Barrel length and Velocity question

[jackD]

   I am looking at a .308, but have always wondered how much velocity is lost with a shorter barrel? I have looked at 3,  a 20", 22" and 24" barrel. I will never take a shot with it past about 300 yards. Will a 20" barrel really have much affect on velocity or energy? Thanks

[diggler1833]

You can load a .308 hot enough to take it to 1K with a 20" barrel so I think that 300yds is fine.

The difference in velocity in the .308 with 20"and 24" barrels is pretty minimal.  It would matter more with a magnum caliber and slower burning powder.

[nomosendero]

No it won't.  We are talking about a 308 here. I recently vel. tested some 308's, a 16"DPMS, 20"BLR, 24"Optima Elite & 26" M700VS. The velocity difference between the 20"-24" is not much with this cartridge.
Actually the 26" did not add much & the diff. from 24-26 was VERY minimal. The 16" was disapointing, but not surprising. You can't draw definite conclusions by testing one each of a given barrel length, but my results mirror the results of a test in 308BR & these guys shoot more 308 rounds in a year than most would do in a lifetime. This small diff. is why you see more "Tactical" 308's now with a 20" barrel. Of course if you have a speciality rifle for 600-1000 yd. targets then you would even go to 32" in some cases, as it is only for that purpose, thus beeing long is not an issue.

Here is the article:   www.6mmbr.com/308Win.html

I am a proponent of long barrels in 25-06, 257WEA, 264WM, RUMs & others, but that is a whole different deal.

[Zachary]

I agree.

I have shot a .308 with 150 grainers out of 26" and 24" and 22" barrels, and I hardly notice a difference between 22 and 24, and even less between 24 and 26.

Now for me, I think that 22" for a .308 is ideal, which is probably why most modern bolt action rifles in .308 wear 22" barrels.

Zachary

[jackD]

Thanks for the help guys.. very knowledgeable group

[SHOOTALL]

I have shot one with a 16 , 20 , 22 and 24 inch bbls . Anyone who did not notice the difference in LOUD with regard to the 16 just plain can't hear . Even with plugs and muffs on !

[mcwoodduck]

Not sure about a rifle.
But for a shotgun the basic 1200 FPS load is based on a 28" barrel out of a 12 ga.
for every inch you go shorter you loose 5 FPS.  My guess with the rifle is you are going to loose about the same between the 22 to 26"
even if it is twice the shotgun  40 FPS is not a whole lot when looking at 2600 to 2800 FPS loads.

[trotterlg]

Velocity loss in high pressure small cal's is about 50fps per inch of barrel.  This is less if the barrel is longer and more if the barrel is shorter, not as much from 28 inches to 27 but more from 17 to 16 inches.  Just depends on the rifle.  There isn't any way to generate a firm number that can be applied across the board.  In gereral (like the spam email's say), longer is better.    Larry

[SHOOTALL]

Got to thinking i have shot steel rams at 500 yards with a 15 inch bbl. XP-100 along side a guy shooting them with a 22 in bbl rifle . both were in 708 and when hit they went down about the same . his might have got there a touch faster . There were more 308 rifles there but the difference wasn't that noticable with them either .
worst case if you go to a 16 inch socom over a service rifle you turn a hot 308 into a hot 30-30 that is easier to use up close . Is that bad ?

[poncaguy]

I think 7-08 and 308's do well with 18-20" barrels. I agree that 270 WSM, 25-06, 300 WSM and other like rounds do better with 26" barrels or longer.............

[mannyrock]

   Most factory loads for high powered rifles are test-fired in a 24 inch barrel.  These are the ballistic numbers you see in the charts that are in the back of gun catalogs,  the Shooter's Bible, etc.

   A .308 will lose approximately 50 fps in velocity for every inch that the barrel is shortened.

   So, look at a factory load in a catalog, and subtract 200 fps to calculate the velocity loss for a 20 inch barrel.  As a practical matter, this will be very close.

   Personally, I find that a 20 inch barrel is just too much noise and muzzle blast for me in a .30 caliber rifle.  I prefer to buy a standard 22 inch, and then have a gunsmith cut one-inch off of the barrel off, to give me a final barrel length of 21 inches.  A 21 inch barrel is extremely handy and quick for most people, especially in a light rifle. 

