Good size of blank and preferred woods

Let's do some number crunching (with a good cup of coffee, that is);

The best slingshot size really depends on the hand size involved, but a ballpark in terms of suitable dimensions for an average hand size is roughly:

- A total length of 11 to 12 cm (4.3 to 4.72 inches) for a "pinch grip" slingshot design. For a 11 cm long slingshot frame, this implies roughly a 1 inch fork height, 1 inch for the pinch grip grooves below this, and 2 to 2.5 inches for the lower grip section length.

- A total fork width of 10 cm (3.93 inches) with an inner fork width of 5 cm (1.96 inches) if it is a "pinch grip" slingshot. This is because a pinch grip width (index finger and thumb) just below the forks larger than 6 cm (2.36) tends to become uncomfortable (from my experience, standard hand size).

- A fist grip slingshot may have a larger inner fork gap, although this does usually not exceed 7 cm in most cases, including "Wrist-Rocket" designs.

- Lower placed forks are better than higher placed forks with regard to the holding hand in terms of wrist torsion effects (i.e. fatigue).

- Lower placed forks are structurally stronger (I prefer naturals with short forks for that very reason).

Chinese slingshots commonly have a total length of 11 cm (4-3 inches) and a total fork width of up to 9 cm (3.54 inches), with an inner fork gap of 4 cm (1.54 inches), and generally a fork tip width of 20 mm (0.78 inches). This is because most Chinese shooters prefer lighter band sets (0.40 to 0.50 mm thick flat band rubber) to shoot 6 to 8 mm steel ammo with straight trajectories and high accuracy in mind for competitive shooting at 10 yards (hunting is prohibited in the land of the dragon from what I have read).

Lighter draw weights also mean less shooter fatigue during extended shooting sessions - so their approach makes sense.

A maximum fork tip width up to 25 mm (0.98 inches, i.e. 1 inch) is usually sufficient, because the higher draw weights of flat bands with widths larger than that are simply not practical - unless of course the slingshot concerned has a wrist brace, or is a "starship" design with a wrist brace for "magnum" size ammo.

Bear in mind that stronger flat bands or tubes will need the appropriate structural strength in the fork area. On this note, Baltic birch plywood should not be less than 18 mm (0.70 inches) in thickness for safety reasons. Be careful with other hardwoods too from that perspective.

A metal core (stainless steel or aluminum) in a slingshot is an excellent way to solve the critical wood thickness issue - and it looks great too with its "sandwich" type layers: they take time to make, but it's worth it. Here is some inspiration from a maker based in Germany:

https://slingshot-germany.com/19-edelschleuder

In terms of wood board thicknesses (based on my numerous homemade slingshots since 2011), a wood thickness (hardwoods) of 20 (0.78 inches) to 25 mm (0.98 inches) is probably ideal for most pinch grip slingshots. Grip thickness for a fist grip slingshot seems to be best somewhere between 35 mm (1.37 inches) and 40 mm (1.57 inches): the dimensions measured when you connect the index finger and thump tips is a ballpark indication.

Well, I hope that was a large cup of coffee... . Hope this helps.

A quick search on the web came up with this:

"The average hand length of an adult female is 6.8 inches, whereas the hand length of an adult male is 7.6 inches."

Gender

Hand Length (Average)

Hand Breadth (Width) (Average)

Circumference Of Hand (Average)

Female

6.8 inches

3.1 inches

7.0 inches

Male

7.6 inches

3.5 inches

8.6 inches

https://www.theaveragebody.com/average-hand-size/

An approach that I adopted when making board cut slingshots is to cut out the slingshot shape A-4 print glued on grey cardboard to see how that fits the hand. Although you do not have the wood thickness aspect, it generally gives you a pretty good idea as to whether your template will yield a comfortable slingshot frame or not.

Another approach is to use a piece of clay to get an idea of what you need to match your hand size.

Essentially, less grip width will require more grip thickness: thus, if a nice piece of wood board comes with a thickness of say 0.8 inches (common for Baltic birch plywood), you will most certainly have to optimize grip width to compensate for the lack of thickness - and vice versa if the wood board is thicker to start with to find a good ergonomic compromise. More thickness also means more structural strength = more safety against fork breakages, a factor that definitely needs to be considered with any slingshot made of wood.

I would also suggest scouting the web for different slingshot designs to see what others have done in terms of pinch grip and fist grip slingshots: I personally feel that the Chinese, for whom slingshot shooting really is a national sport, have a significant headway in this respect - have a look:

https://piaoyu.aliexpress.com/store/group/Metal-slingshot/2934060_511401723.html?spm=a2g0o.store_home.pcShopHead_7591491.1_0_2

It may be better to sacrifice some birch plywood board to know what dimensions work for you before using more expensive hardwoods.

By definition, it's a bit like a pair of shoes: if they're too small, they ain't gonna fit, right? (don't listen to Joe the salesman trying to convince you of the contrary). Big hands and small slingshot frames therefore generally do not match too well.

There is always some trial and error involved, which is part of the fun.