You need to get the measure of this to ensure your gun fits properly, says David Turner
Here I outline some of the most important aspects of gun fit and explain how to line up cast to check gun fit. The aim is to help newcomers have a clear understanding of how important it is and the implications of the wrong fit and how to make clear assessments.
Why do I need to understand cast?
You need to line up cast to check gun fit so that when your gun is mounted in the correct position, your dominant eye sits centrally over the rib without the need to move or roll your head in order to put it there. If the cast is wrong for you it may cause you to miss to one side as your eye is in the wrong position.
How much cast do I need?
The amount of cast required will depend on your body and head shape and it’s common for cast to be measured at both heel and toe (typically around 3mm at heel and 5mm at toe) because of the natural shape of the body. Take a look at your shoulder pocket, the position on your body where the butt sits when you mount the gun – the chest is bigger than the shoulder, so the toe end of the stock generally benefits from more cast in relation to the heel end.
A check to line up cast to check gun fit
Stand in front of the mirror, with your gun empty. Then see if your eye sits centrally on the rib of the gun without having to roll your head or adjust your head position. You should have a natural and upright head position that puts your eye in the correct place. Right-handed shooters will need a gun that is ‘cast-off’, while ‘lefties’ will need a gun that is ‘cast-on’. In drawing below we can see the difference between the two ‘casts’.
Most new guns have very little or no cast and are usually cast only at the toe of the stock, effectively presenting a very slight twist to the stock. I think that in reality this allows for most left-handers to shoot most guns without noticing any adverse effects. A ‘leftie’ friend of mine, who has shot all his life with right-handed guns, came into a little money and treated himself to a ‘proper’ left-handed gun, only to discover he couldn’t hit a “cow’s a*** with a banjo”. He returned to his right-handed gun and recovered form.
How to make alterations
This is a job for a qualified gunsmith, whereby a gun with a regular stock needs to be bent to achieve the required cast. A word of caution: some guns, once bent, can over time return to their original shape. The straight, slimmer side-by-side hand-stock can often be bent more easily, whereas the chunkier pistol grip of an over-and-under can sometimes be a little difficult to bend.
Autos are generally very easy to adjust as most manufacturers provide shims to alter both cast and pitch or comb height. Shims, such as those pictured here, fit between the butt and the action, which then allow for various alterations to fit.
In the diagram above, we can see a crossover stock for a right-handed person but with a dominant left eye. We don’t see too many of these around nowadays and they are usually used on side-by-side game guns. Note the fairly extreme cast-off, once again on a side-by-side.