Do Extended Chokes Improve Patterns?
For
the answer to this, first we can turn to The Mysteries of Shotgun Patterns by George Oberfell and Charles Thompson. Oberfell & Thompson documented
the pattern efficiencies of both conical style choke tubes and the prevalent
style today, the parallel-conical choke tube, of different lengths through
the same gun with the same exit diameter of the choke. First, the O &
T conical choke results.
For a 1 inch choke, exit diameter of .690 in., the pattern efficiency was 63%. A 1-5/8 in. choke gave 61%, a 2-1/4 in. choke gave 68%, a 2-7/8 in choke 67%, and a 3-1/2 in. choke yielded a 63% average pattern efficiency, with all results listed here from conical chokes with a .690 in. exit diameter.
With the conical parallel choke style, even more extensive tests were performed and tabulated. In this case the exit diameter was .684 inches throughout all of the testing. A 1-5/8 choke length yielded 72%, 1-3/4 in. yielded 74%, 2.0 in. yielded 77%, 2-1/2 in. 64%, 3 in. 67%, with both 3-1/2 and 4 inch chokes averaging 65%.
Note that the O & T tests (p. 81-93) with the conical parallel choke did not use different choke tubes, they used the very same choke tube that was shortened between tests. The choke area was not tampered with, that remained a constant. Only the parallel section length was varied. What O & T was able to document was that yes, parallel section length clearly affects patterns, that there is improvement with a longer parallel section, but that improvement was not endless. The most efficient patterns were achieved with the 2 inch choke.
The choked section is a different matter, also explored by O & T. A one inch choked section was required for a .710 exit diameter, a 1.5 inch choked section for a .695 in., a 2 inch choked section for a .685 exit diameter. All of these were approximations; all were for a 70% pattern. What O & T were able to show as far as pattern efficiency is that, yes, the length of the parallel section clearly does have an effect on pattern percentage and that a longer parallel section may be a more efficient choke, up to a point. For a far more recent, computer analyzed set of documentation we can consider “Sporting Shotgun Performance” by A. C. Jones. A Nigel Teague short taper choke produced 72.9 % pattern efficiency, while a Teague long taper choke produced 77.6 % pattern efficiency at 40 yards. The difference here is not in the parallel section, as there is no parallel section in a Teague choke. The short taper tube has somewhere around 1-1/2 in. of length, the long taper about 2-3/4 inches of length.
Courtesy of Browning Arms is the official "Browning published stance" on expected pattern percentages based on choke designation. Like essentially all firearm manufacturers, the percentages are not remotely close to exact. Above, you can see, "25 - 45%" is the "expected" pattern percentage from an IC marked tube when firing a 2-3/4 in. shell in a 3 in. chamber at sea level.
I'm all for direct answers whenever possible, but sometimes a unsophisticated answer is insufficient when the question itself is a sophisticated one. No choke does much of anything without a shell. Using the same identical “Full” choke, a promo shell (I think you know the type, with the seasonal scribbles of the duckies and birdies on the box) labeled as 3 dram eq. 1-1/8 oz. #7-1/2 shot produced an average pattern percentage of right at 55% at 40 yards, a ten shot average. I duplicated that patterning using the same gun, the same choke, the same day, the same laser-verified 40 yards with a different shell, a “premium target” shotshell also labeled as 3 dram eq. 1-1/8 oz. #7-1/2 shot. The premium target shell was the only change. The ten shot average pattern percentage was just over 72%. When you have a cheap shotshell that weak, barely managing a “modified” level of performance, expecting any choke tube to change that into an ultra high efficiency pattern isn't particularly realistic.
As far as more recent specific results, testing a Caesar Guerini Tempio 12 gauge with CG extended tubes improved pattern efficiency by 10-15%. Testing a Trulock Precision Hunter Extended tube in a Browning B-80 12 gauge improved patterns by 15 – 20% vs. a flush Tru-Choke tube. In that case, the barrel was never used with any factory tubes at all, starting out as a fixed choke barrel that was line-bored then threaded to accept Tru-Chokes.
Do Extended Chokes Improve Patterns?
Back to the original question posed, “Do Extended Chokes Improve Patterns?” The best available answer is that yes, based on best documentation available extended tapered portions have been shown to improve patterns. Extended parallel sections have been shown to improve patterns. High-quality extended chokes as a class have been shown to improve patterns anywhere from 5 – 20% efficiency. Moreover, I have never seen a quality extended choke tube go the other way, but the individual shell itself as well as the individual shotgun both have a large effect on potential pattern efficiency, independent of the choke tube itself. Don Zutz (Shotgunning Trends In Transition) felt that the conical parallel choke was superior with one piece plastic wads. The reason stated was the slight slowing effect of the wad in the parallel section of the choke, allowing a cleaner release of the pellets from the wad upon muzzle exit.
Another question rarely asked is, "Extended from what, exactly?" One of the most popular choke tubes for many years has been the "standard invector" or Winchoke, along with its many copies and clones. That is a very short, stubby little choke. An extended std. invector is quite a substantial difference. The consideration is that with a fixed screw choke length, a choke designer is locked into that length for both the tapered section and the parallel section. An extended choke tube gives the choke manufacturer far more real estate to work within, enabling optimized chokes for specific shells. Trulock has done this, for example, with both Black Cloud and their Super Waterfowl chokes. It is difficult to lengthen a taper or lengthen a parallel section, much less both, when the length you want is constrained by the overall length of the tube.
Do I Always Want an Extended Choke?
A reasonable answer to that is, "No." For short range (skeet, grouse) you may not want any choke at all, much less an improved one. The whole idea of a choke in the first place, dating back to Fred Kimble, is to improve patterns by making them smaller and better populated at range. The jargon applied to chokes reflects this, "Improved Cylinder" is supposed by an improvement beyond what a cylinder bore can do and "Improved Modified" is supposed to be an improvement upon a modified choke level of performance. Why "Extra Full" was not designated as "Improved Full" I have no idea.
At close ranges, meaning out to 20 yards or so, you may have far more pellets in your pattern than you can use. The idea behind "reverse" or negative chokes (something like .005 in. larger than bore size) is to try to get the pattern to spread just as fast as possible. A high percentage pattern at 40 yards is of no value if you are not going to shoot at 40 yards. Although Browning's chart above calls "Cylinder" a 25 - 35% pattern at 40 yards, in practice that isn't usable information with birdshot and a cylinder choke, as it isn't used beyond 25 yards or so. If you can get an extra couple of inches of effective spread diameter, you'll likely take it.
Personal preference still measures in. Whether you say you love the looks of an extended choke or you say you hate it, you are of course 100% right. That's your preference. As a practical consideration, there are other benefits to an extended choke tube beyond patterning performance.
An extended choke tube protects the muzzle of your barrel from nicks and dents. A whack on a choke tube is preferable to a ding on your barrel everytime. In the case of many guns, barrel replacement is not remotely economical. With doubles, it can be extremely painful. There is no need to stick your snootle down the muzzle to see what choke you have installed, either, nor is there need to remember notch codes or remove the choke to know what is in the gun. You also don't have to worry whether your choke is steel shot rated or not-- all quality extended choke tubes are, regardless of constriction.
Copyright 2011 by Randy Wakeman. All Rights Reserved.
