Bullet Molds and Bullet Weights -- A Question

[Thomas Traddles]

I have the following molds: RCBS 38-140-WC; RCBS 38-148-WC; RCBS 38-158-CM and NOE 360-155-WC (5 Cav)

When casting from range scrap, the NOE mold throws bullets at 155g. Just as Advertised.
The RCBS 38-158 Casts at 159g with the same melt.
The two WC molds, however, cast bullets that are consistently 7-8 grains over the weight specified on the mold --The 140 throws a 148 grain bullet and the 148 a 154-155 grain bullet.

I'm curious to know why the two WC molds casts heavier bullets? I'm also wondering if others have this experience and whether or not you take this into account when working up charges from the loading manual.

[bangerjim]

Cast 'em..........load 'em..........shoot 'em. You will spend more time and frustration weighing each boolit that you will shooting them. Unless you doing some kind of uber-accurate competition, a grain here or there is normal and I never concern myself about it. But that is totally up to you and how much time you want to waste weighing and sorting. Some do.......I sure don't! Especially on pistol slugs. Your alloy, casting temp, mold temp, phase of the moon ( [smilie=s:) will all cause variations.

I use the same powder load for every boolit of that generic weight. Load several hundred at a time with no concern about minor weight variations vs powder quantity.

Just go have fun! And think about all the (supposed) money you are saving by rolling your own!~!~!~!~!~!

[Thomas Traddles]

Banger, I can't say I've weighed every bullet and don't shoot competition. But I have weighed 10 or twenty here or there to try to have some idea how different alloys might effect bullet weights, just to satisfy my curiosity. I'm happy to know that the weight variations are not enough to concern myself about.

[JSnover]

"The two WC molds, however, cast bullets that are consistently 7-8 grains over the weight specified…"

Molds often have their quirks. They cast a little heavy or a little light, a little small or a little fat, maybe they take longer to warm up or don't hold heat well, it's all part of the game. Consistency is all that matters, though, and if your 140 gr mold always drops 147-148, you're good to go. My 350 and 500 gr molds are consistently 2 grains light and I'm happy with them because they're consistent.
If it bothers you, use data for a 150 gr wadcutter.

[tazman]

Bangerjim is correct. Your particular mold and batch of alloy may drop different weights by a few grains than nominally specified. I have never had a problem with using loads for the nominal weight. If it concerns you, use data from a boolit of the actual weight or one closest to it. For instance, for the ones coming out 155 use data from the 158 bullets.
You just need to be aware of seating depth differences since that can cause some pressure issues. SWC boolits loaded long use heavier powder charges than full wadcutters loaded inside the case.

[rintinglen]

IIRC, originally, RCBS designed their handgun boolits for 10-1 Pb-Sn Alloy. Later they changed the specs to more closely reflect the alloys in general use, which typically use much less tin. That may be the reason your WC boolits run heavy, that they are older molds designed for lighter alloys.
But I concur with those who say to ignore the slight (2-2 1/2%) increase. For the purpose that most target ammo is used, that slight variance, as long as it is consistent, is meaningless. Just treat 'em like you would your wife and consider that there's just more to love.

[tazman]

IIRC, originally, RCBS designed their handgun boolits for 10-1 Pb-Sn Alloy. Later they changed the specs to more closely reflect the alloys in general use, which typically use much less tin. That may be the reason your WC boolits run heavy, that they are older molds designed for lighter alloys.
But I concur with those who say to ignore the slight (2-2 1/2%) increase. For the purpose that most target ammo is used, that slight variance, as long as it is consistent, is meaningless. Just treat 'em like you would your wife and consider that there's just more to love.

I choked a little bit on my coffee when I read that. LOL

[Larry Gibson]

RCBS moulds are cut for linotype alloy. Using the softer alloys gives a higher % of lead. Thus the heavier weight.

Larry Gibson