True Ballistics and Barrel Length

[SalCucco]

I was just wondering about the ballistics charts (muzzle energy, muzzle velocity and bullet drop out ot 500 yards) that the various bullet manufacturers put on their web sites and on their ammo boxes.

Does anyone know the standard that the industry uses re barrel length and i guess it would be thickness to come up with these charts they advertise.

JUst curious because i was looking at the ballistics for the .308, .270 and .270 wsm and in the 2 or 3 different rifles i am considering buying the barrel length varies between 21.5 up to 24.5 and in between also consisting of sporter barrels (which i would believe to be lighter weight)

Also i would assume that the longer heavier barrel (eg; varmint rifle) would get the best ballistics.

Thanks.

[James B]

The barrel length thing is a rule of thumb in a way. While it is true that longer barrels will usually produce more velocity, its not true in every case. Some calibers do not benifit from more barrel length and some do. A few years back a gunsmith friend and I bought about 25 6.5x 55 Swedish Mausers. They all came with 29 inch barrels. We sporterized and sold them in my shop. We cut them all down but on many we cut them off one inch at a time and chronographed them with the same load. Some lost velocity as we shortened the barrels. A few gained velocity and a few didn't change at all. Most of them lost velocity if we went below 22 inches of barrel so we cut most of them to 24 inches and left it at that. We didn't take time to work up different loads for the shorter barreled guns to try to gain back lost velocity but powders of different burning rates can do just that. The gun makers have set their barrel lenths at 22 inches for standard calibers and 24-26 inch barrels on Magnum models figuring that the longer barrels will burn the larger powder loads better. For the most part this holds true. Most of the reloading manuals use barrels of 24-26 inches for their test data which tells me that that would be about the best length to perform to their max.

In the real world of the average hunter the barrel length and velocity are probably not as important as a consistant load which produces the best accuracy in your gun. A shot through the vitals is far more important that the speed it arrived at and eeking out the last FTLB of ME. I try to arrive at that load then mess with it some more if I have the time or need.

[48thguns]

Hello Salcucco. Great question! Unfortunately, not a easy answer. First, there is no "standard" barrel length. The famous German K98 Mauser of WWII famewas a fairly short barrel carbine. The US 03A3 sniper rifle had a 23? or so inch barrel. David Tubb wins the national match with a 27 inch barrel with a one in 7 1/2 twist with a 6mm caliber. Did I mention "twist?" Yep, the twist of the land and groves is really, IMHO, more important than the barrel length. For instance if your barrel is 20 inches long and the lands and groves make 2 complete revolutions....you have a 1 in 10 twist. Some barrels are extremely accurate with a 140gr bullet and totally spastic with a 160gr bullet!

Well, I'm confused so you should be too. I would do this. Pick your caliber based on what you want to hunt or plink then do some research on that combination and come back to the forum. There is a brain trust here that will maximize the barrel length from there.Regards, Rick.

[stubblejumper]

It may also surprise you to know that it is possible to shoot the same load in two rifles with different barrel lengths and produce a higher velocity with the shorter barrel.This is because the chamber and barrel internal dimensions are also a factor in producing velocity.A tighter chamber will produce higher pressure which will usually produce more velocity.If the shorter barreled rifle has a tight chamber and the longer barrel has a loose chamber,the pressure difference may more than offset the difference in barrel length.By the way,the barrelthickness is not a significant factor where velocity is concerned.