Why lap dies to a mirror finish?

[customcutter]

OK, maybe it's a dumb question, but I'm going to ask it anyway. Why does a die need to be lapped to a mirror finish? Millions of rifle and pistol chambers have been reamed. Their chambers have little brass cylinders inserted and fired at 50-60,000psi and the brass is ejected no worse for the wear. Has anyone tried reaming a die without polishing to 1000grit and tried it? I'm not convinced it's necessary, if you're not trying to shoot 1/4 MOA groups. As long as it is reamed and symetrical(sp), no burrs, etc. I don't see the need. You're going to have to punch it out anyway.

CC

[Reload3006]

so the bullet will release cleanly from the die.

[customcutter]

Exactly my point, all those fired cartridges in those chambers release, and they are fired at far higher pressures than I'm probably capable of with my little Redding Ultramag press.

[Cane_man]

cc i like the way you are looking at this from different angles, but with your analogy of the cases they are empty and have nothing pushing them against the chamber walls anymore and they can flex some to be ejected, but the swaged cases have the lead formed inside of them keeping pressure on them against the inside of the die... just my opinion

when i made my swage dies for 40/10mm the swaged cases released much easier after the dies were hardened after heat treating, and also the more i polished the die...

harder & smoother surface = lower coefficient of friction, makes the cases easier to eject from the die

that is why i am taking the extra time for heat treating and tempering, and polishing the die as best i can

[LatheRunner]

When a brass cartridge is fired in a gun the brass will swell to the diameter of the chamber and then it will shrink back down a little. This allows the brass case to eject from the chamber. In a swagging die the finish has to be real smooth to allow the swagged bullet to be pushed out by the ejection pin. If there are any ridges in the die the bullet will get stuck and you will bend the ejection pin.

[customcutter]

LatheRunner,

I agree if there are any ridges, you ain't getting it out. Also your die is not properly made. The only rifle I ever fired I couldn't get a case out of had a burr in the chamber. A brand new Sako 7mm magnum about 30 years ago. I returned for a Ruger 30-06, because they didn't have another Sako, and I needed a rifle to go hunting with that weekend. I'm still kicking myself over that decision. They were actually the same price, because the Sako was on sale for about half price.

Cane,

I agree with your analysis that the empty brass shell shrinks back, and the lead in the case will keep it from shrinking. You said your .40's were easier to eject. 6oz ball peen hammer vs 2lb sledge? One tap vs. two? Did the tips deform you were striking them so hard? Just trying to be subjective, not being argumentative.

I guess experience is always the best teacher, I guess I might have to make one and try it myself.

thanks,
CC

[BT Sniper]

Don't forget the actual caming action in the design of the bolt to remove the case as you lift the bolt. Plus the ejection groove on the case that the bolt grabs on too to pull the case. We have none of these available when attempting to eject a bullet from a die.

A lot also depends on the size of the ejection pin used. On a 500 call bullet/die with a .312 ejection pin the surface isn't quite as critical, with a .062 ejection pin in a small caliber riffle die, very critical.


BT

[customcutter]

Don't forget the actual caming action in the design of the bolt to remove the case as you lift the bolt. Plus the ejection groove on the case that the bolt grabs on too to pull the case. We have none of these available when attempting to eject a bullet from a die.

A lot also depends on the size of the ejection pin used. On a 500 call bullet/die with a .312 ejection pin the surface isn't quite as critical, with a .062 ejection pin in a small caliber riffle die, very critical.


BT

Yes, you're absolutely correct. However, my .41 magnum doesn't have a bolt or any camming action. Fire six shots, slip the cylinder lock forward, rotate the cylinder out and they slide out like they were on hot butter. I think it's because the cases are shrinking back slightly after they expand. However, as a couple of people have noted, after you seat the core the lead is keeping the brass from contracting back. Again not trying to be argumentative, just trying to think outside the box.

thanks,
CC

[EDG]

>>>Exactly my point, all those fired cartridges in those chambers release<<<
This is not even close to an accurate comparison. A cartridge case is elastic. It pulls back from the chamber walls and will fall out without any force being applied with normal pressure.

[DDriller]

The chamber is made to grip the case when it expands when fired. This helps in keeping some of the back thrust off of the bolt face. Mirror polish of a swage die and good lube aids in the release from the die.

[Idz]

I've been reading some old gunsmithing books and the way they get swaged bullets to release is to build the die in two pieces. A tapered nose section and a cylindrical body section. They say the bullet will stick in the body section so you remove the nose section and just push it out. Today it looks like the dies are built as one piece with a tiny pin that will hopefully push out the bullet assuming everything is perfectly polished, lubed, and pressed just right. It seems a two piece die would be much more forgiving of amateur's mistakes. Any thoughts on that?

[perotter]

I've seen pictures or illustrations of two piece swage dies. It was the only ones shown. I think it was in a WW1 era technical book on ammunition manufacturing. I'll have to look around and see if I can find it.

[perotter]

The picture I was thinking of was for full metal jackets for 30/06 bullets in the WW1 era. The steps in the process for this are/were different than for for what most are doing here. There are more steps and more dies in the process. Forming the nose is a multistage process and was finished before the core was put in the jacket. Without automatic equipment, there is many times labor doing this. And pulling a lever on a press isn't my favorite thing to do.

There is a video on making bullets at an Eastern European factory that shows using cores that have the nose shape when they are put in the jacket. are. If one cast the core with the nose shape, the die MIGHT not need to be polished as well.

FWIW:
The same book has making 8mm Lebel bullets(solids) with a two piece die set. I didn't restudy it in detail last night, but I'm reasonably sure that left flash on the bullet that was removed latter.

[Idz]

In Vickery's book "Advanced Gunsmithing" he shows a 22 LR de-rimmer and a 2 piece die and press to make 22&25 caliber bullets from 22 LR jackets. He says if you get a slight flash you just run it through the body die section to remove it. Surely these bullets would be more than adequate for plinking loads.