SBR at a KD shoot?

[modeler]

I just signed up for my first KD shoot, scheduled for the weekend after Valentines Day. The problem is that the only centerfire semi-auto rifle I have is a short-barreled (11.5") AR. Will that work out to 400 yards or should I try to get a rifle with a longer barrel?

[Mudcat]

Shouldn't be a problem for the rifle. Goes without saying make sure you follow all NFA rules.

[Caliper]

Best to go to your state board and get in touch with your Shoot Boss so they can verify that the host range doesn't have any rule prohibiting NFA arms. 

Aside from any legal issues, some folks actually claim that a shorter barrel makes a rifle more accurate because it is stiffer. 

If you are shooting irons, be sure you know how many MOA per click for sight adjustments with your sight radius.  I'd probably choose an optic due to the short sight radius though.  If you know the approx muzzle velocity with your ammo, plug some numbers into a ballistics calculator online and get a feel for your wind drift in a full value 10mph wind because it'll likely be more than the typical 1moa/100yd/10mph rule of thumb. 

[modeler]

Best to go to your state board and get in touch with your Shoot Boss so they can verify that the host range doesn't have any rule prohibiting NFA arms. 

Aside from any legal issues, some folks actually claim that a shorter barrel makes a rifle more accurate because it is stiffer. 

If you are shooting irons, be sure you know how many MOA per click for sight adjustments with your sight radius.  I'd probably choose an optic due to the short sight radius though.  If you know the approx muzzle velocity with your ammo, plug some numbers into a ballistics calculator online and get a feel for your wind drift in a full value 10mph wind because it'll likely be more than the typical 1moa/100yd/10mph rule of thumb.

I'm comfortable with the legal issues; there is no issue in this case.

Even though the barrel is short, the upper has a standard carbine length gas system with iron sights on the gas block and the rear of the upper receiver. It's no different than any other AR with a carbine length gas system. What I'm wondering is if the shorter barrel will effect bullet velocity and stability enough to significantly effect accuracy at longer distances.

[George Hacker]

Even though the barrel is short, the upper has a standard carbine length gas system with iron sights on the gas block and the rear of the upper receiver. It's no different than any other AR with a carbine length gas system. What I'm wondering is if the shorter barrel will effect bullet velocity and stability enough to significantly effect accuracy at longer distances.

One of the benefits of a KD event is that you will get a lot of DOPE on your rifle.  Don't take our word on what your rifle is capable of doing... take it to the range and see what it can do.  That is probably worth the price of admission by itself.

ShadowMan

[yellowhousejake]

We have seen that done at Atterbury. Be advised that bullets over 55 gr bounced off the coroplast backer beyond 200 yards. The short barrel simply cannot burn enough powder to reach the velocity needed at distance with 62 and 75 gr loads. Once we switched ammo for the student to 55gr, he was able to get hits.

M855 didn't work, M193 did.

YHJ

[MostlyHarmless]

Be advised that bullets over 55 gr bounced off the coroplast backer beyond 200 yards.

M855 didn't work, M193 did.

Seriously??!!

Coroplast body armor FTW!



It does give some perspective on the M4's many detractors.

I've heard that SBRs have trouble stabilizing heavier rounds, but haven't tried it myself. Now I'm curious....

[Nickle]

The M4 is OK, but, in my opinion, on the low end of barrel length practical.

I've seen them get consistent hits at 800 yards with M855 ammo.

In your case, I'm more concerned by the gas system than the barrel length.

Now, some of the things you hear bad about the M4 and M16 are legit, but many aren't.

Sometimes a good shooter sees a real problem. Sometimes, a lousy shooter blames rifle performance, when the real problem is lousy bullet placement. Seeing that those are guys putting bad people down, we in the US don't tend to run into those problems.

I'd try both 55 grain and 62 grain loads and see what you get.

[yellowhousejake]

I've heard that SBRs have trouble stabilizing heavier rounds, but haven't tried it myself. Now I'm curious....

Stabilizing was not the problem, the dimples were all well placed, they just didn't have enough oomph to get through both sides of heavy coroplast. Now this is not your neighborhood yard sign corplast, this is heavy stuff, but it was still coroplast. I was in the pits on that frame and SPQR was with the student. When he switched ammo I thought he had switched to SPQR's AR, that much difference in the impact.

