Which Calibre Pellet to Choose?
All my views below are based on United Kingdom (more specifically England and Wales) where, as at 2022, the maximum power of an unlicenced air rifle is 12 foot-lbs. More powerful air rifles can be purchased and used but these require the user to hold a Firearms Certificate (FAC) and are outside the scope of this article.
Air rifle power is calculated as a function of the weight of the pellet and the speed of the pellet. A smaller, lighter, pellet can therefore be fired at a greater speed and stay within the UK power limit than a larger, heavier pellet. As soon as a pellet leaves the muzzle of the rifle it starts to fall vertically under the influence of gravity. The longer the pellet is in the air the further it has fallen before it hits the target. It follows therefore that a faster pellet arrives at the target sooner and has fallen a shorter vertical distance. Given that all the pellets have to comply with the UK power limits.
The examples below show the typical weight (in grains) and speed (in feet per second) of a pellet in various calibres when all are fired at 11.5 ft lb power (Probably as close to the 12 ft lb limit as you want to go to give a margin for error). Remember that, in the UK, if your rifle exceeds 12 ft lb in power, and you don't have a Fire Arms Certificate, you have committed a serious Fire Arms Offence which can result in a custodial sentence. The table also shows the time for the pellet to reach the target at a distance of 25 yards and how far the pellet has dropped below the muzzle of the rifle by the time it hits the target at a variety of distances.
To 25 yard
at 10 yards
at 25 yards
at 45 yards
Examples Above all fired at a power of 11.5 ft lb
Examples below using a lighter weight .22 pellet or more power
Calibre choice - .177 or .22
I'll ignore anything more than a passing glance at the .20 and .25 calibres as if you are considering these then you probably already know enough to make your own decisions and have your own views.
Let's get this out of the way first, there is an often quoted fallacy on air rifle forums that .22 rifles are less accurate than .177 rifles. This is complete bunkum. All calibres can be as accurate as one another. It is your ability to estimate target range accurately and make the appropriate adjustment to your zero point that makes the difference. In general a lighter .177 pellet will have a flatter trajectory, when fired at UK air rifle power levels, so will be more forgiving of poor range estimation. A heavier, slower, .22 pellet will have a more curved trajectory so will require more adjustment of hold over/ hold under for different ranges than a .177 pellet fired at the same power level BUT it is no less accurate when zeroed in, it just requires more skill from the shooter to make the appropriate adjustment to their aiming point for the different ranges. If you shot a larger heavier .22 pellet at the same speed as a lighter smaller .177 pellet it would, more or less, follow the same path as the .177 pellet BUT the .22 would have to be fired with more power to achieve that speed - The power would be in excess of the UK limits for unlicensed air rifles so it is in effect a legal issue that causes the differences not a physical constraint. In countries where these limits do not apply the the .22 pellet fired faster and therefore at higher power would be the obvious choice especially for hunting. Every action has an equal and opposite reaction so, especially for a spring powered rifle, the more powerful you make it the more recoil it will have. The more recoil it has the less pleasant it is to use and the greater the potential for inaccuracy as the barrel moves more before the pellet leaves it so it may be dragged off the target. Trying to make a rifle more powerful, apart from potentially being illegal, can be counter productive as you potentially make it less accurate. Target shooters will often use rifles in the 10-10.5ftlb power range rather than pushing the legal limit as the smoother more gentle recoil can be potentially more accurate. Furthermore if you increase power to the point where pellets start to get near to supersonic speeds then they become very unstable and inaccurate.
In the UK, unless you go to FAC power levels (again if considering this you will already have your own expert opinions) then .25 is really only suitable as a very short range vermin control calibre (at which it excels) as the slower speed of the pellet (due to the UK 12ftlb power limit for non FAC air rifles) gives a very curved trajectory.
I did consider going for the .20 calibre as a happy medium between .177 and .20 but there is currently a more limited choice of pellet in the .20 calibre and I can either use a light weight .22 pellet or a heavy weight .177 pellet to obtain nearly the same trajectory as a .20 calibre. .20 does have it's devotees however and for some this may be the ideal do everything calibre.
