Subsonic rifle (eg 300 BLK) vs ordinary pistol calibers

[Mosin77]

I was thinking the other day, it seems like people are buying or building guns in .300 Blackout with the idea that it’s a great home/self defense round out of a shorter barreled weapon ....subsonic and suppressed.

So, silly question: we’re talking about a .30 caliber 125 or 220 grain bullet at ~1000-1050 FPS. Exactly what does this do that a regular 9mm or a hot .45 doesn’t? Is it just the 30 round mag capacity?

I was thinking that .458 Socom would be better in terms of stopping power (if you’re going to limit velocity then make up for it in bore size?) but there again... what does that do that a 12ga slug doesn’t?

Am I missing something?

 

[Demi-human]

Verity is the spice of life.

Exactly what does this do that a regular 9mm or a hot .45 doesn’t? Is it just the 30 round mag capacity?

Penetrate at subsonic velocities, it’s all about sectional density and hollow points, or lack there of. Yes.

I was thinking that .458 Socom would be better in terms of stopping power (if you’re going to limit velocity then make up for it in bore size?) but there again... what does that do that a 12ga slug doesn’t?

Recoil less.
I was going to say “comes in an AR”, but that isn’t so nowadays...

 

[BreechFace]

The 300 BLK is very similar to a 45 ACP when talking subsonic, but with greater sectional density and better BC bullets which means more accuracy at range. 45ACP has a greater selection of HP bullets but 300 BLK has a few really good expanding bullets available in Lehigh Defense and Makers Rex bullets.

Now switch a magazine to supers and out of a 9” barrel the 300 BLK leaves the 45 ACP in the dust with 110gr Barnes @2,050-2,100fps. This is a very great SD round out of a short barrel.

Not to mention 30 rounds in a PMAG is a lot shorter than 30 rounds of 45 ACP in a stick mag.

Good question and thoughts though, don’t just buy into the hype without research.

 

[Crosshair]

Subsonic loads you are correct, basically a skinny FMJ pistol bullet as far as terminal ballistics is concerned.

A supersonic 125 grain load basically gets you close to a 7.62x39 in a 5.56 magazine.

The advantage is that a 300 Blackout does better out of a short barrel. Both in terms of short range ballistics and in terms of muzzle blast and flash. Supersonic 300 BK unsuppressed will still cause hearing damage, but not as much as 5.56. Plus a bigger hole even if the bullet doesn't expand.

 

[edwardware]

. . . we’re talking about a .30 caliber 125 or 220 grain bullet at ~1000-1050 FPS. Exactly what does this do that a regular 9mm or a hot .45 doesn’t?

For me: my .300BO pistol cost ~$450. As far as I can tell you'd be hard pressed to buy a .45ACP AR for twice that. You'd also sacrifice almost all of the parts interchangeability; that's important for those of us who store our spare parts as assembled ARs..

 

[jmorris]

I have all of the calibers listed in the op and I generally use either a suppressed 9mm or 458 Socom, don’t really use the 300 blk much.

The reason I went with the 458 wasn’t just bore size but the only way you can have energy go up once you set a speed limit is an increase in mass. Not a lot of 400-500 gn bullets out there for .30-.355 calibers.

 

[FL-NC]

I shot a deer with a Hornady 190 grain sub-x from about 30 yards a couple years ago, using a suppressed RAR ranch. The deer went about 20 yards and piled up. The bullet performed very nicely and exited the deer.

 

[taliv]

a few factors to consider:

- ARs are very easy to shoot where most people struggle with 45acp pistols, so if youre going to choose the AR platform, go 300blk as it's way better suited than 45acp. and with a sling, as we saw in kenosha, retention is enhanced. major advantage for AR for people with low to moderate training

- those "heavy" 220g 30cal bullets are the same "high BC" bullets we'd shoot out of 300winmag et al. The BC on flying ashtray pistol bullets flat out sucks. so 300blk has a pretty big advantage beyond normal pistol ranges, like 25yd. major advantage for 300blk outside the home

- for over a hundred years, 45acp bullets were designed to expand and perform at 800-900fps. 30cal bullets for the most part need to be going much faster than the speed of sound to reliably expand, though as was mentioned above, there are a few notable exceptions like lehigh but they cost $1/ea. major advantage for 45acp

- 30 round mags standard vs 8-15 round mags. major advantage to the AR

- ime, suppressed 45 sounds much much quieter than suppressed blackout, and you don't get the gas in your face with a pistol like you do an AR. advantage 45acp

- in terms of mass, 45acp pretty much stops at 230g. subsonic 300blk goes up to 265g, but it also goes down to the 150 range which allows you to trade low noise for intermediate rifle ballistics just by switching ammo

 

[doubleh]

Even a 20 guage shotgun beats the hole size of all of those.

