MP-312-440 gas check shank issue

I have a 4C, MP-312-440 mould that I got from a board member in Australia a few years ago, and I finally got around to trying some boolits that I had cast right after I rec'd the mould. Alas, now years later, I discover that the gas check shank measures .288-.289 and neither the Hornady nor the Gator .30 cal gas checks fit on easily. The alloy used was 10:1(ww:lino). Could I "shrink" the gas check shank diameter with another alloy? If so, what alloy should I try? Is there a better solution?
The mould drops 4 boolits, each time, all hollow pointed very nicely, and the boolit diameter is .314, which sizes down nicely to my desired .311. Any suggestion to a solution will be appreciated. Thanks, --Shuz

Coupla' ways to go about this. First you could build or buy a gas-check flare tool (I believe NOE sells one). Then you give a little loving attention to each check you want to use and it should go on OK. Once the check is started nicely the sizing should finish it off.

Or get a Star sizer. Since I figured out how wonderful the Star is for applying gas checks I have never looked back. I won't tell you how many years I stupidly thought I had to get the check seated straight before the boolit went into my Star sizer, but it was too many. You put your boolit nose down in the die, run it down until the base is a bit below the die top, place check on top and run her on through. I think the Star could seat a 7mm check on that 30 cal boolit as long as you have good sizing resistance (which you certainly do going from .314 to .311).

Over on the Gas Checks portion of the forum there a lot of folks talking of annealing the gas checks in an oven to soften them just a bit.

I have several MP molds and the only one that has ever given me issue is a 311-159 mold. They have to be pressed on to get them on the shank and square. All of my other GC molds in various calibers are spot on and Hornady checks go on with a slight snap.

Anybody been able to decrease shank size by changing alloy?

I got nuthin' for ya except to say I feel your pain (literally).

While mine isn't the 440 (I have the 312-640 Sledgehammer) I am going to have to get tricky to get checks on my bullets. As mentioned, try annealing as it can't hurt and may well help. It's only the MP 312 mold that makes a fat shank for me. My 357 and 44 MP molds let the GC click on no problem even after being PC'd.

Try a lead/tin alloy (20/1 or so) and see. I know the binary mentioned doesn't grow over time. The problem is they are soft and if you've had to go caveman like me to get the checks on, 20/1 won't like it as much as the harder alloys.

I ordered a NOE 30 cal expander today and don't look forward to doing all those checks! I didn't like pointing my HP rifle bullets either!

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I have 312-440 in PB and GC version, both 4cav. Cast with ww at the beginning, last ones on a photo are ww/pure (1:1) and in both cases Hornady GC’s snapped on perfect, but tight with finger pressure.

I did one batch where I powdercoated them first (purple), then attach GC with push through sizing die. As you see, too tight as I shaved a bit of coating from base.
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My solution was to take a marbles to slightly widen mouths of GC, then attach GC. I used reloading press: putting GC on a top of push through sizing rod, put a marbles on top of GC, then slightly pressed marbles up, against some flat surface (don’t damage threads in reloading press)
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My limited experience with very hard alloy- it grows. My super hard 9mm sized to .357 went to .358 in 1y. My softer alloys stays pretty much the same.

I make my own checks so I adjust the dies and use a different thickness of material fo the checks