At the range this afternoon working on loads for my new (to me) 223, a Remington Model Seven with an 18 1/2" barrel. A Hornady 50 grain V-Max in front of 24.0 grains of H322 and a CCI-400 primer clocked 3077 fps. I had along my Remington M700VS with a 24" barrel and tried the same load getting a reading of 3253 fps. That works out to about 32 fps gain per inch of barrel. I've always wondered how much gain or loss you get as barrel length changes so it was interesting and informative to be able to run a real-life test. As a bonus the load shoots nice groups from both guns.

The V-Max is a very accurate bullet

Several reloading manuals address this subject. Of course, there are variables such as chamber dimensions and barrel condition that may affect velocity differences.

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I've always wondered how much gain or loss you get as barrel length changes

Depends on bullet diameter. Smaller=more, larger=less

Barrels of the same length can vary by 100 fps. Comparing two different barrels of different lengths is not a valid test. In tests where they have cut a barrel off one inch at a time cartridges such as the .223 have varied by approximately 25 fps per inch. Small bore magnums have varied much more, depending on caliber.

I have a 223 with a 24" barrel and one with a 22" barrel and the 22" barrel is on average 20fps faster than the 24". Internal barrel dimensions and design are probably more significant than length.

Yep, comparing two DIFFERENT barrels tells you little, or perhaps nothing, about the real impact of barrel length on velocity.

I have two rifles in .221 Fireball, and both of them are deadly accurate. When fired with the same load, the one with the 22" barrel registers velocities (chronographed with an Oehler 35) at essentially the same speed as those fired in the rifle with the 26" barrel.

If I wanted to know the real impact of barrel length, I would have to cut the 26" barrel off to compare the pre-cut with the post-cut velocities.

On the other hand, if you compared the average velocity of 10 barrels of one length with that of 10 barrels of another length, then you would have a reasonably valid statistical comparison which would not vary significantly from the results obtained from cutting a single barrel.

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I've always wondered how much gain or loss you get as barrel length changes so it was interesting and informative to be able to run a real-life test.

Welll, you have a comparision but not a test. There is no way to make any firm predictions on fps vs. barrel length because the actual change varies by bore size, bullet weight, powder burn rate (the peak and average pressures) and the individual rifles. Mostly it doesn't much matter, we just learn to shoot what we have.

Develop optimum loads for both barrel lengths & my thought is that the difference in velocity would be more marked.

I think if you could make all things equal you would find that velocity and barrel length also have a direct correlation to the amount of powder you are tying to burn too.

The larger the volume of powder the greater the barrel length, but then again this is probably one of the most basic principals too.

I've seen a couple of 20" .308s run some numbers within 50fps of my 26" one.

I kind of suspect that in small bore cartridges like the .223 when you start shooting heavy for caliber loads like the 68gr and up stuff that barrel length becomes less of an issue due to the bullet taking up so much space in the case.

Depends on the individual gun but you will come pretty close at 25 to 30 FPS per inch on most guns.

My .416 Rem. 20 inch barrel lost absoltly nothing It gets me an easy 2400 FPS on the chronograph time after time.

Here is a test in the reloading pages.

http://www.accuratereloading.com/223sb.html

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you will come pretty close at 25 to 30 FPS per inch on most guns.