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Noel
October 14, 1998, 04:56 PM
I need good reference data on the expected change of velocity in a .308 as the length is varied from 20 to 16 inches.

Any tactical shooters who have good data on this out there?

Walt Marshall are you on line??

Noel

Rich Lucibella
October 14, 1998, 09:29 PM
Noel-
Walt emailed me yesterday with apologies. He's doing a week long, low light class which takes him well into the evenings and promised to be with us next week.
Evidently, you know Walt. As I consider discretion the greater part of valor, I didn't bother to demand that he give us his mornings.
Regards and welcome
Rich Lucibella

.
October 15, 1998, 02:31 AM
Noel,

The Hornady Labs list an approximate variation in bullet velocity based on their experimentation. For bullets traveling in the range of 2000-4000 fps, the velocity will vary from 10-40 fps per inch of barrel, respectively (Hornady Handbook, 3rd Edition, page 401).

The Springfield Armory tests showed the 30'06 ball to range from 2709 fps in a 24" bbl to 2848 in a 32" bbl. Another Springfield Armory test indicated an *average* (5-shots) drop of 83 fps when shortening the bbl from 26" to 24" (Hatcher's Notebook, 3rd Edition, pages 399-400).

You may be hard pressed to get relevant data, short of measuring the differences between two or more rifles of the same make & model, but of varying barrel length. Bullet weights and powder burn rates may also be significant factors in this determination, especially if reloads.

If you use good commercial or MILSPEC ammo, I don't believe you will find the differences between the 20" and 16" bbl significant enough to cause you worry about trajectory drop or kinetic energy retention within practical employment ranges.

Noel
October 15, 1998, 11:29 AM
Rich,

I had Walt as instructor in the General Rifle Class at Gunsite a few years ago. Jim Swanson was the rangemaster in that class and they were both very knowlgeable I wonder if you would be able to ask Walt if Jim would come online someday?

Is Walt a little testy if he misses sleep? He was cheery as could be (except for some discussions about tight chambers) when I last saw him (grin).

Mykl-,

I saw some data on the .223 for a range of barrel lengths and a article in Rifle Magazine I think that discussed a variety of calibers. I have lost those references. I think your references are the "conventional wisdom". Thank you for the effort in getting this as a basis.

I believe the change is not linear for all barrel lengths and am interested in the shorter changes more than the longer ones.

Are there any tactical rifle people that can add to this data?

Thanks all,

Noel

.
October 15, 1998, 12:59 PM
Noel,

You're right, muzzle velocities do not follow a linear function with changes in barrel length, when all other variables are constant (as practicable), as is indicated by the first set of data.

If you're unable to find *reliable* data that is meaningful to your endeavors, then you really should consider conducting your own tests. Should you undertake such an effort, I'd be happy to assist you, or put you in touch with Operations Research Systems Analysts that can advise you on test design, data analysis and interpretation.

Should you pursue this venue, I'd encourage you to post your results on this site, as a donation to the public domain and enhancement of the body of firearm knowledge.

[This message has been edited by Mykl (edited 10-15-98).]

Rich Lucibella
October 15, 1998, 03:17 PM
Noel-
Nope, I've never seen Walt get testy either...had him as Rangemaster at my 250 and 350. I was referencing the fact that Walt, along with our other Moderators, donates his time to The Firing Line. So, when he requests a few days to put meat on the table, I'd prefer to give him the room.
Rich Lucibella

DC
October 15, 1998, 06:02 PM
This may be of some help: I scanned this from the August 1996 issue of Guns and Ammo "The Thirty-Foot Barrel" by Bob Forker. Mr. Forker and Bob Clerke wanted to know how long a barrel had to be before velocity dropped to zero. They chose .32 caliber because they had access to 40,000 inches of .32 rifled tubing.

<img src=http://www.tcsn.net/doncicci/barrellngth.jpg>

.
October 15, 1998, 07:36 PM
DC, *They* say that a picture is worth a thousand words. You just illustrated that point. Thank you!!

Not too many years back a similar test was done with the .22lr cartridge. I recall that 19-20 inch barrels gave peak velocity and thereafter the velocity dropped. I guess this is why so many of the modern .22lr rifle barrels are of the 20-inch length. I have an old Remington Model 34, which has a 24-inch barrel. This gun always gave me the subjective perception that it was quieter than my 20-inch Ruger. That bears out as more than just the function of distance from my ears. It meant the fire column in the barrel had been spent and the gases began to cool as the bullet continued to open up space in the bore. The cooling gases cause a reduction of the pressure that is pushing the bullet, allowing a greater effect from the sliding friction between the bullet and bore wall. Cooler gases exit the muzzle at a slower velocity (silencer & suppressor principle)resulting in a pressure wave (report) of a lower amplitude.

UH-OH... I wonder if this means I have to pay a *device* tax on my old Remington 34, since it technically reduces the report (c.f. the XM177E2 flash can)?

DC
October 16, 1998, 01:17 AM
Mykl..

Yes, this article makes a mention of the .22 study...22 ER is optimum in 16 inch barrels, whereas using the same calculations the maximum .30'06 velocity would be in a 200 inch barrel.

This is a pretty neat article...I'll be glad to scan it and e-mail it to you if you wish. Let me know

.
October 16, 1998, 05:06 AM
Thank you. Please do. I'm an inveterate collector of reference data, and this is probably the more comprehensive of tests done in recent years. Several smaller tests have been conducted to determine pistol barrel length effect on bullet velocity, but none that take the issue to the extreme values.