Every rifle is different, but I would test before I bought 500 rds of 75gr TAP.

YHJ

[Nickle]

This might hurt a few feelings, but it's something that I've known for quite some time. Very relevant, too.

I agree with YHJ's assessment on the ammo, especially the 75 grain TAP ammo.

Now, that isn't bad ammo, but ask yourself if it really is the right fit for your rifle.

And, in this case, I'll come back with a pretty adamant no, that it isn't.

Like I said, it isn't bad stuff. In fact, I understand it's pretty good stuff. But, it has a use, and rifles to be used in. Probably won't be right in a rack grade AR with a 20 inch 1 in 9 twist barrel. Might be real good in a 20 inch 1 in 8 or 1 in 7 barrel. Cut length off the barrel, and velocity drops. When velocity drops, then stability drops.

Like I said before, there's a reason why the military went with 14.5 inch for the M4. So you know, back in the late 60's, they built the XM177 rifle, also know as the CAR-15. 11.5 inch barrel. Now, my understanding of why they went with 14.5 inch was velocity and stability issues.

A potential workable answer for this situation?

Build an upper with a 16 inch barrel, and use that. If you stay up to 69 grains, it will still stabilize well. And, there are 68 and 69 grain match bullets available. Ammo with them too.

Here's an example. It's remanufactured, but good stuff. http://www.midwayusa.com/product/745215/black-hills-remanufactured-ammunition-223-remington-69-grain-sierra-matchking-hollow-point-boat-tail-box-of-50

[Aromatic]

I have witnessed, on several occasions, a shooter with an 11.5" upper make hits on a 4/5 D-ring target at 400 yards with 55 gr bullets.  It can be done.

[AFTERMATH]

Best to go to your state board and get in touch with your Shoot Boss so they can verify that the host range doesn't have any rule prohibiting NFA arms. 

Aside from any legal issues, some folks actually claim that a shorter barrel makes a rifle more accurate because it is stiffer. 

If you are shooting irons, be sure you know how many MOA per click for sight adjustments with your sight radius.  I'd probably choose an optic due to the short sight radius though.  If you know the approx muzzle velocity with your ammo, plug some numbers into a ballistics calculator online and get a feel for your wind drift in a full value 10mph wind because it'll likely be more than the typical 1moa/100yd/10mph rule of thumb.

I'm comfortable with the legal issues; there is no issue in this case.

Even though the barrel is short, the upper has a standard carbine length gas system with iron sights on the gas block and the rear of the upper receiver. It's no different than any other AR with a carbine length gas system. What I'm wondering is if the shorter barrel will effect bullet velocity and stability enough to significantly effect accuracy at longer distances.

Only one way to find out for sure!   


I would echo the suggestion to ensure that it's 'kosher' in regards to the actual location - especially if SBR's aren't prolific in your area.  Also, might be a good idea to see if you can't sweet talk someone into letting you borrow a standard upper, just in case. 

[modeler]

Best to go to your state board and get in touch with your Shoot Boss so they can verify that the host range doesn't have any rule prohibiting NFA arms. 

Aside from any legal issues, some folks actually claim that a shorter barrel makes a rifle more accurate because it is stiffer. 

If you are shooting irons, be sure you know how many MOA per click for sight adjustments with your sight radius.  I'd probably choose an optic due to the short sight radius though.  If you know the approx muzzle velocity with your ammo, plug some numbers into a ballistics calculator online and get a feel for your wind drift in a full value 10mph wind because it'll likely be more than the typical 1moa/100yd/10mph rule of thumb.

I'm comfortable with the legal issues; there is no issue in this case.

Even though the barrel is short, the upper has a standard carbine length gas system with iron sights on the gas block and the rear of the upper receiver. It's no different than any other AR with a carbine length gas system. What I'm wondering is if the shorter barrel will effect bullet velocity and stability enough to significantly effect accuracy at longer distances.

Only one way to find out for sure!   


I would echo the suggestion to ensure that it's 'kosher' in regards to the actual location - especially if SBR's aren't prolific in your area.  Also, might be a good idea to see if you can't sweet talk someone into letting you borrow a standard upper, just in case.

