The inside diameter is the nominal gun size. There may be a little leeway, some 0.50" are actually 0.051", or a 12" gun might actually be 11.9 or 12.1" but they are going to be close. Divide by scale to get the scale size so a .0.50" machinegun on a 1/35 tank would have a bore size of .50" divided by 35 or .014". A 16" gun on a 1/700 ship would be 16 / 700 = 0.02"
Kinda overkill if you ask me… The smallest bit you’ll be able to buy is a Number 80 (.0135"), so drill it with that, then widen it with the next size bigger until it looks right…
You’ll also need to know if you’re actually drilling out a barrel (like the .50’s on a Hellcat) or a blast tube (like the .50’s on a P-47)…
Even then, given that you’re wanting to drill the inside diameter to scale, you also need a lathe to turn the stock you’re using for barrels to a taper and the correct scale OD, right? Oh yeah… Then you’ll need to be able to turn the flash-hiders for some weapons as well…
Not to mention that you’ll need rod/wire to turn the ammo casings to scale as well, and also the open ends of the expended ammo too… And don’t forget the crimps if the weapon’s loaded with blanks…
Sorry for the tongue-in-cheek, or even flippant tone of my reply, but I don’t know if you’re really serious or, since it’s your first post, just trolling…
Forget all the BS! Take a #11 blade, poke it to the center of the barrel and spin it til there is just the tiniest bit of “flat” left at the end of the barrel.
“Close” counts in horseshoes, hand grenades AND scale modelling!!!
I like to replace barrels with hypodermic needles and this math formula is a way to know if I am close as finding a exact match is usually a stroke of luck.
I have to agree with Hans, slight over kill, unless you building a 1/1 scale. I just drill it until it looks right. I would love to meet the guy who measures the hole on a 1/72nd 7.92mm gun to make sure its right.
And by the way, a post to introduce yourself might have been a better start. And you will have to excuse the suggestion of trolling, but we have had our fair share. If you an’t a troll, my apologese for any suggestion that you are and welcome to the forum.
Yes welcome to the forums, I think it is a relevant question and I have more to add to further the discussion.
By western standards and caliber over .50 (1/2 inch) is considered a cannon. Most military calibers are standardized such as NATO 7.62 & 5.56
Realize many popular calibers (bullet diameter) have various cartridges (brass length and shape holding the propellant) manufactured to their specific design.
30-30 Winchester
30-06 Springfield
308 (7.62 NATO)
300 Win. Mag, Rem. Mag and other manufactures custom magnum cartridges in 30 cal.
Basically a 30 caliber (7.62mm) in diameter bullet can be used to reload all the above cartridges, using manufactures ballistic charts to measure (weigh) the amount of propellant required along with type IE IMR 4060 ect. Best to cross reference two or more charts*
The common civilian measurement is in Imperial, such as .223 (inch) where the military uses a metric designation 5.56 (mm) for the same cartridge.
ALWAYS be positive the cartridge matches the chamber in the rife, this should be stamped on the receiver or barrel of the rifle and match exactly the stamp on the base of the cartridge.
If unsure DO NOT FIRE the weapon and have a qualified gunsmith investigate it further.
Someone did a chart exactly like you are asking about a few years ago here on the forums. For some reason I think it was Triarius, maybe wrong.
I printed it out to keep for reference, thanked him for the effort. And ya know what?
I’ve never used it once. I drill to look right or in some cases install hypo tubing. Such information, while maybe interesting, is trivial and very near impossible to apply to scale modeling unless the scale is rather large. One just don’t see many drills smaller than an #80.