SBR & Terminal Ballistics / Fragmentation ?

[SupaRice]

So I've started down the path to SBR and I'm reading here and there. It seems there is a lot of talk about bullet fragmentation and other terminal ballistics when using M855 or M193 in a SBR.

 

I found this:

http://counterstrikefox.freeservers.com/mv.htm

 

http://www.ar15.com/archive/topic.html?b=3&f=16&t=273352

 

 

Which is a short summation of what I've read elsewhere. My SBR (already have some of the parts) will be a 11.5" barrel.... Does that provide enough velocity to give good downrange ballistics? What are alternative ammunition options?

Edited July 22, 2013 by SupaRice

[SupaRice]

Should probably list also that my setup is 11.5" with a 9 twist....

 

 

What do you guys think of this post?

 

 

My research indicates that a 11.5" barrel should reach a muzzle velocity between 2,300 and 2,800 fps, depending on ammo. Heavier ammo will be on the low end of the velocity range and lighter ammo like 55gn will be on the high end. Premium 5.56 ammunition, like Hornady 5.56 TAP, will fragment at these velocities (partial fragmentation occurs below 2,300 fps, there will be no fragmentation below 2,150 fps). M193 should reach fragmentation velocity (2700 fps) at the muzzle and M855 probably wont.

from the Oracle

Fackler's 2700fps rule for M193 is more like 2600fps.
Though the dramatic fragmentation seen over 2700 fps in M193 and M855 is clearly an effective wounding mechanism, the lesser fragmentation seen at 2600 - 2650 fps in M193 is still impressive. Wound channels from rounds at 2650 fps are certainly not as devastating as 2700+ fps but they are still larger than from controlled expansion rounds. Really, we should not be discounting the performance of M193 until its under 2600 fps. This should extend M193 fragmentation standards out to slightly over 200 meters from a 20" barrel and 150-175 meters from a 16" barrel.

The fragmentation range, or effective range, of a 11.5" barrel should be out to around 50 yards (150 feet). At distances beyond that, the bullet will most likely not fragment. You could run your intended ammo through ballistics software and determine the distance at which it drops under fragmentation velocity to determine its effective range.

MSTN has some velocity numbers for short barrels and different ammo in their industry forum
http://www.ar15.com/forums/topic.html?b=2&f=134&t=149575

 

http://www.ar15.com/archive/topic.html?b=6&f=22&t=286571

Edited July 22, 2013 by SupaRice

[Cruel Hand Luke]

The short answer? An 11.5" is at most a 75 yard gun from a terminal ballistics standpoint with ball ammo. Yes...I said 75 YARDS.

 

You can increase that range with 70+ gr HP ammo but the 11.5" 5.56 is never going to do what a 16" or 20" gun will do. 

[SupaRice]

That's close to what I'm reading... I mostly have it for fun and cool factor. But if it proves to be reliable I would possibly use it in a SHTF scenario. And in that case I would want it to be capable of suppressing immediate threats with rapid succession... Also, if it'll kill a coyote out to 100yds decently I'd be OK with that too.... :pleased:

 

I have a 16" M&P AR15 also, and would rely on it for longer work of course...  I'm mostly wonder what thought others have given to ammo in this sort of setup, for a defensive weapon.

Edited July 22, 2013 by SupaRice

[Oh Shoot]

My understanding is that you need something around 2450 fps at target for 5.56/.223 fragmentation and/or tumbling to do it's thing.

 

I don't know the curve for muzzle to various distances drop off but I did chrono of some rounds from my 10.5" 1:9 pistol not long ago -- these were all various bulk .223 rounds but they were all 2700+  to 2900+ fps. The average between my 10.5" and my 16" rifle was less than 500 fps best I remember.

 

Surprisingly the highest velocity was with el cheapo Monarch lacquer coated steel. Note that I didn't get around to testing actual 5.56 rounds with full NATO load either, as battery died on chrono first, so they should fare even better, and of course your 11.5 incher should do better than my 10.5 incher also.

 

The actual results are on my other puter, I'll try to remember to post them here when I get home at end of week.

 

Skinny is I feel pretty confident that most any round will do it's thing at 100 yards with this heater, how much farther couldn't say. With full length receiver extension on it to rest against cheek as third point of contact, it's pert close to same torso accuracy as my rifle at that distance also with iron sights.

 

- OS

Edited July 24, 2013 by Oh Shoot

[StPatrick]

This seems like something* a slower twist rate could improve.  Wasn't the M16 originally fielded in 1/11"?

 

*Not fragmentation, but tumbling upon impact due to less stabilization.

Edited July 24, 2013 by StPatrick

[SupaRice]

That's what I read... Seems most are 1/7, mine is a 1/9.. Plus it's got another inch (that's what she said :yuck: ) so that doesn't hurt.

