18.5 inch barrel vs 26" barrel muzzle velocity....

[bm11]

Hello,

Just wanted to share my findings, as this is an often debated topic.

I chrono'd Southwest Ammo 175 matchkings out of my 26" barreled AIAW back in December. Conditions were about 40 degrees.

I observed muzzle velocities just over 2700 fps, with a few dropping into the 2675 range.

Shortly after this, I sent the barrel out to get cut, crowned and threaded. Finished length is now 18.5 inches.

Conditions yesterday were similar, 35 degrees F. I was using the same suppressor, but the barrel was installed on my AIAX, thought he headspace was identical, using onced fired brass and an RCBS chamber measurement tool as a gauge.

Muzzle velocites averaged in the 2580 fps range.

So, I experienced a loss of around 120 fps, or about 16fps per inch.

Just wanted to share this info, as often times what is being compared is two different barrel makes, etc. This was at the same range, with the same exact barrel, and same batch of ammo.

-Bob

 

[Lowlight]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

That tracks with what most see, a 10 to 20fps difference per inch.

Now if you run the numbers with that information you find

2580fps is roughly 11.5 mils to 1000 yards, with the round going 1198fps at the target. (conditions 70 degrees, 29.92) and your transonic region is around 1075 yards.

for an 18.5" gun that is pretty good...

 

[ChadTRG42]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Yes, that is right in line with typical speed reductions. Good info and thanks for posting!

 

[81sfo]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Bob ,did you gain any fps with your suppresor on the 18.5" barrel?

 

[bm11]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Forwardeyes</div><div class="ubbcode-body">Bob ,did you gain any fps with your suppresor on the 18.5" barrel? </div></div>You know, that question came up at the range yesterday. I haven't chrono'd it with it off vs on. The 26" MV was taken with the suppressor on, same thing with the 18.5", so it was an apples to apples comparison, but I'll have to do an on vs off comparision.

Meant to do it, but the suppressor was too hot to touch when we were talking about it, and forgot about it later when it was cool.

One other thing I noticed, and I'm not sure if this were an anomaly or is common place with a suppressor- I find that when I allow time for my suppressor to cool, the first round is often about 25fps slower than the following rounds. Could definitely just be a fluke, but I saw it multiple times yesterday. It will require further testing.

 

[MontanaMarine]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Thanks for sharing your results.

My results were almost identical, about 16 fps per inch.

My 308 lost about 90 fps cutting from 26" to 20.5".

 

[81sfo]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Did you happen to chrony your Aw fluted factory 20" barrel yet Bob,curious how the 20" vs 18.5" compares?

 

[jbell]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Bob, remember the 1 round was a little low (PIO) after cooling some also. I dont think it really had anything to do with the velocity drop but maybe.

To any one out there, is this normal for a suppressed rifle in the cold air? I told Bob it was his fault

.

 

[bm11]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Forwardeyes</div><div class="ubbcode-body">Did you happen to chrony your Aw fluted factory 20" barrel yet Bob,curious how the 20" vs 18.5" compares? </div></div>I did, but it was all over the place (velocity.) I attribute this to heating the ammo to ensure warm day stability, but them cooling because I didn't have a portable heat source to keep the temp constant.

The warmed loads were doing in the 2850 range, but that was with 46.2 grains of varget and not 45.8 grains of H4895.

 

[Black Ops]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....


Been doing the short barrel thing for over 20 years and to be honest they are the ticket...

But who am I to say that

<span style="font-weight: bold">Mike
Tac Ops</span>

 

[bm11]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Black Ops</div><div class="ubbcode-body">
Been doing the short barrel thing for over 20 years and to be honest they are the ticket...

But who am I to say that

<span style="font-weight: bold">Mike
Tac Ops</span> </div></div>Your article advocating the 18.5 is my reason for going this direction, Mike!

 

[Shortdraw]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Mine went from 2660fps @ 26" to 2540fps at 20". Approximately a 13fps loss per inch with a Hart 308 barrel.

 

[Shooter21]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bm11</div><div class="ubbcode-body">Hello,

Just wanted to share my findings, as this is an often debated topic.

I chrono'd Southwest Ammo 175 matchkings out of my 26" barreled AIAW back in December. Conditions were about 40 degrees.

I observed muzzle velocities just over 2700 fps, with a few dropping into the 2675 range.

Shortly after this, I sent the barrel out to get cut, crowned and threaded. Finished length is now 18.5 inches.

Conditions yesterday were similar, 35 degrees F. I was using the same suppressor, but the barrel was installed on my AIAX, thought he headspace was identical, using onced fired brass and an RCBS chamber measurement tool as a gauge.

Muzzle velocites averaged in the 2580 fps range.

So, I experienced a loss of around 120 fps, or about 16fps per inch.

Just wanted to share this info, as often times what is being compared is two different barrel makes, etc. This was at the same range, with the same exact barrel, and same batch of ammo.

-Bob
</div></div>

I'm suprised nobody else asked this, but, why the hell would you spend $8k on a rifle to put a new tube on it immediately?

 

[MontanaMarine]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

He had the existing bbl cut down from 26" to 18.5".

 

[bm11]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Shooter21</div><div class="ubbcode-body">

I'm suprised nobody else asked this, but, why the hell would you spend $8k on a rifle to put a new tube on it immediately? </div></div>Simple- the barrel that came on it is a Bartlein 1 in 10 with a SAS brake. It is threaded 3/4x24. My suppressor is threaded 18x1.5 (standard UK threads) and was a direct fit (I did it myself.)

So it was no cost to me. Finally- I figured it would be a good way to pound some rounds through the rifle and if I didn't like it, I could throw the factory barrel back on with 0 round count and have it bring a higher premium. But that is not going to be the case on this rifle. I really like it and it is a keeper. I'm going to either buy the SAS suppressor designed for the brake, or I'm going to send the barrel off to get the threads turned down to 18x1.5.

-Bob

 

[Shooter21]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

ok, that makes better sense

 

[dvdt]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bm11</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Black Ops</div><div class="ubbcode-body">
Been doing the short barrel thing for over 20 years and to be honest they are the ticket...

But who am I to say that

<span style="font-weight: bold">Mike
Tac Ops</span> </div></div>Your article advocating the 18.5 is my reason for going this direction, Mike! </div></div>

Anyone have a link to the article ??

 

[Turk]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dvdt</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bm11</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Black Ops</div><div class="ubbcode-body">
Been doing the short barrel thing for over 20 years and to be honest they are the ticket...

But who am I to say that

<span style="font-weight: bold">Mike
Tac Ops</span> </div></div>Your article advocating the 18.5 is my reason for going this direction, Mike! </div></div>

Anyone have a link to the article ?? </div></div>
http://www.tacticaloperations.com/SWATbarrel/

 

[Iggy]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

Good read on that article. I guess my 24" Bartlein has plenty of life to cut short and re-chamber when needed.

 

[bm11]

Re: 18.5 inch barrel vs 26" barrel muzzle velocity....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Iggy.</div><div class="ubbcode-body">Good read on that article. I guess my 24" Bartlein has plenty of life to cut short and re-chamber when needed. </div></div>Now it should be noted- the article claims no loss of velocity going from a 26" barrel to a 20" barrel, but from everything I have found, that is simply not the case. However, I think it's a fair tradeoff for handiness with not-that-much loss of velocity.