Thanks. I'll say it again: There are no legal problems with the SBR. I've already checked, it's ok to use at the range in question.

I work part time at a local gun shop, I could pick up a full size AR for a reasonable price but I'd prefer to use what I already have and use the money towards some sort of an optic (I had problems with my eyes and iron sights last time).

[Caliper]

YHJ, what brand of ammo was the shooter running?  Not having a SBR to chrono I'll have to rely on the great interwebs, but from what I'm finding online ( http://www.ar15.com/content/page.html?id=213 ), the low end for a 11.5" barrel should have a MV of 2500fps.  Even if I knock is down to 2250 with a 62 grain bullet, JBM ballistics is putting velocity at 200 yards at 1670fps and the round should stay supersonic until just past 500yd.  That means at 200yd the round should have similar power to a 22mag at the muzzle and at 500yd is similar to a 22LR at the muzzle. 

Not doubting the incident, but it really seems like something else was up.  The round should have plenty of energy to penetrate a backer at 200yd.  Were any of the bullets recovered after bouncing off the coroplast? 

[Audrey]

I would say that a short barrel could be less accurate, but I guess it depends on the specific barrel. You will need to be able to get good sling positioning, so make sure to test that out at home. If it is accurate with repeatable sling positions then I don't see what other issues there would be?

[Kimber Custom]

The backers are fabric so we shouldn't have an issue with penetration and the club, the state and I are all good with SBR's.

For a nice quality optic for the price check out the SWFA SS. I have the 6x on my AR10 and the 10X on my Howa 1500 http://swfa.com/SWFA-SS-6x42-Tactical-Riflescope-P47326.aspx

Sent you PM Modeler 

[yellowhousejake]

YHJ, what brand of ammo was the shooter running? 

Dunno... I was in the pits and didn't ask later. You should hit up SPQR and ask if he remembers. I do know it was not reloads, factory ammo was used. While three years ago I would have looked up charts and compared velocities to standard info to try and figure out what happened, that was before I had much line experience. Rifles can have such a wide variety of aftermarket parts, mixed and matched pieces with stacked tolerances, nothing I see on the line surprises me anymore.

Rifles cannot read.

YHJ

[Nickle]

I can tell you a few things that I know, and are relevant to this subject.

Stabilization of the bullet hinges on 2 things. Rifling twist rate (in the barrel) and velocity. They work hand in hand to create the revolutions per minute of the barrel. It can get complicated if you dig into the facts, but knowing the basic rules isn't hard, and will get you close enough.

First off, I'm mostly going to be talking about the 20" barrel length, because we're talking "apples to apples" and there's a wealth of information out there. Plus, the only detriments of the short barrel is loss of velocity, in this regard.

The key item is related by the weight of the bullet, but the length of the bullet.

A1 series AR's are generally 1-12" twist. This stabilizes 55 grain bullets out to 400 yards at least, given factory velocities. Issue M193 ammo uses a 55 grain boat tail, and these stabilize. 62 grain bullets, at factory velocities, are much more "iffy", at best, The general rule of thumb is that they don't. Why I say it this way, is simple. Some do stabilize, out to a certain distance, then they don't any more. Just because it is good at 25 meters, or even 100 yards, doesn't mean they're still good at 400 yards.

A2 series AR's can really vary. Some are 1-7" twist (Colt and issue), some are 1-8" twist, many are 1-9" twist. And, some are 1-12" twist. It all depends on who made it, and what it was intended for.

Colt is almost always 1-7" twist, as are issue M16A2's, M16A4's, M4's and M4A1's. The reasoning for 1-7" is to stabilize 62 grain tracers, which generally won't stabilize in anything slower than that.

1-8" twist is really 1-7.75" usually. These will be match barrels, for the most part. They stabilize up to something like 80 grain bullets, apparently.

The majority of A2 type barrels will be 1-9" twist. These are probably the most versatile barrel available, though there are exceptions to this rule. They work well with 55 and 62 grain bullets and the limit on these is about 70 grains.

Now, factor in the effect of barrel length, which leads to lower velocity. The drop to a 16" barrel is apparently not that significant, as the rules apparently take that one into play (from what I see). I do know, from my background that 14.5" barrels do see the effects of velocity loss, but a 14.5" barrel with 1-7 twist does reasonably stabilize 62 grain M855 bullets out to 800 meters. That is to say, I've seen that done, well enough to hit shiloettes at that distance (not me as the shooter, but I was running the computerized tower).

