Some posts back, parashooter recommended I try a .311 diameter lead bullt. My 1898 rifle slugs at .308 and my 180 bullet sized at .309 doesn't group the greatest. I don't have the molds, but I can buy a .310 dia. and also .311 dia. Would the .311 increase pressure?

Usually one starts .002 over bore dia. with a cast lead bullet. This often gives the best accuracy. It will of course raise pressures some, but usually you are not pushing a cast bullet any where near pressure levels where you need to worry about it. Pressures can also be changed with bullet hardness. The softer the bullet, the higher the pressure. I would start with .310's out of wheel weight material. Use the books starting load and work up. Good shooting.

You will run into a chambering problem with a cast bullet before you run into pressure issues. Even "hard" cast lead bullets are much softer than jacketed bullets and will swage down to bore diameter under even moderate powder pressure. If your bore slugs .308 and you aren't achieving good accuracy with a .309 sized bullet, chances are something else is amiss. What does the bore slug just ahead of the chamber? Is the muzzle crown scratched (even a small amount can make a difference). What powder and loads did you try? In my Krag, SR4759 gives good results. However, there are other good cast bullet powders out there (5744, 2400, 4198, etc). For best cast accuracy with minimal effort, strive for 1600-1800 fps muzzle velocity range. Chances are, your best accuracy will be found there.

remington wrote on Apr 26^th, 2012 at 7:01pm:

Some posts back, parashooter recommended I try a .311 diameter lead bullt.

Here's what I actually posted, ". . . size your bullet to fit the throat, not the grooves. That will probably be more like .311" but a chamber cast or throat slug will let you know precisely what you're dealing with." That's not a recommendation to try .311" bullets. It is a suggestion that you learn more about your rifle before proceeding.

Bullets sized smaller than the throat can yaw off-axis because they're not supported during the critical time when entering the barrel proper. The hotter you load them, the more likely to yaw.

Maybe I should repeat the rest of my post, too. "Slow down a bit! 16 or 17 grains of 4759 will get that bullet to 100 yards just fine and will be less inclined to deform in the throat or engrave off-axis, especially considering that you're using a soft alloy more suited to .45-70 than .30-40."