Colt Conversions?

[.22-10-45]

Hello, everyone. I have a question on ctg. conversion cylinders for 2nd. gen. Colt percussion revolvers.
Fisrt off, let me say I have been handloading for revolvers for years, and understand the relationship of cyl. throat dia., to bullet dia. to bore dia.
I have a Kirst .38 long-colt cyl., I fitted to a 1972 era. Colt 1851 .36 navy revolver. The cyl. mouths measure .378. a .359 dia. bullet is a light thumb press in the bore. Using .359 dia. hollow-base bullets, accuracy is surprising with groups under 2" at 25 yds...recovered slugs show full groove depth expansion along whole bearing surface..this with 1.8gr. to 2.0gr. Bullseye.
I inspected this revolver last weekend, and I guess I need to do a better job of cleaning..there were slight lead smears in cyl. More on this later...
The other revolver, Is a 1980's era Colt 1860 army .44 percussion, that I sent off to Ravens Roost for a full conversion to a 1st. model Richards conversion in .44 Colt....at my request, they even installed the hardened disk in hammer face as per originals, all pins & screws fire blues, re-case-colored frame & dark carbona type blue.
I had found a Rapine .430 hollow-base mould, and was told by RR, that this would be perfect for this revolver.
The mould drops a .435 dia. bullet from very soft lead alloy.
The chamber mouths measure .434" & bullet is a tight fit..with the thought of the
.38 colt fit to bore..I tried one of these slugs for fit in the .44.
It fell thru with alot of wobble room!
Now I have fired these guns in percussion guise & use a .451 ball..completely forgot about this.
I have not yet fired this gun.. too darn cold now...but maker seemed assured it would work fine.
Now I have been trying to imagine just what happens when the big light hits that bullet...As powder ignites, bullet is forced from case, since it is a tight fit in cyl mouth..it holds back pressure & is guided straight.
As bullet base clears chamber mouth..pent-up pressure starts expanding thin skirt of hollow-base.
The forcing cone is the limiting factor at this point & as base expands outward..grabbing bore surface, pressure forces more of bullet surface onto bore & into grooves.
Now I know this is all backwards..that cyl. mouth should be at least groove dia. or slightly over..and any expanding of bullet should take place in cyl. throat.
But remember that .38 long colt..and it's good accuracy..and that leading I spoke of earlier.
Here we have .378" cyl. mouths..but only a .359" dia. bullet...019" oversize!
Now I don't know for sure if those hollow-base bullets expanded to .378"..but some part of them were leaving lead smears..richocet?
I suppose in a perfect world..I could imagine that bullet "floating" centered in throat, with .0095" of airspace around it, and being perfectly obturated to fit throat?
So I wonder what the "fix" (if one is needed) would be..if I ream throats to .452,
bullet will be .017" undersize?
The original .44 Colt was 'heeled"..but still was only .443 dia.
I guess I'll just have to wait for warmer weather to find out..but it sure is a puzzle
that some of these old guns work as well as they do! Thanks guys!

[MtGun44]

There are a lot of weird things with seriously undersized boolits, especially very soft lead and
hollow based designs that worked reasonably well in the BP era. Apparently the pressure
spike from BP is abrupt enough to do a LOT of obturation.

Another example is the .38-55, where many guns will not chamber anything larger than
a .377 boolit and the bore is .381. With a solid base soft lead boolit and BP these
are reported to work just fine. Mike Venturino reports similar issues with several different
cartridge-rifle combos in the BP cartridge era.

I think if you consider that the original HB is the Minie bullet, and they had a large clearance
to the bore, yet expanded to grip the rifling just fine, getting good results with similar large
clearances in the revolver shouldn't be all that surprising.

I was quite surprised when you said "light thumb press" with those huge clearances. I wonder
of something isn't out of round to make the interference.

Bill

[.22-10-45]

Hello, MTGun44. Thanks for reply..I have read somewhere that the ability of a black powder charge to obturate soft lead...covered alot of early barrel making sins!
Nothing out of round on the .36 Colt...I have a 1901 army Colt in .38 long colt that also has light thumb-press fit in bore..NOT grooves mind you..but on top of lands.
I understand a .41 Colt bullet falls thru bore also.
These things must have worked after a fashon...Colt made a few of their Bisley flatop target in .38 & .41 Colt!

[MtGun44]

I went back and reread it, now I understand. I originally had somehow a .359 ball
a light thumb pressure fit into the .378 cylinder! Makes more sense now.

But - the facts still stand HBs make up for a bunch of fit problems.

I have a very oversized bore trapdoor springfield that throws solid cast sideways, but
shoots the Lee 405 HB very well. HBs have their structural limits apparently, I have
heard reports that the bases can blow out and upset the boolit as it leaves the
muzzle, but until you reach that limit, they can fix up some pretty large differences
in boolit and groove diameters.

Bill