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Ordnance
28 November 2014, 10:11
This is a VERY good read that might help others to provide insight on barrel length effects...

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

schambers
28 November 2014, 16:15
Interesting article. Definately going to poke around that website some more.

GOST
28 November 2014, 17:40
Very good read, thanks Ordnance.

GOST
28 November 2014, 17:53
The velocity graph makes an 11.5" look like a good choice for a SBR.

SwissyJim
28 November 2014, 18:28
wish I'd seen this before I ordered my 10" barrel! LOL Guess we'll see how she does. Actually not TOO worried...

Former11B
28 November 2014, 20:06
wish I'd seen this before I ordered my 10" barrel! LOL Guess we'll see how she does. Actually not TOO worried...

Clearly beats a 7" barrel when it comes to effective wounding velocities based on that article

Since this is in the NFA section and a lot of people use cans on SBRs, it's worth mentioning a suppressor does increase velocity, but ever so slightly...around 1-3% based on suppressor length.

UWone77
28 November 2014, 20:40
wish I'd seen this before I ordered my 10" barrel! LOL Guess we'll see how she does. Actually not TOO worried...

That's a good and accurate article, but I don't think there's going to be too much of an issue with the 10.5 Jim. I think you mentioned before, this won't be used more than what 100 or 200 yards out? You'll be fine. I can ping steel all day at 300 with my 10.5's

SwissyJim
28 November 2014, 21:35
Clearly beats a 7" barrel when it comes to effective wounding velocities based on that article

Since this is in the NFA section and a lot of people use cans on SBRs, it's worth mentioning a suppressor does increase velocity, but ever so slightly...around 1-3% based on suppressor length.
And I fully intend on using a can on this... a LOT. And the 7.5 is hard to get a can for - my incoming Specwar556 is only rated to 10, altho the Specwar762 is good for the 7 it resides on my 300BLK


That's a good and accurate article, but I don't think there's going to be too much of an issue with the 10.5 Jim. I think you mentioned before, this won't be used more than what 100 or 200 yards out? You'll be fine. I can ping steel all day at 300 with my 10.5's
Agreed.... I don't carry a weapon for a living, thank God. I can predict a fire's behavior MUCH better than I can a humans. So yes, steel pingers, range toy and all around fun gun for the hell of it. Since I got the 300BLK sbr, I figured I may as well add a 5.56 upper since I can. Nice having the lower registered... next is a 458Socom I think. With that upper it may become my 'hike in the woods during bear season' gun.

But that was a really good and educational article.... well worth the read.

DutyUse
29 November 2014, 03:34
Good read thanks for posting Ordance

voodoo_man
29 November 2014, 04:43
several issues I have with this article.

#1 they used one 24inch barrel that they cut down
#2 only used ss109 and m855 - for NATO that's fine, but here in 'murica we use soft tip ammo and 77gr ammo.
#3 the barrel they used was 1-7 twist
#4 no chrono at impact point
#5 no grouping analysis
#6 they made it a single shot weapon - why?
#7 muzzle velocity is not the end all be all of firearm application

CarbonScoring
29 November 2014, 06:51
several issues I have with this article.

#1 they used one 24inch barrel that they cut down
#6 they made it a single shot weapon - why?


My guess is that they would need to rig a system to cycle the action that could be moved when they cut the barrel down. Not worrying about cycling the system meant they didn't need to figure that out.

This raises the question of how different gas systems affect pressure. A rifle length would bleed off more gas than a carbine length wouldn't it? How does that change the results. It may skew the results, especially when you're talking about different lengths with the same gas tube length or when you transition from, say, 18" rifle length to 16" mid length.

Regardless, the article just, more-or-less, reaffirms what we all know; the shorter the barrel, the more pressure, thus more flash and sound.

voodoo_man
29 November 2014, 07:36
Regardless, the article just, more-or-less, reaffirms what we all know; the shorter the barrel, the more pressure, thus more flash and sound.

