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I did a quick search for a thread on this question, but didn't see one. If it has been addressed before, forgive my failure to locate it.

Anyhow, I am considering building an SBR on the 5.56 AR platform. I currently have a 16" carbine and like it, but as I look at the cost associated with going the SBR route I am wondering if it's really worth the investment. From what I can tell, you lose velocity and accuracy, thus making it less effective as a defense weapon except for distances less than 100 yards (of course, I can't imagine needing to engage a human target in a defense situation at a range greater than that). Is there any real advantage to an SBR other than the coolness factor?

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You're not going to lose enough velocity or accuracy to notice a difference. I'm not a big fan of VSBRs but 10 and up, you'll be fine.

The $200 sucks but once you do it, it's not like your stuck with only an SBR. You can stick whatever upper you want on there and be fine.

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Guest lostpass
With folding stock, you can stash it in a back pack or computer bag and carry it every day. Illegally, but what the hey.

- OS

Yeah but why? I don't see the advantage over carrying a a kwik pistol or something. Just paint the tip orange and lug the thing openly!

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You get some pretty defenitive improvements in mobility (Inside vehicle use, room clearing that sort of thing) and several people feel that there faster to get on target in CQB Distances (Myself included). Absolutely usefull if you plan on suppressing it to keep overall length down. Even as a home defense weapon a SBR would probably fulfill that role nicely. Some one will probably be along shortly to argue that the 223/5.56 isnt a very good manstopper especiall out of a shorter barrel. I contend that its still better than any pistol caliber. If your plan on using it that way ammunition choice obviously plays a major factor. I cant think of any realstic self defense situation that would put you past the range and accuracy limits of an SBR, I can think of many self defense situations where a rifle length would have been entirely to long.

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Yeah but why? I don't see the advantage over carrying a a kwik pistol or something. Just paint the tip orange and lug the thing openly!

Ah, but accurarcy difference -- with the no true butt stock ala the Kwik approach you're just another spray and pray terrorist rather than a precision patriot commando.

- OS

Edited by OhShoot
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You're not going to lose enough velocity or accuracy to notice a difference. I'm not a big fan of VSBRs but 10 and up, you'll be fine.

The $200 sucks but once you do it, it's not like your stuck with only an SBR. You can stick whatever upper you want on there and be fine.

The useable difference between a 16" and a 10.5" gun is amazing.

Most military FMJ ammo, as in M855, needs 2700+ FPS to fragment reliably. Out of a 10.5" gun M855 runs about 2600 FPS so even at the muzzle, much less down range, it will not fragment. Tumbling can reduce the velocity needed for fragmentation but if the twist is too fast the bullet will never tumble. This is why we are hearing of the problems overseas. We have reduced the barrel length which causes a reduced velocity, on top of that they have increased the twist. The combination of a slower bullet that is spinning faster results in a bullet that is too slow to fragment and spinning too fast to tumble. Which results in a 22 lr type wound.

At 16" the muzzle velocity for the M855 is ~3000 FPS. This increases the fragment range of the bullet to a little over 100 yards. But as I said a slower twist rate can increase the fragmentation range some.

With a 10.5" gun FMJ rounds are not going to fragment in anything beyond 50 yards under the best of conditions. The best you can do is slow the twist down or increase the bullet length in order for the bullets to tumble upon impact. Problem is it seems everyone wants a 7 twist which only exacerbates the problem.

I would consider a 12.5" barrel the bare minimum for a 5.56 SBR. Any shorter and the muzzle blast and velocity become a problem. Couple this with the the fact the bullets will not fragment at anything beyond CQB distances with a shorter barrel and it is a no win. The only saving grace in all of this is if you can use a suppressor. It will elininate most of the muzzle blast.

If you are going to build an AR for SBR use pick a better caliber. The 5.56 needs barrel to work best. There are much better calibers for a 10.5" gun.

I have used 10.5" guns as part of work I used to do. They are definitely easier to manage when getting in and out of vehicles as well as clearing operations. But in the end if I had a choice I would pick a 14.5" or 16" gun anyday over a 10.5" gun for the extra velocity.

Dolomite

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The useable difference between a 16" and a 10.5" gun is amazing.

