"Guns & Ammo AR-15" for September tested 19 different ammo loads with 20 different barrel lengths, to arrive at 380 different tested velocities. Everything from super lightweight 35gr Hornady NTX up to Black Hills 77gr OTM. Fairly comprehensive test, all at one time that is. There were some variables not taken into account, due to the nature of the test barrel. Namely, gas system length, chamber type, and barrel material, finishes or treatments. The test used a 26" Stainless White Oak Armament 1/8 Match barrel, with no gas system. After each ammo was tested the barrel was chopped down in 1" increments all the way down to 7".

While not being all inclusive, I did find it an interesting read. One thing I found interesting was the velocity difference between 10" and 11" barrel was small, frequently less than 100fps. From what I understood, perhaps mistakenly, was that it was generally accepted there was a fairly significant, relatively speaking, difference in velocities between the two lengths?

Since I'm pretty sure it's verboten to post the entire article, I'm only going to post an image of the velocities chart, which, IRRC is ok since its a small excerpt from the article and being posted  for discussion?  



ETA: Corrected spelling and rotated chart for easier reading.

Thanks Mike for posting this

Cheers
Shannon

There are some very interesting variations @ the 24" 25" 26" range.

22" seems like the sweet spot in some of the loads

12.5" just gets better and better.

 
What's also interesting is that you don't really gain much in terms of velocity with those lengths, over a 20". With a few exceptions, they barely gained 100FPS with the additional 6" of bore.

 
Good point. I've read that as well. Which brings up another question.


Why do most of the ammo manufacturers still quote velocities from 22-24" barrels with .223?


For instance, I'm testing some 50gr and 55gr Hornady GMX loads. They both quote velocities from 24" barrels.


e.g.:

Did the article say where the velocities were measured?  Are these like 10 feet from the muzzle or are they corrected to the velocities at the muzzle?

I believe that is because the testing "standard" is for bolt action guns and most of them are in that 20-26" range.

Probably this.  It's a legacy from a former era when most ammo was shot  bolt action rifles, including .223.  Obviously they should be using a 20" BBL today, but if they did , people would go "woah woah woah! These other guys list like 100 FPS faster!" (with the other guys using the longer BBL).

I'm going to guess and say it's because most of their test barrels are 24".    The few 20's they have are for 223/5.56 testing.   Just a guess though

No, not that I saw. He only mentioned he used 2 chronos simultaneously, a PACT in front of the barrel and a Labradar adjacent the muzzle.

I'm on mobile, which is a pain to multi-quote, so I can't respond to everyone without cluttering/bombing the thread, sorry guys.

I agree. While I do appreciate the effort, I think the test would have had more meaningful results had the ammo selection been less ambitious. Using half, or even a third or the selection of ammo would have allowed the tester to directly compare individual rounds within the same environment. 6 of some of the most widely used rounds would have been sufficient, IMO.

As it stands, it's an interesting test, and the tester should be applauded for the effort, but at the end of the day were left with too many variables to consider the test absolute. Or, as the author put it "The short answer to the question of how much velocity you lose per inch? It depends"

Wonder how many rounds he had to shoot to get a reading out of the PACT for all of those?

I'm wondering about the quoted velocity for the BH 40 gr V-Max. That just seems low across the board.

Fiocchi states 3600 fps with that bullet in .223. I've never chrono'd that load but it's clearly the fastest I've ever fired from either my 16" or 20" barrels. Screaming fast.

I doubt that BH loads that bullet on the weak side.