I just got a S&W M10-5 and it has a problem...

It didn't when I was looking at it, but now once home with a closer inspection, it does. Here is the issue, 85 % of the time it works great.

15% of the time when the cylinder lock drops it quickly jumps backup and the gun seems jammed. Since the lock re-engages the cylinder before it rotates and due to the fact it is in the locking groove - locked in, the gun wont cycle. Usually when it jams it just catches the tip of the lock and isnt fully in the groove. I don't want to force anything, and the grooves on the calendar seem undamaged.

This problem occurs when the gun cycles - both single and double action.

I need feedback....

From quick reading and looking at it, maybe it is the spring or the actual cylinder lock? or is the timing totally off & it needs an overhaul.

Here is the bad part - I am in Canada and we have draconian gun laws and this thing needs to be fixed north of the 49th due to all the paperwork that would be required to have a real US smith work on it.

Several parts are at work here so it's difficult to diagnose properly without examining the gun. During operation, the tang or "hook" at the front of the trigger pulls the cylinder stop down, allowing the hand to then engage and rotate the cylinder. The most common cause of your malfunction would be excessive wear on the hook located at the front of the trigger, or wear/improper angle on the bevel of the stop. Both of these problems could contribute to the cyl. stop not be pulled down in proper sequence with the start of the cylinder rotation, and the cylinder remaining locked as you describe. One or both of the parts may have been improperly fitted or perhaps the part(s) (trigger/cylinder stop) have been modified by a previous owner to the extent that they no longer function properly. If you don't want to send it to S&W, a competent, local gunsmith or S&W armorer should be able to diagnose and repair.

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Ret. LE, FA Instr, S&W Armorer

Send it to s&w. Should be totally free.

Try a new cylinder lock and spring after a complete cleaning and lub of the internal parts.
A good chance that "Bubba" has stoned too much metal fron the front of the trigger.

First best thing to do in instances like this is detail strip the gun, clean and inspect it, then reassemble. It's kind of like rebooting a computer -- it occasionally clears the problem without revealing what the problem was. Magic.

Beyond the simple approach, what you're describing sounds like:

1) A malfunctioning cylinder lock spring. This is a fast easy swap out for a new one.

or 2) One or both of the contact edges between the cylinder stop and the trigger have worn (or been bubba-ed) down. This requires either a replaced cylinder stop, trigger, or both. That's more involved and unless you're experienced or handy and willing to learn before you try it, best done by a qualified revolversmith.

Remove the sideplate and clean the cylinder stop and the area around it thoroughly. Pay particular attention to the stud and the elongated hole in the cylinder stop.

If that doesn't fix it install a new MIM cylinder stop and spring. They're normally a drop-in. The MIM cylinder stops have slightly more engagement with the trigger. See how that does.