Most military FMJ ammo, as in M855, needs 2700+ FPS to fragment reliably. Out of a 10.5" gun M855 runs about 2600 FPS so even at the muzzle, much less down range, it will not fragment. Tumbling can reduce the velocity needed for fragmentation but if the twist is too fast the bullet will never tumble. This is why we are hearing of the problems overseas. We have reduced the barrel length which causes a reduced velocity, on top of that they have increased the twist. The combination of a slower bullet that is spinning faster results in a bullet that is too slow to fragment and spinning too fast to tumble. Which results in a 22 lr type wound.

At 16" the muzzle velocity for the M855 is ~3000 FPS. This increases the fragment range of the bullet to a little over 100 yards. But as I said a slower twist rate can increase the fragmentation range some.

With a 10.5" gun FMJ rounds are not going to fragment in anything beyond 50 yards under the best of conditions. The best you can do is slow the twist down or increase the bullet length in order for the bullets to tumble upon impact. Problem is it seems everyone wants a 7 twist which only exacerbates the problem.

I would consider a 12.5" barrel the bare minimum for a 5.56 SBR. Any shorter and the muzzle blast and velocity become a problem. Couple this with the the fact the bullets will not fragment at anything beyond CQB distances with a shorter barrel and it is a no win. The only saving grace in all of this is if you can use a suppressor. It will elininate most of the muzzle blast.

If you are going to build an AR for SBR use pick a better caliber. The 5.56 needs barrel to work best. There are much better calibers for a 10.5" gun.

I have used 10.5" guns as part of work I used to do. They are definitely easier to manage when getting in and out of vehicles as well as clearing operations. But in the end if I had a choice I would pick a 14.5" or 16" gun anyday over a 10.5" gun for the extra velocity.

Dolomite

We all tend to forget... not being military, we're not locked into hard bullets. We get to pick our terminal performance. :D

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The useable difference between a 16" and a 10.5" gun is amazing.

Most military FMJ ammo, as in M855, needs 2700+ FPS to fragment reliably. Out of a 10.5" gun M855 runs about 2600 FPS so even at the muzzle, much less down range, it will not fragment. Tumbling can reduce the velocity needed for fragmentation but if the twist is too fast the bullet will never tumble. This is why we are hearing of the problems overseas. We have reduced the barrel length which causes a reduced velocity, on top of that they have increased the twist. The combination of a slower bullet that is spinning faster results in a bullet that is too slow to fragment and spinning too fast to tumble. Which results in a 22 lr type wound.

At 16" the muzzle velocity for the M855 is ~3000 FPS. This increases the fragment range of the bullet to a little over 100 yards. But as I said a slower twist rate can increase the fragmentation range some.

With a 10.5" gun FMJ rounds are not going to fragment in anything beyond 50 yards under the best of conditions. The best you can do is slow the twist down or increase the bullet length in order for the bullets to tumble upon impact. Problem is it seems everyone wants a 7 twist which only exacerbates the problem.

I would consider a 12.5" barrel the bare minimum for a 5.56 SBR. Any shorter and the muzzle blast and velocity become a problem. Couple this with the the fact the bullets will not fragment at anything beyond CQB distances with a shorter barrel and it is a no win. The only saving grace in all of this is if you can use a suppressor. It will elininate most of the muzzle blast.

If you are going to build an AR for SBR use pick a better caliber. The 5.56 needs barrel to work best. There are much better calibers for a 10.5" gun.

I have used 10.5" guns as part of work I used to do. They are definitely easier to manage when getting in and out of vehicles as well as clearing operations. But in the end if I had a choice I would pick a 14.5" or 16" gun anyday over a 10.5" gun for the extra velocity.

Dolomite

Baaaaahhhhh... who cares about ballistics? I just want it for the tacticool pics I'm gonna post of Facebook, then tell all the chicks that I'm a super secret spy guy!

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Guest RebelWithACause

Willard hit it....SBRs exist for vehicle crews and for some CQB applications. This is a role that has historically been filled by a SMG, but a SBR M4 has been filling the role very nicely.

With the massive array of choices a civilian has in choosing PDWs, their calibers, and their ammo, I personally don't see a need for a SBR. (Just my own personal prefs, though.)

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Is there any real advantage to an SBR other than the coolness factor?