I know, shotguns aren't all that thrilling but they are effective for defense. If you have 30 bad guys attacking you might want more.

 

[mcb]

I love my 300 BO pistol but I don't use it for home defense. Just a regular handgun pulls that duty. The ability to maneuver in my home and have a hand free is far more important to my home defense plans then the additional capabilities for a SBR/S or AR-pistol in the confines of my home.

But as other have said the exterior ballistics of a 200+ gr 30-cal bullet at ~1050 fps is frequently going to be more accurate at range than a 200+ gr 45-cal. There are several good expanding bullets (Lehigh, Maker, Hornady etc) for 300 BO subsonic so terminal effects between the two is very similar. 45 ACP is going to be cheaper but if you reload that advantage is reduced a fair bit. I can also use my 30 caliber suppressor on more powerful rifles too.




My favorite Maker 220gr REX bullet.

 

[Crosshair]

those "heavy" 220g 30cal bullets are the same "high BC" bullets we'd shoot out of 300winmag et al. The BC on flying ashtray pistol bullets flat out sucks. so 300blk has a pretty big advantage beyond normal pistol ranges, like 25yd. major advantage for 300blk outside the home

Except these bullets are subsonic in a 300 BK. Those "High BC" values are for supersonic flight. Subsonic is a whole diffrent game.

Note how all the subsonic airliners use a rounded nose? That's the more aerodynamic shape if you're never hitting the speed of sound.

 

[adcoch1]

Two points.
1. The 300 blk offers exceptional reliability in the ar15, quite a bit better than any blowback action cartridge.

2. 458 socom is like a brenneke black magic 12 ga slug from a much smaller package. My 458 SOCOM pistol is even smaller than my Mossberg shockwave was. And quick mag changes.

The ar15 may not outdo a 45 handgun for certain home defense scenarios, but it'll outmode the handgun in almost all other categories.

 

[mcb]

Except these bullets are subsonic in a 300 BK. Those "High BC" values are for supersonic flight. Subsonic is a whole diffrent game.

Note how all the subsonic airliners use a rounded nose? That's the more aerodynamic shape if you're never hitting the speed of sound.

By definition the Ballistic Coefficient (BC) of a bullet is a constant, independent of velocity, if based on the correct ballistic model (G1 and G7 being the two most common models used but there are many others). That is the point of BC, it is one constant number that captures and scales the velocity dependency of the Coefficient of Drag across a broad range of Reynolds numbers (basically velocities in this context) for use in an external ballistic model.

Subsonic airliners have round noses because they need the volume for their radar, the round shape is easier to make, and robust to damage. That said, it is not more aerodynamic than a sharper nose even at subsonic velocity but the small aerodynamic penalty at subsonic velocities is offset by all the other advantages.

 

[taliv]

i am not a rocket scientist, so i could be misunderstanding. i believe the rounded nose of a subsonic aircraft has less drag but also primarily beneficial because it flies at numerous different angles. it may be worth noting that gliders, which are way slower, are often pointy.

mcb, BC is velocity dependent. if you'll note most ballistic calculators allow multiple inputs for different BC at different min velocities. The published BC are often a blended average across what the mfg assumes are typical ranges.

even so, i believe typical round nose 45cal 230g ball is going to have a subsonic G1 BC somewhere in the .12 - .15 range whereas a 230g 30cal is going to have a G1 BC over .5, and while that will definitely drop, i don't believe it will drop all the way to .15

 

[mcb]

i am not a rocket scientist, so i could be misunderstanding. i believe the rounded nose of a subsonic aircraft has less drag but also primarily beneficial because it flies at numerous different angles. it may be worth noting that gliders, which are way slower, are often pointy.

mcb, BC is velocity dependent. if you'll note most ballistic calculators allow multiple inputs for different BC at different min velocities. The published BC are often a blended average across what the mfg assumes are typical ranges.

