There is a Video on YouTube (it wasn't one of yours i think?) of an old man with arthritis that build himself a battery powered Crossbow with a self-reloading mechanism that actually had about i think 10-15ish Arrows in it's magazine and quite good cadence.
Also did you ever try to rebuild something like this?
Also comparing all of your recent contraptions I'd say you probably be better off with your compression-powered Arrow-Gatling, probably even more so if you managed to adapt a regular 300bar Paintball Air Tank so that you wouldn't have to pump all the six coke-bottles by pure muscle-power
And regarding the Paintball-Markers how do they actually regulate that they just have 7,5Joule?
To my knowledge you Guys are limited to about 215ish fps right? And this is achievable with regular 7,5Joule Markers i guess?
So comparing the weight of a regular Paintball which goes in at about 3 to 3,2 grams we are talking about a difference which is at best twice the weight (6grams).
I just weighted a regular marble which comes out to be 5,36g with an additional rubber-coat it would probably get at the maximum to a weight of (6grams) if at all. a thin bit of rubber layer barely acting as a sealant isn't going to ad that much weight.
Also please correct me if i am wrong, but isn't the 7,5J Limit measured with regular (therefore 3g) Paintballs and would an increase in projectile-weight of almost the double result in significant higher Joule-Output if the velocity drop wouldn't be too big? (That is the big IF as i couldn't find any numbers where this was tried out with "German" paintball guns.)
Still i hardly doubt that the velocity would drop drastically with this kind of ammunition to a level on which it would be considered "not harmful at all", i found a Video of as far as i can tell a German guy which tries out shooting marbles with silly results, but i wouldn't consider this something out of the ordinary as regular marbles are 14mm wheres .68 are 17mm so no sealing no velocity...
Also don't underestimate the effects of your regulated Paintball-Gun even with regular Paintballs.
On close distance (5-10M) you definitely get bruises that hurt like a mofo.
And now imagine getting shoot with 20-40 of those in a second if need be right in the face? And still having at least 80 more left if it really need be?
Lets face it in Germany you are screwed if you don't want to go the close distance way of fighting of an attacker and aren't one of the few gun-owners in 82Millions.
The only viable exception you have that is forgiving if you don't hit on first try are probably paintball guns & nail guns, although you probably gonna tell me next that they are restricted too
Regarding Bows, as an avid archery nut since childhood and a bow-hunter since adolescence i can tell you forget about a Bow as a self-defense weapon in close quarters!
There are techniques to reload and shoot arrow pretty fast but forget about doing them in confined spaces an arrow alone is about 30-ish" long and a bow capable of fast reloading with proper training (hardly imaginable with shorter axle-to-axle compounds) is at least 56" axle-to-axle.
And BTW. the only benefit a sling-bow is its compact size that might sound intriguing at first (confined space remember?) but doesn't change the fact that in all other regards it fells behind a regular bow as the arrows are just as large and reloading them as fast is simply impossible.
There are just two things Pro-Slingbow and that is compactness and that you will get a good aim with them faster than with your regular bow.
Also lets do some reality-check here shall we?
Most home invasions happen ether on holidays on broad daylight / night or at night on regular days so now imagine hearing noise coming from downstairs so what would be the first thing i do?
Getting my Quiver and Bow in my half-asleep state and go "hunting" for those sneaky little thieves?
It just doesn't sound realistic at all to me, also one should never underestimate the impact that this could have legally if you happen to kill somebody by pinning him to your wall and that somebody happened to be armed with nothing at all.
"Yes Mr. Coroner i totally acted in self-defense when i pinned that life threatening thief with my self made spear-gun contraption to the wall... twice."
Doesn't sound right now does it?
I guess you could still dig up a hole in the backyard if SHTF (or better yet SHTT Spear hit the thief
), which is one of many benefits of country-side living, aye?
EDIT: @BeMahoney not long at all, even Bows & Crossbows shouldn't be left stringed up for a prolonged time because the bow-strings get longer&longer and rubber is even worse by a multitude in this regards but to give you a few numbers, Recurve-Bows shouldn't be left stringed for more than 3-6months tops if you want to have adequate String-Life the same applies to Crossbows except that you can actually cock them and to quote a Crossbow Manufacture CEO you shouldn't let your crossbow cocked for more than 1-2 hours tops or else your string-life will be reduced drastically.
@DaveyJones
In Germany where an invader is most-likely not in possession of a gun i would go with a chainsaw if it would need to be a close-range weapon for two reason:
1) Is there anything more frighting than the sound of a chainsaw in a room that was previously dead silent in the middle of the night?
2) It is a f... chainsaw!
EDIT2: Sorry for the Text-Wall