[nightrunner]

Ive heard that the 70gr Barnes TSX load is what you want to use for terminal performance in a SBR.

[Dolomite_supafly]

I will go into great detail about this in the next day or two.

I have pages of infor regarding this on here. You can search "twist" with me as the author and find a lot of info.

[austin7.62]

Maybe you should SBR an AK! Neither 5.45 or 7.62 are as dependent on velocity as the 5.56.

[SupaRice]

I will go into great detail about this in the next day or two.

I have pages of infor regarding this on here. You can search "twist" with me as the author and find a lot of info.

 

Please PM me with anything you have!

[Lumber_Jack]

are you just trying to deterime the terminal ballistics of your setup or maximize the maximum terminal ballistics of an SBR?  Are you dead set on keeping it a 5.56?

[jcluff]

Build your SBR as a 300 blackout. 9" barrel performance appears to be not that far off from 16" barrel and seems to have been made for SBR.

http://en.wikipedia.org/wiki/300_AAC_Blackout_(7.62×35mm)


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[SupaRice]

I have an AR pistol, and I want to make it an SBR. So... I'm going with what've I've got basically.... I just am wondering what would be the best ammo for terminal ballistics with that setup. I've not got my stamp yet, so I've not converted it yet... Just wondering about ammo choices

[Dolomite_supafly]

I have an AR pistol, and I want to make it an SBR. So... I'm going with what've I've got basically.... I just am wondering what would be the best ammo for terminal ballistics with that setup. I've not got my stamp yet, so I've not converted it yet... Just wondering about ammo choices

Enjoy the wait. I am 4 months into my wait and when I called last week I had just went pending and was told it was going to be another 6-8 months before I could SBR mine.

 

As far as terminal performance most any ammo will be acceptible inside of 100 yards with a 11.5" barrel providing the twist isn't too fast. Personally I would go extreme. That is I would use either a really heavy bullet or a really light bullet but nothing in between. I would also use modern designs that are designed to fragment even if they do not tumble. With a 9 twist I would also plan on shooting heavy bullets because they loose less velocity from the short barrel than lighter bullets. a 9 twist will shoot 77 grain bullets out to 100 yards easily and they WILL tumble when they hit.

 

Twist has a significant affect on terminal perfomance when using FMJ's or target style rounds. Fragmentation with FMJ is secondary to tumbling. If a bullet does not yaw or tumble is generally does not fragment, at least not FMJ. And the 5.56 will tumble and fragment providing the velocity is high enough AND the twist is slow enough. I will have to go back and look but I believe it is generally accepted that FMJ bullets need at least 2,600 fps to fragment AFTER they begin tumbling. So if the velocity is below that threshold at the target then you will only get a tumbling bullet and that is only if the twist is slow enough that the bullet becomes unstable

 

If you have a short barrel with a fast twist it is the worst possible combination for self defense. The twist will not allow the bullet to tumble and the velocity will not cause the bullet to fragment even if it does tumble. In those cases I would choose the heaviest bullet I could find in hopes it will be unstable and tumble. Or use modern bullet designs like the Harnady TAP.

 

Most people are going to survive a clean 22 caliber hole so long as it doesn't hit vital blood supplies or CNS. The damage from a 5.56 comes frm when the bullet tumbles and/or fragments. And when a bullet is overstabilized it will not tumble and the if velocity is below the bullet's fragmenting threshold it will just pass through just like a 22lr. I have seen it first hand. Had a guy we brought in that had been hit in the upper left thigh. He was walking and talking with very little blood.

http://www.texassmallarmsresearch.com/TechInfo/556Performance/556Performance.pdf

Note page 4 that M855 bullets do not reliably fragment at velocities below 2,500 fps in a 7 twist barrel. And considering out of a M4 (14.5" barrel) the M855 is at 2,900 fps but at 200 yards it is only going 2,400 fps, well below the fragmenting threshold for that round. This means at roughly 150 yards the m855 fired out of a M4 will no longer reliably fragment. Or out of a 16" carbine that range is extended to roughly 200 yards but not much more. All of this is because of the twist rates. The tumbling is what starts the fragmenting process with FMJ.
 

M855 runs about 2,500 fps out of a 11.5" barrel which means fragmentation is pretty much out of the equation. So you have to rely on the bullet tumbling for all of its damage.

 

The reason we hear of all the problems overseas right now is because the military decided to try to turn what is a short range cartridge into a long range cartridge. The 223/5.56 is a 300 yard cartridge under ideal conditions. When they decided to go with a faster twist it over stabilized the bullets and reduced the chances of them tumbling. Them they shortened the barrel which reduced the velocity and reduces the range at which the bullets will fragment if they tumble. And finally they went to a heavier bullet which reduced the velocity even more.

