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If one were to enlarge the design of Lyman 457130, the 45-70 "Collar Button," How might one expect such a boolit sized ~ 0.470 - 0.475" to perform in a Martini Henry with its odd Henry rifling? Say the boolit is pushed by 10 to 15 gr of Unique and flying at 1000 - 1300 f/s?
I am contemplating this with a call to Accurate Molds in mind.
Thanks for any constructive ideas on this.
NOE has a couple of versions of the collar button maybe they could make a custom one for your Martini's diameter.
If you are searching for a lighter slug for reduced loads, have you considered the 265gr 455 Eley bullet? Using a chamber insert, I have loaded the bullet in 45 Colt, and have had really good accuracy out to 50yds. If a little loose for the case, you could paper patch it.
Just a suggestion.
Be sure to slug the bore before ordering. The Martini-Henry bore sizes can vary. Stay with the heavier bullet to match the bore twist if you want best accuracy. I used to shoot one in 1000 yard matches, and held my own.
Martini Henrys are a law unto themselves. I have used a 462.500 boolit in several rifles with great success.
https://i.imgur.com/X53xURLm.jpg
https://i.imgur.com/OQwuJaUh.jpg
https://i.imgur.com/G56WByxl.jpg
The barrels had some 'freebore' to account for powder fouling and getting good accuracy relies on swaging a soft lead boolit into the rifling
thank you for your replies, gentlemen. I am looking at paper patching as the unwanted, but apparently necessary burden for another project, and I wouldn't like to add the 577-450 to that list. Besides, given the purpose of the "Collar Button" for 45-70: a boolit that weighs as much as a round ball but, because of the deep grease groove, is long enough to be more compatible with the rifle's twist, is relatively long.
I do have 45 Colt moulds that might otherwise work, but for the purposes of my question, those boolits are heavier and shorter than I'd prefer trying. And, like I said, I'd rather not have to paper patch them.
I think 0.462" migh be a bit thin for my Mark IV. I have an Accurate 47-475XR and a RCBS 480 Ruger mould for the Martini right now. I'd like something small and "plinker-like", such as the Collar Button I have for the 45-70. This Martini Business is the biggest challenge I've faced in my arsenal of oddballs.
What I was wondering was, the Collar Button works for 45-70 bores, but the Henry rifling in the 577-450 is a very different animal, as Mr. Wallace, your diagrams clearly show. The long throat adds to the list of challenges the 577-450 presents. The 45-70 Collar Button is not a full wadcutter, but it does have a very blunt nose. How this might stabilize in the Martini Henry's long throat is also a question in my mind. Would the nose help get it centered, or would it be of no aid in straightening out the boolit as it enters the throat?
a Chamber cast might be a good place to start.
Then you'll have the throat diameter and the neck diameter also. Take the neck diameter subtract the case wall thickness, give it .001-.002" clearance to expand the brass and let the bullet go and you'll have the absolute max bullet diameter. Then compare that to the throat.
Hopefully the throat is at or smaller than the max bullet size, and larger than the groove.
If so, order your bullet mold at just a tad larger than the throat, so you'll get a snug fit and good alignment with the barrel.
If I'm off on anything here, please someone correct me.
It always helps to have an ingot of chamber cast alloy hanging around and is fairly easy to do.
Take your measurements as soon as the cast is cool as some of the alloys will grow in size over a few days.