pistols, gunsmithing, handgunsThere are several bottom-ejecting shotguns available on the market.
If I want to replicate this behavior in a handgun, what smithing consideration will I need to take into account?
I realize that position of the magazine, etc will need to be shifted (perhaps a la a bullpup).
What else needs to be considered?
Sidebar - background information
Q - Why do I want a bottom-ejecting handgun?
A - To use it in a truly ambidextrous fashion
Ejection
The ejector itself would be tricky. In a traditional side-ejecting gun, the ejector is mounted to the frame opposite the ejection port. On your bottom-ejecting pistol, the ejector would have to be stationary relative to the frame, but above the ejecting casing somehow.
Now that I think of it, the extractor would somehow have to live on the bottom of the slide, riding on the frame. I can’t imagine that would be a very good place for such a part.
Feeding
The problem with bottom ejecting in a handgun is there’s just no good place to put the magazine. You could side-mount it if you’re into the whole Sten gun look, or you could top mount it like an FN-P90. Neither are terribly conducive to being a balanced handgun though. Also, the feed ramp won’t be able to live in a traditional frame.
Design
The more I think of it, the more I think this could be done in a non-traditional manner. Rather than having a slide-on-frame like most handguns, this could be one with an internal bolt. If you had a heavy barrel and a rearward, top-feeding magazine, there’s no reason you couldn’t make a balanced (if heavy) handgun that ejects downward.
The fundamental difficulty that I see is that semi-auto handguns feed from the bottom, so you want to eject in the same direction that you feed - which poses serious difficulties. The length the action moves when cycling is generally only that of one cartridge plus some extra. This allows for feeding from one axis and ejection from another. In order to feed and eject along the same axis you will have to either double (and then some) the recoil stroke so there is room to eject an old cartridge and feed a new one, or move the magazine off-axis to a horizontal or top position. (or go with a tubular magazine or similar arrangement. The result in any case would be highly unconventional.
I think that the solution to the problem that you face would be a caseless round. If I’m not mistaken the Germans experimented with such a design in the second world war. Caseless rounds have their own inherent problems, but for your specific use case they may be preferable, that is your decision to make.
Of course, this assumes that you are able to engineer the round and not just the firearm. If the question was more practical than theoretical (i.e. you intend to modify or create such a firearm) then I do not think that a home engineer will be manufacturing his own rounds! However for gedankenexperiment the concept is sound.
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