Because they are illegal for the general public to own. :D

If you want a SBR just buy a PLR-16. SBR out of the box, no tax stamps or ATF to deal with, and they are $500.

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We all tend to forget... not being military, we're not locked into hard bullets. We get to pick our terminal performance. :D

Yes but the majority of shooters do not buy anything other than FMJ. I would be willing ot bet the number is well above 95% of AR shooters buy FMJ. People don't buy high end hunting rounds when they stockpile ammunition, they buy the cheapest ammunition they can get. This is generally surplus military rounds or commercially avaialable FMJ ammunition. And because of this the majority of what is going to be available if ammo is no longer available commercially is the FMJ rounds people have stockpiled.

I found this it might help make the SBR barrel length decision:

MK 262 VELOCITY DATA

__________________________________

7.5" 2053 FPS ... 10.5" 2363 FPS

DIFFERENCE 310 FPS

DIFFERENCE/INCH 103 FPS

10.5" 2363 FPS ... 14.5" 2576 FPS

DIFFERENCE 213 FPS

DIFFERENCE/INCH 53 FPS

14.5" 2576 FPS ... 16" 2669 FPS

DIFFERENCE 93 FPS

DIFFERENCE/INCH 62 FPS

16" 2669 FPS ... 18" 2769 FPS

DIFFERENCE 100 FPS

DIFFERENCE/INCH 50 FPS

18" 2769 FPS ... 20" 2818 FPS

DIFFERENCE 49 FPS

DIFFERENCE/INCH 25 FPS

M855 VELOCITY DATA

__________________________

7.5" 2244 FPS ... 10.5" 2639 FPS

DIFFERENCE 395 FPS

DIFFERENCE/INCH 132 FPS

10.5" 2639 FPS ... 14.5" 2861 FPS

DIFFERENCE 222 FPS

DIFFERENCE/INCH 56 FPS

14.5" 2861 FPS ... 16" 2938 FPS

DIFFERENCE 77 FPS

DIFFERENCE/INCH 51 FPS

16" 2938 FPS ... 18" 3046 FPS

DIFFERENCE 108 FPS

DIFFERENCE/INCH 54 FPS

18" 3046 FPS ... 20" 3061 FPS

DIFFERENCE 15 FPS

DIFFERENCE/INCH 7.5 FPS

XM193 VELOCITY DATA

_________________________________

7.5" 2364 FPS ... 10.5" 2755 FPS

DIFFERENCE 391 FPS

DIFFERENCE/INCH 130 FPS PER INCH

10.5" 2755 FPS ... 14.5" 2984 FPS

DIFFERENCE 229 FPS

DIFFERENCE/INCH 57 FPS PER INCH

14.5" 2984 FPS ... 16" 3075 FPS

DIFFERENCE 91 FPS

DIFFERENCE/INCH 61 FPS

16" 3075 FPS ... 18" 3245 FPS

DIFFERENCE 170 FPS

DIFFERENCE/INCH 85 FPS

18" 3245 ... 20" 3254 FPS

DIFFERENCE 9 FPS

DIFFERENCE/INCH 4.5 FPS

And remember the standard for fragmentation is 2700 FPS and these numbers are at the muzzle. Tumbling can increase the fragmentation but the twist needs to be correct. The chance of having a barrel that will tumble a 55 grain bullet is minimal at best. A 12 twist barrel is what is needed for a 55 grain bullet to tumble reliably. Even 9 twist is a bit overstabilized for a 62 grain M855. 9 twist is even fast enough to stabilize 77 grain bullets out to moderate distances.

Using this calculator tells everything you need to know about twist:

JBM - Calculations - Stability

And 1.4 is considered perfect as far as stability goes. The smaller the number the less stabile the bullet becomes. I would prefer a lower number so the bullets tumble over a higher number.

