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Choke - What, Why and How Much?

Thankfully asphyxiation isn’t generally a part of clay target shooting, and choke isn’t just what you do when you find out the price of a new Kreighoff or Purdey gun. Choke is a constriction at the muzzle end of a barrel, and the reason it’s there is to influence how much your shot spreads as it leaves the barrel. With each cartridge holding 350 or so pellets, or shot, it is that spread that allows us to hit a moving target.

There are a huge number of variables affecting what happens to shot when they leave the barrel. Within the cartridge, the shot is held in a column with a wad behind it to act as a piston when the cartridge is fired. The simplest of wads is paper or fibre, which allows the shot on the outside of the column to touch the barrel wall as they get pushed along. Any deformation of shot is likely to result in more erratic flight of those pellets, and thus a wider spread of shot compared with perfectly spherical shot.

A plastic wad (some fibre wads, too) has “petals” which cushion the shot from the barrel wall. This reduces deformation of pellets on firing, so they stay more spherical and their flight is straighter. The result of this is less spread of shot. More expensive cartridges usually have shot with a higher antimony content which increases hardness compared with pure lead, and reduces pellet deformation and therefore spread of shot. And all this is before we explore the effect of muzzle velocity (premium cartridges tend to be faster) on spread of shot, or the effect of different internal barrel profiles!

Despite all these apparent efforts to reduce the spread of shot, we actually need some spread of shot to be able to hit moving targets. It is the spread that allows us a margin of error. For a very close range target, it stands to reason to have the shot spread out as quickly as possible because there isn't much distance for that spreading out to occur. For a long range target though, a wide spread of shot might mean the gap between pellets is so wide that you can be on target without a single pellet hitting the clay. Among the variables which affect how much shot spreads on leaving the barrel, choke is the one we have the most control over, assuming we're using a multichoke gun.

Choke is a constriction at the muzzle, usually within the last 3”/7.5cm of the barrel, and the amount of constriction varies up to about 0.04”/1mm for a 12g gun, and slightly less for a 20g gun. The useful thing about the constriction being near the muzzle is that it’s a reasonably simple, albeit very precise, matter to engineer removable barrel sections with different amounts of choke. These are called choke tubes, multi-chokes, or often just chokes, and they can be screwed in and out of the barrel quickly and easily.

Each gun manufacturer has their own type of choke tube - some put the screw threads at the back of the tube, some at the front; some sit flush with the end of the barrels while others extend out from the barrel; some have O-ring gas seals. Even within a brand of gun, there is often a newer design of choke tube which isn’t compatible with older guns (particularly with the most popular brands - Browning and Beretta). Guns which were made without interchangeable chokes can have them retrofitted – Teague is the pioneer of retrofitting in the UK – for several hundred pounds. The barrels, having been altered, must then be submitted for proof testing. If you’re buying additional choke tubes, whether from the original manufacturer or one of the many makers of aftermarket choke tubes, it’s vital that you buy ones of the right type for your gun.

If we’re going to change chokes and potentially buy more choke tubes, we need to know how much constriction we’re actually getting. For that, we have a naming convention which, like so much else, differs between the UK and North America. Starting with zero constriction and working up to the maximum available, here is a comparison chart.

Just to confuse matters, a relatively recent phenomenon is intermediate chokes – a 3/8 UK choke would be “light modified” in the US and 5/8 would be “light improved modified” (both of which are in the photograph above, with the constriction marked on the choke tubes). For the super-duper, hottest of the hot, Olympic Trap shooters, extra full chokes are available too. If we’re being picky, we shouldn’t really measure choke by the constriction but instead by the effect on the pattern. Hypothetically, full choke would put 70% of the pellets inside a 30” circle at 40 yards, whereas true cylinder would put only 30% of the pellets in that same circle. In reality, there are so many variables in the cartridge alone that we won’t know what we’re really getting unless we test each combination of choke and cartridge on a pattern plate (a static target which allows you to count holes or marks). We can though be reasonably sure of the relative effect – all else being equal, a tighter choke will result in a tighter pattern.

