What would be the stardard constrictions for a 20ga?
I have a barrel that measures .605 and .617. I understand that numbers dont make the pattern, I'm just looking for a reference. It seems most newer guns with tubes have different numbers, would fixed chokes measure the same ?
Back in the day when Winchester was an American Co. the chokes for a 20 were :
Bore = 617, full = .025, mod = .014, ic = .006
bill
If your bore is .617, then you'd have cyl. and mod. according to Bill.
.615 is nominal 20 ga so @ .617 Win was using a .002" overbore. Measuring "Just the Choke" is never of any value at all, the bore also has to be measured to determine amount of constriction. Bores varied all over the board from Nominal, even among guns of the same make at different points in time.
When used as a % of bore reduction .025" in a 20 gauge is = to .030" in a 12ga. In the old days of card & felt/fiber wads this was considered IM, but with modern plastic obturating wads with shotcups it is considered full.
RAR, the numbers do indeed tell the tale for patterns. That is, the measured constrictions. Beyond that, there are very few factors that influence pattern performance. The problem with patterning is that patterns are highly variable. You need 10 statistically analyzed patterns to say with confidence how the gun+load performs. Considering that a Cyl at 30 yards and a Full at 40-45 yards are equivalent, it is less of an issue than is commonly thought. If you aren't willing to do 10 patterns per load+gun with the "Shotgun Insight" program, then in the words of the immortal Tony Soprano, "Fugidaboutit."
DDA
It has been my observation that choke tubes with XX amount of constriction generally pattern tighter than a fixed choke with the same constriction. My surmise is that because the bases of the tubes are essentially upset relative to the bore, they allow the charge to open up just a bit before encountering the actual choke portion of the tube. In a tubed gun I will typically use a step more open choke than what seems natural.
Choke tubes are slightly over bored on the chamber side. It was explained to me this was done so the wad never gets caught by the edge of the choke tube with dramatic results. So if a slight over bore segment causes tighter patterns using a more open choke tube would remove this effect. Perhaps you get tighter patterns from the tapering f he choke tube with a short parrel segment.
I think we over think chokes too much in all but extreme conditions. It's like shooters are thinking I missed that last shot because of my choke selection not because I did not put the pattern in the right spot. It's the Indian not the bow or arrows fault.
Thanks guys and your right it is easy to over think it. I was just curious what the standards were for a 20ga. I think I got it!