Velocity loss (5.56) per inch

Advertised velocity is generally for 20" barrels right?

So a 10" would basically have a loss of upwards of 250fps from the advertised rate.. not too bad.
 
Personal experience here, out of three diifferent rifles (of course, I didn't feel like chopping down barrels)

Ammunition were reloads, using 55 grains Hornady bulk FMJBT with IVI brass, all loaded in the same batch, with 25.0 grains of H4895

Chrony is a Shooting Chrony Beta Master, set-up at 10 meters from muzzle, used indoors with LED lighting.

Velocities shown are averages of 20 shots strings fired from a given rifle.

Rifle #1 : 20" Barrel : 3143 FPS

Rifle #2 : 16" Barrel : 2932 FPS

Rifle #3 : 7" Barrel : 2224 FPS

We can realize that the velocity drop is far from being linear :

- From 20" to 16" : Loss of 221 FPS for 4" : 52.75 FPS per inch

- From 16" to 7" : Loss of 708 FPS for 9" : 78.66 FPS per inch

Too bad I didn't have my 12.5 rifle built when I did that testing, I would be really curious to see where the drop curve starts to increase.

That being said, I have to agree that H4895 is a fairly slow burning powder for use in the 223. While the longer barrel might have benefited from that slow burn rate, most of the energy was probably wasted out of the barrel with the shorty, hence the very poor performance.

I'd like to re-do the same tests using a faster burning powder, like H335.
 
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Velocity loss cannot be linear guys, that just doesn't make any sense in this universe. In this case a barrel of 0.5 inch in length would have a bullet velocity loss of 650fps, and that just cannot be.
1 inch loss from 26inch to 25inch cannot have the same velocity loss as 1 inch loss from 16inch to 15inch, so I have strong doubts about the data.
 
mikethebike said:
Velocity loss cannot be linear guys, that just doesn't make any sense in this universe. In this case a barrel of 0.5 inch in length would have a bullet velocity loss of 650fps, and that just cannot be.
1 inch loss from 26inch to 25inch cannot have the same velocity loss as 1 inch loss from 16inch to 15inch, so I have strong doubts about the data.
Click to expand...

The data isn't linear at all. Take a better look. In some cases, The loss was just 5fps well others was 80fps. In some cases, they even had more velocity than the last inch.
 
These sorts of tests have been conducted many times and come up with the same conclusions every time:

- there is no "rule" that can be applied to determine how much MV is gained or lost by changes in barrel length, the only way to know for sure is to do it. Some barrels will actually gain MV when shortened by an inch or two, but ultimately MV will drop as the barrel is shortened; and

- the powder that produces the highest MV in a long barrel will produce the highest MV in a short barrel. That powder will lose or gain more MV for each inch change in barrel length, but it will still be fastest. There is such thing as a short or long barrel powder.
 
I once converted a 30" match 308 barrel to a 20" hunting barrel. We cut the barrel off with a hacksaw in 1" increments and tested with a chrony. (One type of ammo.) Velocity drop was about 30 fps/inch.
 
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