Straight razor on a plane to Moscow from abroad

You have to differentiate between 3 things:

1. Government air travel security restrictions
2. Airline policy
3. Customs restrictions

Number 1 depends on the airport of departure (and any other airports where you get re-screened). For example, if you fly from the USA to Moscow, a straight razor would be most likely allowed in checked-in luggage (but forbidden in carry-on) by TSA rules. If you fly through a re-screening airport like AMS, the rules of the security agency at that airport will also apply (which I'm guessing are similar). I can't imagine why security rules at any airport would forbid blades in checked-in luggage.

Number 2 depends on the airline. Airline policies try to reflect #1 above, but don't always match it exactly. From what I know, airline policies that are not also government rules are poorly enforced, and besides, I can't imagine why any airline would forbid checked-in blades.

So you probably don't have to worry about #1 or #2.

Number 3 can be tougher. It has to do with whether something is allowed into the country at all, and has nothing to do with air travel. For example, Canada is very strict about it - many things (including many types of knives/blades) are considered weapons and are completely prohibited, failing to declare them is a serious offence. For customs, it doesn't matter of course if the luggage is carryon or checked in - everything can be searched. However, I doubt Russia's customs rules on potential weapons are as strict as Canada's, and I think a straight-razor should be fine - after all, they must be used by Russian barbers : ). But if you want to be sure, you need to check the customs rules (as well as Russian laws about carrying such a blade in public).

By the way, there's another concern in Russia, both in airports and elsewhere: There are many security checkpoints (at entrance to railway stations, airports, etc - even before you have a chance to check your luggage) with X-Ray machines. They are mainly designed to detect guns, bombs, etc, nobody will probably care about a blade (as long as it's generally legal to import and carry, see above). But if you bring one to the airport, you might get a talk from the security checkpoint operator about the fact that you must check it in and can't carry it on (this happened to me once when carrying a souvenir knife into a Russian airport).

According to the S7 Airlines baggage policy, there is no restriction on blades in baggage (or even carry-on baggage, which is surprising and probably not accurate).

From the Federal Customs Service, The list of personal-use goods which import and (or) export from the customs territory of the customs union is banned or restricted, blades are also not mentioned. I don't imagine a razor would fall under the category of "civilian weapon".