What is the dimension of the longest projectiles able to be loaded into most 37mm and 40mm launchers?  I can find the OAL length of 40mm flare rounds, but what is the OAL if the projectile. Trying to determine the maximum payload by volume for both 37mm and 40mm.

Also, what would be a decent launcher to pick up?  I’d like to go with 37mm for specific reasons and would prefer one with a longer barrel and break action design to take advantage of longer rounds.

Finally, since 37mm is not considered a firearm...does it require a FFL06?

I’m going somewhere with this without being to specific.

All I can tell you is that 37mm launchers are firearms if they use a firearm receiver. For example, M203 and M79 receivers are firearm receivers. Unless there is a 40mm barrel involved, they would transfer as firearms through any regular FFL.

There are some 37mm launchers which do not use firearm recievers.

edit: Sorry, I was thinking cartridge length and not projectile length.  Here's a couple numbers and a pic that don't really help


My rail mount M203 measures 5.407" barrel to breech face.
The pictured casing is 4.880" long.



another edit:
You might run into a payload mass/velocity/chamber pressure tradeoff that limits you before the projectile length.
I did some napkin math for you:
assuming a solid 60/40 KNO3-sugar smoke mix projectile, 40mmø and 4" long, it'll weigh about 0.53lb
M781 is about 0.39lb at 250ft/s
I've seen reference to some HEDP projectiles at around 0.44lb and 250ft/s

Obviously, increasing mass will require a hotter load to maintain velocity.  (Does anyone have max load info they can share)
Bearing surface,projectile to bore fit, and other things will all have an affect.
I made a lot of assumptions and simplifications, but I hope that's at least helpful as a point of consideration.
Of course, if you're loading cotton balls and packing peanuts, it might not matter much.  

I’ve never reloaded for launchers. Assuming I wanted to get the max payload of powdered chalk in a flare sized projectile...and I’m willing to sacrifice velocity for payload...I can assume about 1/2 lbs is the most I’m going to stuff in there.

Go to Grogs.

Save your fingers.

Max load is going to depend on the case youre using mainly since ideally that will go before your barrel blasts from your receiver.