Low Tech cannons mortars and shells

[Rupert]

Originally Posted by Varyon

LE also shows up in 4e HT, on page 169. It notes they first showed up in the late 15th century, but didn't become common until the early 19th. It gives a value of 15% shell weight being explosive filler (black powder); it notes there is fragmentation involved, but as is the general rule for generic explosive shells in HT, it doesn't give any inkling of how much fragmentation is appropriate.

Fragmentation damage is 1d per 20mm of warhead diameter if there's enough fragmentation to give a fragmentation effect as GURPS understands it.

I use a general rule of thumb that you can give up 1d of cr ex for 2d of fragmentation (to a maximum of fragmentation equal to the explosive damage), with the exact amount basically determined by whoever designed the shell.

UT doesn't seem to assume any loss of blast damage to get fragmentation. Nor do the stats in HT for the 105mm M2A1's HE shell and the 3" Stokes mortar.

Of course the DM51 hand grenade does, going from 5d to 3d+2 exp when the fragmentation sleeve is used (3d frag). This suggests half the explosive energy goes into the fragments. However, the way GURPS does fragments implies that as the warhead gets bigger the energy put into the fragments drops, as a fraction of the total (which is questionable), and for artillery shells it could well be negligible.

At low TL's, I don't think fragmentation is properly understood, so it might have a maximum of 1/2 the explosive damage, and I'd probably treat shells that aren't designed with any specific amount of fragmentation in mind as having 10% to 20% of the explosive damage in fragmentation (to be clear, this means a nominally 10d cr ex shell would typically max out at 6d+2 [6d+2] cr ex, at low TL's would max out at 8d [4d] cr ex, and if not specifically designed with fragmentation in mind would probably be around 9d+1 [1d+2] cr ex. This isn't necessarily realistic (it's based on the performance of the Diehl fragmentation sleeve, which is rather different from typical fragmentation), but at least it allows one to make explosive rounds that didn't exist historically (or at least aren't statted up anywhere)...

The big change in fragmentation of shells hasn't been an increase in the damage they'll do, but in the amount of fragments and the consistency of fragmemtation. In fact, a TL3-4 shell would most likely create only a few fragments, but they'd be very dangerous for a great distance assuming you were unlucky enough to be hit by one. The primary damage from those old shells was the blast and incendiary effect.