baikal makarov mp-654k tool problem

[tgonzo]

hi to all !
I own a baikal makarov mp-654k and the magzine's rear (faced to firing pin ) gasket is leaking, so i have to replace it.

The problem is, i can open the co2 screw (where the co2 cartridge is screwed /placed in) to the expansion chamber with the baikal multi wrench (which had come with the air-pistol). But in case I can't open the special-screw a the rear top of the magazine, where the firing pin hits the valve to expand the air to the bb.

Any ideas how to open this special screw, or how a wrench or bit is called?
how is this screw called? (screw with a hole inside)
Please help me !!

http://two.xthost.info/studentshare/mak-mag.jpg
(i added a photo to the link above)

Thanks Tobias

[Firestorm]

Hold firmly in a vice, then use flat blade screwdriver as a punch and "tap" the nut loose by putting the blade of the screwdriver against the slot (anti clockwise).

Russ

[tgonzo]

thanks