Barrel Contours - What's the purpose?

[Kristian_Jensen]

Why do barrels have contours and does it affect accuracy?

Are contours merely one way of reducing weight while preserving precision?

...or is barrel contour a remedy from a time where barrels was made to fit stocks and not the other way around?

 

[diverdon]

Look at any living object in nature, the trunk of a tree is biggest where it leaves the ground, your leg is biggest where it leaves your hip. In only makes sense that the barrel should be thickest where it meets the action. I don't think that having a barrel the same thickness all the way to the crown would be detrimental to accuracy, but most people prefer to shave a few pounds off of something they plan to carry for miles.

 

[lash]

Barrels have contours because a straight cylinder barrel weighs a ton and in any shooting discipline that requires the rifle to be carried, held or maneuvered in any way you will want to reduce barrel weight to a manageable balance between weight and repeatability of accurate shots.

 

[Supersubes]

The cartridge is going to require a certain amount of material around it. Pretty rare to see .308 size cartridges and up with anything less than 1.1” dia. at the breech. The chamber and receiver do expand in all directions during firing. Anything after that will be a reflection of the usage. Length, weight, thermal stability, etc.

 

[DHwreckage]

Yea all that ...plus.

Removing or adding material to the barrel (the thickness and length) affect the barrel harmonics to a great degree. That's why you see precision barrels with almost no taper. The've all but eliminated the harmonic amplitude with a straight 1.25 barrel. When you're tailoring a load for a rilfe,...all your really doing is timing that bullet to exit within the optimal amplitude of the barrel frequency. A thinner barrel gives a higher amplitude frequency..a fatter barrel give a much weaker/lower standing wave.
And the thickness also helps with shot stringing from a hot deformed barrel. A hunting rifle is assumed to have mostly one shot cold bore shots,,,so the extra weight isn't needed.

Check out a video of a barrel in slo motion when a bullet is fired. It whips like a rope. A thin profile barrel is a compromise to removing weight albeit at the cost of accuracy/ performance.

This plus, a smaller diameter barrel will heat up quicker then a larger diameter one. this also affects accuracy thats why guys that are going to make repeated shot/long strings of fire generally want a thicker barrel to better manage the heat. Also why hunters can get away with sucj skinny barrels as they are usually only making 1-shot. also if you are hanging a suppressor on it that plays into it aswell, the thicker diameter the less it will move the barrel which could affect POI shift.

 

[Greg Langelius *]

Barrels are contoured the way they are because back at the beginning nobody knew what worked and they did a lot of trial and error. After they saw some trends, they did some refined trial and error. Things got better.

After all that some scientific types came along, wrote some formulae to fit the data curves, and claimed all the credit.

Maybe they were right. Maybe...

Different applications require different contours.

Lightweight barrels are more maneuverable, and I'd like something like that in the woods. But they also heat up more quickly, and many get less accurate when they do.

Heavyweight barrels are easier to shoot from a stationary firing point, in some part because the extra mass serves as a heat sink, and more rounds can be fired before heat induced inaccuracy emerges. Unfortunately, just as it takes longer to heat these barrels, it also takes longer to cool them back down. And nobody wants to haul a mega-barrel around on the deer trails for hours on end.

How the mass of the barrel is distributed can be important, especially if one treats the barrel as a tuning fork, and begins to equate frequencies with bullet transit times. This is the origination of barrel harmonics, and that goes a long way toward finding accurate load recipes.

There are these many, and more, factors to consider.

Greg