.359 mold for my loose GP100

[swingpress]

I'm just getting started casting and everything seems fairly straight-forward except mold selection. I'm looking for an accurate load for USPSA (major) and small game.

I've had leading problems with my GP100 in the past, but the last batch of bullets measure .359 and the leading problems are gone.

Can I expect any mold to cast over .359 and leave the finer adjustments to the sizing operation, or will they tend to be closer to .358?

If not, is there a particular brand of molds that tend to run on the large side?

If a larger cast is needed, can a person use an abrasive to hog out the mold a bit as indicated for a different problem in the Lee thread without too much trouble? Presumably Lee molds would be easier to modify since they are softer.

Is there a more obvious solution that I've missed?

Thanks

[454PB]

First, welcome to the forum, swingpress.

I read a lot of posts about undersized Lee moulds. I must be really lucky, all of mine cast at least .001" larger than advertized. For instance, all my Lee .357 caliber moulds (I must own six of them) cast right at .358" to .359" in wheelweight alloy.

I also own about five "other" steel moulds, and they all run at least .357", even the ones designed for 9mm.

My suggestion would be to buy a Lee two cavity for $19 and see if you're as lucky as I've been. If not, you can do some of the other various tricks to attempt a larger diameter. One that is sure fire is to increase the amount of antimony, linotype usually casts at least .001" larger than WW alloy.

The other solution is to order a custom mould and specify the as cast diameter......a little more costly than the Lee, but returnable if it fails to meet your requirements.

[Buckshot]

...............swingpress, welcome to the clan.

"I'm looking for an accurate load for USPSA (major) and small game."

I'm taking this to mean they're more then plinkers? So first up you're looking for a GC design

"I've had leading problems with my GP100 in the past, but the last batch of bullets measure .359 and the leading problems are gone."

There can be more to leading issues then boolit size, although I'll grant that that would be my first place to look. I'll take it that the previous batch must have been smaller then .359".

"Can I expect any mold to cast over .359 and leave the finer adjustments to the sizing operation, or will they tend to be closer to .358?

Most boolit moulds intended for the 38/357 will as a rule drop boolits close to .359" and hopefully a tad on the large side of the measurement. This leaves the option of sizing smaller if necessary. Your problem isn't unique :-) Just check the Group Buy forum and you'll see several 38/357 moulds done that spec a minimum of .360".

"If not, is there a particular brand of molds that tend to run on the large side?"

I don't think there is one makers list of moulds that as a rule run toward the generous side. If there is I'm not aware of who it might be. I know at one time Lymans (Ideal at that time) had enough complaints about oversized cavities that they might have errored on the small side a bit too much in fixing it.

I bought a 4 cavity IDEAL from BruceB for a 150gr WC for the 38. The mould was the 35863 and it will drop a slug of dead soft lead at .363"! I'd suspect one cast of lino might go .365". I bought the mould gladly, as I had a couple revolters in 38 S&W to feed.

Remember that the slug (if oversized) is going to wind up being sized to whatever your cylinder mouths are when fired. A bigger boolit might help in case alignment in the chamber, by either making the case larger in OD, and/or helping to center the nose better in the cylinder throat. That is, if it's of a design that would allow it.

"If a larger cast is needed, can a person use an abrasive to hog out the mold a bit as indicated for a different problem in the Lee thread without too much trouble? Presumably Lee molds would be easier to modify since they are softer."

You may to a degree, but the larger you have to go a heavier price is paid in blurring of details. For example sharp corners and narrow features are the first to be affected. Probably better to 'Beagle' the blocks. Have you miked the chamber mouths and slugged the barrel?

Edited to add: Check out the GB forum. There are currently a couple GB's going on for 38 type boolits

...................Buckshot

[swingpress]

I'm taking this to mean they're more then plinkers? So first up you're looking for a GC design.



USPSA major is 1044fps for a 158g boolit. I was hoping to get away without using a gas check. Please let me know if you still feel like I'll need one for sure or be better served by one.



There can be more to leading issues then boolit size, although I'll grant that that would be my first place to look. I'll take it that the previous batch must have been smaller then .359".


All of the other boolits I've tried were .358. I had trouble finding any .359 or bigger.




Remember that the slug (if oversized) is going to wind up being sized to whatever your cylinder mouths are when fired. A bigger boolit might help in case alignment in the chamber, by either making the case larger in OD, and/or helping to center the nose better in the cylinder throat. That is, if it's of a design that would allow it.



My throats are .359. My bore has an odd number of lands so I don't know what size it is for sure.



Thank you both the welcome and the advice!

[Buckshot]

"USPSA major is 1044fps for a 158g boolit. I was hoping to get away without using a gas check. Please let me know if you still feel like I'll need one for sure or be better served by one."

Okay, you shouldn't need a GC for that velocity.

"All of the other boolits I've tried were .358. I had trouble finding any .359 or bigger."

Yup, buying commercial you have to buy what they have. You should give Bullshop a look. Scroll down to the bottom of the page for his website. If you have a lube-sizer press you can pretty easily bump size a WW type alloy SWC from .358" to .360". Lyman makes a .360" size die.

"My throats are .359. My bore has an odd number of lands so I don't know what size it is for sure."

If those .359" slugs are doing it for you, your groove is probably .358" at the largest. And since the throats are .359" you're in good shape there.

...............Buckshot

[Bob Jones]

I have the same problem with one of my .357's. I ended up using small slivers of .001 aluminum tape (found it at the local small town hardware store, it's nothing exotic) between the mold halves. My mold now throws .360 bullets, they work great in my gun. You can also enlarge the Lee sizing dies very easily with some emery paper. The aluminum tape method on the molds is easily reversible, so it's worth a try.

BTW, I'm shooting loads in the 1300-1400 fps range with no gas check, just tumble lubing with Alox, and no leading at all, it just depends on the gun and the load, need to experiment to find the right combination.

[mooman76]

I have about 1/2 dz. Lee mould in the .358 and they all run at least that. they run anywhere from .3585 to .361 depending on alloy and temp. They would be easy enough to lament and get another .001 or .002. Lee seems to be generous on the pistol moulds especially the .357.

[deadguy]

I've never had a Lee mold that made boolits that were larger than advertised. The regular production Lee molds that I have throw the boolits right at their advertised value down to .001" smaller. The .360" group buy molds that I have throw their boolits at .359". So, good luck finding a Lee boolit mold that drops at .360"!