Could somebody tell me how many thousanths of choke constriction equals what choke in a 20 ga.
For example... .015 = Improved Cyl.or Modified etc.

I bought a JP Sauer Royal 20ga SxS in an internet auction and it was advertised as Imp Cyl/ Modified, but when it arrived I saw Halfchoke / Fullchoke engraved on the barrel bottoms. The gunshop owner told me he had measured the bores and chokes and thought they were imp cyl and mod. He told me that the bore diameters were .617" and as I have no way to measure that, I'll use that number. What I measure at the muzzles is .610 and .600 using dial calipers.

So my questions are..
Does .617 sound like a reasonable bore diameter?

What chokes does .007 and .017 get me.

Keep in mind that I don't want to fire it and count pellets because I might have to send it back.

By the way, if anyone can date this shotgun for me, I would be much obliged. The serial number is B33xx

Thanks
Elmo

Elmo,
The bore in a 20 gauge should be 0.615 and a .007 choke will be improved Cylinder and 0.017 will be improved modified. Modified is 0.011 to 0.012.

Thanks Chic

By the way, while I was measuring the muzzles I noticed that the horizontal diameter was about .002 less than the vertical diameter on both barrels when viewed head on. Is this anything to be concerned about, or is it just a side-by-side thing. This is my first sxs and also my first 20 ga, so I'm still on the learning curve.

Elmo