Algodoo

Hope you read this comment, Algodoo's collisions are hideous at low densities (<10) so that's why everyone uses unrealistic densities, frictions and restitutions. One way to get away with default densities is by cranking the frequency a crapton, but remember that CPUs with no hyperthreading (especially AMD) work horribly bad on Algodoo so what you'd be doing is bogging down the sim speed for us poor people. So density helps a lot (always above 50), size helps even more (big guns, like 10 meter long, have nicer collisions, but tend to behave like in slomo, so you should avoid that), and frequency is something you should only increase if really needed, cause it gives the most lag. Avoid polygons whenever you can, those have worse collisions than simple shapes like boxes or circles.

i haven't seen your scene cause i don't have a computer close, but I'll see it later maybe this week and tell you some tips to make it better. Scripting would help you some but you can make perfect guns without it. good luck