"No pin... not a problem at all!". Yeah - unless you are 'in the field' rather than the basement/garage/office. Enjoy removing the cylinder quickly, too.
Ah, the 627 Pro has a 'tweaked' mainspring - which lately means, at least for this and my nearly four year old 625JM, a ground strain screw. This offers less pre-load on the leaf spring when the screw is tight, as it should be to prevent working loose. This also makes the DA pull lighter. If you replace that spring with even a standard strength Wolff leaf, with that hollow rib, the DA pull drops appreciably as the pre-load is lessened even more. The end of the strain screw - especially if it has been filed or ground - will intrude into the hollow rib, further lessening the pre-load - and the energy available for the firing pin. Failure to fires will occur - sometimes even with Federal primers. A stock, ie, full length, strain screw will get you back to no ftf's with Fed primers, but a simpler 'fix' exists.
I change the strain screw to a #8-32 x .5" hardened SS socket headed set screw. You'll need to travel to your local Home Depot - they have them plastic bagged in a big drawer-filled cabinet for 2/$.56. Get some blue Loctite, too. Get to the range, bringing a proper sized Allen wrench. Insure the revolver is empty. Replace the OEM spring and strain screw with a full power Wolff leaf and the new set screw, after coating it first with blue Loctite. Adjust it to where the leaf looks like it was - and test it with Win/CCI primed ammo. If you get ftfs, turn the screw in (CW) a quarter turn and repeat. Continue until you have no ftfs, then add a quarter of a turn and put a drop of blue Loctite on the set screw's threads and let it dry at least overnite. If the revolver initially has no ftfs, turn the set screw out (CCW) a quarter of a turn at a time until you get ftfs. Then repeat the earlier steps.
This works great with a .22LR rimfire, like my new 617, and takes little time to accomplish. It's well worth it, too. Future removal of the set screw is easy - returning to the original good setting is mechanical - and easily accomplished. Boy did I get 'off topic'!
Merry Christmas!
Stainz