  The final overall length of a .308 with a 21 inch barrel is extremely close to the overall length of a long action rifle (such as a .30-06) with a 20 inch barrel.  If you are going to install a recoil pad, you can also shorten the overall length of the .308 by just cutting 1/4 inch to 1/2 inch off of the buttstock during the installation process, and you will never know the difference. 

   With a slightly shorter buttstock, and a 21 inch barrel, your rifle will "point" very well, and yet be short and quick enough for anything you may need.

Regards,

Mannyrock

[nomosendero]

   Most factory loads for high powered rifles are test-fired in a 24 inch barrel.  These are the ballistic numbers you see in the charts that are in the back of gun catalogs,  the Shooter's Bible, etc.

   A .308 will lose approximately 50 fps in velocity for every inch that the barrel is shortened.

   So, look at a factory load in a catalog, and subtract 200 fps to calculate the velocity loss for a 20 inch barrel.  As a practical matter, this will be very close.

   Personally, I find that a 20 inch barrel is just too much noise and muzzle blast for me in a .30 caliber rifle.  I prefer to buy a standard 22 inch, and then have a gunsmith cut one-inch off of the barrel off, to give me a final barrel length of 21 inches.  A 21 inch barrel is extremely handy and quick for most people, especially in a light rifle. 

  The final overall length of a .308 with a 21 inch barrel is extremely close to the overall length of a long action rifle (such as a .30-06) with a 20 inch barrel.  If you are going to install a recoil pad, you can also shorten the overall length of the .308 by just cutting 1/4 inch to 1/2 inch off of the buttstock during the installation process, and you will never know the difference. 

   With a slightly shorter buttstock, and a 21 inch barrel, your rifle will "point" very well, and yet be short and quick enough for anything you may need.

Regards,

Mannyrock

"A 308 will lose approximately lose 50 fps in velocity for every inch that the barrel is shortened." Wow, I have never seen that with even 1 308, much less anything similar to a trend." My tests with barrels of several lengths was actually a little less than 25fps an inch & I feel it is quite close comsidering it mirrors the findings of the 6mmbr link I posted, these guys shoot an EXTREME volume of 308 rounds, I am willing to bet far more rounds than all
but maybe a few on this forum.

On the noise part, I did not set up any sound measuring equipment & the shorter 308 has not been loud to me at least, except for the 16"DPMS with flash sup, it was obviously louder.

[mannyrock]

  Many years ago, either G&A or the American Rifleman, had an article, where they started with a .30-06 with a 26 inch barrel, and cut it off, one inch at a time, down to 20 inches, and calculated that it lost 50 fps per inch.  I was basing my advice based on that test.

  If the .308 loses less than 50 fps for each inch that is cut, then great!  No problem by me.

  But, that 20 inch barrel still produces too much muzzle blast for me.

Best Regards,

Mannyrock

[SHOOTALL]

saw that test also . and another with a encore bbl that concluded  the same thing both were avg.

[mannyrock]

   And, that test used standard factory ammo, in a standard bullet weight, to yield the 50 fps loss.   Perhaps the results are different (less velocity loss) if a hot, fast burning powder is used by a handloader.  I would imagine that folks shooting benchrest are using handloads.

Regards,

Mannyrock

[SHOOTALL]

it was an average , don't get defensive mannyrock you have a good point . the interior finish of the bbl itself could cause a big change along with several other things . temp.  alone with some powders could be 25fps or more change .

[nomosendero]

saw that test also . and another with a encore bbl that concluded  the same thing both were avg.

Remington did another test and their finding was 20fps per inch. I hate these tests really when used as a broad brush of calibers, that's why I was speaking of specific 308 results.

The 50fps per inch results were closer to what I found with the 300WM going from 26"-24", could be with 30-06 also with certain powders as Mannyrock stated. I would encourge everyone to read the 308 article in 6mmbr.

On the muzzle blast, I can't tell much difference with the 20"BLR & my M700VS 26", it's such a mild cartridge anyway. I am going to shoot them again soon, I will pay closer attention this time. Can't see why the blast will be more than my 22" '06 or 24"300WM, no biggie with any of those.

[1sourdough]

 I agree a 308 generally uses a faster burn powder than say a 300 wthby mag. So if compared the velocity loss per inch for these 2 could be very different. Just like a 30-30 can get by fine with an 18" barrel but an 'over-bore' cartridge needs a longer barrel to get the most from the charge of slower powder.