New shooter. New gun. Just did field disassembly and inserted mag loaded with snap caps. Not sure how but slide locked open with cap in barrel and one in chamber. Cant reset slide forward. Cant release mag. What the heck might i have done and what is remedy?

Was the gun fully assembled before you inserted the magazine? Can you take a picture from the right side and from the top?

With the slide lock engaged use the eraser end of a pencil and press back and down on the top snap cap in the magazine. While depressing the snap cap - press the mag release and withdraw the mag. Disengage the slide lock and let the slide go forward. Retract the slide and eject the chambered snap cap. If it won't extract poke it out with the pencil. If that snap cap continues to cause trouble trash it. Another way is to use a pointed object inserted into the mag floorplate to depress the locking tab. Depress the tab, slide off the floorplate and spring,the follower and other snap caps will fall out. You may want to do this in a plastic bag to contain things. Disengage the slide lock and let the slide go forward. Retract the slide and eject the chambered snap cap. If it won't extract poke it out with the pencil. Pay attention to the arrangement of the mag parts so you can reassemble it correctly.

Best Regards,
ADP3

Thanks to both quick responders! Pencil eraser was a good fix. Have a safe but fun new year!