Safe loads for a .69-75 cal

[Leatherneck]

I'll be ordering 2 barrels from a machinist later this year. One will be a 2ft long with 2 1/2+ wide base and the other one 17in with a 2in base. Both in 69 cal (musket) bore diameter.
I've damaged my carriages in the past because of violent recoil. Simple physics told me that the heavier the projectile, the heavier the powder charge and the more compressed and waded the entire thing was the more recoil I'd have. The overall weight of the gun itself would be also be factored in offcourse. 
What I'm getting at is, what is a safe and accurate load. I need to hear other people's avg loads for some consensus
The weight of the musket ball will be around 500+grs. I've had some success in the past while using as little as 40-60grs of BP as a charge.
Anything over 100gr is a waste of powder.
 
 
 
 

[Zulu]

Leatherneck,
One thing is sure.  If you have damaged carriages in the past, they were not built properly.  If you need help with that, please let me know.  A properly built carriage will absolutely withstand the forces of live fire.
Zulu

[carmy53]

One will be a 2ft long with 2 1/2+ wide base and the other one 17in with a 2in base. Both in 69 cal (musket) bore diameter.

Two feet long and only 2 1/2" wide. Is that right?

[Leatherneck]

Carmy, approx 20in long with 2 3/4 -3 in at the breech end. But Im gonna have to re-check.
Zulu, this was when I was working with barrels and carriages that were too light and out of proportion to everything else.
The new metal ones Im having made will be heavy enough to take the recoil alone than transferring too much of the force into the carriage.
I'll be using hex bolts to hold the cap squares down

[Double D]

In standard small arms calibers, such as .69, use the standard loads for the caliber as maximum...remember this is a cannon that is free to recoil un restrained not a rifle or pistol that is held to control recoil.  Use Fg or FF to keep pressure down in the .69 caliber.  The one blackpowder loading manual I have calls for .69 caliber round ball loads in the 70- to 80 grains of FG Max with round ball

Also heavier projectiles calls for reduced loads.  You don't need to compress in cannons.

 

[Zulu]

"I'll be using hex bolts to hold the cap squares down???"
 
Cap square bolts should run full length vertically through the side cheeks to properly secure them.
Zulu

[Leatherneck]

Zulu, yes that was my intent. It'll be easy on the naval gun, a bit trickier on the wheeled carriage.
DoubleD, I agree on the charge weight.