If you are considering entering competitions, unless you specifically want to enter a .22 class competition, then .177 is normally the calibre of choice. The higher speed of the lighter .177 pellets give a flatter trajectory which can be more forgiving if you are not so good at estimating distances - basically you can get away with being less good at estimating distance with a .177 than with a .22. For various reasons to do with weight, surface area, ballistic co-efficient, etc that I won't go into .22 pellets can be launched more efficiently than the smaller .177 pellets so in a spring powered air rifle you may find a .22 rifle feels less harsh/has less recoil than a .177 rifle shooting at the same power. Likewise for a PCP rifle you will find you get more shots from a single fill of air in the .22 version of a rifle than in the .177 version of the same rifle.A point in favour of the .22 pellet here.
Most telescopic sights these days will have markings on the cross hair lines above, below and either side of the central crosspoint and if you want to shoot at varying ranges, rather than just always at a target at a fixed distance away, then these are essential. . Most popular are the "Mil Dot" markings. Using these you will set up your rifle so that when you are shooting at your most used range the central cross hairs are dead on the target - i.e. you have set the "Zero" at that range (but only for the particular pellet you are testing - if you change weight or type of pellet then you will need to zero your rifle again as different pellets will have different flight paths).
Once you have zeroed your rifle at this distance you can then place targets at 5 metre intervals from the closest range you are likely to shoot at up to the longest. Now shoot at each target in turn with the cross hairs centred on it and see where the pellet actually lands. It will generally be above or below the centre point. Make a note of the distance and which of the "Mildot" marks on the telescopic sight crosshairs is closest to the actual impact point of the pellet. Once you have done this for each of the ranges you will have compiled for yourself a list of the hold over, or hold under, values for that particular pellet with your particular rifle. Now when out shooting all you need to do is estimate the range (or even better use one of the readily available and very accurate laser rangefinders) , look at your table then put the relevant mildot from your table over the centre of the target and shoot. In this way it is quite possible to be accurate at any distance whether using a .177 or a .22 pellet.
So in summary (as it applies to England & Wales for an Air Rifle NOT requiring a licence) :
1. A .22 is just as accurate as a .177 (or any other calibre).
2. At a fixed range it makes no difference whether you use .22 or .177 once you have zeroed your rifle at that range. Both will hit the target at the dead centre of the cross hairs in your sights (assuming the shooter has the skill)
3. At the same power a .22 springer may feel smoother and have less recoil than a .177 and in a PCP you may get more shots per fill from a .22 (and the .22 may be slightly quieter).
4. At longer ranges a .22 may preserve more energy than a .177 (i.e. it will retain more hitting power at longer distances)
5. A .177 will get to the target faster than a .22 so the prey will have a shorter time to move before impact (for competition target work it doesn't really matter)
6. A .22 will need more holdover/holdunder to compensate for different ranges than a .177 so you need to be better at estimating distance from your target (or have a laser rangefinder) to be accurate. A .177 is more tolerant of incorrect range estimation as the flatter curve means you will be less far out if you get the range wrong.
7. At short range for vermin control a .22 may deliver more energy to the target and create a larger wound channel to provide more/quicker stopping power with less likely hood of over penetration (passing right through). A .177 pellet may over penetrate small vermin carrying more energy with it so delivering less power to the target and creating a smaller wound channel and the fast small pellet may then have more energy to damage say the roof of a barn after passing through the target.
9. Either calibre will stop air rifle prey effectively if hit in the right place at an appropriate range - Your skill will determine if you hit that place or not. A.177 is more tolerant of range estimation errors to do this.
10. It takes less lead to make a .177 pellet so pellets will be cheaper especially in these days of rising lead prices.
11. If a threatened lead ban comes into place then it may be that .22 pellets, which can be made proportionately heavier in alternative lighter materials, may end up being more efficient/accurate.
12. It doesn't matter what calibre you use as long as it suits you and the type of shooting you do so don't get offended or protective if other people prefer other calibres (I have both!)!