Somebody put in attachments of a copy of an old
American Rifleman article written by a Finnish ordnance officer who was an army ammunition inspector in another AS forum topic a good while back. This gave details of a Finnish State Cartridge Factory study which was part of developing a national free rifle cartridge in that country's days of using the old 7.62X54R Russian number. The study was primarily concerned with the effects of the bullet v groove diameters match with specific reference as to how different sizes coped with barrel wear and tested three diameters of 200gn Lapua D46 FMJBT match bullet - 0.3118-3122 / 0.3087-3091 / -.3063", the first / largest size matching the grooves. The rifle and 27.37" length barrel are described as being 'of a special make' and the chamber, leade and rifling were cut to closer / tighter sizes than on a standard military Mosin rifle, the rifled section at 0.300/0.3118. There is no mention of barrel material or rifling method, but presumably chrome-moly and a faster / cruder form of cut rifling than employed on
@FrankG 's Bartleins. Ballistics were 39,000 psi maximum chamber pressure from Dupont #17 powder for 2,362 fps MV from the long barrel.
Unsurprisingly, the bullets sized to groove diameter shot the smallest groups and the more the bullet was under groove size, the larger the average group size. This applied throughout the very high round count test with no change in relative performances between the barrel being new and at 14,000 rounds. After that round count, groups became larger but those for the smaller diameter bullet grew more and faster.
Testing the two smaller sizes was discontinued at 18,000 rounds down the barrel, but carried on until 23,000 for the 0.3118" model.
There is no description of the daily testing schedule, but unless the exercise lasted many, many years, one presumes a lot of rounds were fired each day - no shoot 10 and wait an hour for a completely cold barrel type regime I'd have thought! A graph showing average daily group sizes for each bullet diameter is a pretty well horizontal line for the 0.3118" dia bullet from the 1,600 shot mark to 14,000 rounds. Groups started larger with the new barrel and fell until 1,600 rounds when they stabilised - the report talks about the barrel being 'run in' at that point. (6.5-284 this is not!) After 14,000 rounds groups grew steadily by plus an inch / 1,000 rounds.
I remember being astonished at the Finnish barrel's longevity on reading the article. It compares favourably with another barrel life feature I saw elsewhere at around the same time which commented on two military spec AR-15s used for training in a US shooting school or club which were retested after having fired an estimated (IIRC) 9,000 and 15,000 M855 rounds and produced large / scattergun 100 yard groups respectively. Their barrels were then sectioned with pics in the feature and the 15,000 round count example was a smoothbore for most of its length. Little cartridge, but 55,000 psi pressure and I presume lots of rapid semi-auto (full-auto too?) fire.
It is rumoured score benchrest competitors who use the .30BR - a lot less powder behind a 30-cal bullet than 7.62X54R but 55,000 psi + (?) pressures - don't know the cartridge's barrel life as nobody has ever worn one out. A range myth I'm sure, but with enough truth in it to hint at astronomic accuracy life round counts by BR standards I'll bet.
I would rather spend my money on reloading components than rifle barrels. Our game does not require guilt edge bench rest accuracy. The silhouette targets are big. When I can out shoot my barrel it's pulled and replaced. You PRS guys by now are seeing how long or not your barrels are remaining accurate.