Dolomite

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So far, this discussion has pretty much reinforced what I found while researching the topic yesterday before posting my question here. I originally considered the idea of the SBR in a 5.56 AR for the improved handling properties. Once I looked at the negatives, I started to wonder what the point is. Without sounding too tinfoil hat-like, I wanted to stick with the 5.56 caliber just in case there was a major SHTF scenario because I expect that .223/5.56 ammo would be easier to come by instead of 6.8 SPC or other calibers. My plan is to SBR one receiver and just swap out uppers between the standard 16" M4 upper I currently have on it, the SBR upper, and a rifle length upper. I did see multiple recommendations to purchase a Noveske upper (or at least a Noveske barrel) if I do plan to go less than 12.5" since they perform better than other barrels regarding muzzle velocity (I assume it's the polygonal rifling?).

Being realistic, the SHTF scenario is very unlikely and if I had to grab one upper for my AR, I'd probably go with the 16" since it's a good balance between portability and the advantages of barrel length. So, how does the 6.8 SPC round perform out of a shorter barrel? Anyone have experience with it in an SBR?

Crap. I guess I might as well just SBR the lower I have and I will have plenty of time to decide what I want to slap on the top of it. Knowing my luck, I'll wait and the feds will either jack up the price or do away with it completely. Now I get to decide whether to bother with the NFA trust route or not...

Edited by East_TN_Patriot
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People don't buy high end hunting rounds when they stockpile ammunition,

....I do. FMJ kinda sucks for almost everything unless you need to punch a hole.

I stock in quantity

*50g soft point, mostly Midway's Dogtown bullet.

*62g ss109, my only FMJ

*70g Barnes TSX

*75g Prvi HPBT match

*80g Amax

Admittedly, the Barnes and Amax not in any real quantity, but I'm workin' on it!

For my "S is Hitting TF as we speak, grab it NOW!" AR load, the barnes is tough to beat. A few magazines full ain't cheap, but a 70g TSX from a 1/7 barrel will really do the trick. I won't remember the money I've spent on the day I use them.

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Pistol calibers for one.

I would also say maybe the .300 BLK with a suppressor? Or anything subsonic for that matter as a loss in velocity will not be as detrimental.

+1

Even 7.62x39 would be a better choice than 5.56 in a 10.5" gun. And 7.62x39 is about as plentiful as 5.56. There are reliable magazines available now. 458 SOCOM would be an awesome SBR caliber. 6.8 SPC is another candidate for SBR. Any caliber that doesn't rely on barrel length for velocity is a good choice.

In a 7.5" gun I would rather have a 9mm than 5.56. The muzzle blast isn't worth it with a 5.56 especially when you consider how much the 5.56 loses out of such a short barrel.

Dolomite

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Guest pdogkilr

Last year some friends and I made the trip to my son's place in Florida for a "Spring Shoot". The first day and a half was doing chronograph work with multiple barrel lengths and two calibers - 5.56 and 6.8. We wanted to know actual velocities from our firearms. We had various factory loadings, and several handloads. Spreadsheet below details the data gathered, and the average velocity loss per inch of barrel. Not trying to hijack the thread and I hope you find the data useful.

BTW, I have a 10.5" LWRC SBR in 6.8 SPC with a matching upper in 5.56. Photo at the bottom.

Page-1Small.jpg

Page-2Small.jpg

Page-3Small.jpg

IMG_1637SBRbothuppers300PPISized1024.jpg

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OK, I have considered a 9mm AR as well. How do the mags work? I assume you need a filler block in the mag well. Is that a removable piece? Are the mags reliable and easy to purchase for a reasonable price?

Maybe magic will chime in. He seems to be doing well with a Spikes Block. I am looking at building a 9mm SBR right now. (7.5" barrel, flat top) Main reasons; shoot at indoor ranges, can shoot steel plates we have set up, and can shoot it cheaper. Eventually get a can for it. :yum: Been wanting an SBR for years.

I started a thread for people to sound off on what they use for 9mm mag blocks. Hadn't got much of a response though.

LINK

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Maybe magic will chime in. He seems to be doing well with a Spikes Block. I am looking at building a 9mm SBR right now. (7.5" barrel, flat top) Main reasons; shoot at indoor ranges, can shoot steel plates we have set up, and can shoot it cheaper. Eventually get a can for it. :yum: Been wanting an SBR for years.

I started a thread for people to sound off on what they use for 9mm mag blocks. Hadn't got much of a response though.

LINK

So is the block an easily removable part or is it basically a thing where once a 9mm AR, always a 9mm AR? Can you register an SBR as multi-caliber?

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