muzzle velocity versus barrel lenght

[one shot ST]

I've a question..

do you have a good or accurate rule of thumb to calculate for example how will be the difference in muzzle velocity if you use same load but in different barrel lenght ?

today with a friend of mine I've done some load test using a manometric barrel.
This kind of barrel is 23.622 in long..... my AWSM has a 27 in long...... the results was 870 m/s...... my PVM-08 crono test was 892 m/s.....
I've seen on the web that for every one inch you get about 20 ft/s increased velocity..... so in my case about 70 ft/s.... equal 21 m/s, if this rule is correct the result match..
do you have more accurate info ?
Also the pressure was very accurate, I've tuned QL esactly to match my rifle/case parameters.
The result was deadly accurate.
the total cost was a little high.. but it's ok
6 euro for every rounds + the .338 LM case cost 2.15 euro + 320 km road trip + highway fees...... about 230 euro's... http://www.snipershide.com/forum/images/icons/default/cry.gif

 

[308sako]

Re: muzzle velocity versus barrel lenght

It is not quite that simple, because the differences in individual barrels, and components. I am sure you are aware that not every barrel is identical. That your results show as well as they did proves you have a superior understanding of the concepts you ask about, and were able to control some of the variables.

Taking just a single cartridge and beginning with a barrel that is too long, I would expect only a small velocity loss per inch. But when I approach the barrel length where the cartridge and loading density is very efficient I would expect to see an increasing loss of velocity when shortening the barrel beyond that point. Which could be meaning that the powder has not had time to impart it's energy to the bullets forward momentum.

It is known that a .22 rimfire actually slows down in a barrel which is too long for the propulsion behind the bullet, shorten the barrel and speed up the bullet... to a point.

 

[one shot ST]

Re: muzzle velocity versus barrel lenght

ok.. thanks for info..

 

[kraigWY]

Re: muzzle velocity versus barrel lenght

I think it would be differant with each individual caliber, rifle, load, or any other of the unlimited veriables.

I helped my grandaughter with a science project, to determine the shortest you could go on a barrel yet keep the ME up to 1800-2000 ft lbs at 300 yards, then compair her numbers with what is normal supplied by Gun Companies in hunting rifles. She chose a 308 Win (because that was the rifle/barrel I was willing to donate. It dosnt really mean much as it was only one rifle and on brand of factory ammo. But it was fine for a middle school scince project. Like I said, it dosnt mean much but here it is for what its worth. We started with a 26 in. barrel, cutting it down 2 inches at a time to 16 inches. Each cut with an average of 5 rounds through the chrony using factory Rem 180 corlocks.

The first colum is barrel lenght, muzzle vel. muzzle engery, velocity a 300 yards, KE at 300 yards.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Barrel Lenght 180 Vel Ke Vel KE
26 2826 fps 3,192 2240 2,005
24 2722 fps 2,961 2149 1,846
22 2713 fps 2,942 2141 1,832
20 2677 fps 2,864 2109 1,778
18 2654 fps 2,815 2089 1,744
16 2552 fps 2,603 2000 1,599

</div></div>

 

[one shot ST]

Re: muzzle velocity versus barrel lenght

thanks

 

[ChrisGarrett]

Re: muzzle velocity versus barrel lenght

Sierra will tell you in their manual, that 20-50 fps per barrel inch.

Speer will tell you 20-40 fps per barrel inch.

There's a test, much like the fellow's above, on www.6mmBR.com (if I recall correctly) that shows the differences in 1" increments. The longer the barrel, say going from 30" to 29" is going to give LESS of a difference, than going from 24" to 23". It's not linear in their opinion.

Chris

 

[MitchAlsup]

Re: muzzle velocity versus barrel lenght

The problem in making general sweeping statements, is that this is not the kind of problem where generalized statements are very useful.

If you have a load that is designed to get a complete burn in a 20" barrel, the 24" tube sill not see much gain. On the other hand if you have a load that is developed for a 26" barrel, the 20" tube may see a big decrease.

Thus, we see reports from some companies using factory ammo that shows little loss in MV as the barrel is decreased in size. These statements accurately reflect that ammo in that barrel.

Ww could also see relatively massive changes in the MV from PALMA loads designed and tuned for 30" tubes using slow powders. These kinds of reports ALSO accurately reflect that ammo in those barrels.

 

[308sako]

Re: muzzle velocity versus barrel lenght

Mitch, a very worthy addition and point of perspective which gets to the meat of this subject while avoiding the variables.