ballpark as above, but with an expanding bullet vice a target bullet.

 

[pdsmith505]

To add one more factor, it is my understanding that rifle bullets are generally manufactured with tighter tolerances (jacket thickness, etc) than pistol bullets, and will be more accurate.

 

[.455_Hunter]

When I was Active Duty Army, I thought a 10mm carbine would be an excellent weapon for Senior NCO / Company Grade Officer leadership who's primary mission was NOT directly engaging the enemy unless the SHTF at close range.

 

[Casefull]

It's not a big factor, but those pointy bullets do feed better.

 

[Zaydok Allen]

This is an interesting conversation. I agree with pdsmith505. Logic dictates the 300 will definitely do better at mid range and the platform offers some advantages.

However for my purposes I have no interest in a 300BLK. I shot 10mm already, and load my own 10mm, so I got myself a Kriss carbine. I don't think I'd have any problem taking a dear out to 100 yards (16" barrel) with the right anmo, but that's probably where I'd draw the line. Maybe not.

There certainly are a lot more options in 300 BLK than there are 10mm carbines.

 

[Gtscotty]

Hornandy's free calculator, with given BC's for Hornandy bullets gives:

10mm, 1000fps, 200gr, .199 BC - drop of 40 inches at 200 yards when sighted at 100 yds, velocity of 846 fps, energy of 318 ftlbs

.30 cal, 1000fps, 200gr, .597 BC - drop of 36 inches, velocity 939, energy 391

The 10mm has 20% less energy than the BLK at that point... which is concerning since you are already limiting yourself to subsonic velocity and wont see much damage due to shock.

Even at 100 yds, the 10mm has 10% less energy (416 vs 370 ft lbs).

True, but a bullet's effectiveness has much more to do with how it behaves at impact velocity than how much energy it has. It will be quite easy to find 10mm bullets that reliably expand at these lower velocities, not so with heavy .30 cal bullets. Most will not deform or expand at all (especially the ones with the highest BCs), the best you can hope for is random tumbling. The specialty bullets that do expand at subsonic velocities will come with a price several times that of the basic hp pistol bullets, not to mention the increased powder consumption they'll require.

There's certainly an argument to be made for the advantages that heavy pistol cartridges bring for subsonic use depending on your goals.

 

[MachIVshooter]

Aside from the CMMG Guard series rifles, the .300 BLK has the advantage of not using blowback actions.

This is important. Blowback guns tend to have a great deal of port noise, well over 140 dB. Doesn't really matter how quiet you are at the muzzle end if it's still not hearing safe at shooter's ear. Even guns with very heavy bolts like the Suomi tend to be over the limit.

The AR is also unique among gas operated rifles with the Stoner gas system being much more conducive to suppressed use. Typical op rod guns vent near the gas block almost as soon as the piston starts moving, producing "piston pop" that is equally as loud as blow back port pop. Not at all uncommon to see 145+ dB shooter's ear figures on AKs, FALs, SCARs. The Stoner system, when regulated properly for suppressed use with an adjustable gas block, is not terribly difficult to bring under 140.

True, but a bullet's effectiveness has much more to do with how it behaves at impact velocity than how much energy it has. It will be quite easy to find 10mm bullets that reliably expand at these lower velocities, not so with heavy .30 cal bullets. Most will not deform or expand at all (especially the ones with the highest BCs), the best you can hope for is random tumbling. The specialty bullets that do expand at subsonic velocities will come with a price several times that of the basic hp pistol bullets, not to mention the increased powder consumption they'll require.

There's certainly an argument to be made for the advantages heavy pistol cartridges bring for subsonic use depending on your goals.

This was the whole premise of my developing a gas operated 10mm magnum AR. Custom .400" 300+ gr. bullets at ~1,000 FPS using a cartridge that can still offers decent capacity in standard magazine sizes. Harder hitting than .300 Blk with fatter bullets that will expand at those low velocities, but with less recoil and more capacity than .458 Socom or .50 Beowulf.

Unfortunately, I was never able to overcome feeding issues from standard AR mags, more than 8 or 9 rounds loaded causing binding that jammed the gun. I need to revisit the project.

 

[pdsmith505]

True, but a bullet's effectiveness has much more to do with how it behaves at impact velocity than how much energy it has. It will be quite easy to find 10mm bullets that reliably expand at these lower velocities, not so with heavy .30 cal bullets. Most will not deform or expand at all (especially the ones with the highest BCs), the best you can hope for is random tumbling. The specialty bullets that do expand at subsonic velocities will come with a price several times that of the basic hp pistol bullets, not to mention the increased powder consumption they'll require.

There's certainly an argument to be made for the advantages that heavy pistol cartridges bring for subsonic use depending on your goals.

Which is why I pointed to Hornandy's measured data for their 190gr SUB-X ammo ($1.12/rd at midway) that actually does expand well at subsonic velocities. I would have pulled that BC and shoved it into the calculator too, but they dont sell just the bullet yet (much to my dissapointment), so no data. Looking at it as a reloaded, you are correct in that the available bullets are all stupid expensive. Powder costs for subsonic 300 blk are low though, less than 10 grains of h110... I dont have my record book in front of me.

