Barrel length and ballistics with the 5.56.

[JMoses]

This article is a couple years old, but it's an interesting read. I think we all know that with barrel length reduction, there is velocity loss, thus energy loss, but SBR's are very popular, especially with sound suppressors, which is also discussed in the article. There's no doubt that the author went through a lot of trouble doing an in depth study, but if this is the case, why are more and more military units using SBR's, such as the MK18's so much more? It would have been interesting if he study would have included the 6.8 and 300 Blackout. It would also have been nice if 69 and 77 grain ammo would have been used in the testing.

Barrel Length Studies in 5.56mm NATO Weapons

 

[daddyusmaximus]

I love my little SBR, but I know it's just a close range home defense tool.

 

[BigMoose]

Wow.... now I wonder why they bother to sell anything longer then 20 inches. It actually DROPs with the longer barrel using M855.

Call me uncool, but if I had an AR, it would be a 20 inch.

 

[Dead Duck]

The OPs article doesn't pull up completely.
Is it just a block on my computer, or are others having the same problem?










I wanta see it too!!

 

[JMoses]

The article just opened for me.

 

[Dead Duck]

Arrrg-
OK - The header and the column at the left were opening but the rest of the page was blank.....So I thought.

I had to scroll way down to start the article.


Weird - Thank You. Now I start reading.

 

[Vamptepes]

Wow.... now I wonder why they bother to sell anything longer then 20 inches. It actually DROPs with the longer barrel using M855.

Call me uncool, but if I had an AR, it would be a 20 inch.

I guess you can call me uncool. The ar I built has a stainless 20" bull barrel. Threaded and addad a flash suppressor so it's like 21.5 now. Shes heavy but worth it.

 

[Leo]

Good article, good test.

I did not have sophisticated equipment but I had a 26" AR barrel, a Chronograph and a saw. I was not using 855 ball, and I was using stout Varget loads. Taking 10 shots and sawing one inch of barrel off at a time showed almost nothing was gained past 22 inches. Very little was gained from 20 inches to 22 inches. below 20 inches velocities started dropping pretty fast. With a faster burning powder than Varget, the sub 20 inch velocity drop would not be as much.

With the (at that time) new found knowlege, I took a current 24 inch barrel and had it counter drilled by 3 inches, so my sight radius would be the same but the bullet only had 21 inches of bore. The rifle shot great, and was a little lighter up front, little loss of velocity and the brass did not get beat as much with Max power loads

I think 24 inch barrels are sold because that is what people will buy. It is pretty had to find a "varmint" barrel for an AR that is not 24 inches in length. Over 24 inches also makes timing problems on the gas system, part of why the case rims were so beat up. Some have an extended gas tube with the 26 inch barrels, I tried one of those also. That barrel (3 groove Pac Nor) really shot well but still had no velocity real velocity gains. If you could increase case size so a good charge of slower powder like IMR 4350 could be used, you could maybe use a 26 inch barrel and gain something.

(of course with more case capacity, you would have a 22-250)

 

[daddyusmaximus]

I think 24 inch barrels are sold because that is what people will buy.

^^^ this right here. Same goes for the short barrels. People will buy them.

I had the chance to use a 9.5" barreled one in Iraq. It worked very well, but I never shot at anything past 100yds. It was great when getting in and out of the truck or firing back from within the truck. Real great, and I spent more time doing that than I did firing it. Very easy to live with day to day.

Then I got home and got crazy with a 7.5" build. The muzzle blast is fierce, and it will do me no good at distance, but as a house gun, it works fine. Walking around down the narrow halls of my 116 year old home it is very handy. Ballisticlly, it's down almost into pistol energy levels, but I'm much better with it than I am with a handgun. As a toy to shoot at the range, it's fun as hell. I'm wanting to redo this with an 11.5 in barrel in the future. This will give me significantly more muzzle energy and still remain short and handy.

As far as a general purpose gun, I like my 16" carbine. It will do almost anything a 20" can do because I can't see that far out there anyway. I feel the short barrels have their place if you need something to get around with in tight places, and can afford more than one gun. Overall, it comes down to people buy what they want. I hate rap music and low profile tires on lifted 4x4 trucks but people (idiots in my view) do it all the time. Doesn't bother me if people think I'm an idiot with my SBR. It will do it's intended job at the range I need to use it.

Yes I love my SBR, but if I could only have one gun, it would be my 16".

