I recently got a new Exceed Forza .18 buggy and the stock glow plug died so I put in an MC-59 plug that the hobby shop gave me, but it's a tad to long, and I'm pretty sure I hear it bumping against the piston. Is this really bad, or is it okay until I get a new one? The car still runs, but I just hear the noise. which leads me to...
What kind of glow plug should I get that's short? It's around 70 degrees around here and I have 20% fuel, so I'm thinking a medium to hot plug?

Add some shims to it. I'm not sure where you can get it, but if you add shims, you raise the glow plug.
However, doing that will make it lose some compression too.

If it's hitting the piston, remove it immediately before you do terrible damage to it...

Either add an extra copper gasket like Doonagoowin said or replace the plug with an OS plug..OS plugs are shorter than MC's...

Since your using an MC-59 (hot plug) try an OS A3 plug, it is also a Hot plug but like i said it's shorter.

dont cause big bucks worth of damage and major repairs over a 5 dollar glow plug.. get that sucker out of there..

There is no way the plug can hit the piston.

o. well, i thought i heard a noise. but it might be something else......
how rapid would it be if it was the piston?

Most r/c car engines can rev up to at least 30,000 rpm's.

wow. so would I not be able to hear each click distinctly if it were hitting? cause i can count each one if i count as fast as i can

I can't speak for this particular engine and plug combination, but I can assure you that it is possible in some engines, particularly airplane engines that I can think of. I had an Enya .15 which was designed for a short plug but would allow you to install a long plug - try to turn it over and the piston would hit the bottom of the plug at TDC.

That said, I don't think the exceed engine would still be running if this were the problem......possibly detonation caused by the timing being advanced too far with that plug/fuel/shim combo?

How fast can you count?

i can count to 7 in one second...

LMMFAO. . . . Any idea how many people just counted to 7 as fast as they could after reading that.