7.92 x 64 from 7.92 x 57?

[wmitty]

I was using .270 Win brass to form 7.92 x 57 for a Zastava Mauser action sporter by running the brass into a f.l. die and then using 5 gr. of 700 X to fireform the case (blowing the neck forward, if that makes sense). I am trying to use the 8mm Maximum design mould which produces a high sectional density boolit (.353) which I thought might make a nice hog boolit. I noticed the portion of the untrimmed case neck which expanded to throat diameter would allow the long boolit (1.245") to be seated with the gas check flush with the beginning (bottom) of the neck if it had expanded to the same diameter as the neck. Now this would make the cartridge a 7.92 by 57mm plus about 7mm additional neck length . Anyway, I like long necks on cast boolit bottleneck cartridges and was wondering if a new reamer would have to be made up to ream a 7.92 x 57 chamber longer (in the neck only) to allow using the full length blown out .270 case expanded to the .357" diameter of the case neck. I realize lengthening the neck would require reaming a new throat.

So my question is, can the existing chamber be modified to allow a 7mm longer neck without having to have a complete new reamer ground? I figured John Taylor or one of the other gunsmiths might be able to answer this. Sorry for the convoluted attempt at explaining what I am trying to ask.

[MostlyLeverGuns]

I have live piloted neck only reamers for 35 cal and 30 cal. Desired neck diameter should be specified if you order such a reamer. I have Clymer from 30+ years ago. Pacific Tool and Gauge or Dave Manson should have them. You can order with an integral throater or throat separately using a throating reamer. I recommend a live pilot for whatever reamers you buy, rent or use. Some of the rental places may have what your looking for. A straight reamer can be made much more simply than other chamber reamers, no taper required, just a uniform diameter.