Picking a Shotgun Choke
Unfortunately, the marking on a choke tube is meaningless. That poor, dumb old choke tube has no idea how many pellets you are going to blow through it, what size they are, or at what velocity. The brainless choke has no clue whether hard or soft shot is used, the sphericity of the shot, and so on. A choke tube does not know what the ambient temperature is, nor the elevation. Of course, the not-so-bright choke tube does not know the diameter of your bore.
Selecting a choke tube by constriction is imprecise as well, for that assumes that all choke tube lengths, tapers and parallel sections are identical. Nothing could be further from the truth.
The classic Browning fixed choke dimensions (12 gauge) with a .729 inch bore are .724 in. for Cylinder, .719 for skeet, .716 for Improved Cylinder, .705 for Modified, .695 for Improved Modified, and .685 for Full choke. It is a nominal .004 inch constriction as Cylinder, all the way to .044 inch as Full. Rarely will a current choke tube marked Full get anywhere close to .044 inch constriction.
The old Browning dimensions were was one way. Here is another, from Krieghoff:
12, 16 and 20 Gauge
Cylinder = .000 in. constriction, Skeet = .005 in. constriction, Improved Cylinder = .010 in. constriction, Light Modified = .015 in. constriction, Modified = .020 in. constriction, Light Improved Modified = .025 in. constriction, Improved Modified = .030 in. constriction, Full = .035 in. constriction
Krieghoff uses the same constriction scheme whether 12, 20, or 28 gauge. Others, like Browning, do not. Unfortunately, there are no universal standards for bore size, choke length, choke thread, or constriction.
Extended chokes improve screw-in pattern efficiencies, but with target load payloads of small diameter shot, sometimes not by much. Tests by Neil Winston showed a 2% improvement. However, with hunting loads the difference can be up to 20%. The short, stubby type of chokes (Browning standard Invector style) usually benefit the most. I took a fixed choke Browning B-80 12 gauge, had it line-bored, than had Tru-Chokes installed. Using extended Trulock Precision Hunter chokes tubes with the same constriction yielded a 15-20% improvement. No exact data is possible for your individual gun and one specific shell. As always, we have to pattern our own combinations if we want to know.
THE USEFUL CHOKE
Celebrated champion clay-smasher George Digweed has this to say: "My gun is 100% standard, full & full chokes, because I firmly believe if you can't hit it with full chokes and a White Gold 7.5, then it can't be killed! Last year, I asked Perazzi to make me a spare set of barrels because some FITASC targets were being set that were about 15-25 feet away."
Gil and Vicki Ash have long touted the Modified choke as being perhaps the most useful choke. The complication is that there is no universal agreement on what Modified is, nor is there agreement on what constitutes a killing pattern. Browning publishes that their standard Invector or Invector Plus Modified chokes produce 35% to 65% patterns at 40 yards. Small wonder there is more than enough confusion to go around.
WHAT IS A MODIFIED CHOKE?
Joe Hunter used a 12-gauge Browning Citori with 28 inch Invector-Plus barrels and Briley flush Modified choke with the 2-3/4 in. Federal Premium Upland load using 1 ounce of #5 lead shot (216 pellet count, average of five shells) at 1,400 fps MV (patterns average of five shots at 40 yards, 30 inch post-shot scribed circle): Modified choke pattern = 58% (126 pellets).
In the 55-60% range might be what most people expect. Yet, using a 20 gauge M2 shotgun with a Trulock Precision Hunter Modified Extended Choke, 1-1/4 ounce Remington buffered #5 lead 3 inch loads at a laser-verified 40 yards, I get 69% patterns. It is not 126 pellets in the 30 inch circle, it is 148 pellets. The Trulock PH Modified in this specific gun has only a .015 inch constriction. Far from being a downgrade, the 20 gauge in this instance is a 17% upgrade in 40 yard pattern efficiency.
THE FUZZY LOGIC OF CHOKES
Although some applications are easy (American Skeet, use a .002 to .004 inch constriction choke) there is not much that exact. While the constriction of a choke suggests a pattern efficiency, it does not guarantee it. The specific shell has a lot to do with pattern efficiency.
From shot to shot, pattern efficiencies vary by 20-30% with promo loads and cheap shells in general. This means the next shot could be a Full pattern percentage, or it could be Skeet in terms of pattern percentage. It can drive you nuts, if you let it, and I am already half-way there.
High quality shells and chokes may vary about 10% shot to shot, which makes the process easier. It is still fuzzy logic, but less fuzzy and more useful. For most hunting and sporting clays applications, a 20 to 25 thousandths constriction is in the ballpark. Shorter presentations allow less constriction, longer ones require more constriction.
These are only starting points. Pattern your shotgun and adjust as necessary, based on one gun, one range and one shell. With heavier payloads, you can use less constriction, maintain pattern density, yet have a larger effective spread.
REASONABLE STARTING POINTS
For American skeet, grouse hunting and all varieties of 20 yard shooting: .002 to .004 inch constriction.
For general purpose hunting applications of wild birds and many sporting clay applications: .020 to .025 inch constriction.
For American trap, pass shooting waterfowl and so forth: .030 to .035 inch constriction.
Remember, shell quality is just as important as choke quality. For best performance, you absolutely need both.
Copyright 2016 by Randy Wakeman. All rights reserved.