400 GNR - Short?

If you factor a .400" bullet then a 0.010" average case mouth thickness on the full length cartridge (it gets thicker as you shorten it) you end up as big at the mouth as at the base diameter. I argued with Dave Manson, who designed the .400 GNR for Gary, that I didn't like his taper dimensions. He said they are necessary for extraction. I've personally found Starline "thin" wall .38-55 brass most suitable for .400 GNR easy forming and shooting. It is about 0.008" thick at the mouth. So figure a .401" cast bullet + 0.008" + 0.008" = 0.417" (about right). Thing is, Manson's chamber is only 0.418" at the mouth tapering from a 0.420" base. That is as thick as you can tolerate for brass, and as big a bullet that will fit. You can play with going to a .400", but it just gives you a badly needed thousandth. The once fired .30-30 brass I measured ranged from 0.009-0.011". Most were right at 0.010". You can't run 0.418", you need some slack for variances or dirty chamber etc.

The .225 Win. cases I examined were simply .30-30 base cases with a different rim, so it fit the .30-06 bolt face.The small but thick rim it makes is robust, but does not reinforce any pressure bearing part of the case that I can see, it's great for extraction. I could not find any .225 cases for making 7mm Merill so I made some from .30-30, cutting the rims in my lathe. They worked fine after trimming down, necking, and fire forming.

JD Jones necked the .454 case to 10mm for the Encore handgun only. But it shoots the 10mm bullets about 1000 fps faster (or more) than they were ever designed to go. I don't think it would be too good for a wheelgun. GNR's .429 GNR and .410 GNR are about as necked as you should go, at higher than .44 Mag. pressures. They work fine, there is a point smaller (neck-down ratio) where they begin to prematurely stick. Gary's .300 GNR is an example. His .30 on the .357 case might even be better. But the brass that far down on a .30-30 is quite thick and they usually don't stick with a little care. As the firings add up the brass looses resiliency and they all stick. Time to retire those cases.

Look over this drawing and see what you think. I find the conversation very interesting. I am considering reworking my chamber to what "I" think it should be. If I ran a 10mm "magnum" reamer into the chamber to the chamber mouth it would change it to 0.423" mouth - 0.425" base. Still tapered but big enough to handle most varied .30-30 brass thicknesses. Since it is made world over the dimensions do vary wildly. Rim thickness too, but that is another story.