12 ga choke sizes

[Bigscot]

I have seen but can't recall where, a listing of the nominal diameters for the constrictions for the various chokes in 12 ga, i.e. full, modified and improved. Could someone point in the right direction?

Thanks,

Bigscot

[Cimarron Red]

Bigscot,

This is from memory:

Nominal cylinder bore is .729.
I.C. -- .719-.720

Mod. -- .710

Imp. Mod. -- .700

Full -- .690

[Cimarron Red]

Bigscot,

Here's a link to a Wikipedia entry listing choke constrictions:

http://en.wikipedia.org/wiki/Shotgun

[Blackwater]

Don't know what you're needing the info for, but just FWW, the cited dimensions, while correct, vary a lot in actual experience. Also, old guns made before plastic wads used @ .040" for a full choke, whereas the value's nearer .030" now for our modern plastic shot cup shells. This makes some older gun, IF they actually had a full .040", shoot extra tight nowadays.

I think the game of Sporting Clays has done for shotgun chokes and choking what benchresting did for rifle accuracy. Strange things happen when you change the contours of the choke in a shotgun. My son once owned a M-870 Rem. Lwt. with the mahogany stocks, and I saw him kill a wood duck at an honest 80+ yards, putting four #4 shot in the bird's breast. It folded like a cheap lawn chair. I didn't condone that kind of skybusting, but he just got "buck fever" and couldn't help himself. As a youngster at the time, I just corrected him, though it was awfully hard to do given that kind of results. He was shooting 20 ga. Fed. 3" #4's, and I later patterned his gun and it gave 96% patterns at 40 measured yards from his 28" full choked barrel.

This was just a fluke, of course, and other brands gave from 65-75% patterns and other sizes of shot gave different results depending on velocity (generally) and shot size. Shotguns are all female. They just have trouble following "rules" of ANY kind sometimes. HAR!

[Bigscot]

Thanks for the replies.

A friend of my wife brought her dad's old db shotgun over for me to clean. It has what seems to be long barrels (haven't measured yet) and a .729 muzzel dia. for both barrels. I was curious as what choke they may as there are no markings on the barrels. From the information here it sounds like they are cylinder bore. May have to try it out during the upcoming dove season.

Bigscot

[KCSO]

Inside muzzle diameter has very little bearing on what a gun will shoot. Nominal choke diameters were set in the day of paper hulls and were based on assumed standard diameters of bore. What you NEED to know on chokes is what the actual amount of restriction is between the actual bore diameter and the choke diameter. You also need to take into account wether the gun is back bored and whter it has a standard or a long taper forcing cone. Therefore... A shotgun with a 729 bore and a 695 choke diameter wold be full with paper hulls and would be extra full with plastic, assuming standard forcing cone. The 729 diameter on your double IF it is a 12 and IF it doesn't have an oversize bore should be clyinder. This is why every tin=me I see an armchair expert stick a dime into a gun and confidently say, "Yep it's (your choice) choke", I bite my tongue and try not to laugh.

[obssd1958]

Here's a link to a page that has a chart near the bottom that gives nominal dimensions for standard guages and also shows the point in the barrel where those measurements are taken. Maybe more info than you are interested in, but still interesting.

http://www.shotguncombogauge.com/multiboregauge.html


Don

[mtgrs737]

Shotgun chokes and bores are a can of worms. There are many variances to be considered, and it is not a hard and fast science. Many manufacturers are going to "over bored" or "back bored" barrels as a selling point claiming reduced recoil and higher velocity etc. The reason I bring this up is because choke is really the "difference" between bore and choke or amount of constriction. Other things like barrel forcing cone length and choke cone length and if the choke has a parallel section section in it will affect performance.

I recomend testing the shotgun at the distance it will be used at by shooting at a large board with a large piece of paper on it. Shoot it. Then draw a 30" circle that is centered on the pattern with a felt tipped marker, now divide the circle into 4 pie shaped sections and count the pellet holes. How did it perform? What was the percentage of pellets in the 30" circle? Was the pattern uniform or did it have a lot of holes in it? Did the shotgun shoot to point of aim? This test is known as patterning and gives the best indication of how the shotgun shoots with the ammo you are using, also try different brands, or types of ammo and you can taylor your gun to the task that you will be using it, maybe without even changing chokes. I would guess that the majority of shotguners have never patterned their gun, this is a mistake as the pattern board will tell you a lot about the gun and where/how it shoots.

I have seen guys spend a lot of money on after market chokes and barrels and sights and still not shoot worth a darn, but it makes them feel like they have an edge. My advice is pattern your shotgun and see where it shoots and how the patterns are looking before spending any money on chokes and barrel work etc. The pattern board can tell you if your gun has a problem or if you might be better off to spend money on shooting lessons or more shells and targets for practice.

I have a Wheatherby over and under trap gun that kicked hard and shot poor patterns with my trap loads. The culprit was extremely short forcing cones (the area just ahead of the chamber). The gun was made with 3/8" long forcing cones that funneled the shot charge down to the barrel bore too rapidly and deformed the shot in doing so (and added to the kick) this was probably a hold over from the days of short fiber wads in shotshells. I had the forcing cones lenghten to 1& 1/2" inches and it made that gun shoot wonderfully, the patterns evened up and the kick was changed from a sharp jab to a much nicer push. If your forcing cones are less than 3/4" long I would consider this modification. Good luck!