Now, the original short barreled AR was the XM177, and it was 11". When the M4 came out, it was 14.5" and the story was that there were issues with the 11" barrel and stabilization, apparently with the 62 grain tracer and a 1-7" twist.

Now, that's what I know about the subject, and my sources are usually pretty good. Here's what one of them (Shilen barrels) says:

.224 CF
- 7" for bullets heavier than 70 gr.
- 8" for bullets heavier than 70 gr.
- 9" for bullets up to 70 gr.
- 10" * for bullets up to 65 gr.
- 12" for bullets up to 63 gr.
- 14" for bullets up to 55 gr.

A few qualifiers to that info. It doesn't assume use of the 223 cartridge, but generally speaking, uses the faster 224 calibers, say from 222 Rem and up. It is approximate, and doesn't assume use of boat tailed bullets. Now, I know that the 22-250 and 220 Swift with 1-12" barrels will stabilize the 63 grain Sierra flat base soft point. I've shot enough of them from the 22-250 many years ago (I had one, as a teenager). It doesn't assume use of less than 16" barrels, either. They generally make rifle barrels, and most of the ones used are 16" or more.

So, I'm not saying to use or not use that SBR. Nope, not my way. What I am saying is to make sure your ammo choice will work, that your bullets will stabilize.

If it were me, and I wanted to use that SBR, my choices would be 55 or 62 grain. Rack grade is good enough for Appleseed. Want premium? I'd go with handloads, made with 52 grain boat tails, or 53 grain flat base, and they would be match bullets. Mass produced (like Sierra, Hornady, Speer, Remington or Winchester) are just fine.

Either way, check the ammo out for stabilization and accuracy before the Appleseed.

[jmdavis]

The accuracy issues, if any, with irons would be more related to the short sight radius than to barrel length per se.  That will be taken care of with an optic to put everything on one plane rather than 3 (rear sight, front sight, target). 55 (M193) or 62 (M855), should work just fine out to 400. Try to have a good 100 yard and 25 yard zero before you get there if possible. Having a good zero ALWAYS makes a KD easier.

62gr ammo out of an 11 inch barrel  makes one heck of a clang on steel at 300 yards. It will certainly penetrate paper attached to coroplast or other target backers.

[Nickle]

The accuracy issues, if any, with irons would be more related to the short sight radius than to barrel length per se.

Correct, outside of stabilization issues. And, they aren't that common. 7 through 9 twist, I see zero reason why 62 grain won't work, even with an 11" barrel.

Now, a funny tidbit on barrel length and accuracy.

Originally, the M4 was only going to be fielded to people needing real short and/or light rifles, like the airborne, and combat vehicle crewmen. Then the Army looked at qualification scores. They expected them to drop slightly, but they didn't. They went up slightly.

Now all light infantry units (division size basis) is slated to carry M4's. Other combat arms may be on the list to get them as well.

[modeler]

Thanks for the info everyone! I went about replacing the handguard today, underneath the barrel is imprinted as being 1:9 twist.

Kimber Custom was nice enough to invite me out to the range in question in a few weeks to try it out. Hopefully I'll be on paper and all will be right with the world. I'm also working on an optic, we have a 3-10x40 in stock right now that might work well.

[grunt soldier]

I shot my noveske Infidel 13.5 inch barrel at atterbury out to 500 yards and had no problems at all.  I shot m855 factory ammo.  remember the fundamentals as any play will be more exaggerated out of the shorter barrel.  It's a lot of fun to shoot the shorties and see what they really can do. 

here is a pretty cool video.  guy has done a lot of work with his and a lot of testing but this is a 10.5 inch upper at 773 yards on steel. 

http://www.youtube.com/watch?v=AcSSwyfZcy0&feature=youtu.be

[Nickle]

I went about replacing the handguard today, underneath the barrel is imprinted as being 1:9 twist.

Then, my advice would be to use 62 grain ammo. 55 grain is also OK. If your rifle shoots it accurately, then the match bullets I would use are 52 or 53 grain. I use them in my 1-12 twist center fire rifles, 222 Rem, 22 PPC, 22 BR and 219 Don Wasp.

