12.5 inch barrel vs 13.7 inch barrel velocity

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Looks like 12.5 is kind of a sweet spot for the heavier projectiles.


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Velocity loss/gain per inch of change steepens under 12.5”. It is moderate between 12.5” and 16”, and fairly flat 16”- 24” or so. As we look at medium length barrels like 13.5” or 14.5”, an inch in either direction makes very little or no difference, but down in the 10.3” region, an inch can be a big change in noise, flash, trajectory/ballistics, reliability, and silencer wear. In the opposite extreme, there is almost no difference between an 18” and 20” barrel, in practical terms. As in, you really need a chrono to see the difference.

Handling difference between a 12.5” and 10.3” is nil.


In my view of general purpose rifles, which is merely my opinion, the sweet spots are:
11.5”-14.5” for silencers (Mk18/M4 role),

12.5”-18” for A2 flash hiders(M4/M16 role),

16”-20” for light support weapons (M27/M38 roles).