Bore size.

Hi Guys, I`m into barrel making and was looking at what is the standed size gun drill you would use for a .50 cal black powder barrel. My .45 bore is .457", The gun drill was .444" , .006.5" cut rifling brings it out to .457". So would a .50 bore be .490" and .005" per side for the rifling, this bore stuff can be quite confusing. , Cheers, Homebrew.357.

Typically, a muzzleloading rifle barrel has a bore size which is exactly the same as the common name for the barrel.
That is, a .45 caliber barrel has a bore size of .450 diameter. A .50 caliber barrel has a bore size of .500 diameter.

The size of the rifling grooves are larger than bore or caliber size so, a .45 caliber barrel might have rifling in it with grooves that measures .470 diameter if its grooves are .010 deep.
Your .50 caliber bore should be .500 in diameter and adding the .005 deep grooves you mentioned would make the groove diameter .510.

I don't know what is happening with your gun drills.

All of the gun drills used at the company I worked for drill holes a few ten thousandths oversize. For instance a .4995 diameter gun drill could be expected to produce a hole that was .5000 in diameter.
These machines and drills were not the sort of thing most people would own.
The machines were built in the 1940's and used to produce military rifle barrels.
The drill bits had solid silicone carbide ends brazed to long length of hollow tubing which supplied the cutting/coolant fluid to the cutting edge.
One drill could cost several hundred dollars.

These gun drill machines rotated the barrel or shaft while the gun drill did not turn at all.
This allowed the chips produced by the single cutting edge and the coolant to flow along a indented area in the tube towards the mouth of the hole.

Resharpening these drills required using diamond wheels in ultra precision tool grinders.

Thanks for your reply Jim, so a .50 bore is .500 + the grove depth for p r ball. My drill was .444" and drilled to that size, but I`m doing this in a back yard way, just a home machinist, and I got my second hand drills from EBay in U S A. Just google, "Making a barrel on my lathe" . Cheers, Homebrew.357.

You might want to be careful using terms like ".50 bore" around muzzleloaders.

If you say it rather than write it, people won't hear the decimal point. All they'll hear is "50 bore".

Back in the 18th and 19th century, muzzleloaders were described by the number of balls per pound they shot. That is, a "50 bore" shot a ball that weighed 1/50th of a pound or put another way, a pound of these balls would have 50 balls in it.

Likewise, a "45 bore" would be a gun that shot balls which would be 1/45th of a pound or, there would be 45 of these balls in a pound.

To add to the confusion, a 45 bore ball is .469 in diameter. A 50 bore ball is .453 in diameter.
A .492 diameter ball like we would shoot in a patched ball load in a .50 caliber barrel would be a "39 balls per pound" and a .531 diameter like we would shoot in a patched load in a .54 caliber barrel would be a "31 balls per pound".

Now, to get even more confused, as you might have noticed, in the example I just mentioned, a patched ball load uses a undersized ball. That is, a .50 caliber barrel shoots a .490 diameter ball. A .45 caliber barrel usually shoots a .440 diameter ball.

Although the ball they shoot is smaller than a ball that represents the bore size, it is the bore size ball that is used to describe the size of the bore.

If your confused, your not alone.
Several authors of historical works seemed to confuse the balls per pound and the ball size in inches so we get authors saying some famous person shot a .36 caliber rifle when he should have said the person shot a 36 bore rifle. (There's a lot of difference between a .36 caliber ball and a .506 diameter, 36 balls per pound ball.)

Probably best to just use the term "caliber" rather than "bore" to avoid any confusion.

Interesting discussion. Thanks for posting.

YEE gods, from now on it will be "Caliber" , you got me lost in the woods there, :idunno: . Anyway will be having a go at making a few .45 Caliber black powder barrels, I can now get a right hand twist of 1-48" as I have changed to a sine bar system on my lathe, nobody makes black powder barrels in N Z. Homebrew.357.

And, just to add in one more tidbit for confusion; with artillery, such as big guns on ships, caliber can also be used to designate barrel length. The USS Missouri's big guns were 16" 50 caliber, or the tube length was 50x the diameter of the shells, or about 66'.

With ML'ing artillery, that is principally how one distinguishes between mortars (2-6x bore) howitzers (6-12x bore) and cannons (12+x bore).

well in my army training I was on "25 lders," I think the bore was 82/88mm?. Now for a tack driving .45 shooter, what twist would be best, 1-48" or 1-60", for p r b I`m thinking the 1-60" would be the go? or is it the nut behind the gun!! :hmm:

From what I have picked up from the forum conical bullets do better with a faster twist round balls do better with a slower twist. If I'm not mistaken 1-48 is average for most commercial black powder barrels. There is also another can of worms to open,,,, deep round bottom rifling vs shallow square bottom rifling. Really ,,,,, dont overthink it just make a barrel and see how it shoots then make a different one and try it.

Yer I think you are right a 1-48 is ok for both and in my home made one I`m happy the way it shoots p r b as I got a 1-33" twist. Now my idea is to just make and sell a few blank M L barrels for some one to build a rifle on in .45 cal and as it will be for P R B I will go for the slower twist. I see now T O T Wolf have G M .45 barrels with 1-66" twist so one is spoiled for choice. The slower rate of 1-70" seams to be for .50/54 cal. There`s so much imfo on here on this black powder stuff, you guys weaned your milk teeth on black powder rifles. :thumbsup:

FWIW, the finished bore diameter has always been established by reaming, not by the initial drilling (or, historically, forging around a mandrel). The gun drill is several thousandths smaller than the desired final bore diameter, and most manufacturers use at least 2 reamers to bring the bore to final size. Reaming leaves a much better surface finish, and a properly designed, maintained and operated reamer will produce a bore which does not vary significantly in diameter from end-to-end.
The making of forged barrels involved the use of the 'long bit' to clear the irregularities left by the forging, and the square reamer, which was mounted on a long shank, and 'packed-up', often with slips of paper, to bring the bore to a smooth and even final finish.
Both old-time and modern barrel makers also often lap the bore, either before or after rifling, or both, to give the best possible surface finish to the lands and grooves, and, sometimes, to provide taper or choke in the bore.

mhb - MIke

You could get a .445 ball and a thick patch to work.

As previously stated the bore must be carefully reamed after its drilled. Also use a 48" twist. It was the traditional twist for American long rifles and from my reading it was the only twist the J&S Hawken used. Most modern barrels are twisted too slow IMO. Based on experience a 50 caliber 48 twist will shoot 1/2 ball weight of FFF without any issues and will shoot extremely well. I think a lot of the slower twist stuff came from Douglas using a 66" for everything. Then people read Forsythe and really get off the rails.