O’ Wise and Honourable One,
A shooting friend and I were enjoying a cool beverage following a round of sporting clays recently with a AA sporting clays shooter in my home state of Oklahoma. We were discussing the finer details of screw chokes with this seasoned veteran, who told us the following:
“All other things equal, a screw choke system with a “step” where the wad enters the choke (where the bore is larger where the wad enters the choke) will shoot a tighter pattern than an identical shotgun barrel with either a fixed choke or custom, bore-dimension chokes of identical muzzle-end diameter.”
In plain English, my Beretta A-390 with a .722″ bore and a Briley IC choke measuring .740″ at entrance and .712″ at exit (muzzle) would shoot tighter than a .722″ Beretta barrel with a .010″ fixed choke.
He went on to say that the reason my hunting gun, a Browning Gold, has an IC factory choke of .007″ and a MOD choke of .012″ is to compensate for this phenomenon.
What sayest the All-Knowing One?
Well, I never want to argue with someone as august as a genuwhine double A shooter, but my experience has given me results that are different from his.
In theory, the relief at the rear of the common mass-produced screw choke should indeed produce a “jug-like” effect and tighten the pattern. “Jugging” a cylinder bore barrel is a common way of introducing some choke.
In practical terms, I have not noticed this effect. As a matter of fact, I have found it extremely difficult to achieve high pattern percentages with today’s mass-produced screw chokes compared to traditional solid chokes. Apparently others have too. The serious pigeon shooters that I know won’t touch a screw choke. Nor will most of the better handicap trap shooters I know. They feel that they get the most reliable full choke patterns from old fashioned fixed chokes. I agree with them.
Using the excellent Remington STS 3 dram #7-1/2 loads, I was never able to break a true 75% using a Beretta factory “Full” (.035″ measured) in my 303. The Briley 2X long screw choke of the same measured constriction produced identical percentages. A Briley 2X “XFull” choke of a measured .040″ could touch 78% with the STS. While 75% certainly classifies as a “full” choke by SAAMI standards, I certainly have tested a number of my Belgian Browning B-25s with top barrels in the .037″ to .038″ area that could produce patterns of 83% to 85% with the same shell.
That isn’t saying that all screw chokes produce inferior patterns. Nigel Teague in England does a fabulous screw choke job with virtually no discernable “step” at the rear of the choke. His screw choke patterns are reputed to be among the best in the industry. I have shot a number of guns with his chokes, but have never put one on paper so I can’t say for sure.
I have had a couple of Belgian Brownings set up with Briley’s Series 1 “Thin Wall” custom chokes retrofitted to the solid choke barrels. These chokes have less step at the rear than my factory Beretta ones do and they pattern tighter given identical constrictions. Less step, tighter pattern. Not more step, tighter pattern. The Briley Thin Wall installations which I have had done have been of high quality.
My guess is that the steps that we find on current factory screw chokes like my Beretta aren’t long enough to produce a true jug choke effect which might well tighten patterns, but they are enough of a disturbance to give the shot a rougher ride and cause it to spread out a bit more. That’s my guess anyway.
As to the Browning Invector Plus chokes, they are indeed generally of looser constriction than the name stamped on the choke would indicate. I don’t think that this is because they pattern tighter with lead. My guess is that it has something to do with the tighter patterning qualities of steel. My experiments with the early short Browning Invectors on some B-80s were that they patterned perfectly normally for the actual constriction measured. Of course, that usually had very little to do with the wildly optimistic choke name stamped on the choke. The Invector Plus chokes are bigger, fatter and heavier, but no more truthful.
I am afraid that the only way to really answer these questions for your particular gun is to get your patterning paper and go out and do the work. Every gun really is a little different. There really isn’t any easy way around it. Make sure that the paper is 40 yards from the muzzle and that you use a high quality target shell. Some of the cheap promo loads won’t pattern modified from a pea shooter.
Shotgun Report’s Technoid
(Often in error, never in doubt.)