PETE
posted this
27 March 2008
George,
What are your breach seat rifles throats set up like for your tapered bullets??I had never given any thought to that.
The same applies whether your bullet is straight or tapered. When I have a gun chambered I go with a 1/2 degree included. Some will go with a 1 or 1 1/2 degree throat. This might seem excessive but only amounts to about a 5/8” long throat.
The idea when breech seating is to shove the bullet up into the throat till about 1/2 the base band is engraved. With your straight sided bullet the sides of the bullet should show even engraving all around it. If not you know it's not going in square. This is nominally about 1/32” to 1/16” ahead of the case mouth. This is also one of the dim.'s we play with as a coupla thousandths one way or the other can markedly improve accuracy. Most of the Schuetzen shooters will size the base band .001” to .0015” larger than the groove diam., or the whole bullet if straight sided.
With fixed ammo I would cut your throat so just the base band is in the case and the bullet is tight in the throat. Sound familiar?? :) Just about what CBA shooters do preparing GC match ammo. Engraving should show evenly all around the sides of the bullet to show it's centered up properly.
Also when sizing your case either don't size it so that it squeezes that base band, or use an expander plug that is the same size as your sized bullet. That will put on just enuf “squeeze” to hold the bullet, yet “loose” enuf so the bullet can move and adjust itself to the throat without deforming the base or base band. .003” seems to be about the max. pressure you can put on. You can't be to careful here, and if a pulled bullet shows a change in dim. then make a slightly larger expander plug.
Custom guns today usually have the chamber, throat, and bore lined up fairly well. But I have heard that factory guns are something else so you need to have a way to allow a fixed ammo bullet to move if needed without deforming it. Factory guns made back in the Schuetzen era were not lined up to well either, maybe worse, and that's why breech seating came into being.
The whole idea, whichever way you do it, is to get the bullet lined up central to the bore, without deforming the base, and into the rifling tight enuf that you don't get blow-by. Thus the nice gradual throat. PB bullets just won't take the “kicK", or abuse in seating, that a gas checked one will.
As you can see all this care is that PB bullets are easily damaged and you need to mould them out of a relatively soft alloy if breech seating. I use 1-25 Tin/Lead as a good starting point. I've never tried it but I think a bullet cast out of something like Lino(especially a straight sided bullet) would be pretty hard to breech seat. Have to try that sometime.
PETE
