Cold Weather Shooting

Shooters that continue clay shooting throughout the winter months may have noticed that the colder weather can sometimes have a detrimental effect on their scores. The warmer and heavier clothing required in the winter doesn’t help, but there is a fundamentally different problem that most shooters are probably unaware of; namely the velocity sapping effects of the colder winter air.

It is widely known among clay shooters that colder storage and conditions of use can change cartridge velocity, slowing it down a little. This is because in some cases, the cold can make some powder types burn less efficiently, producing a slightly lower velocity; this is a variable situation, but is generally in the order of 50 feet per second or so. This reduced efficiency of the powder is not the main reason for the velocity reduction however. In the warmer months, an extra 50 feet per second at the muzzle does not make a massive difference to the breaking power of a shotgun pellet.  

The primary reason for the lowered pellet speeds is the colder temperatures themselves, quite apart from any other mitigating factors.

When the winter temperatures plummet, the general cooling down increases the density of the air – making it heavier. This is because the colder air is thicker and more viscous than when it is warmer, making it much harder for the pellets to maintain their velocity. This extra braking effect on the pellets slows them down faster. 

The effects of this velocity drop can be compared to walking along a flat surface at a steady pace, then attempting to maintain this same rate of progress whilst climbing an incline. Either a greater effort is has to be made to continue at the same pace when going uphill, or if this is not possible (as in the case of a shotgun pellet), the walker’s pace will have to be slower.    

It is in fact a very similar problem in principle (although not to the same extent), that the much lighter non-lead pellets (such as steel) have – the air resistance slows them down much more quickly than the heavier lead pellets.  

The velocity chart shows these effects and the potential solutions to the problem. Using a top of the range clay target load containing hard 5 per cent antimony alloy lead shot, its performance has been adjusted for both air temperature and a slight cold weather muzzle velocity loss (50 feet per second).

In fairness to the manufacturers, this does not mean that any particular cartridge will automatically suffer this loss, but it can happen if cartridges are stored in cold and unfavourable conditions.

The effects of the colder weather can be seen to slow the pellets down more rapidly than in warmer conditions – dramatically cutting their target-breaking potential and ultimate ranging power. The actual loss in range varies a little, but generally speaking a drop off of five yards can be expected. The colder air also increases the pattern spread over and above that achieved in warmer conditions, so a tighter control of the pattern spread is definitely advisable, even at the reduced ranges.

To restore the lost target breaking power, increasing the velocity is simply not a practical option, as it would need an additional 230 feet per second to make up the losses caused by the colder air at 60 yards, with an increase in recoil of 50 per cent! Going up a pellet size from a number 7.5(2.3mm) to a number 7 (2.4mm), does the job, but unfortunately this solution also lowers the number of pellets in the load: 28grams of number 7.5’s (2.3mm) has approximately 403 pellets, whereas 28grams of number 7’s (2.4mm) has approximately 343 pellets. To help us counteract this, an increase in choke of a quarter (or perhaps even more if it is very cold), is probably also advisable to maintain the pattern quality at long ranges.