Choosing Shotgun Chokes!
Shot Column & Wad
Many very experienced (and successful) shooters I know say “Use Skeet & Skeet and leave the others in the box!” At least one of these actually sells shotguns and this is the advice he gives. If a new shooter spends several thousand pounds on a top brand shotgun they are entitled to ask the question “If you only need Skeet & Skeet why have the manufacturers spent millions developing a choke system?” Good question, especially when you consider the added cost.
While choke manufacture is an exact science the effect of using a choke with a particular cartridge and gun combination is unpredictable. The only way to quantify exactly what the effect a particular cartridge & choke combination will achieve is by use of the pattern plate at measured distances. This will reveal the density of the pattern and its diameter. Because the pattern plate is two dimensional it cannot reveal the length of the “shot string” or “shot column”. Shot leaves the barrel in an expanding column which becomes ineffective as velocity reduces, both in striking energy and pattern density. Velocity reduces quicker for smaller shot sizes.
The theory behind modern choke systems is: that the rate of expansion of the shot column can be controlled to provide a “killing” pattern at the required range for a specific target.
Most modern shotguns are provided with the best engineered chokes for that particular gun. In fact quality manufacturers will pattern the chokes to ensure quality. However there is an unpredictable factor lurking in the background! – which cartridge does one use? Cartridges can have different lengths, can have felt or plastic wads, differing amounts of shot, size of shot and different types of powder. All these and more have an effect on the expansion of the shot column and the final effective shot pattern at a specific range.
For clay pigeon shooting a new shooter does not need to worry about chokes. A modern shotgun, skeet chokes and 28 gram of Number 7. shot, clay pigeon cartridges, will be sufficient for most targets on the average clay ground. With more experience, and the ability to read individual targets, choosing a tighter choke on an "edge on midi" at 35 yards will make sense. For game shooters larger shot and tighter chokes will be the choice and there are some excellent game cartridges on the market. Wildfowl require non-toxic shot and most manufacturers place an upper limit of ½ choke (Modified) when using steel shot. This is because steel does not "crush" in the same manner as lead.
For the experienced shooter it does not hurt to pattern your regular cartridge at different ranges with different chokes. It can be an eye opener! Check out my video on the Analysis Page.
In order to cater for a perceived need, US manufacturers have added some "in between" chokes like Skeet (in between Cylinder Bore and Improved Cylinder) and Light Modified (in between Improved Cylinder and Modified).
Not disregarding “Cartridge Factor” there is a general rule for chokes - reproduced below.
Note; Extended Chokes can be used to extend barrel length and can be rifled for Section 1 ammunition etc.
Constriction in Inches
70% of the shot in a 30” circle
Here's an interesting link to "widen" the discussion on chokes. More open chokes for Trap Shooting using 24g
What Chamber Length for Your Shotgun?
Many shotguns are now chambered for 3 ½” cartridges. There are several reasons for this, to accommodate steel shot being one. This is fine when using the cartridges designed for the chamber but I am of the impression that if you don't regularly use 3 ½” cartridges then have a gun specifically for using them. I know this sounds extravagant but, if shooting 2 ¾” carts in a 3 ½” chamber compromises the pattern, then you are reducing your effectiveness for the majority of your shooting.
Why then would using 2 ¾” cartridges in a gun chambered for 3 ½” cartridges compromise the pattern?
*A shotgun barrel has two points of constriction, one at the end of the chamber which is the “forcing cone”, the other before the end of the muzzle which is the “choke”. When the wad drives the shot from the cartridge past the forcing cone there needs to be as little disruption as possible. A gun shooting 2 ¾” cartridges in a gun chambered 2 ¾” is ergonomically designed to reduce disruption to a minimum. When using 2 ¾” cartridges in guns chambered for 3 ½” the ¾” gap is wide enough to allow disruption, leading to poor shot patterns.
Although this effect is also present in shooting 2 ¾” shells in a 3” chamber, with only one third of the gap, it is far less pronounced and problematic. If the potential reduction in pattern efficiency is not significant, compared to the added flexibility of a 3” chambered gun, then most shooters would accept this slight disadvantage.
*Not applicable in "Backbored" Barrels. - Backboring
Interesting articles on this by Randy Wakeman can be found here - chuckhawks.com & Why Backboring does not work.