I understand that these rifles' accuracy will be heavily influenced by the ammo. Keep in mind that the Russian army has used the 7.62x54 RR for firearms (sniper rifles, Moisin Nagant 91 Infantry Rifles, and MG's ) back to the late 1800. This round is also manufactured for the Russian PK and PKM General Purpose Machine Gun. In this case, for machine guns, it is desirable to have some dispersion in machine gun fire. Ammunition made for this purpose can be made to looser tolerances. Thus, if you use ammunition manufactured for machineguns in this rifle, this may cause some disappointments as the rifle will surely not perform to your expectation. The 148 grain LPS ball ammo or the 181 grain yellow tipped heavy ball load (this was made for the M 1910 Maxim) may yield marginal accuracy, perhaps 2-3 MOA at 100 yards.
Commercial ammunition such as in the 180 grain loading, is available in the US from companies like Norma, or those from Sellier and Bellot. However, these are made for hunting and can be quite expensive.
Wolf comes to mind as a supplier of ammunition for this type of firearm. Russian 7N1 ammunition will be the most optimal ammunition as this is Russian ammunition made for modern Russian sniper rifles. But this type of ammunition is harder to obtain. I understand that due to their primers, Russian ammunition has an effective life of about 10 years. After this, the accuracy begins to deteriorate. If you could obtain the dedicated Russian sniper ammunition, you should see sub MOA accuracy.