If I was to take that on, I'd make a steel case up to the neck, and chamber ream it to take a 45-90 case.  That way, you'd have long lasting piece of brass, much more durable than turned brass, and you could replace the case after it got worn out.   

the .45-90 would fireform to take the larger bullet of the 577/450, and that would lock it into the chamber adapter/case nicely.

It'd be easier to turn the steel half cases than it would be to turn brass cases, with the thin neck section.

As Gert mention there is an issue with  Martini chamber dimensions. These guns predate standardization.  The cartridge had a steel head and a brass foil body.  Only the head was standard.  The shoulder length varies slightly but enough to be inconsistent.   The shoulder is an ogee with varying radius. The is no correct OAL for the case.  In fact the case mouth section of the chamber is the same as that seen for heeled bullets. The throat is the same diameter as the outside of the case neck.  Throat diameter is between .468 to .472 in a bore that tapers from .468 at the breech to .464 eight inches from the breech.  

The South Africans only had turned brass and they fit the brass to the gun by filing and sanding to fit.  The usually made an index mark in the rim and timed the brass when they loaded a round. I have 5 rounds of turned brass sitting here on my desk-new unfired that I brought back for SA. A .468 bullet will not fit in the neck, a .458 will.

This brass was bored straight internally and had slightly more capacity than 45/70.  

Turned brass is made for bar stock and does not have the same characteristics drawn brass.  It is hard, but brittle.  It tends to split longitudinally, even in the thick heavy body.  

If you run turned brass into  sizing dies it has a tendency to stick-it does no have the elasticity qualities of drawn brass.  Trying to pull a case out the die tends to rip off rims.

Although some may do it, I would never suggest shooting smokeless in a turned case.  Even the semi balloon head shotgun case are nor safe with smokeless.  They showed a propensity to bulge head with pyrodex.   

For smokeless use only solid head drawn brass.

dragonblood9 wrote on Aug 22^nd, 2025 at 6:52pm:



What gun are you shooting? An original Martini Henry?  That gun has a tapered breech.  it starts at the  breech at about .468 to .472 major diameter, depending on which gun you have.  It tapers 8 inches up the bore to the cylinder  portion of the barrel where it is .450 minor diameter/.464 Major diameter.

Notice I am saying major and minor diameter.  No lands and grooves as we know them,  Rather peaks and flats.  The minor diameter is the top of the peaks and center of the flats.  Major diameter is the corner of the flats at the bottom of the peaks.

If you are going shoot smokeless get some Bertram cases.  They are solid head. Do your research.  This is a massive old bottle  black powder cartridge.  If you apply American straight wall cartridge loading techniques, even with black powder, this cartridge will punish you.  Bottle neck technique is different.  

The late  Mike Venturino wrote an article on the 577/450.  This cartridge beat him. He expressed a strong dislike for this gun and sold it right after.

The standard load for the 577/450 is 85 grs Fg.  Mike and  others using American straight wall black powder cartridge loading methods seem tocenter around 109 grs of FFg.  I can assure you that load is unpleasant 

If you are going to shoot smokeless in this cartridge learn Nitro for Black loading technique. (NfB)  Acquire a copy of Shooting the  British Double  Rifle by Greame Wright.  He goes in to great detail on the process, and is backed by Birmingham Proof house testing.  The book is available from Buffalo Arms.

If you use a program like load from a disk, be careful.  I did that some years ago trying to build smokeless loads.  Recoil was so vicious that after two or three rounds, I had to stop shooting because my arm went numb.

When I did learn NfB  load is saw great potential.  But I never did follow through as shooting black was more fun.  One of they things you will need to learn is the difference between a filler and wads.  Sometimes they are the same thing but they are not always.  Lots to learn there.

Let us know how we can help. 

Let me give my sincere advice.  Don't try to re-invent the wheel on this one.  The Brits perfected it in the 1880s.  Just strive to duplicate their load.



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The bullet to be used can be had from Buffalo Arms.  Theirs is swaged of pure lead, but works just fine.  The diameter you want is .449-.451.  Theirs is .451 and works great. 
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Patch it with onion skin paper.

Use 24ga. MagTech brass shotshell cases necked down and trimmed.  You can do that yourself, or there is a guy on the British Military Forums named Martyn Robinson who will do it for you and charge a very reasonable price.  These cases are balloon head, which you want because it gives you the original interior case dimensions.

Use 85 grains of 1F or 1-1/2F black powder.
Stuff cotton, dacron, kapok, or other wadding on top of the powder and up to the bottom of the neck.

Then figure your wad stack, card wads and bullet lube, to meet the base of your bullet at proper OAL cartridge length.

The result will work if you do your part.

Here's what they look like:

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And here's what you can reasonably expect:

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Believe me, the recoil is nothing to fear.  These rifles are big and heavy and designed to handle it.

Good luck,
Curly

thanks for all the input fellas.  I now have ~30pcs of Magtech brass, 50 Bertram brass, press, dies and patching supplies.  Currently reading through "shooting the english double rifle" and the "martini-henry notebook".  hoping to get through it all in time to warm it up in nov.

ok, so I'm most likely going BP, but BP is measured volumetrically. so .... now looking a suggestions for measures. i do not plan to use a drop tube. i figure the "fluff" would work in my favor.