If you drill in for the fuse hole at a 90 degree angle, and you use aluminum foil bagged powder charges, you have to deal with making sure that the hole points to the right location no matter the charge size. If you drill too close to the rear, it may miss the back of the powder bag. If you drill too far forward and are shooting small charges, it may miss the front of the powder bag. Be aware that a short charge loaded with a round ball projectile may not sit perfectly flat when loaded.
On my mortar, which has no powder chamber, I drilled in at a slight angle that starts closer to the muzzle and enters the chamber pointing to the lower third of the bottom of the bore. It enters far enough forward that it won't miss the rear of the bagbag, and since it points toward the bottom of the bore it will hit that bag no matter how small it is.
Such an angle is prefered on a mortar due to the 45 degree angle that the mortar sits at.
On a horizontally mounted gun, you can face the angle either forward or rearward a few degrees to accomplish the same goal. I believe that traditionally they enter closer to the rear and angle forward upon chamber entry. I think the angle was there for the same reason as had when drilling my mortar. An angle that starte from the rear and enters the bore right at the base of the chamber, angling towards the muzzle, could utilize a steeper angle than the mere 4 degrees that I chose for my mortar. More angle going from rear to muzzle, and entering very near the base of the chamber would guarantee powder bag puncture no matter how long or short the bag was. A hole that entered from the rear of the chamber on the same axis as the bore would be the ideal angle from the perspective of ignition.
However, Like CW says, consider where it is pointing the residue. A hole that is ideal from the perspective of ignition would be far from ideal from the perspective of bystander safety. Some sort of compomise is mostly likely in order.
On my carronade I drilled in at a 90 degree angle. I forget exactly, but I think the center if the hole was something like .200 from the rear of the chamber. Unlike a mortar, there is no need to use light charges to adjust range so I am not afraid of ever having a charge so short that I will miss the front of the powder bag. On the mortar, which has no powder chamber, my charges are full bore diameter. Light charges (100 Yard shooting) are really, really short. Even with the angled fuse hole Ignition is sometimes a bit flaky if I reduce charges much below what will land a lead ball at 100 yards. A 7 inch long, concrete filled piece of muffle pipe weighs half as much as a lead ball and I can't get reliable ignition at anything less than a 200 yard load.
Another factor is projectile shape. If you are using a round ball you won't have this problem, but if you are using a cylindrical projectile and the charge is light, the base of the projectile might be so far rearward that the hole is blocked by the projectile base. I found that our when shooting my concrete filled muffle pipe rounds. I guess that would give an advantage to a hole that starts very close to the bottom of the chamber and enters angling somewhat towards the muzzle.
Rick