Ballistic Coefficient by definition is to be a single value for a bullet and thus velocity independent. The reason we are seeing bullet manufactures publish different BC for different velocity ranges and external ballistic software programed to accept this is because many of these new VLD (Very Low Drag) bullets do not fit to the G1 or G7 models. Instead of doing the work to create a new ballistic model for these VLD bullets and all the required testing to create the Coefficient of Drag tables for this new shape, they simply shoe-horn these new VLD bullet into the old dated ballistic models with a piecewise continuous model.


This is the G1 bullet. All the dimensions are a ratio of the bullet's diameter.


This is the G7 Bullet. Again dimension are ratio of the bullet's diameter.


This is a plot of the Coefficient of Drag for the G1 (CD 1) and G7 (CD 7) ballistic models for a bullet with a BC of 1 in each respective model. If you have a bullet that has a BC of .5 (G1) you are saying that the G1 model captures the coefficient of drag over the enter velocity range but my bullet being smaller and lighter sees twice the drag compared to the base G1 model at any give velocity. If you have to pick different BC at different velocity then by definition you are admitting the the selected model does not represent your bullet.

Some of the latest generation of VLD bullet are approaching length to diameter ratios of nearly 6 to 1 and yet we try to use a ballistic model based on the G7 bullet that has a length to diameter ration of 4.23. And why we even report a G1 BC for these bullets is beyond me as they aerodynamically have almost no dimensional similarity.

I am surprised that we have not seen a new Gx model in this age of new VLD bullets. It would make sense and be relatively easy for current Ballistic software makers to accept a new model. That was a big reason the original array of models were created.

 

[Crosshair]

By definition the Ballistic Coefficient (BC) of a bullet is a constant, independent of velocity, if based on the correct ballistic model

It's understandable to believe this, i did for many years, but it is incorrect.

https://www.sierrabullets.com/exter...with-muzzle-velocity-near-the-speed-of-sound/

"There is one velocity region within which the ballistic coefficient of every bullet we have tested exhibits dramatic, radical changes. This velocity region is from about 900 to around 1200 fps, which includes the speed of sound..."

https://www.hornady.com/support/ballistic-coefficient

"Ballistic Coefficient (BC) values can, and usually do change in value with changes in velocity. Most bullets exhibit a lowering BC as velocity slows. The extent of how much a BC will change depends on each unique bullet shape..."

https://www.aircraftnerds.com/2017/...ed-nose-while-some-have-pointed-nose.html?m=1

"In case of subsonic aircraft with rounded nose, speed is not so high for production of shocks. Instead cone shaped nose at subsonic speed causes increase in skin friction drag. Hence cone shaped nose is not used in subsonic aircraft. A shape with a round front is more aerodynamic in subsonic flow than a pointed nose..."

 

[mcb]

It's understandable to believe this, i did for many years, but it is incorrect.

https://www.sierrabullets.com/exter...with-muzzle-velocity-near-the-speed-of-sound/

"There is one velocity region within which the ballistic coefficient of every bullet we have tested exhibits dramatic, radical changes. This velocity region is from about 900 to around 1200 fps, which includes the speed of sound..."

https://www.hornady.com/support/ballistic-coefficient

"Ballistic Coefficient (BC) values can, and usually do change in value with changes in velocity. Most bullets exhibit a lowering BC as velocity slows. The extent of how much a BC will change depends on each unique bullet shape..."

https://www.aircraftnerds.com/2017/...ed-nose-while-some-have-pointed-nose.html?m=1

"In case of subsonic aircraft with rounded nose, speed is not so high for production of shocks. Instead cone shaped nose at subsonic speed causes increase in skin friction drag. Hence cone shaped nose is not used in subsonic aircraft. A shape with a round front is more aerodynamic in subsonic flow than a pointed nose..."

Just because they do it does not mean it was the original intent when BC created. Look at the chart in my previous post. Notice how the coefficient of drag changes dramatically in exactly the velocity you mention above 900 to 1200 fps. If you use the correct ballistic model your BC never changes over the entire velocity range for which the original model was created. Again assuming your bullet is shaped fairly close (a scaling of) to the bullet your selected ballistic model is based on. For what ever reason current manufactures are unwilling/unable to create new drag models for these new bullets that do not fit the old model and simple use this piecewise continuous method on the old G1 or G7 models to get acceptable results. That was not the original intent for the Ballistic Coefficient. It was to be one number to capture the entire velocity dependent coefficient of drag over the entire usable velocity range. And for bullet that are close in shape to the G1 or G7 model you only need one number for the entire velocity range.

