Originally Posted by
NicfromAlabama
Deadshot,
That's a complicated question. I'm not expert by any means, but I will give you my 2 cents on the topic. There certainly is an optimum length, but I guess you have to ask, "What are you trying to optimize?" If you are talking about reaching the highest velocity, a barrel will often tend to be longer than most prefer. I hate to repeat what you said, but it really does boil down to what you want to do with it. If you want to squeeze every bit of velocity out of a cartridge, for something like long range shooting, the barrel will be long.........at least with the cartridges I have used. For a hunting rifle, which may be carried, a shorter, lighter profile is more practical, and the rifle will be easier to hold shooting offhand and better balanced. The bullet may be slower from a shorter barrel, but not by enough to adequately kill the critter the hunter is shooting, at the range he intends to shoot. Also, you reach a point that there is very little to be gain by going longer. The bullet may still be increasing in speed, but not enough to justify another inch of barrel, as other factors like harmonics come into play. Barrel thickness is another matter to consider. All other things equal, a bull barrel will shoot better overall than a skinny barrel of the same length. A shorter barrel of the same profile should shoot better than a longer one, although velocity is sacrificed. Heavy weight barrels resist accidental movement by the shooter when shooting on a bench. Thicker barrels take longer to heat up, which may allow for better groups longer. But, I have gotten off on a tangent with the weight thing, as I think you are concerned about velocity.
I guess it all depends on how much velocity you are trying to achieve for what you are doing. I really believe for a 5.56mm/.223 rifle, the optimum length is 20", especially with an AR-15 type rifle. (However, you can achieve higher velocities with a barrel longer than 20".) I recently decided to build a 5.56mm 16" AR-15 lightweight upper for a vehicle/carry rifle. The reason being that it will be more handy in that situation than a rifle with a 20" barrel. Yes, I will be sacrificing ballistics, but for a short range SHTF rifle, it really doesn't matter to me.
Anyway, there is data out there, especially for velocity per inch of barrel..if that is what you want.
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