I have a new mold for my double rifle, and it casts nice 650 grain x .620 diameter bullets to match my .614 x .621 grooves and lands. Before I was losing considerable accuracy with a mold producing .615 diameters. So far I have not shot the new slugs, and wonder since these go into the cartridge with a lot of pressure, have I gone too far with increasing the diameter? I definitely do not need to crimp these at all, where I had to put a real hurt on the old ones to keep recoil from moving them. I cast with WW and do not cold drop them, but let them cool at ambient.
Thanks all!

Your original bullets were too small and prob were gas cutting in the .621 groove barrel. Your new ones are still .001 small, which, for cast bullets is usually bad. Will they chamber? That is more important than how hard they seat in the case; you can make a bigger expander if that is an issue. How hard are they? Soft bullets might work better as they will bump up. With black powder, that will work; with smokeless, not as much "bump". Wheelweights? really should be groove dia or bigger. Use a base wad.

I measured one of the ones that I took out of a loaded case, and what is happening is, that case itself is acting like a swage, and reducing the bullet down. These a very heavy RMC cases, and don't give a bunch. I am going to make a slightly smaller mold, and then force both the new bullet, and the ones down the barrel to see how well they really FIR THE GROOVES. The much smaller .615 were definitely too small, never worked well.

From what I understand, you want the bullet to be .001 larger than your groove diameter. I think it's just a rule of thumb, though.

It sounds like your brass is too hard and the expander is too small.

Your brass needs to be annealed down to about .150 below the base of the bullet.

But first your bullet mold needs to produce a bullet that is .001 to .002 oversize. Even .003 to .004 oversize is not normally a problem.

I hope your barrel is not thin walled because the best results with cast bullets come from softer oversize bullets.

Once you get a bullet the right size have 2 expander plugs made. One should be .001 under the bullet size and the other should be .002 under.

Load up and see if the bullet is damaged with a .001 and .002 expander. See if the bullet is secure with either one.

You may need an really undersize expander for hunting loads. Range loads ande practice can be loaded with the .001 under expander.

The lead alloy that you are going to use depends on how fast you want to go.

Can you say what your top FPS is going to be?

Do you have a neck expander die? I suspect it will have to be custom cut, but you definitely need one; it swells the neck of the case enough so the projectile goes in un-damaged.

quote:

...I am going to make a slightly smaller mold, and then force both the new bullet, and the ones down the barrel to see how well they really FIR THE GROOVES. The much smaller .615 were definitely too small, never worked well.

That will not really tell you how they will fit when fired. Some undersized Lead bullets can slug up when fired to better fit the grooves....others will not. It depends on the alloy hardness and the chamber pressure.

It is best to use bullets at or slightly above groove diameter but some chambers do not permit this. As stated above the OP should obtain an expander plug either at or a few thousandths under bullet diameter. This will hold bullets firmly without damaging them.


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I don't have a neck expander, but can make one, also, I annealed the brass, but possible not enough..This RMC brass is very thick, and may need another time under the torch and water...Thanks all, I'll take everything into account. It is nice that these do not need a crimp though as recoil is a bit heavy even with the reduce bullet and load..

quote:

Originally posted by MotelAlpha:
I don't have a neck expander, but can make one, also, I annealed the brass, but possible not enough..This RMC brass is very thick, and may need another time under the torch and water...Thanks all, I'll take everything into account. It is nice that these do not need a crimp though as recoil is a bit heavy even with the reduce bullet and load..

Water has nothing to do with annealing (softening) the neck and shoulder area of the brass case, it is only used to stop excess heat traveling further down the case towards the base.
Best annealing is achieved if the case can be slowly turned while held in the flame so the heating is even and just to the point of colour change, not dull red as some mention.

Definitely need to have a neck expander to give a slight flare to the case mouth and then you will find the cast bullets will ease nicely into the neck. If you have good dies your bullet seating die should actually size the flare back down again so the cartridge will chamber perfectly.

I turned down the flaring plug in a 45ACP die for my 404 and set up the die so that when the shoulder contacts the mouth of the flaring die the plug has put just the right amount of flare on the case mouth to enable a cast bullet to sit snugly in the mouth as the whole lot is put into the press to seat the bullet. The seating is nice and smooth and my seating die straightens the flare ready for crimping, not that I need to or do crimp.

On the odd occasion where I have forgotten to flare a case and not noticed the bullet not starting too well by hand into the case, the seating process is very noticeably harder with high neck tension.