Muzzle Velocity: 16" vs 20" in 223

[Tarvis]

What kind of losses can I expect going from a 20" to a 16"? Im planning on loading 55gr vmax's pushed by win 748. The good book says 2900 fps from a 20" barrel at max load from whatever rifle they shot it out of, but I'm considering the shorter barrel for a lighter setup at the cost of MV.

Any ideas on how much MV I can expect would be great. FWIW, the rifle in question is a home built ar15.

Thanks

 

[rg1]

Approx 90-125 fps depending on the gun would be my estimate.

 

[moosehunt]

Pretty well acepted that you will loose 100 to 150 FPS per inch. If you're lucky, maybeso only 75 FPS per inch. As the barrel gets shorter, the effect gets lesser, but you're likely looking at 100 FPS per inch.

 

[Bullet]

You might look here -

http://www.ar15.com/content/page.html?id=213


.

 

[Tarvis]

Pretty well acepted that you will loose 100 to 150 FPS per inch.

I have heard that before, but I posted the same question on the rifle country section and everybody seems to concur on 100 or so fps gong from 20" to 16" on an AR, including Bullet's link.

 

[steve4102]

According to this test you will lose about 175fps from a 20-16 inch barrel. That comes to roughly 44fps/inch.
http://www.accuratereloading.com/223sb.html

According to QL with a 50gr Hornady you will lose 178fps or 44.5fps/inch.

 

[dagger dog]

Standard guidelines on approximate velocity changes for each 1" change in barrel length. Based on 20" to 26" barrel.
muzzle velocity up to 2,000fps change expected, about 5fps
"" "" " " 2,001fps-2,500fps "" , about 10fps
"" "" "" 2,501fps-3,000fps "" "" , about 20fps
""" """ """ 3,001fps-3,500fps "" "" ,about 30fps
""" "" "" 3,501fps-4,000fps "" "" ,about 40fps

The word used above , APPROXIMATE , is important. This is a general guide based upon a veriety of firearms and calibers all averaged together.


From UNDERSTANDING FIREARM BALLISTICS Basic to advanced Ballistics
Simplified,Illustrated & Explained, By Robert A. Rinker
ISBN 0-9645598-4-6 Library of Congress Catalog Card Number: 98-68591

Published by Mulberry House Publishing
P.O. BOX 2180
Apache Junction AZ 85217, U.S.A.
Toll free 1-888-738-1567

 

[rcmodel]

That's pretty close to exactly right.

I found a load test in the "Book of the AR-15" that tested 24 different 55 grain factory loads in different length AR's.

The average velocity loss between a 20" and 16" barrel was 92 FPS, or 23 FPS per inch.

Slower loads then the .223 use faster powder as a general rule.

The Big fast Magelums use much slower powder then the .223.

So, velocity loss is less with the slow ones then the very fast ones.

The .223 fits nicely right in the middle.

rcmodel