			Constriction Required for Gauge Listed
Degree of Choke	% in 30" at 40yd	Pattern dia at 40yd	10	12	16	20	28	410

Nominal dia			0.779*	0.729	0.667	0.617	0.550	0.410
English Full	70%	33	0.035	0.035	0.028	0.025	0.022	0.015
3/4	65%	35	0.025	0.025	0.020	0.019	0.016	0.011
1/2	60%	38	0.02	0.02	0.015	0.014	0.012	0.008
1/4	55%	41	0.01	0.01	0.007	0.006	0.005	0.004
Imp Cyl	50%	44	0.005	0.005	0.004	0.004	0.003	0.002
Cyl	40%	51	0	0	0	0	0	0
American Full	70%	33	0.035	0.035	0.028	0.025	0.022	0.015
Imp Mod	65%	35	0.025	0.025	0.020	0.019	0.016	0.011
Mod	60%	38	0.02	0.02	0.015	0.014	0.012	0.008
Imp Cyl	55%	41	0.01	0.01	0.007	0.006	0.005	0.004
Skeet	50%	44	0.005	0.005	0.004	0.004	0.003	0.002
Cyl	40%	51	0	0	0	0	0	0

Note: Most American 12 ga guns are bored .775