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Old November 5, 2022, 11:10 PM   #1
Dashunde
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Long 10mm vs short 5.56

I’m kicking around buying a CMMG Banshee in 10mm, but I wonder how well the ballistics of a long 8” 10mm compare to a short 10” 5.56 on meat and bone? I tend to carry alternating Underwood 150gr JHP and 140gr monolithic. Both are 1500fps out of 5” iirc.
All of my 5.56 is bulk Federal 55gr XM193.

I already have a couple of nice 10” AR’s, but I also have a G29, G20, G40 mos and a DW Razorback.. so the Banshee 10mm is really calling out to me, but other than shared mags is there any tangible advantage in the Banshee over the 5.56’s I currently own?
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Old November 6, 2022, 06:29 AM   #2
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What is the range for intended use? I ran data at the muzzle and 100yds. If you plan to shoot to 200 or 300yds that is a very different use case imho. As well as if this is intended for indoor or outdoor use.

Well, out of a 10in barrel xm-195 55g is going 2767 fps with 933fl-lb of energy. At 100yds it is going 2401 fps with 704 ft lbs of energy.

A 10mm 150g jhp cor-bon out of an 8in barrel is going 1446fps with 696 ft lb on energy at the muzle, and at 100yds is going 1078fps with 387ft-lb of energy.

With that said, while not quiet, the 10mm will have a lot less muzzle blast, which i would lean heavily towards if you intend this for indoor use. I dont like short barrel 5.56 in general, they rattle my teeth.

The way i would think about it is this.5.56 is somewhat frowned upon as a deer cartridge, although i feel it is adequate under the right circumstances. However 10mm is often a go to for bear defense. 10mm is also legal for deer where i live, while 5.56 is not. And i would really not want to have to hunt or defend myself from a bear with a 5.56 While purely circumstantial i feel it has some relevance and speaks to the capabilities of the cartridges for hunting and or defensive use.

Personally, my vote is 10mm
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Last edited by Shadow9mm; November 6, 2022 at 06:36 AM.
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Old November 6, 2022, 02:14 PM   #3
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Here's an example to consider, when looking at the energy of different rounds for various purposes...

A .45-70 and a .22-250 can be loaded to identical Ft/Lbs of muzzle energy. IDENTICAL.

This is because energy figures are numbers on paper derived from math formulas. They represent a value, but are not the entire picture.

Ask yourself, which would you choose, to stop a large, dangerous beast such as a bear or buffalo, the .22 cal or the .45 cal, when the energy is identical??

I would go with the bigger bullet, but, that's just me...

Muzzle blast is the result of how much powder you are burning, the "size of the hole in the pipe" and distance from your face.

A quick look in a Hornady manual shows the 10mm burns about 15gr powder in its heaviest loads and a .223 burns about 25gr or so. I would expect the greater powder charge to have a larger "feeling" muzzle blast, and the closer to your face the muzzle is, the greater the effect you feel.
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Old November 6, 2022, 09:23 PM   #4
Dashunde
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Excellent info from both of you, thanks.
The CMMG would be an outdoor item, 100 yards or less, generally defensive from huge furry problems - it seems I may move to Northern Idaho, if not we’ll be there 6mo of the year, spring thru fall. We tend to wander around the boonies of Western Colorado to Moab on up into Idaho in a RZR and/or truck, camp out of it… the more North I go the more interested I become in more than just a G20.

The analogy of 45-70 and 22-250 is exactly the kind of head scratching that led me here - plus I need to justify a seemingly redundant additional pricey toy - I know that even a 5.56 with 25% of its powder flashing beyond the barrel whups the 10mm on paper, but I’m curious if a fast 55gr FMJ would be able to deposit its energy as effectively as a fat heavy 10mm at 20-50 yards out of a longer than normal barrel. I think I got my answer, and it’s likely still a better choice for short range two legged problems… and the CMMG is definitely a better option than an angry pistol or (short 5.56) for my wife/daughter.

I dont mind the blast of my current shorty 5.56’s, but sure as hell wouldn’t want to have to shoot it without ears on, be deaf for days, especially if there’s anything that’ll reflect the sound back for added insult (canyon wall, rock face, etc). The 10mm is no fun either, but its tolerable, kinda.

Last edited by Dashunde; November 6, 2022 at 09:28 PM.
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Old November 6, 2022, 09:36 PM   #5
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The energy formula, is mass times velocity squared. So energy heavy favors velocity.

Momentum is a bit different its simply mass times velocity.

For the 223 55g above, it provides a momentum of 21 and a taylor KO score of 4

Whereas the 10mm provides a momentum of 30, with a taylor ko score of 12.

Ft-lb is not an end all be all. If you look at momentum or taylor score 10mm is much better. And there are other formulas people have created to estimate knock down power. None offer a definite answer imho. But it can give us some rough estimates or insights into how much energy a bullet has, how well it will retain than energy, and how effective it will be at transferring that energy.
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Last edited by Shadow9mm; November 6, 2022 at 09:41 PM.
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Old November 6, 2022, 11:16 PM   #6
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Aside from calculating energy, and its transfer (and yes, it an important and valid means of comparison between rounds) when considering the actual physical effect of the bullet, do not overlook the fact that it is physically a chunk of metal, that occupies space, displacing organs and leaving a hole behind it.

It is energy (as velocity) that gets the bullet to the vitals and through them, but don't discount the effect of the size and mass of the slug and the hole it makes.

All the factors play a part, some a bigger part than others...
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Old November 7, 2022, 12:53 AM   #7
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I feel the 223 is marginal to start with and severely reduced in effectiveness with a short barrel.

The 300 BO is not a long range gun to start with, but 10" barrel does not hurt it nearly as much as it would a 223. Finding the right ammo (bullet weight and construction) is very important when considering this round for serious use.

For short AR-15 based guns, the 350 Legend and the 45 cal rounds can retain a decent maximum effective range with a short barrel. And all three would be hard hitters at closer ranges even with a short barrel.

Of the PCCs, the 10mm is the only one that I would want to rely on to be more than a "fun gun" or a inside the house defensive round. However, the effectiveness of the 10mm is much less than the 350 Legend or the 45s.
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Old November 7, 2022, 10:53 PM   #8
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I'm also interested in the Banshee, but would be looking at 200 grains, or more, to take advantage of the 8" barrel.
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