Sizing question

[JJC]

My barrel slugs .457 & a few inches before the chamber it goes down to .456/4565 nearest I can measure. I am sizing .459. So my questions are:

1. Does lead have any spring back or the small variation does not matter?

2. Do you think I should size smaller .458 or lap a die out 4585?

3. I tried as cast .460 accuracy improved some but I lost 168 fps, is that to fat?

Thanks John :drinks:

[RobS]

Boolits can spring back but it takes a harder alloy. The reason for slugging a barrel with pure lead is so it doesn't spring back and you can get an accurate measurement of the bore. Using the same sizing die, a water quenched WW bullet at the caliber you are talking about can size .001 larger than a bullet that is softer i.e. 50/50 lead or even straight air cooled WW because harder boolits can and do spring back.

There is also the idea of obturation where a soft alloy is used in hopes that it bumps up and seals the bore from the expanding gases. I personally do not like to go this route as it makes for yet another variable. I would possibly look into firelapping that constriction out as it shouldn't take much since it is only .0005-.001.

[JJC]

I thought about fire lapping also but wanted to see what you guys said first. I never slugged the barrel after the first time I lapped it. X bullets were shooting fine. How many lapping loads do you think 4 maybe then slug it? Thanks John

[Larry Gibson]

The question is; is the small restriction causing inaccuracy that is measureable? Assuming you're talking about a 45-70 here? What kind of accuracy are you now getting and do you think fire lapping will improve it?

Actually a softer alloy in this case will allow the bullet to obturate to small differences in bore sizes. This is especially the case the closer to the chamber the restrictions are. For example; I once had a trapdoor that someone had changed barrels on. About 2 - 3 " in front of the ther was a .002 - .003 about .4" wide constriction where the barrel vise had compressed the barrel in. I shot it quite a while that way and found that softer than 1-20 alloy bullets of 350+ gr shot very well, as well as they shot in my rifles w/o constricitons. This was with both smokeless and BP loads. What happens is the inertia of the bullet during accelleration was aloowing obturation back out once the bullet passed the constriction. With lighter bullets of 250 -300 gr, even of pure lead, accuracy was never really good. The exception was with the thin skirted Rapine 260210HB bullet.

I did try fire lapping with the kit then available (forgot the name and it is packed away). I ended up with a .002 larger throat, a small reduction in the depth of the restriction and no improvement in accuracy. I suggest if you do try fire lapping that you get the kit and follow the directions. It will take about 50+ firelapping shots to do it correctly and without removing too much metal. My decision as to whether to firelap or not would be based on a realistic apprasial of the current accuracy.

Larry Gibson

[mroliver77]

+1 to what Larry said adding only; is leading acceptable? I would load the .460 and not worry about the loss in speed. If accuracy and leading is acceptable quit worrying over minutia.
Sometimes I get a gun and try a load I have made up before doing any measuring. If the gun performs to my standards I dont worry about measuring it and fiddling about unless I am looking to drag the last bit of performance from it or am really bored.
Jay