Steam works great! I used them on my C&R Mosin Nagants. Lowes has a nice unit with several attachments under $100.00. It was a holiday gift to my wife but she lets me use it too!
Here is a before/after picture of a steam cleaned oil can from a Mosin Nagant :
Should work fine as said. Be careful on the wood. Steam can be helpful and a hinderance. Some finishes will be ruined with steam. It can be used to swell the fibers of wood to remove all or part of a ding without having to sand a dimple into the wood.
I used a 5 gal bucket and a quart of mineral spirits and poured it over each part of my Mosin.. then wipe... then pour and all done... It disloves all the the cosmo and does not harm the wood...
Be sure to dry and oil ASAP or rust will form.
Mineral spirits was the only thing that got the bore clean as well
I know this is old, but i figured I'd just throw in this. Bissel is a good brand name and I have this steamer. It works perfectly on cosmoline on the metal parts, not so good on the wood, and the last Mauser I bought was covered bore to butt in the stuff.
If i still have it in the garage i have a cosmoline oven(metal trashcan with lights in it) that i havent used in a while, i would gladly give it to someone who could use it. If someone is intersted Ill have to go look and see.
I've always used mineral spirits. I break the rifle down and place everything into a wallpaper tray (http://www.doitbest.com/Paper+hanging+tools-Leaktite+Corporation-model-30-doitbest-sku-774736.dib ) and pour in enough MS to cover. Let everything sit for a while, depending on the extent of the cosmo coverage. Then wipe everything off with a rag. Once all of the cosmo is off, I rinse everything in hot water and then let dry thoroughly before continuing. For all metal parts, after rinsing I dry and them wipe down with oil to prevent rust.
If you don't want to use MS for whatever reason, then Simple Green or Purple Power works as well. Both are heavy duty cleaners and are available at hardware or automotive store. If using Purple Power, make sure to wear rubber gloves as it will do a number on your skin.