I saw those cool machines that pushes the tobacco into an empty filter cartridge. So instantly "light bulb", what if instead of tobacco you use weed. You would have a perfectly rolled joint with a roach and undetectable by police from looking at it. My questions are would the filter take out THC and other good shit?, How much weed per cigarette?, and personal experiences?.

The regular cigarette filter will filter out the THC. It's better to make a long cardboard roach the size of the filter and squeeze the cig filter out and replace it with the roach. You have to roll the cig filter between your fingers until a little bit of it is above the filter paper, then grab it with tweezers and rip the whole thing out.

"Secret Agent" cigarettes are virtually undetectable, but the smell could possibly give you away if you get too close to someone who can recognize it. That's not very likely though. Use about as much weed as you would put in a normal cigarette.

I've heard cig tubes burn shitty when you put weed in them, but I've never tried them myself. I use a rolling machine made for regular papers, and no one has ever said anything to me. You can make these "secret agents" without any kind of machine though. Like this:
http://420genetics.com/forum/showthread.php?t=1672&styleid=28

I made a few just like that and smoked them with my girlfriend when we were out one day. Nobody noticed anything, but like I said, nobody notices anything when I smoke an unfiltered machine-rolled paper either. However, if you're super paranoid or you're going to be in an extremely public place, give the secret agent a try.

I've done this before because I was out riding around and had no papers, make sure you stuff its decently enough so it doesn't end up being loose, make sure that it is broken up good without any stems or it'll fuck it all up. The filter can be ripped off just as easily as any regular filtered can be.

Works alright in a pinch...

While I don't doubt cig filters take away some THC, I have used them for years in my joints and have noticed absolutely no difference between filtered and unfiltered. I can honestly say that the loss is very minimal, practically nil IMO. I do cut the filters in half though.

you roll filtered joints?

you roll filtered joints?

Yeah, pretty often. I just use the cut filter as a roach. Makes rolling easier.

I've never seen anyone do that one before man...

you could also take something like a tiny screwdriver and punch it through the filter, creates a more open hole for the smoke to be pulled through...

or just buy a roller...

from a distance people would think your just smoking a cigarette. not all cigarettes have the brown filter, like marlboro lights...

Mix it with a teeny bit of tobacco, makes for a smoother burn, and the smell becomes virtually undectable

You could just push/pull the filter out and replace it with a piece of cardboard and put half a cm of tobacco for the sake of smoothness while smoking the weed part. I used to do that all the time back when I'd smoke joints while going for walks. Another thing is that you could just carry around rolling tobacco, some papes, and some rolling filters and if anyone asks just remind them that pre-made cigarettes are a spectacular rip off. I do this all the time. The rolling tobacco even tastes better than rolling a spliff with tobacco from a cigarette.

As for the cigarette machine that pushes the smoking material into a pre-made tube, its kinda shitty. You can do that by hand, the machine only saves some time. I recommend getting the rolling machine. I have one from back in the day when they were common, got it at a yard sale. It rolls one, extremely long cigarette and you cut it into 5 standard length cigarettes using a razor blade. No filter, but it came with the original papes. They're so stale that they're as hard as regular printer paper XD but the glue still sticks.