 

Why is it we hear the Army complain and not much from the Marines? It is because the Marines chose to keep the 20" barrel. This increased the velocity which in tirn increases the chance of fragmentation over the 14.5" barrel.

 

If I were to build a dedicated SBR with termianl performance in mind it would have a 10.5"-12.5" barrel but most importantly it would have a 12 twist barrel and not a 7, 8 or 9. 12 twist was the original design and it worked extremely well because a 55 grain bullet is barely stable which ensures the bullet will at least tumble. It will also shoot 62 grain bullets inside of its useable range of 100 yards. And when the 62 grain bullet hit a "soft" target it would tumble. And even if you shot 77 grain bullets and they tumbled in the air they would still be deadly.

 

My SHTF AR has a 12 twist 20" barrel. It is extremely accurate with everything up to, and including, 62 grain bullets.

[Guest semiautots]

This is what you want.  The powder is burned completely within about 10 inches of barrel, unlike 5.56.  You get a bigger bullet, better terminal ballistics, and easier suppression.

 

 

Build your SBR as a 300 blackout. 9" barrel performance appears to be not that far off from 16" barrel and seems to have been made for SBR.

http://en.wikipedia.org/wiki/300_AAC_Blackout_(7.62×35mm)


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[RWF]

who cares they are just plain fun! and if you are really worried about it get in a 6.8

[Stegall Law Firm]

Federal Fusion 62 gr. is well-regarded in short barreled rifles.  Check out this thread: http://www.m4carbine.net/showthread.php?t=73955.  There are a few more reviews and discussions out there if you search. 

 

I've got an 11.5" and a 16" AR and I think the Fusion would be ideal in both, so I just ordered 200 rounds from Palmetto State.  They've got it for $17 a box of 20 this weekend.

[Stegall Law Firm]

Federal Fusion 62 gr. is well-regarded in short barreled rifles.  Check out this thread: http://www.m4carbine.net/showthread.php?t=73955.

 

I've got an 11.5" and a 16" AR and I think the Fusion would be ideal in both, so I just ordered 200 rounds from Palmetto State.  They've got it for $17 a box of 20 this weekend.

Edited July 27, 2013 by Stegall Law Firm

[Oh Shoot]

As I mentioned earlier, here are the limited chrono results from some rounds, comparing 16" rifle and 10.5" pistol:

 

3 shot average (the fps from pistol was not as high as I "remembered" in previous post). I was surprised that the brass cased 'mericun Federal was the lowest overall with both:

 

Monarch 55gr .223:
Rifle: 2929  Pistol: 2611

Wolf WPA 55gr 223:
Rifle: 2872  Pistol: 2546

Tula 55gr .223:
Rifle: 2843  Pistol: 2612

Federal Bulk 55gr .223:
Rifle: 2840  Pistol: 2536

 

- OS

Edited July 27, 2013 by Oh Shoot

[Dolomite_supafly]

As fun as guns are they are ultimtely a tool that is used to defend yourself. Every caliber I own has that in mind and the vast majority of the guns I own are tools first and toys second.

[SupaRice]

So..... for a black out if I'm reading correctly, I just need a different barrel? Seems I can use my 5.56 bolt and carrier?

[Lumber_Jack]

So..... for a black out if I'm reading correctly, I just need a different barrel? Seems I can use my 5.56 bolt and carrier?

 

 

Thats correct.  all other parts are the the same. Depending on the gas port location (pistol length gas is recomended) a new gas tube and possibly an adjustable gas block although some have had good success with just a standard block.

 

I have a 10.5" barrel with pistol length gas, and a Siekens precision adjustable gas block.  once adjusted I can run super heavy sub sonic or Hornady 110gn VMAX without adjusting the block.

 

for a time I had a 5.56 and a .300 BLK and only had one BCG that I switched between the two. 

[molonlabetn]

I own a Lewis Machine & Tool MRP, with 10.5" direct impingement and 12" gas piston barrels chambered for 5.56, both are 1-7 twist. Here's my take.

 

An SBR is a compromise... We either wanted less weight/length, or wanted to mount a suppressor and retain some compactness and balance... Thing is, short barrels simply offer less time for a bullet to accelerate, and result in loss of effective range. You have a few choices... either you simply live with the reduced effectiveness, because the gun is intended for sub-100 yard engagements and you are a super-ninja who can home in on a badguy's CNS, because shot placement trumps everything. Or, you switch calibers, since now that you have a lighter gun on your shoulder, your need to lighten that heavy wallet off of your butt in order to maintain balance... My recommendation is, you can just do what I and many others have, and keep practicing with cheap .223 and 5.56 (or .22 conversion), and invest in some good 75gr TAP or 77gr SMK ammunition for the fighting. Those bullets have thinner jackets, longer ogives, and thus will tumble and fragment at SBR velocities, the data is out there.