Pound Slug Made...Now What Size?

[5Shot]

Free Bore measures 0.3110, the Groove measures 0.3093 - what sizing die should I use? From what I have read it should fit the throat, but how much clearance, 0.3100, 0.3105, or ?

[leadman]

If there is enough neck clearance in a case fired in your gun to load a .311" boolit this will fill the freebore area to prevent gas blowby. If the neck does not have enough room to load a .311" boolit so it will release the boolit safely go to the next size down. A too tight neck will cause the pressures to increase, sometimes dramatically.
I have a gun that I have to load a smaller boolit than bore size so I went to a softer alloy and a poly-fil filler in the case. Shoots very well with no leading.

[geargnasher]

Go .311" or a couple tenths smaller, and make sure the neck is concentric with the body of the case (measure it or roll it on a flat surface and look for the bob).

Measure the inside of the neck of a case fired in that rifle, after you have removed all traces of crimp or rough case mouth, that will be close to your max safe bullet diameter. I'm betting fired case neck ID will be several thousandths larger than your throat dimension.....but you already made a pound cast so you have chamber neck ID right there, just measure it and subtract your neck thickness times two and subtract another half-thousandth from that to get the absolute safe maximum bullet diameter you can use.

Now, keep going, and observe the leade angle and freebore to determine what nose shape will work best with your rifle.

Gear

[5Shot]

The rifle is a 2010-ish FN M70 Winchester. I compared the pound slug to the SAAMI chamber drawing for a 308 Win, and it appears to be a match - mine being +0.001 over SAAMI Minimum specs.

I have begged a few samples from members here, and I will be doing some experimenting.

[5Shot]

Neck measures 0.3450", and based on a loaded round with a Jacketed Bullet, I should have about 0.002" clearance on a loaded round with a 0.311" Cast Bullet.

[geargnasher]

I doubt that you'll see clearance that close. Most case necks are around .0013" to .00135" nominal thickness with thicker parts being between half and one thousandth thicker, which will give you about seven thousandths loaded neck clearance with a .311" bullet, which is a whole bunch but unfortunately, quite typical.

The chamber neck should have a good bit of taper to it, usually .3435"x.3450" or so. I always measure in the middle of the neck to keep from confusing myself.

Gear

[runfiverun]

dang.
if it's that tight you might just better sell me the rifle.

[5Shot]

dang.
if it's that tight you might just better sell me the rifle.

Sorry...Gear was closer. I forgot that the case I measured was resized from a 30-06 case and it therefore had a really thick neck.

[geargnasher]

That's a useful trick, 5-shot, don't forget about it! I took up something like eight thousandths neck clearance in a 7mm-08 using reformed '06 brass.

Gear

[5Shot]

That's a useful trick, 5-shot, don't forget about it! I took up something like eight thousandths neck clearance in a 7mm-08 using reformed '06 brass.

Gear

I will - I'll find some sap selling a pile of military 30-06 brass with cracked necks and I'll get them for $1/lb!