On the Mosin, You have to bleed the cosmolene out of the stock bit by bit or have sustained heat. A simple way is to take the rifle, put it in a black trash bag, leave it in bright sunlight in the summer, and it will cause the cosmolene to liquify and make a puddled mess at the bottom of the sack (make sure no holes and it is a good strong contractor type bag. There are also quick and dirty ways that GI's used that I do not recommend for safety reasons.
The other slower way is to use some sort of absorbent powder and acetone (well ventilated and no nearby flames). First, clean off all visible signs of cosmolene including breaking down the Mosin into its parts and removing from stock. Swabs, paper towels, etc. Use a hair dryer or very carefully a heat gun (most generate too much heat) on a section until it oozes, shut off the heat source, apply the acetone, then the whiting powder (Brownell's sells it or in a pinch, baking soda will work, haven't tried the grease absorption stuff as most are too coarse to stay on the stock) which absorbs the grease. Clean it off, heat, and repeat until the stock is natural color. Did that process once on a fully cosmo'ed Mosin because I had used it pretty well with other stocks that were not nearly so impregnated. A lot of Mosins have shellac finishes and this will damage that. However, shellac is the easiest to reapply if you really want to but not really that good for a stock finish application versus oil or other finishes.
The whole sticky bolt action and chambers of Mosins is a known problem (
http://www.russian-mosin-nagant-forum.com/viewtopic.php?t=29477,
https://www.thehighroad.org/index.php?threads/mosin-nagant-chamber-question.434855/ ,
http://forums.gunboards.com/showthread.php?334235-Mosin-Nagant-m91-30-Extraction-issues )
The easiest solution is boiling water, repeatedly applied to the barrelled action via the chamber until the metal is hot enough to hold only with oven mitts. Then run a patch and bore brush through it. Repeat as necessary and then oil--the last thread and the last comment best describes this way. Also break down the bolt itself and soak/scrub in mineral spirits--although if you have an ultrasonic cleaner it would also probably work. Hardened gun oil and grease make for a bad experience with a bolt gun.
On the shotgun, I recommend calling up the folks at Brownell's and ask them about replacing the front sights as they sell them or it is a simple fix for a gunsmith--there is a calculation based on the length of barrel, the height of rear sight, and the needed height for the front sight which you can find on the internet. Usually, it is easier to use a taller sight and work it down than building up a shorter one but both work. I am currently having to find an acceptable front sight base and blade for an old Berthier m16 rifle (/sarc on/ the French assault rifle of WWI that is feared as the original M16 /sarc off/) that someone has thoughtfully shortened to a non-std. length.
