Cast Boolit Weights

[Johnw...ski]

It's not something that ever really concerned me but recently I have been trying to shoot some groups from the bench with my 45-70 (as I mentioned in another thread).

I shot a reasonable group (2.5" @100 yds.) with store bought boolits.
The next week I shot a horrible group (6+" @ 100 yds.) with my own gas check boolits.

Upon weighing them after the fact, I am finding my boolits weigh from 395 to 405 gr. That would seem to indicate the problem but, the store bought boolits that are supposed to be 480 gr. weigh in at 500 to 510+ gr. and shoot well enough.

I realize it can't hurt to have them all the same, but is it normal to have to weigh each individual boolit to get any kind of accuracy? And what about the bought boolits, they are inconsistant as far as weight and shoot OK?

MOA would be great but if I can just cast em and shoot em for 2.5" I would be happy.

Thanks,

John

[BABore]

You didn't mention how the "good" store bought bullets compared to your "bad" cast bullets in style, type, diameter, alloy, hardness, lube and velocity. All of those items will have to be addressed first for accuracy. You really need to slug your barrel first to determine what size bullet your likely to need. The throat configuration, of your rifle, will also help determine what bullet style will be more condusive to accuracy. Weight variation comes into play, but to a lesser extent. You didn't mention if you were using a multicavity mold or not. It's not uncommon to have the cavities cast at a different weights and even diameters. Slag inclusions, air pockets, and slight band rounding (poor fillout) can all be causes of high weight variation.

Most everything I ladle cast, up to 500 grains, will run less than +/- 0.5 grs in variation. It's relativily easy to get +/- 0.1 grains variation if I do things right. Weight sorting is useful if your already shooting into an inch or less at 100 yards. But it has to be done in conjunction with a good micrometer. Bullets need to be sorted by diameter, taken at several points, first. Then you weight sort those groups. A larger diameter bullet, with trapped air pockets or inclusions, may weigh the same as a smaller diameter bullet with no internal voids. Which one is more apt to be a flyer?