For comparison, a defensive/hollow point 10mm will run you about 0.80 to 1.00/rd, and then your have to find a load that is subsonic to meet the stated goals. Or, you could reload it to get subs... so in that case it makes sense... except...

Hornandy does sell a .40 s&w load with a 180 gr bullet. Still around a dollar a round.

Dunno. Could go on forever. I dont have anything that shoots 10mm, and going 10mm in an AR platform is significantly more expensive than .300 blk.

 

[pdsmith505]

Unfortunately, I was never able to overcome feeding issues from standard AR mags, more than 8 or 9 rounds loaded causing binding that jammed the gun. I need to revisit the project.

I forget the name, but there is a company that sells an insert for p-mags to feed 9mm ammo now. Performs all the functions a mag adapter block does.

 

[CraigC]

Which is why I pointed to Hornandy's measured data for their 190gr SUB-X ammo ($1.12/rd at midway) that actually does expand well at subsonic velocities. I would have pulled that BC and shoved it into the calculator too, but they dont sell just the bullet yet (much to my dissapointment), so no data. Looking at it as a reloaded, you are correct in that the available bullets are all stupid expensive. Powder costs for subsonic 300 blk are low though, less than 10 grains of h110... I dont have my record book in front of me.

According to the page for the loaded ammo, BC is .437.

https://www.hornady.com/ammunition/rifle/300-blackout-190-gr-sub-x-subsonic#!/

 

[ATLDave]

It would be a fine choice, if any were available. The 10mm would be great in a good carbine but for strictly subsonic use, the .40S&W would work better with factory ammo. I'd like to see something like the Ruger PC or CZ Scorpion in 10mm. Subsonic handloads with 220gr cast bullets would make for a nice, quiet mid-bore thumper.

Yeah, for subsonic stuff, the 10's ability to accommodate 220's is its advantage over .40. I shoot a lot of 10mm 220's... you're basically shooting a .45ACP round with better sectional density and BC.... but still quite a bit bigger around than, say, .30.

 

[jmorris]

30 caliber bullets have better ballistic coefficients than 10mm or .45 caliber bullets. Driven to the same muzzle velocity, the .30 cal bullet will retain energy longer and have a flatter trajectory.

Not to any usable degree. Even with a 6.5 bullet that has a superior BC to the .30 caliber, it doesn’t matter much subsonic.

Might be worth plugging in some numbers to see difference between the two and what setting a speed limit does to trajectory as well as get a better idea of what would be a “useable range” for each.

If we took the 123gn SMK and loaded it to 1050 FPS the first thing we do is take a hit in the BC, normally .510 over 1635fps but drops to .420 subsonic (not that it matters much going that slow).
https://www.sierrabullets.com/store/...mm-123-gr-HPBT

Anyhow zeroed at 100 we get

0 yd -1.5” 301 ft/lb energy
50 yd 3.4”
100 yd 0
150 yd -12.1
200 yd -33.5
300 yd -105.3 229 ft/lb energy

Keeping everything the same but using a .458”, 405 gn bullet with a .281 BC we get

0 yd -1.5 991 ft/lb energy
50 yd -3.5”
100 yd 0
150 yd -12.7”
200 yd 35.2”
300 yd -111.5” 674 ft/lb energy

So the big old bullet that has the BC of a brick doesn’t loose that much before trajectory gets almost unusable, with both loads. It is also worth noting that it has more than twice the energy at 300 yds than the lighter bullet has at the muzzle and over 3 times the energy upon exit.

Mathematically the better BC bullet will catch up and surpass the other, in energy, at some point but it will be beyond their usable range. At 2000 yards the lead for energy the 405 has over the slicker 123 is cut to just 63 ft/lbs but you are looking at 879.5 FEET of drop at that point...

 

[CoalTrain49]

Seems like the pistol calibers would have the advantage of more compact magazines and cheaper practice ammo.

I think that's the main attraction of a PCC. People will say that the conversion to 300 BLK is cheap but I'm wondering how many people actually switch their uppers everytime they want to shoot a different cartridge or even shoot subsonic. I'm also wondering if people consider that 300 BLK is 0.40/rd where 45 ACP ammo is about half that.

If you want an AR that shoots a PCC this might be a good one.

https://www.thetruthaboutguns.com/2017/04/jeremy-s/new-cmmg-mkg45-guard/

Of course if you want to shoot hawgs you will have to have a 300 BLK with a suppressor and thermal optics.

 

[jmorris]

I shoot coyotes with a 9mm AR, sub 147’s with point click results.




Hogs with a 458 subs and thermal.



I’ll figure out what to do with the 300 one of these days.

 

[Gtscotty]

For comparison, a defensive/hollow point 10mm will run you about 0.80 to 1.00/rd, and then your have to find a load that is subsonic to meet the stated goals. Or, you could reload it to get subs... so in that case it makes sense... except...

Hornandy does sell a .40 s&w load with a 180 gr bullet. Still around a dollar a round.

I wasn't talking about loaded ammo, I was talking about the bullets themselves, good expanding .40 cal bullets are clearly much, much cheaper than expanding .30 cal heavies, and that's an advantage. I think most folks who are taking up subsonic suppressed projects probably reload, so component costs would be much more important than loaded ammo costs. .300 BLK is a pricey round for the performance you get, I think that's a worthy consideration if you are considering different options.