 

[daddyusmaximus]

Thanks for making me think of it guys... I got to thinking about the loss of MV in my 7.5" SBR, so I put it's original Arms Tech Compak-16 upper back on it. The 7.5" upper is back on the pistol lower, and will become a truck gun. I feel better with the Arms Tech upper as a home defense tool. The Compak-16 is only a 9.5" and wouldn't seem to offer much help, but their combination of the progressive gain twist with polygon rifling in the same barrel makes for 2703 fps with ss109 ball. Better than some 14.5" M4s. Also This upper has significant sentimental value to me as I have used it in combat. I know it is accurate, and will put down bad guys. Now retired, and not subject to military ball ammo, (ammo selection, another thing to think about with barrel length) I keep my SBR loaded with 53 grain Cor-Bon DPX. Now I have a SBR with it's proper upper, one I have seen do the job, and better ammo than I ever got to use before.

 

[rvb]

I got to thinking about the loss of MV in my 7.5" SBR, so I put it's original Arms Tech Compak-16 upper back on it.
...
The Compak-16 is only a 9.5" and wouldn't seem to offer much help, but their combination of the progressive gain twist with polygon rifling in the same barrel makes for 2703 fps with ss109 ball.

what velocity did you see w/ the 7.5?

-rvb

 

[daddyusmaximus]

Don't know the numbers, I've no chronograph.

If anybody does have a chrono, I'd love to do a little test.

I was reading ballistics tables on barrel length after being reminded of shortys on here. Then remembered the article that made me want to buy the Arms Tech. Back in 2004 we were getting ready for a deployment to Iraq and I saw an article in "Special Weapons for Military and Police". We had inherited some real nasty M4s from another unit that had sit in a connex for quite a while and were rusted to hell. After buying the Compak-16 upper, (yes, I had my commander's permission) I had kept the magazine with the article, so I dug it out. I had been running my SBR with my 7.5" pistol upper because it fits in this cool little Storm case. Problem is, the pistol upper requires a stronger spring and heavier buffer to run right. I put the Arms Tech upper back on and it wouldn't lock back on an empty mag. I talked to Joe Rustic, the designer. He's a Dr out in Arizona, but also has an arms business. He said put the regular buffer and spring back in, I did, perfect. Joe has been sick lately, and the company had to fight off a law suit from the Garand family. Seems the gas trap system used on this Compak-16 upper is very similar to the one on the M1 Garand. Kinda hoping he gets back on his feet and gets the company to secure a government contract. I like the idea of the gas trap better than going with a piston for those wanting a cleaner system than a DI gun. I went through a lot of rounds in Iraq, and this upper never failed me. Good feeling to have it back on my SBR for home defense. Even without seeing the chrono numbers myself, I can tell you that this upper can do it's job on the intended target.

 

[rvb]

so I put it's original Arms Tech Compak-16 upper back on it ... only a 9.5".... makes for 2703 fps with ss109 ball.

Don't know the numbers, I've no chronograph.

then how did you get the very exact numbers above? marketting material?

-rvb

 

[HoughMade]

I prefer 20" the way God and Eugene Stoner intended...but I'm an old man without an ounce of tacticool in me.

 

[daddyusmaximus]

The Arms Tech Upper in Iraq with a GG&G rail system. Early 2005.



Today it has a POF rail. I may switch this. Kinda bulky.

 

[daddyusmaximus]

then how did you get the very exact numbers above? marketting material?

-rvb

Numbers are out of the 2004 magazine article from when this upper was first introduced.

 

[daddyusmaximus]

I prefer 20" the way God and Eugene Stoner intended...but I'm an old man without an ounce of tacticool in me.

I have a longer AR too, and I love it, but these little things are real nice walking down hallways, and jumping in and out of vehicles.

 

[HoughMade]

I I have a longer AR too, and I love it, but these little things are real nice walking down hallways, and jumping in and out of vehicles.

...And in certain situations, that's an important issue.

For most others, it's almost like the measure AR maniless inversely to "manhood" manliness.

 

[Hop]

I can't comment too much on down range velocity or energy but I can say my DD MK18 10.3" barreled SBR is accurate. It does not like cheap ammo. It doesn't like light ammo. It sure does like MK 262 Mod 1 77 grain though. The cheap light stuff shoots as bad as 6 MOA at 100 yards depending on how much Mt Dew I've had. But, loaded up with even Brazilian clone CBC MK 262 Mod 1 77 gr ammo it makes really really nice groups even at 500 yards. My best iron sight 3 shot group at 500 yards was 1 MOA. <- that was Appleseed style, sling only, no mono pod using the mag in prone position. That group took some luck + a lot of concentration though. I'm pretty confident that I could shoot a rifleman score at full distance with this gun even with iron sights.

Does this little gun have enough oomph at 500 for a kill shot? Maybe... my ballistics app says 1509 fps & 850 lb/ft of energy.