Okay, lets figure out what you really want here because you have haven't really told us what you are looking for.

Oh, before I get on a roll, the reamer is the easiest. I have one in my tool box. I got mine from JGS Tools. http://www.jgstools.com/ Pacific Tool can make you one also. http://pacifictoolandgauge.com/

Just specify what barrel dimension you are need, because CIP is the standard and for .467 groove barrel. That is what my reamer is.

The barrel.

What part of the Martini barrel do you want?

Henry rifled?

Tapered bore?

.464 cylinder groove, .450 cylinder bore?

You could use a barrel from a MK IV Martini, either as is, or turned into a sleeve and inserted in blank.

TJ Barrel liners can furnish you a Henry rifled barrel straight cylinder .464. I have a 30 section here in my shop. Wanna buy it?

I believe at one time Krieger barrels made Henry rifled barrels. I could be wrong. Badger barrel did before the sold out.

Or do you just want a 577/450 chamber in a standard .458 groove barrel. Any barrel maker can provide that.

Once you decide which barrel you want can tell the reamer maker to make the throat and neck of the reamer to match the barrel dimensions.

If you stick with CIP yoi will be fine for reloading dies.

If you go with .458 dimensions, you are going to need to have a resize reamer made also. This reamer you can send off to some one like David Davidson at CH4D tools and have a set loading dies made.

The Gun.

I don't think the Encore action would big enough, you would have measure and find out. If it was, go for it. My choice would be the Ruger number 1.

This next part may sound negative, but it's not intended to be that way. just read with an open mind.

There are two types of people who would even consider this project.

1. Some who is intrigued with the Martini 577/450 chamber and has no experience with it.

2. Some who is intrigued with the Martini 577/450 chamber and has lots of experience with it.

Which am I? This why I have a reamer.