I got a C&R ffl just so I could have 1895 Nagants delivered to my front door. The Serbian ammo is the way to go here. It bridges the b/c gap, as it is designed for safe use with the Nagant. Starline briefly made brass for them, too, dropping them due to the thin mouth tearing during subsequent reloads, similar to Fiocchi's brass. What to use is up to the owner, but $25-$30/50 Serbian made beats the $50+ for Fiocchi - and it seems to be just as 'hot' - if 750 fps can be considered 'hot'.
The Nagant's chamber is tapered, thus the straight cased .32 S&WL (and H&RM) will bulge near the rim, the softer S&WL cases actually tearing. The reverse forcing cone forces more propellant particles, etc, out the gap if shorter cases are used, too - so always wear safety glasses when shooting anyway, but especially with the Nagant. I think the pressure of the H&RM cartridges may be too high for the Nagants, so I would limit it to S&WL, if you can't find the Serbian ammo.
I mostly shoot .32-20 cased ammo in my Nagants. Really! Okay, they are all modified... I do obscene things to the cases first. I take off ~ .010" off the rim thickness - and ~.024" off the rim's OD. Then I size it with a carbide .30 Carbine sizer - and load it with the rest of the Lee '1895 Nagant' die set - basically .32 dies. I use SP primers, ~2gr Titegroup, and a 100gr DEWC (.312") from Meister - it gets close to 700 fps and the spent cases drop out. FYI - real Nagant ammo, like the Serbian Hot Shot, bridges the closed gap from the chamber's concave exits to the forcing cone's convex extension. The thin case mouths expand slightly, making ejection somewhat more difficult than the typical DA cf revolver, so the Nagant includes a rod, a la the typical SA revolver, for case extraction. It holds 7 rounds - but takes a while to reload. Of course, then there is the typical 20+ lb DA pull... It really is pretty much a PITA... but neat!
Here is one of my Nagants - with some of my homebrew ammo described above:
Stainz