What's in a choke?

Understanding choke

Richard Rawlingson believes that we should all have enough knowledge to make an informed choice when it comes to shot size, loads and choke. Respect for our quarry demands it.

Going back through the literature (and not so far back at that), you will find more myth and mystique than hard facts. Everyone it seemed knew of the fabled ‘hard hitting' gun that brought towering cock pheasants down stone dead when all else failed, but few explained how or why. Then, there is the ‘choke is the devil's invention' school of writing that says all you need is true cylinder boring and an ounce of number seven shot - and if you miss it is just plain bad shooting.

In fact those old timers probably weren't too far wrong if they took most of their birds at around 25 yards range (as I suspect most did). The trusty Eley Shooter's Diary shows us that at 25 yards true cylinder should throw a pattern of around 38 inches diameter, with 69% of the pellets within the centre 30 inches. At this distance number seven shot should retain sufficient striking energy (around 1.8 foot pounds) to deliver a clean kill, for it is the energy from multiple pellet strikes that is important. To be effective a pattern must have sufficient density to deliver the required number of strikes and those pellets must have enough energy to do the job.

Take that traditional open-bored gun and light load down to Devon, however, and it will prove woefully inadequate on birds at an average of, say, 50 yards range. Let's look at the diary's figures again for this distance:

Pellets in 30 inch circle – 27%

Striking energy (no.7) –  0.7 foot pounds

The diary does not give figures for pattern spread but it will be significantly greater than the quoted 58 inches at 40 yards – that is not so much a pattern as a loose formation of low energy pellets.

Clearly then we need to take steps to increase both pattern density and striking energy. Even with full choke we cannot get back to the 69% pattern of true cylinder at 25 yards; the diary says it will give us 49% at 50 yards and 70% at 40, so full choke would seem to be the obvious choice.

Secondly, to get back to around 2.0 foot pounds energy at 50 yards we need to increase pellet size substantially (for larger pellets retain greater energy for longer). At 40 yards no.5 shot would do, but at 50 yards no. 4 is needed, delivering 1.97 foot pounds.

As ever with cartridge choice though, there is a trade off. Our one ounce load of no.7 shot gave us 340 pellets, but with the larger no.4 shot that has fallen to just 170, seriously compromising our pattern density. A third adjustment is therefore needed to increase the weight of shot as much as is sensible while still being comfortable to shoot. A popular choice would be a 1 1/4 ounce load (36 grams), giving 213 no.4 pellets. 

Range, choke selection, size of shot and weight of load are therefore always interlinked; change one and other parts of the equation need to be re-examined. 

I am not going to get into the ethical debate on high bird shooting, but it is a part of the modern shooting scene. However, traditionalists who criticise fellow shooters for taking to the field with tightly choked guns and heavy loads of large shot are seriously misinformed. These combinations are essential for consistent success and to go with less is to guarantee pricked birds.

I hope you have stayed with me through this barrage of numbers. As a reward here is my pocket guide to chokes and loads for small game at different ranges:

30 yards: Improved cylinder (1/4) choke,
(1 1/16 oz 30 gram) load, no.6 shot

40 yards: 3/4 choke, 1 1/8 oz (32 gram), no.5 shot

50 yards: Full choke, 1 1/4 oz (36 gram), no.4 shot

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