[modeler]

I went to the range today with a friend and his father. I have once again come to the conclusion that iron sights are not to be for me...

My friend's father had an FAL with a Nikon P223 scope, it seemed like a good unit and has held up to .308 punishment so I went ahead and ordered one today. It has a reticle with markings for .223 every 100 yards; I'll be curious to see how the marks line up with reality.

http://www.nikonsportoptics.com/en/Nikon-Products/Riflescopes/8497/P-223-3-9x40-BDC-600.html

[Mudcat]

I have this optic on my MVP it has served me well.  My son has the fixed 3x P223 on his 14.5" AR. He shot a perfect score on KD with that set up this last spring, backed it up with a passing score with his back up irons this fall.
The main thing to keep in mind is go in with an open mind and have fun. It is the shooter not the rifle 99.9% of the time. Your 11" AR will get the job done no problem. Is it the best choice for a KD event? Probably not, but it is your rifle of choice so take it out and learn your rifle. Listen to the instruction apply the fundamentals and let the chips fall. You will have a great time, learn a lot about your rifle and learn that shooting KD really is not much different than shooting 25. Just learn your come ups write your data down and adjust for the wind.
Have fun and be sure to let us know how you do.

[Kimber Custom]

Listen to the instruction

Hey Hey Hey! I don't need that kind of pressure! 

[SPQR]

The AR in question above was a 10" barrel on a standard A3 upper with an optic.  The shooter was using 62gr M855 fresh out of the can. In fact, the can had only been opened once to throw a desiccant pack in.  Not only would it not reliably penetrate the backer beyond 200, it cycled oddly.  After trying 75gr with same results he switched to 55gr pmc and it functioned flawlessly.  I knew the guy, he had been to a couple of my shoots before, which is why he got a fresh can of green tips out of my stash.  I can confirm that follow up has proven the rifle to not provide results with anything over 55 grainers.

Maybe jmdavis' experience will hold true.  I can speak to yhj assertion that a 10 inch barrel and 62gr and heavier ammo did not penetrate the backer.  The shooter produced acceptable groups.

[jmdavis]

http://sadefensejournal.com/wp/?p=1093

According to the article M855 has a Muzzle Velocity of 2500 out of a 10 inch barrel. At that velocity it will still be supersonic beyond 600 yards.  This is based on an assumed BC of .304 and the 2500 Muzzle velocity.

At 300 yards this round will be traveling 1727 FPS and have over 400 ft.lbs. of energy. I would not want to stand behind a sheet of corroplast and serve as a target for such a carbine. 

See the video below for some testing at 300 yards of .22 lr. I can state with certainty that 22LR will penetrate and knockdown popups at 300 yards even with Eley subsonic ammo.

http://www.youtube.com/watch?v=-DzLQGv-w5M

[SPQR]

Okay, fine, a webpage said some things. They are probably reporting what they have seen, as I am.  what would you have me say? That what I saw didnt happen? 

You're at least smart enough to know that what is written by a ballistics calculator does not always match the real world performance of the arm and that not all arms match their advertised performance.  ALL that I am asserting is that i witnessed the above activity worth me own eyes.  It does not matter in this instance what the Internet says should have happened.  Something else IS what happened.

I hope the OP takes their SBR and has a whale of a time.  If the tag wasn't obnoxious I would have an SBR of my own.  Everyone I know that had one looks cooler worth it, kinda like smokers with a cigarette.

[jmdavis]

 

Okay, fine, a webpage said some things. They are probably reporting what they have seen, as I am.  what would you have me say? That what I saw didnt happen? 

Actually, they are engaging in  demonstrable and repeatable experiments and using the scientific method. They are not just making an observation ( or even observations) and drawing a conclusion.

My hypothesis is that the corplast was "healing" with the 62gr .223 bullets from the sbr at greater than 200. I further hypothesize that someone working such a target at Atterbury would hear the supersonic crack and that targets placed on such a target would show holes when examined whether on or off the target. If they were indeed boucing off of the coroplast, that would indicate a velocity insufficient to penetrate the backer. It would also mean that they would be bouncing "somewhere."