Reference site:
http://7.62x54r.net/ is excellent. There is also an excellent web page on the PU scopes with FAR more info than Lapin who claims there was only one manufacturer of the scopes. Evidence clearly shows many more makers.
Note that there are mistakes wherever you look. For example, the Soviets never called these rifles a Mosin-Nagant. Lapin's book and the 7.62x54r.net website perpetuate that myth instead of trying to correct it. It is more accurate to say Mosin (pronounced moe-zeen) 91/30 but even that is not their official terminology.
Lapin's book "The Mosin-Nagant Rifle" is very skimpy on the sniper rifles but is excellent otherwise. Mine is the 6th Edition. These sell for about $23-25.
http://northcapepubs.com ncape@ix.netcom,com in Tustin, Calif., USA. Sometimes for sale at bigger gun shows.
WWII Lee-Enfield No.4 Mk. I (T) sniper rifles. I bought my first one for $75 from Lever Arms about 1970 NOS in the chest (sadly let that one go later). About 26,000 were made during and just after WWII. Many were sold off surplus for low prices in the 1960s and early 1970s. The British and Canadians tend to sell off obsolete rifles quickly (they hate paying for storage!) and do not stockpile captured weapons (other than a few for training aids and museums). In contrast the Soviets were pack-rats. They cleaned, overhauled and STORED FOR about 65 years (!!!!) captured P-38s, Mauser Kar98ks etc. by the thousands and these are now on the market. Look also at the arsenal reconditioned (out of war reserves) Mosin 91/30, SKS and SVT-40 rifles. THOUSANDS of their warehoused guns are on the market now. In contrast to the c.26,000 Lee-Enfield No. 4 Mk. I (T) snipers built, over 185,000 Mosin 901/30 sniper rifles were made between 1932-1947 (Lapin 6th Edition p211) and even he does not know for sure and had no figures for 1943-1947! This is SEVEN TIMES as many Mosin sniper rifles compared with Lee-Enfield No. 4 Mk. I (T).
I have carefully examined about 10 of the Mosin 91/30 snipers sold to Canadian dealers by Molot as "sporting rifles" (rough translation). These came direct to Canada from Russia I believe, and I have no doubt that they are originals. The Americans are desperate for original snipers and are often rescoping de-snipered rifles (scope and mount removed, mounting holes plugged and rifles reissued as regular rifles by Soviets). They are now jealous of Canadians (!!!!!) as we can import SVT-40 etc. that they cannot. I doubt that the Molot rifles came through the USA as they would have gobbled them up. I do admit that I have not dismantled any to see if there are hidden USA required import markings, but I can say that no such markings are visible on the outside. Some of the Mosin 91/30 rifles imported into the USA have made their way to Canada and I saw one with a replica scope set-up in a store a few months ago.
Buyer beware, try to examine it. Know what markings to look for.
I have also seen other Mosin 91/30 faked snipers. New replica PU scopes are lighter, have a blue tint and often say MADE IN RUSSIA. Original PU scopes ARE available of eBay contrary to what some dealers say. Buyer beware of course. Originals MAY have a year or may not. A 1943 rifle would notmally have a 1943 PU scope BUT may also have an earlier PU scope made for the SVT-40 and moved to a Mosin when the SVT-40 was phased out more or less as a sniper after 1942.
When a rifle is converted recently, the bolt handle is either altered or replaced. The stock has a notch cut in the left side to clear the scope mount. (Look for quality of work and especially for ageing, or lack therof, on the cut surfaces).
Interestingly some of the strongest opinions are held by those who have not done their research. I had one collector on CGN tell me that of the two letter prefix in the serial number that "C" as a first letter was a sniper and the second letter was the year. This was info from a US web site, complete with an annotated photo, but it was completely wrong. I have seen enough dated rifles for example to blow the theory out of the water. I suspect that the American who had posted the information originally based his theory on one rifle. The two letter prefix - these pairs of letters appear to have been used in RANDOM order so if one has a 1944 rifles one cannot assume that the one with "lower" alphabetical letter was made before the one with "higher" alphabetical numbers. No one yet knows why nor does anyone have a master list.
Recommendation: Look for a Molot Mosin 91/30 in the white cardboard box (Russian end-label) and including matching mount, scope, tools, oil bottle and mini-sniper manual in Russian with certificate in last few pages listing the rifle and scope SN as it left Russia c.2012. Ideally find one without the electro-pencilled rifle SN on the scope mount (most have it). These are still good but no electro-pencilling is better. If you have a choice, the Tula made are more scarce and more desirable desirable than the Izhevsk made examples. The Tula sniper rifles have the "CH" for sniper stamping (not mentioned by Lapin but clearly indicated in well researched web sites, sites often maintained by people who live in the former Eastern Block countries who speak the language, have access to military surplus and archives etc.) whereas the Izhevsk rifles do not. Expect to pay $650 (if you are really lucky) Canadian and up for a Molot arseanl reconditioned Mosin 91/30 sniper , plus taxes and possibly shipping. Slings are not included. By the way, that is as good as it is going to get because non-reconditioned "factory original" Mosin 91/30 snipers are extremely rare (e.g. Vietnam War captures).
Unconfirmed, but I hear from dealers that the Mosin supply in Europe is drying up. Having seen this happen with other rifles (e.g. Lee-Enfields) in the 1970s etc. I predict that good originals, especially original sniper rifles, will go up in price as the supply dries up. It would not hurt to put away some SKS, SVT-40, Mosin 91/30 and Mosin 91/30 sniper rifles still in the grease in heated storage for a decade or two. If friends are throwing away or selling off dirt cheap original parts from SKS for example that they have sporteized, grab them and put them in long term storage too. Think of the sporterized Lee-Enfields that many owners are working to restore back to military specs now. By the way, all that cheap ammo now for the Mosin/SVT-40 and SKS (two calibres I know) will dry up just as the surplus .303" and 7.92mm and .30/06 has dried up. So put away some crates of sealed ammo to for the long-term. No I am not being a US "survivalist" here, I just feel this is a long term investment opportunity ... assuming of course that the Liberals don't get back in and ban everything.