Correct, but its only one aspect of the industry. I have a 1:8 7.75 wylde piston barrel, will it yield similar results to a 1:7 7.5 556 DI barrel? Maybe? What about accuracy? Chrono on impact sight? I'd like to know these things.

I'm gana end up doing a test on this myself since I can't find anything even remotely to what I want to know.

CarbonScoring
29 November 2014, 08:10
They definitely were gearing the entire article to suppressor concerns which is probably the main reason they didn't address anything but pressure.

Ordnance
29 November 2014, 10:26
several issues I have with this article.

#1 they used one 24inch barrel that they cut down (That's actually harder than just grabbing different barrels of different sizes and as a result your getting more accurate statistics because your maintaining the exact same condition and only altering length.)
#2 only used ss109 and m855 - for NATO that's fine, but here in 'murica we use soft tip ammo and 77gr ammo. (They used that ammo specifically because of what the ammos primary design was for.)
#3 the barrel they used was 1-7 twist (Standard twist rate for most SBR service weapons)
#4 no chrono at impact point (You don't need a chrono at impact. That can be determined from the Muzzle chrono and any decent ballistics program without costly equipment.)
#5 no grouping analysis (This wasn't an accuracy test. Accuracy is determined by more than just barrel length... crown, twist, load, bullet, shooter... too many variables again for what the intended purpose of the test. And if we want to talk real accuracy and velocity at the impact point then why bother with SBR's or 5.56 since we already know it's not going to win?)
#6 they made it a single shot weapon - why? (They had to in order to accurately test the pressure)
#7 muzzle velocity is not the end all be all of firearm application (You and I both know that, but that wasn't what the test was really about anyways. Again... It was meant to really test pressure in relation to barrel length with suppressor use. They should have picked a better title.)

As was mentioned by Carbon, the article is really geared around pressure in relation to suppressor use and optimal length. The title could have been better. You guys need to keep in mind that there is only so much you can do within certain tests and by adding more and more variables to try and gather you only risk skewing results even further.

Ordnance
29 November 2014, 10:35
Correct, but its only one aspect of the industry. I have a 1:8 7.75 wylde piston barrel, will it yield similar results to a 1:7 7.5 556 DI barrel? Maybe? What about accuracy? Chrono on impact sight? I'd like to know these things.

I'm gana end up doing a test on this myself since I can't find anything even remotely to what I want to know.

Voodoo... Lol.... I get where you're going with this, but accuracy is not determined by FPS or barrel length alone. There are so many factors that you really can't test that and come up with any type of reasonable answer. If you want the velocity upon impact then you only need the muzzle velocity and a ballistics solution program and I can show you how to get your impact velocity. As for transference of energy in relation to temporary and permanent cavitation, depth of penetration, and fragmentation then there is a ton of information out there already by different depts which would cover that.

Ordnance
29 November 2014, 11:03
I was looking through the study and another thing I noticed that would make it impossible to get valid results in relation to accuracy is the tool itself they use to measure the gas pressures. It would greatly affect the harmonics of the barrel and skew any result. The crown they use is also not a target crown or anything of note which would help determine proper accuracy which is understandable as I imagine they were trying to get the study done quickly with the same atmospheric conditions and taking the time to try and turn a nicer crown every time would be exhausting.

Above all though one thing really stood out which many will not notice, but as I've seen the argument laid out time and time again where people think a longer barrel equates to more velocity...

http://sadefensejournal.com/wp/wp-content/uploads/2012/02/barrel6.jpg

The reason I bring this up is it's been argued by men who know more about this than I will likely ever know, but when it comes to semi-auto platforms there is no need for a barrel beyond 23" even if you're using a hotter cartridge like the 6mm CM on a large frame. This is due to the fact that it is a gas operated system which has pressure limits less than a bolt there are no advantages to a long 24"+ barrel. Most calibers in barrels on semis <23" will give you the maximum available velocity, and with an appropriate twist stabilization of even the heavier rounds even beyond the point of a round going transonic. I know it's a sidetrack from the topics real focus, but it's a good point that can be observed within the test itself although unintended by the author.