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 cheap, chilled shot is used, the sphericity of the shot, and so it goes. A choke tube doesn't know what the ambient temperature is, is nor the elevation. Of course, the not-so-bright choke tube does not know what the diameter of your barrel's bore might be.
Selecting a choke tube by constriction is imprecise as well, for that assumes that all choke tube lengths, tapers, and parallel sections are absolutely identical. Nothing could be further from the truth.
The classic Browning fixed choke dimensions (12 gauge) with a .729 inch bore are .724 in. as Cylinder, .719 as skeet, .716 as Improved Cylinder, .705 as Modified, .695 as Improved Modified, and .685 as Full. It is a nominal .004 inch constriction as “Cylinder” all the way to .044 inch as “Full.” Rarely will a current choke tube marked as “Full” get anywhere close to .044 inch constriction.
The old “Browning way” was one way. Here is another, from Krieghoff.
Specifications for Krieghoff Factory Choke Tubes
12 Gauge - Available in standard Factory Steel and optional Titanium
00 = C = Cylinder = .000" constriction
0 = S = Skeet = .005" constriction
1 = IC = Improved Cylinder = .010" constriction
1+ = LM = Light Modified = .015" constriction
2 = M = Modified = .020" constriction
2+ = LIM = Light Improved Modified = .025" constriction
3 = IM = Improved Modified = .030" constriction
4 = F = Full = .035" constriction
Krieghoff uses the same, identical 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 style, or constriction.
Extended chokes do improve 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 can 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 one 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% - 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" Invector-Plus barrels using Briley flush chokes (patterns average of five, 30" post-shot scribed circle, yardage taped muzzle to target, and an in-shell pellet count average of five).
12 GA 2 3/4" FEDERAL PREMIUM UPLAND HIGH-VELOCITY LOAD
1 ¼ oz #5 lead (216 pellets) @ 1,400 fps
40 YARDS – Mod / pattern 126 (58%)
In the 60% range might be what some people expect. Yet, using an M2 20 gauge with a Trulock Precision Hunter Modified Extended Choke, with 1-1/4 oz. Remington buffered #5 lead 3 inch loads, at a laser-verified 40 yards I get 69% patterns. It isn't 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 - .004 inch constriction choke) there isn't much that is 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 it.
From shot to shot, pattern efficiencies vary by 20 - 30% with promo loads and cheap shells in general. That means the next shot could be an “Full” pattern percentage choke, or it could be a Skeet choke in terms of pattern percentage. It can drive you nuts, if you let it, and I'm already half-way there.
The 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 – 25 thousandths constriction is in the ballpark. Shorter presentations allow less constriction, longer require more constriction.
These are only starting points that you can pattern your shotgun from 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, and all varieties of 20 yard shooting, use a .002 - .004 inch constriction.
For general purpose hunting applications of wild birds, many sporting clay applications: .020 - .025 inch constriction is a good starting point.
For American trap, pass shooting, and so forth: .030 - .035 inch constriction is a good starting point.
Shell quality is just as important as choke quality: for best performance, you absolutely need both.
Copyright 2015 by Randy Wakeman. All Rights Reserved.