[3975]

MV of .22 WMR

Ammo & Ballistics by Bob Forker has about a page and a half of data for the common factory loadings but they were all done with a 24" 16 inch per rotation pressure barrel. If we want that kind of data I think we're going to have to dig out the chronys and hacksaws. Chipmonk from Rogue Rifle is advertised as 16.125" barrel. If you want to make a project out of this I'm betting that every kid in the neighborhood with a .22 mag would love to have it chronographed with different ammo and you wouldn't really have to do a statistical spread of five three shot groups like the magazines do. Forker lists 12 different loads and data from a 24" barrel just to start.

 

[3975]

barrel length

I think what we're not looking at here is that hot gas continues to expand in the chamber and bore long after the bullet has left. That's what makes it go bang. Just as the powder is still burning and making gas after the bullet has left the chamber, those gasses are still expanding and accelerating the bullet long after the last powder is burned. I read somewhere, think it was Bob Forker, that it takes something like forty feet of barrel before it starts to actually slow the bullet. Where bore friction starts to overcome the acceleration imparted by expanding gas. I think he was talking center fire there so it may be quite a bit shorter for rimfire but it makes sense. Look at pistol barrels, even the long ones by TC. I'd say the longer the barrel the higher the velocity in anything you can hold up but we have to stop somewhere. Even in centerfire most pressure barrels for advertising don't exceed 26".