If your going to do it piecewise you might as well just get rid of BC completely and use the velocity dependent Coefficien of Drag tables directly. BC was created to scale those table rather than deal with the large table directly.

 

[Mosin77]

Thanks for the discussion, gentlemen. I learned a bunch. The big takeaway seems to be that the AR calibers and platform offer a lot more modularity, so you can build a gun that’s a pretty good home defense pistol, then with a change of ammo it becomes a dramatically different gun for intermediate range hunting or combat or whatever, without even the necessity of changing uppers.

 

[jmorris]

Ballistic Coefficient by definition is to be a single value for a bullet and thus velocity independent.

That’s because it’s BC is a formula. Input numbers, calculate and get A number out.



However the drag coefficient does vary with speed, change the value of v and that changes what the Cd=.



Bryan Litz (now the ballistician for Berger bullets), isn’t much of a fan for G1 for low drag projectiles because it is very speed sensitive. He has done quite a bit of research that makes one skeptical of published BC’s. By measuring them vs calculating for them.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a554683.pdf

From the link below:

It’s a relatively well known fact that the BC of a bullet is different at different velocities....

There are several ways to manage the problems caused by the dependence of BC on velocity. One way is to use a G1 BC that’s averaged for the speed range you’re interested in. This will get you close, but what if the BC of the bullet is advertised for a speed range that’s different than what you’re interested in? It’s not easy to adjust the BC for different average velocities. Another way to deal with the problem of a velocity dependant BC is to give the BC in several velocity ‘bands’ (Sierra bullets uses this approach to advertise the BCs of their bullets)....

One obvious difference between G1 BCs and G7 BCs is that the numeric value of the G7 BC is lower than the numeric value of the G1 BC. For example, if a bullet has a G1 BC of .550, the G7 BC will be close to .282 (same bullet). Even though the G7 BC of .282 is a much more accurate representation of the bullet at all speeds…


https://bergerbullets.com/a-better-ballistic-coefficient/

 

[mcb]

The Ballistic Coefficient and its corresponding drag model/function (G1, G7 etc) is simple a way of using one number to scale a table of experimentally found, and velocity dependent Coefficient of Drag values. (These tables for coefficients of drag at various velocities for the various drag models/function: https://www.jbmballistics.com/ballistics/topics/dragfunctions.shtml).

If your bullet does not closely match the bullet used to create the drag model (G1, G7 etc) then it will not model the drag on your bullet accurately. If your bullet does match the model closely than the single value BC will closely model the drag on you bullet in flight over its entire velocity range. Unfortunately rather than create new drag models for bullets the old drag models don't work well for they simply force fit the old drag model over smaller ranges of velocity and we get multiple BC for a older drag model with specified smaller velocity ranges than the original model was created over.

Even Brian Litz admits this:
This gets us to a (usually) single number, called the ballistic coefficient. In theory, this single number is all we need to know and can be used to compare bullets. The one with the higher BC is better, right? No so fast. It is important to know the drag function that the BC is calculated with and how well the drag function fits the bullet. If the drag function is a good model, the BC is relatively constant over the range of useful velocities and we can use a single BC value. If it is not constant, the BC changes and a single number is not good enough. This is why Sierra publishes multiple BCs for many of their bullets. Is this wrong? Not really, but it is not as convenient as a single number.

How do we get to a single BC that is usable? We use the "correct" drag function for the bullet shape. How do we define "correct"? It is the drag function whose BC varies the least over the range of velocities we are shooting.

Most of the BCs published today use the G1 drag function. This is not the ideal drag function for many long range bullets. Unfortunately, the industry is somewhat reticent to adopt other drag functions. When compared to a G7 BC, the G1 is typically higher. This is because the G1 drag function values are higher -- the ratio of the G1 drag function and G1 BC should be the same as the ratio of the G7 drag function and the G7 BC (it depends on the velocity at which the BC is measured). The problem is that many people do not understand the difference between the two drag functions and look at only the values of BC. Since the G7 BC is typically half the G1 BC is does not look as attractive to the marketing department even though it may provide better answers. Additionally, manufacturers can be tempted to inflate the values for ballistic coefficients. This makes a bullet more appealing than other bullets with lower BCs. What is needed is a single comprehensive measurement of long range bullets using the same techniques.

https://www.jbmballistics.com/ballistics/topics/bcs.shtml

Emphasis mine