I have an old Ithaca Model 37 20 gauge pump. It originally had a 28" full choke bore. I had a gunsmith cut it to 25" to try to get a more open choke. The muzzle now measures 0.600". What would that equate to for a 20 gauge choke? Rufous.

To arrive at the right answer,you need to know the bore of your barrel.If the barrel bore is .615,the constriction is .015,which would be a light modified choke.

The length of the constriction as well as the amount will effect the pattern.

Try some test patterns at various ranges with the loads you will be using,to see if the gun is
making a pattern to suit your needs.

If the pattern is too open,it can be jug choked,the forcing cone can be recut with a longer taper,which will tighten up the pattern,usually.If the barrel wall is thick enough
it can be fitted with choke inserts.

I have a choke I machined for one of my barrels,that will place 90 percent of a 1 oz.# 7-1/2
load into a 9" circle at 20 yards.It has a.065"
constriction 2.250" long.

WC

well if you just wanted a more open choke...you went about getting it in the wrong manner for sure. all you have to do was hone out the ID of the muzzle....which would be the propper way to get the more open choke you want....it would be exactly the way the factory would have made it, if it was going to be a less choked gun....now if you havent cut off all , you cut off most of the taper leading down to the choke,. Cut alittle more and you will have NO choke.... if you only have a small LENGTH of choke....your probably going to get lots of incinsistant results with your patterns.....you most likely have NO straight section at the muzzle..... how does it pattern now??????? the pattern density on paper is more important than the amount of constriction at the muzzle......the constriction is only a METHOD of getting to a certain pattern density of your pellets........good luck....bob

rufous, if I had to guess I would say you have a cylinder bore. The chokes on the Ithaca's were not as long as the amount of barrel you cut off. I just miked my son's cylinder bore choke tube and it is .615". You might be in the market for a new barrel.

Numbers don't really mean anything. There is such a great variation in shells that you must pattern the gun.

The numbers do mean that when you have no choke you are not going to get some miraculous shot distribution because of shells. Ain't going to happen. If he wanted a 15 or 20 yard gun he has one.

Thanks for the help guys. I will try to get out and see how it patterns. In the meantime I will use my Remington 870 with replaceable chokes. Rufous.

rufous, you might look at having tubes installed. I am not sure of the price but it is not that much if memory serves me.

Actually your choke isn't realy messured on the gun, but by the desisty of the pattern. I

don't remember the numbers exactly but I think it is usually messured at 20m on 30 cm sircle. I think that if it's full choke 70% of the shot will hold the circle. There are lot of good books on the subject.

Differnt shells will give differnt results. You could get open bore from a full choke and oposite. Most shotguners don't do real tests. It's kinda interresting.

The messure on the gun will mostly give you a rougf estimate and often this is good enough for most practical shoting, but I'd recoment to test it. You can find what shell gives the best pattern for you use at the same time.

Johan