With the stock off and the receiver upside down, just pull the bolt back with your fingers and lift up. I have Marlin Camps in 9mm and .45acp. I upgraded the recoil spring in the 9 to a 16.5lb and the one in the 45 to a 21lb. from Wolff Springs. They are very undersprung from the factory. I now shoot +Ps in both with no battering as well as 45 Super in the Camp 45. The Camp 45 spits out 185gr. Texas Ammo 45 Super's out at 1572fps and 1015ft/lbs, talk about a sweet and handy little deer carbine!! The Camp 9 launches 115gr. CorBons out at 1505fps and 578ft/lbs.
The Ruger carbines are nice looking, but my Marlins will outshoot them all day long and plus I didn't support the man that helped Klinton out with the 10 round mag limit by buying one. "No law abiding citizen needs more than 10 rounds". Damn you Bill Ruger!!