.31 x 10" Twist

[Good Cheer]

Thinking about maybe lapping out a Lee .309 diameter 200 grainer, to make the bore riding and the groove diameter portions fit the rifle ('98 Mauser rebarreled to 7.62 NATO with .310" groove and 10" twist).
Any yall have results to report with that mold?

[Kraschenbirn]

I shoot that Lee boolit in my '98 Krag carbine. My mould drops .312 at the driving bands with a .302 nose and I size to .311 for the Krag's .309 groove dia. Loaded to approximate the original 30-40 ballistics, it produces 2"-3" 100-yd groups off the bench. Sized to .310, it shoots pretty good in my Swiss rifles, too.

Bill

[Good Cheer]

That's good news. Much larger band diameter than what I'm used to seeing on Lee's.

[Ballistics in Scotland]

Thinking about maybe lapping out a Lee .309 diameter 200 grainer, to make the bore riding and the groove diameter portions fit the rifle ('98 Mauser rebarreled to 7.62 NATO with .310" groove and 10" twist).
Any yall have results to report with that mold?

You mean it doesn't fit that barrel? While it is a good idea to have the bullet a couple of thousandths over groove diameter, it isn't essential.
As has been said, check first in case the mould is solving your (possible) problem by casting oversize. If the bullet isn't in some very freakishly hard alloy I think it would bump up to seal very well. In fact though I don't see that mould in the current Lee catalogue, it is most likely for gas-checks, and
fitting the gas checks in a die of .310 to .312 would probably ensure this.

If you did want to enlarge it, I don't know that lapping it is the best way. It usually works best in a hard metal, with the grains embedded in a softer one. If you can turn a steel duplicate of the bullet, minus nose, but with the lands (i.e. grooves in the steel thingy) a couple of thousandths oversize, you could simply squash the mould halves onto it in a vice. With such a small increase, I think it would all end up reasonably concentric.

[Mk42gunner]

Or try the Lee 312-185, the one they advertise as fitting a .303 British. Mine from several years ago casts a bit over .312", I sixe it to .311 for most of my .30 caliber rifles.

Robert

[Good Cheer]

Digging through the boxes. Found the 308284 blocks and a 311413.
If the 308284 casts large enough and will fit up the bore without too much extending into the powder space, it may work out for a heavy. The 311413 will be tried as well.

BIS,
The Lee molds I've used in .270, .38, .375, .41, .44 and .45 never have dropped bullets significantly over their advertised diameter. If that .309 200 grainer does cast large I will be all smiles, thanking my lucky stars.

[leadman]

If it doesn't cast large enough this is how I have lapped out molds to a larger size. For an aluminum mold I cast 2 boolits for each hole. I drill a small starter hole in the base of each boolit thru the sprue plate hole. I then remove the boolits from the mold and drill the hole deeper so a drywall screw can be started in it. I make a thick paste out of scouring powder and water and coat the boolit with it. Place the boolit in the cavity on grab the handles with a finger between them so you can control the closing pressure. I use a cordless screwdriver to turn the boolit and apply more pressure on the handles as needed. Try to keep the boolit centered in the cavity, clean and check often. I cast new lapping boolits as I proceed to keep a check on progress so have the pot hot. Check roundness as you go, you can put some side pressure on the screw if needed to round out the cavity. This will usually work good for a couple of thousands but after that it is too hard to keep the cavity round.

[Ballistics in Scotland]

That sounds good, but a sprue plate hole is rarely truly centred with the axis of the bullet. So you are doing the right thing by using a cordless screwdriver. If without one, I would attach a long wood or metal rod, and roll it on my knee. A high speed electric drill turning an off-center bullet is liable to vibrate and wobble, but a more slowly rotating lap will follow what is in the mould blocks.