So, that’s the “what” of choke but why do we have so many choices and should we change chokes for every target presentation?

When I first attended a Sporting clay shoot, about 40 years ago, multi-chokes were a rarity. The club chairman who leant me a gun at that first shoot used a different set of barrels depending on the stand. For short-range targets, he used Skeet barrels and for the rest he used Trap barrels. Most people made do with one gun and one set of barrels, and therefore one set of chokes. The only choice they had was which barrel to fire first. Now, almost every gun comes with multi-chokes as standard.

The general intent of multi-chokes is to allow you use open chokes, such as Skeet or ¼, for targets at close range, and tighter chokes for targets at longer range. Particularly when shooting the Trap disciplines, the target is heading away from you at speed and is edge-on to you, so it’s possible to be on target yet still leave an unscathed target if the pellets have spread too much to ensure that 3 or 4 pellets hit the target – we want a hard enough hit that the scorer can see that the target is broken.

If you’re shooting Skeet, the choice is simple – use Skeet chokes. If you don’t have Skeet chokes, use the nearest you have available – my 20g gun has IC and ¼ when used for Skeet or instructional duties. Most Skeet targets are shot at less than 30m and you usually use size 9 shot which gives you lots more pellets in the cartridge, so the spread of shot remains dense enough to ensure breaks if you’re on target.

For the Trap disciples, again the choice is simple. Down-the-Line (DTL) is most gentle of the Trap disciplines, and as a newcomer to DTL if you have ½ in the first (usually bottom) barrel and ¾ in the second barrel, your misses won’t be due to choke. As you improve, you might want to put tighter chokes in the gun though it’s unlikely to make a huge difference. If I was only tightening one choke, I would probably make it the second barrel (by the time you need it, the target is 40+m away). For Olympic Trap with its faster targets, the most common choke choice is probably ¾ and Full, though the very best shots are more likely to use Full and Extra Full.

So, what about Sporting? Pretty much anything goes on a Sporting layout after all! Every so often you’ll hear someone say that choke tubes should be rusted in place, and there’s some veracity (minus the lack of gun care) to that viewpoint. There are world champions who use ½ choke in both barrels ALL THE TIME. I have 3/8 and 5/8 in my Sporting gun, and in reality that’s just a fancy way of saying ½ and ½. I change the chokes for Skeet, but that’s about. The only other change I make with that gun is to put flush-fitting chokes in it if I’m game shooting, which isn’t very often. The flush chokes just make the gun about half an inch shorter and very slightly more handy around trees, bushes and mud.

A very important bit of advice regards steel shot. NEVER USE MORE THAN HALF CHOKE WITH STEEL SHOT. Although there is one brand which advertises its new guns as steel shot-capable with all chokes, it’s still not a great idea. Steel is much harder than lead and therefore doesn’t deform as much as it goes through the constriction. This can lead to higher pressures than the barrel is designed to withstand. In any case, the lack of shot deformity also means tighter patterns and less need of tight chokes.

In conclusion, if you aim to be a serious competitor, and even if you don’t but you have the facility to do so, pattern your gun with the cartridges you intend to use. Only the pattern plate can show you for sure what each cartridge/choke combination is really doing, and even then you’re only seeing the 2-dimensional effect. In reality, that pattern of shot is really more of a cloud of shot, and the aim of the game is to make the target fly through that cloud and hit several pellets on the way. It’s easy to get too caught up with things you can fiddle with, and your time is usually better spent working on better shooting rather than fine-tuning your choke choice. If ½ and ½ is good enough for a Sporting world champion, you certainly don’t need more choke for Sporting targets at any reasonable distance. As a beginner particularly, ¼ and ½ is a very reasonable starting point for Sporting. Don’t let the chokes rust into place, but don’t be in a hurry to change them.


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