8 gauge choke dimensions

[Mike of the Mountain]

Craig, the letter for my gun specified it should "shoot buckshot close". I'm going to figure both barrels are either F or XF. It was surmised that since this gun was ordered for a lumber company in the FL panhandle in 1906 that they had either a bear or gator problem they wanted to control. Buckshot out of a 34" 8 bore would be bad-medicine for those critters!

[Cold Spring]

Typical 10 and 8-gauge choke constrictions may be easily calculated using high school math and a "direct proportion" by using the surface area of a nominal 12-gauge .729" bore (Pi x R^2) and 12 gauge choke constrictions, and proportioning by using your measured 10 or 8-gauge bore diameter/surface area. Use 10-20-30 and 40 thou for 12-gauge IC-Mod-Imp Mod and X-Full). I could do that for you by hand or with an excel formula but as my sophomore high school professor Mr O'Hara used to say, that's your homework assignment.

Hey Mike, "a friend" suggested you give me a free round if I do that for you.

[Mike Franzen]

Originally Posted by Frank Srebro

Typical 10 and 8-gauge choke constrictions may be easily calculated using high school math and a "direct proportion" by using the surface area of a nominal 12-gauge .729" bore (Pi x R^2) and 12 gauge choke constrictions, and proportioning by using your measured 10 or 8-gauge bore diameter/surface area.

What Frank said …. I agree ….. 100% …..

[Mike of the Mountain]

By using direct proportions to convert 12g (using a .729 bore) to 8g bore/chokes, it works out to-
IC .010 = .012, M .020 = .023, IM .030 = .035 and F .040 = .046.

My bores are R .846 and L .847. R choke is .828 (.018) or LM. L choke is .831 (.016) which should also be LM.

I know someone will double check this and definitely tell me if I'm wrong.

Using the 3.14 x radius squared I still come up with LM-M choking.

[Cold Spring]

Naaah Mikey, that's an oversimplification. You must use the surface area of the 12 gauge and 8 gauge bores, as measured. On the measurement it's my experience that bore mikes made to measure up to 12-gauge bore diameters will "drift" and read somewhat oversize with 10-gauge bores, and no doubt an even greater drift if the mike can be expanded for 8-gauge bores. From what I understand the nominal 8-gauge bore is .835" diameter. Probably best to "slug" the barrel with a somewhat larger lead slug and measure same with a caliper or regular 1" outside mike.

[Mike of the Mountain]

Using the Pi x R squared for bore and choke of 12 and 8 should give me the surface area. Still came up with LM-M.

[Mike of the Mountain]

As for slugging the bores and micing the slugs, I won't be doing that. I don't need to know an exact choke constriction. Choke is irrelevant. Just put the muzzle at the right place and you break the clay or kill the bird. You know the thought process behind it my friend.

I was just curious as to how the chokes break down compared to the 12g as the OP was asking about. Tight chokes leave diesel smoke. Open chokes leave big pieces. I say "Smoke 'em if you got 'em!!"

[Cold Spring]

Mike et al., I had some time and plugged .835" bore into my choke calculation excel spreadsheet and here are the theoretical constrictions for 8-gauge. As always actual choke efficiency (percentage in 30" dia circle at 40 yards) depends on other factors to include shot sizing, bore "roughness measurement", choke profile and others. Bottom line, there's no substitute for testing on paper.

8-Gauge IC = 13 thou
Mod = 24 thou
I-Mod = 34 thou
Full = 47 thou
X-Full = 52 thou

[Mike of the Mountain]

Good to see our numbers are only off by .001". Probably due to me using .846 instead of .835. THX!!