Modified 31141 for PP ?

About ten years back I won a 31141 single cavity mould on eBay which had the gas check shank removed to form a plain base design. I had asked the seller if the modification resulted in a mould casting same dimensions on drive bands and base; he assured me it did. Upon arrival I discovered the base to be machined concentric with the bands but as cast the base measured.320” . Well, I decided not to get upset about the seller’s fabrication regarding base diameter, as I thought I might be able to use the boolits by running them thru the lee .311” push thru die. Anyway, could the mould be lapped larger on the ogive/ drive bands to .316” to allow the boolits being used as a pp projectile for a .32 special or an 8 x 57? I have opened sizing dies using boolits embedded with lapping compound, but haven’t tried enlarging a cavity.

I would say six thou is a lot to lap and keep everything honky dory.

You may need someone with a lathe with a 1/4" ground hss boring bar a couple of clocks and good measurements.

You could end up with a slick bullet mold at worst.

Hopefully someone with sense will be along soon to help.

I'm with you there barrabruce! I find lapping much over about 0.003" is tough to keep the cavity round and lube groove edges sharp. I'm thinking 0.006" is a no go!

I'd also think sizing down the base band by 0.005" is a lot to go without distortion.

Likely easiest to bore or ream to 0.316" or whatever larger diameter is suitable for your .32 Special or 8x57 needs...

https://www.amazon.com/Diameter-Carb.../dp/B00K36BN3E

Longbow

I’ll just hang on to the mould for use as a plain base boolit. I can bevel the base edge with a file after running ‘em thru the .311” die. Thanks, guys!

I PP the 311041 as cast from 1:1 WW:lead for 8mm. The paper I use is the wrapper paper from reams of copier paper which is .004 thick. Two wraps works great. The mold castst at .314, so I size them to final diameter of .325.

Hah! This reminds me of when I decided to PB my Lyman 314299 that cast undersize with wheelweights. I decided to lap it and remove gas check shank. I made a "D" reamer to cut just the right size to match the driving bands but made the mistake of running this in the lathe under power. Unfortunately the tailstock quill has a bit of slop and doesn't sit exactly on center so the mould spinning in the four jaw chuck got reamed and then scraped a bit large... about the same as your mould at around 0.320". I didn't sell the mould to someone else though!

Had I turned the chuck by hand and reamed the gas check shank out that way I suspect the D reamer would have cut to size. Oh well. I now have an NOE 316299 that casts to perfect size with wheelweights.

Seems to me I sized and shot some of those PB boolits with reasonable success but my bubba'd mould bothered me so I replaced it. I kinda, sorta punished my self by buying a nice new NOE mould. Not much of a punishment!

Longbow

Well , longbow, that is an outstanding idea!

If you are looking for a .30 cal. paper patch mould NOE has two:

https://noebulletmolds.com/site/shop...ity-gc-301618/
https://noebulletmolds.com/site/shop...ity-gc-301620/

I lied! They have four! Two above are for standard .30 cal. and two below are for .303 British/7.65 or fat bored .30's:

https://noebulletmolds.com/site/shop...gc-1pb-303618/
https://noebulletmolds.com/site/shop...ity-gc-303620/

I originally made a push out mould reamed to 0.301" for my .308 which worked fine but when I tried the same core and paper patched to suit my .303 Lee Enfield groove depth things didn't go so well. I wound up knurling to bring the diameter up to 0.303"/0.304" then patched to groove. That worked. My understanding is that the rule of thumb is cast/size to bore diameter minimum or up to a couple thou over then patch/size to groove diameter. That 0.301" was just a hair small... and also smooth which may have played a part.

Like a guy needs an excuse to buy a new mould eh?

Well, I just looked... don't get too excited! Most are shown as out of stock. There are a couple of the 178 gr. 0.301" moulds in stock.

Longbow

I believe it would be possible if you took your time and made a few trial casts along the way, I have lapped a few moulds out by 4 thou or so and made a 378 lee cast sizer from a 357 die and it is as near as perfect as one would get. When I lap moulds out I keep the blocks closed in a vice as they have a tendency to open and make cavity oval. Regards Stephen

Thanks for the tip on the vise, Stephen. I may still try and lap this thing larger on the upper portion of the mould. I’ll check the as cast diameter on this upper portion and see how much I need to increase the diameter in order to reach bore diameter on the Marlin .32 Special and the Zastava 7.92 x 57.

If you wish to only lap one section remove a good section of contact material from the Cast where you do not wish metal removed eg if I want to open a mould up I remove a good amount of material from the shoulder forward yet leave the nose in place as a guide if the makes sense. I have enlarged my gas check area in the same way by removing metal from area I do not want lapped, stop and clean often and make castings along the way. I should mention the vice I like to use in a small hand vice which I hole in one hand while lap with the other, I find the movement of both hands in unison seems to get a more accurate lap. I hope this helps and remember slow and easy checking often and all should go well. Regards Stephen

just edited that for clarity I hope. Regards Stephen

I probably should not even jump in on this conversation not knowing what your bore/groove diameters are in your rifle. A lot of times I read some posts here were some use a groove diameter GG or even a jacketed bullet and patch it making it way oversized for their groove diameter.

If the concentric is not past the driving band it can be saved indicating the mould block properly and match the lower band.
Then all will be well.

But that mould block can be saved but lapping is not the answer trying to make a concentric round, it takes a mill or lathe.
I f the cavity of that mould is less than the caliber you want to use it in you can make a duel diameter like the bullet in the photo that is patched to bore on the shank and the base is patched to groove diameter.
I converted this mould for that purpose but it's a .44 caliber.
Save the mould block and if you ever get a larger caliber like a .38 or .40 and recut it.

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