bore size??

[mainiac]

I picked up an old halfstock cap gun,seems that it is called a new-england kentucky half-stock.Anyways,it has a groove diameter of almost exact .400.
What caliber would this be called? A .38,or a .39??            thanks,

[D. Taylor Sapergia]

The calibre is determined by measuring across the lands.  If the bore has an odd number of furrows, drive an oversized soft ball into the muzzle, and then withdraw it.  Measure the greatest distance across the slug with a micrometer or Vernier's calipers...that's your bore size or calibre.

[mainiac]

cherosafe cast,,,,,,,,,,.400 widest measurment..388 land to land measurement.
This is alot tighter than my colerain .40,,so im thinking that it is close to a .39

[Daryl]

If land to land is .388", I'd call it a .39.  The largest dimension is the groove diameter.  Taylor was just having a Senior's moment is all.  He contradicted himself- happens, I know- been there, done that.

[Don Getz]

Taylor......that's not quite right.    If you push a lead ball thru the bore,  or into it,  the land marks will be the deep ones in the ball.   Then, to complicate this even more,  if it an uneven number of grooves you can't even measure across the land
marks in the ball unless you have one of those special mikes that allows you to span one of the groove bumps.......Don

[mainiac]

This thing has quite small grooves,and the lands are at least twice,maybe 3 times as wide as the grooves.It has a twist at somewhere between 1/60-1/65.

Was this a common way of rifiling many years ago? I wish i could know who made the barrell,,it is very smooth,and has a progressily tighter bore toward the muzzle.

Im itching to shoot this barrell!

[Daryl]

It should shoot.  I would first try some .375" balls and a .022" patch.  Normally I suggest a ball only .005" under bore size, but the wide lands can make filling the grooves difficult. I have a similar dilema with my .32 - narrow grooves, wide lands.  I shoot a .311" ball with a .0215" to .0225" patch. It shoots well with both and both load easily.  The smaller balls with patches swage into the rifling easily as there is little lead to move in comparrison to a larger bore like a .58. Get a bit of compression of the patch in the bottom of the grooves and it will shoot well.

I also suggest starting at  40gr. The slower twist in this small bore will probably require about 50 or even 65gr. to shoot well at 500 yards.  If only shooting 25 yards, just about any powder charge will do.

[mainiac]

Im waiting on some .375 balls,comng in the mail.If they fit good,ill buy a mold.
Just what i need,another diameter roundball mold!

Todays barrells aint rifled with narrow grooves,are they?

[Dave Faletti]

Quote from Daryl.
I also suggest starting at  40gr. The slower twist in this small bore will probably require about 50 or even 65gr. to shoot well at 50 yards

Bad day at the keyboard or is there something special about this rifle?  

[bob in the woods]

He means " Canadian" yards   Altogether different!! 

[Daryl]

oops

[D. Taylor Sapergia]

...and an oops for me too.  Daryl,  our credibility, such as it is, may be in jeopardy.

[FL-Flintlock]

0.388" bore / 0.400" groove combined with the slow twist and narrow grooves could make it a .40 rimfire barrel.  IIRC, the powder charge was around 28 grains pushing a bare round ball - not long after RB cartridge there was at least one .40 rimfire with slow-twist pushing a HB mini style bullet with around a 35gr charge.  Dimick used narrow groove rifling in CF BPCR but I don't about twist.  Hasterum breech-loading percussion used narrow groove slow-twist with a casesless round similar to the Bartholow that was topped with a HB mini.  Some of these post-experimental and those without ammunition supply were converted for use on muzzleloaders.

[Daryl]

Could be FLFlinter - however .388" bore was a very common bore size and no wonder, it is exactly 80 balls to the pound & narrow grooving seems to have been  popular.  I have read records of a number of different orders 'East' for rifles from 40 to 80 balls to the pound. That corresponds with bores of .488" and .388".

[Majorjoel]

Another thing to consider on an old original barrel. The muzzle end may be crowned quite a bit oversized a few inches down bore. I would measure the true bore size from the breech end. That means you must remove the breech plug to do this. I have several small bore rifles that are true 32 cal. at the breech. The muzzle end mics out up to .35.

[mainiac]

Another thing to consider on an old original barrel. The muzzle end may be crowned quite a bit oversized a few inches down bore. I would measure the true bore size from the breech end. That means you must remove the breech plug to do this. I have several small bore rifles that are true 32 cal. at the breech. The muzzle end mics out up to .35.

This barrell is tight at the muzzle,and gets bigger the farther down ya go.

O YA,,,,i shot it yesterday,and i think it is gonna be a real good shooter.Under 2 inch groups,@50 yards.Barrell didnt foul up,nor get hard to load.Think she is gonna be a keeper. Figured out i need a .380 ball though.The .375 is pretty loose,even with a .022 denim patch.

[Daryl]

If it's shooting clean without fouling and not needing wiping, you're doing something right.  Practise, getting used to the rifle and slicking up that bore with some shooting should see the group size diminish.  Good on-ya.