Let's assume we're not talking about a home shop- but an aluminum casting in an industrial application (pressure fed die or maybe a vacuum setup)- I would venture a guess that cast aluminum is going to be more brittle than a forged then machined part- would there be an significant issue as a result of this on a breech- i.e. odd stresses that might encourage cracking?
I really am not qualified to answer your questions as to the suitabliity of die cast aluminum breeches, etc.... nor to the amount of follow-up machining (if any) necessary to complete them....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
Although I was in the metal fabrication business, the more one knows the more one realizes that they are not qualified to give a hard and fast answer. With that said, a guess on my part would be that in addition to the brittle nature you suspect, there could be a porus texture from the crystals that could make the part permeable, that is leak gas (in this case).
I suspect that if it was do-able and cheaper the Asian guns would already have cast breaches
Rob
True enough in respect to porous- but that assumes the breech itself would hold any gas. A huge number of BB guns have cast -something- frames and 'breeches' in as much as an integrated unit could have- but not generally aluminum, but I assume this is a cost factor. Look at the number of Co2 guns with plastic breeches- I think the key to any of this is to keep pressure to a minimal flow length within the transfer system made of more typical airgun materials (steel, brass, forged aluminum). I'm thinking the most stress on a breech is created by holding the barrel in place and possibly at the cocking knob area.
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