doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com MACNAUGHTON Double Rifle - Unknown Caliber

I would not be putting jacketed .510" bullets down that bore. Grease groove or paper patch all the way, smaller than .510". Cheaper than Woodleighs that way, too. At a guess, with a nominal bore of .490"ish, plus 2x a groove depth of a nominal .006"ish, something a tad over .500" will be roughly what you'll need; but it'll also depend on the rifling. Is it Henry? Henry rifling can have some taper in the bore. Sometimes. Slug and chamber/throat cast will be important here.

cadet, I'm assuming the roughly .500" dia. lead bullets you recommend would be grease groove, and paper patch slugs for this particular rifle would be close to bore diameter before patching, correct?

I can't answer that simply, Keith, and I can't profess to be an expert. So with those caveats: probably yes, but there's so many variables: what's the throat like? If tapered, larger (lead) bullets can be used, and they can swage into the bore proper. BP or smokeless? It's generally accepted that BP will kick a slightly smaller diameter lead bullet in the bum and bump it up to fill the grooves. Patched or grease grooved is another variable. Alloy - hard v soft...
Sometimes you've just got to - pardon the pun - bite the bullet, make some arbitrary choices, and just throw some lead down range and see what it does, and make some educated guesses based on what evidence can be gleaned about why it's happening the way it is, then tweak a variable here and there. We can be confident it's some sort of (nominal) .500 Express, but we'd need to know the chambering, so we can make an educated guess about what powder charge and bullet weight it was regulated for. Back in the day, it may have had its own mould, or may have just been fed generic off-the-shelf cartridges of whatever diameter was in use.
Graeme Wright's "Shooting the British Double Rifle" is a great starting point; Paul Matthews' "The Paper Jacket" another.

With a rifle like this the standard practice is to cast the chambers and slug the bores before you start your planning on the loading process.

AND insure the cartridge will chamber with the selected diameter of bullet.

On the other hand, I try to use the largest cast bullet that will seat in the case and still chamber in the large caliber, BIG cased rifles.

I bet I get some comments on the last statement

Skeetx,
You won't get any argument from me for that. As a general rule, black powder rifles used lead bullets, bore sized or smaller, counting on black powder to bump them up. They needed space for black powder residue. Most of us prefer lead bullets around .002-003" over groove diameter, when using smokeless powder in black powder rifles. This creates a case where the preferred bullet to fit the barrel may not chamber. Of course people that don't mind using black powder in their old rifles can still use smaller bullets, counting on them to "slug up". My 43 Mauser M71 has .452" groove diameter, but won't chamber a cartridge with .452" bullet, unless I make it think it is a heeled bullet. With .446" "proper" bullets, it won't shoot, but with .452"(.454" won't fit seating die), it will. The lesson here is try "one", before you load an ammo can full.
Mike

Well,

The rifle is in hand. Its a James Macnaughton and it turns out to be a variation of a 577-500 No.2. Not sure if the "40" stamp makes any more sense now. Its got a 7-groove bore and near as I can measure its .506 - .507dia. That seems undesize. ? ? There is a strange "star" stamp on each barrel above the chamber. Anyone know what those means? (see pics)

Anyone have any suggestions or comments?

Buck, that 40 is a mark from the proofing process that identifies the bore diameter of the barrel before the grooves are cut.

Your .506/.507 number - that's the *groove* diameter that you are stating there, no?
What is the smaller number - what is the *bore* diameter of your rifle?

36 gauge is .506". If the bore is that big it should have been stamped as a 36, not a 40. As stated earlier the 40 stamp would indicate a "Bore" that would accept a .488" gage but not a .492" one. This would give groove depths of from .007"-.009" per side. I think this would be normal for a Black Powder rifle shooting lead bullets.