undersize problem

[wiley]

Although by most standards I am still a novice, I have had pretty good success in the past year casting pistol boolits. I am now trying rifle boolits and immediately ran into a problem with undersized boolits. I am using the RCBS .30/180 SP mold (with gas checks). The as cast size is right at .308 - .3085. When run through the sizing die they obviously don't even touch the die! The alloy was 50/50 wheelweight /lead. What are the various causes of undersized boolits, assuming the mold is good, and it is operator error?

[358wcf]

Your alloy might be part of the problem- some alloys shrink more when they cool than others. I've found that adding linotype to the alloy helps keep the bulk up a bit.
Another factor could be how fast the alloy fills out the mold when casting. I had problems last week with a RCBS 150gr .358swc casting undersize (.356-7) and not filling out properly. Noticing the sprue plate had small holes, I changed it to a sprue plate with much larger holes, and tried again, same alloy- It liked the larger holes greatly, as less restriction to alloy flow. Bullets now fill out properly, and cast at .358-9 as they should.

These are little things that experience will tell you. Ask a question on this forum, and some old guy will share his experience with you for free. Learn all you can, while you can, and pass it on to the younger ones as well--

358wcf

[462]

wiley,

RCBS advertizes that boolit as .309", with whatever alloy they use. I have the same mould, and with straight clip-on wheelweights, it drops right at .309".

Your alloy may be the cause, or you you may have an under-sized mould. Change your alloy before doing any work on the mould. You may want to add some tin, which aids in fill-out, or go to straight wheel weights. Two-percent added tin seems to be the agreed upon amount.

If the mould is, indeed, under-sized you can "beagle" it (do a search) or lap it.

[mooman76]

When are you measuing as apposed to making them. They will probably grow another .001 about a week after casting them. You can also beagle them to get them a little larger.

[MtGun44]

Beagle the mold. You will typically need .310 or .311 to get good results in many ".308"
rifles, altho some folks manage with .309.

Bill