So I've been working on some design notes for a fully functioning (and by functioning I mean useable, not just actually fires) gun blade. First I've identified the ideal place style as the Celtic Falcata, this is a single edged, machete like combat weapon that is short and designed to be wielded with a single hand.
As you can see here the blade in this type of sword curves after a certain point, this drop, while providing a brutal and efficent slashing weapon, also clears the barrel of any potential weapon mounted along the spine of the blade. The real issue as I see it is keeping both weapons comfortably functional within their own rights from a care and maintenance stand point. A revolver based gun blade I see as being impractical, welding or merging the barrel of the firearm with the blade itself would A. impact accuracy by placing pressure on the barrel and B. make a barrel change a nightmare.
I then considering semi-automatic firearms. With the technical consideration that a longer barrel is likely better in this application and that the receiver of the pistol is going to have to be married to the frame, most likely via welding, I think the logical choice is a long slide 1911 in .45 ACP, To retain ease of take down and accessability, "rails" and a slightly fuller on the back of the blade, as well as a groove to let the barrel bushing turn will be required, but they shouldn't affect performance or the bladed part of the weapon. If there's a fouling concern, a small metal insert could be made to bolt in covering the bushing fuller (I'd use small screws here, like pistol sight small)
Attachment of the blade to the reciever is a bit of a bug bear as it needs to be both functional, and look attractive, there isn't much "play" in a 1911 receiver, so except for a small on through the trigger guard, bolts aren't an option, which leaves some very careful and tricky welding. I'm not sure that will be enough to stand up to regular heavy use. With a normal hilt (on a well made sword) the tang of the blade extends well into the hilt providing it strength. With the attachment points so close to the "surface" I'd find certain types of impact on the blade worrying.
Keeping the blade light enough that the pistol still swings easily enough for one handed use is another point that can be countered with fullers (improperly refered to as blood grooves) and just generally keeping everything properly balanced to start with, though excessive fullering of the blade WILL weaken it.
This is just my initial thoughts on the matter, but I think these technical issues are all pretty simple to overcome with some applied research and maybe a few test shots and consulting with local swordsmiths.
