In no particular order -
The bolt is stainless steel. It is threaded into the barrel through one of the three holes in the lock. I assume the hole is provided for the nipple. Actually, it is one of three fasteners holding the lock to the barrel. I do not recall enlarging the hole. I will need to remove the bolt to get the exact size, but my best guess is 1/2" x 1". Let me know, if you want the exact size. Yes, the hole drilled through the bolt is the same size as the OD of the ramset cartridge. Nothing fancy the cartridge just slips into the hole and bottoms out on the cartridge rim.
The bolt (and cartridge) fit into the barrel approximately 3/4". Again, I can get you an exact measurement, if needed. I adjusted the height of the bolt head under the lock hammer with washers to get the proper angle between the bolt head and the lock hammer in order for the hammer to fully contact the rim of the cartridge. The vent hole angles from the bottom of the bolt hole back into the chamber. Vent hole diameter is .136". Originally I planned on using fuse and that was the size of the hole I put on my drawings. If I want to, I can remove the stainless steel bolt and lock and place a fuse in the hole. This WILL require me to puncture the foil on the charge with a pick. I went with a lock because the fuse I had would require a 7 second burn time - not safe and I did not want to wait that long to hear the "BOOM".
Cartridges slip into the bolt hole quite easily - when it is clean. I carry a .25 caliber bore brush in my "kit" to clean the bolt hole, when the cartridges will not easily fit - maybe every tenth round. The cartridges are "self extracting". All I know is that after it goes "BOOM", the lock hammer is still down; the lanyard is still in my hand; and the cartridge is somewhere other than I put it (never have found one of the fired cartridges). Cannons are not toys! I am sure standing over the top of the lock - or even slightly in front of it - since the cartridge most likely bounces off the bottom of the lock hammer - would not be a good thing. Of course, this would not be a good place to stand anyway. The cord on my lanyard is about three feet long. Sometimes I get a chuckle from the folks that want to shoot it, but think the lanyard is not long enough.
When the bolt hole needs cleaned - and I did not do it soon enough, I carry a pair of needle nose pliers in my "kit" to extract the cartridge. I have never had a problem removing a "stuck" cartridge. One pull and it is out - followed by a quick twist with the .25 caliber bore brush.