I'm new to this so forgive me If I don't sound like I don't know much about making mortars ( and I don't) but wouldn't the whole barrel ,trunions and all be cast and then machined as one piece or is that harder to do if it's made of steel? Scott
That's the way and the reason casting is done. It is a process that simplifies things by making an assembly in one piece - the added cost is making a complex pattern and a little machining here and there, but the payoff comes from making a bunch of them with a reuseable pattern from cheap materials (cast iron is very cheap).
The alternative is to put together an assembly - much more machining of every part, fitting the parts together, fastening the parts together - time - time - time! More costly WHEN you make a bunch of them. If you're only making one - machine it - cheaper than casting ONE.