Let's Discuss Expanding Dies.

[wv109323]

If you were to to seat a .432 bullet into a .44 Magnum case what size would you want the neck expanding die to size the I.D. of the case?
I am working with a Marlin 1894 in .44 Mag.
I have a set of RCBS carbide dies and the neck expanding die is .425". ( Per RCBS that is the correct dia. for .44 Mag.) With Jacketed bullets at .429 that is .004" interference. With a jacketed bullet I would expect the bullet not to be distorted and the brass case would expand to accept the .429 bullet.
I am using "As-Cast" Lee 245 gn. SWC at .432 on the top bands and the driving band at .433. When one of these cast boolit is seated and pulled the diameter is between .428 and .429.
Or in other words the cast bullet is being reduced in diameter from .433 to .428 or .005" by my current die set.
Is there a rule of thumb as to the dimensional relationship between a neck expanding die and the boolit diameter being used?
Why would RCBS sell you a neck expanding die that is .004" less than the nominal Diameter of the bore?
By the way I inquired about the expanding die in the "Cowboy" die set and it is .428". The "Cowboy" die sets are meant for shooters that are using lead boolits.

[MT Chambers]

Well you're right about the Cowboy dies, I'd just buy a larger expander for your die, RCBS makes them.

[wv109323]

MT Chambers,
I agree that a larger expanding die is needed but what is optimum for a .432 Boolit? My guess would be .431.
Since the original post I measured the expanding dies on my Star presses. The one for .45 ACP was .452 for .452 Boolits. The one for .38 Special was .357.

[Mal Paso]

The RCBS "Cowboy" expander Plug is .430 and sells for like $5. Call Them

[wv109323]

RCBS Tech said the "Cowboy" Expanding die is .428. They will make you whatever you want for $26.95 plus $4.50 shipping.

[Doc Highwall]

I would suggest .001" to .002" under your bullet size. With HARD Cast bullets you could go .003" but I would stay with .001" to .002" under your bullet size.

[GBertolet]

Similar problem with my 29 S&W. Cylinder throats mike at .433. I have a mold that drops at .433, and in seating the bullets, the case was swaging them down. My expander ball miked at .4275, I called RCBS also and got the same response as you did. I'm not much of a machinist, but I have access to a lathe, and found a piece of 3/4", of what I believe was drill rod, I made my own. I cut the threads and made the expander ball oversize, and after I got done polishing it up with emery cloth, it miked out at .4315. I don't know if I will have to harden the plug additionally, even though I can file the steel, it is pretty hard. It seems to work fine. I love it when a plan comes together.

[EdS]

I'm not sure if it makes as much difference in a rifle (the thread starter mentioned a Marlin) but in a revolver, we need to find a balance between minimizing the sizing by the brass case and avoiding having the boolit pull through the crimp during recoil. The cowboy dies are worth a try, or a "special order" expander if you have RCBS dies already. -Ed

[gray wolf]

My RCBS 44 mag expander die is .4265 My bullet are .432
.4265 is to small for my bullets, I called rcbs and they simply said
" We can send you a .430 cowboy expander NO CHARGE. " and they did.
.002 was not quite enough frictional hold for my bullets and alloy so I polished it down to .429 and I'm happy with that. I also have custom M-die plugs that are
.4275 .4285 and .4295 I don't like my M-dies cause they don't flare the case mouth enough and lube gets pushed to the top of the bullet. It's an extra step I don't like, wiping of the bullets--just me I guess. But they do hold the bullet in-line.
Much depends on case wall thickness and how uniform that wall thickness is
from case to case and different manufacturers, and of course bullet hardness.
For me the bottom line is
" enough frictional fit to hold and not jump crimp AND not to reduce the bullet "
IMHO I don't think .001 or .002 is quite enough hold unless bullets are very soft,
With very hard bullets I understand the factory expander works fine.
Hard bullets = load like jacketed. Don't know for sure cause my bullets are about
50/50 WW and PB air cooled.

[Mal Paso]

RCBS Tech said the "Cowboy" Expanding die is .428. They will make you whatever you want for $26.95 plus $4.50 shipping.

Hmmmmm. RCBS Catalog says .430 (and $8). Thanks! I'll call them before I order one.

Brass springback on 44 is ~.002. I am currently using a custom .430 expander (.431+ boolits) with good results, just not enough flair.

[farmer66]

My Cowboy expander measures 0.4292 and replaces the original that was 0.425 inch. It works well, especially for my 429421 Lyman, but is a little short for my Lee 310. My "expanded length" measures about 0.015 shorter than the original expander, and the original was a bit short as well. Probably the gas check on the Lee expands the brass adequately?

Ken

[geargnasher]

The .44 Magnum needs a bit more case tension than most rifle or pistol cartridges do, so is one of the "exceptions" to any common rule of thumb we might come up with.

For soft boolits and mild loads, .002" interference fit between expanded case and boolit is plenty, much more and you'll swage the boolits when seating. Not much recoil to deal with there, anyway. For hotter loads, you really need harder boolits for best accuracy long-range, and .004" interference fit is more in order to provide good tension and consistent boolit pull. You will need to size your expander to compensate for what ever springback your brass is giving you. At that rate, you'll be able to see the lube grooves through the brass when the boolit is seated, that's a good thing as long as your boolits are tough enough to take it.

For most of the larger calibers using cast boolits, .002" is about right, for .30 caliber and under rifles, about 1.5 thousandths tension works best for me.

Gear