All Finnish manufactured, or purchased 7.62X53 r rifle barrels before 1939 were made to fire the Finnish S-1 bullet, [that's all they made at that time]. The S-1 bullet was a copy of the Russian Model 1908 hollow base bullet, EXCEPT the normal bullet diameter was 0.308".
If your Finnish military rifle has a worn, pitted bore their maybe no problem. However if the bore is mint, and no wear, you can have pressue problems with the cheap Com-bloc surplus ammo. The reason is very simple most Com-bloc ammo the bullet diameter STARTS at 0.311" diameter. Ask any match shooter, about trying to push a 2 or 3 thousands larger bullet down his rifle, I'm sure the response is very negitive.
I had pressure problems with several M-27's and M-28's using Chi-com LPS ammo. Blown primers, and stuck cartridge cases. Now if I fire these rifles, I use 0.308" diameter D-46 Lapua bullets, and save the Com-bloc type L or LPS for the 70 dollar Soviet reblued M-91/30's that are popular on the market today.
Yesterday at the range I shot one round of 1973 Hungarian Steel core heavy ball through my M24, and case would not extract. I tried putting the cleaning rod down the barrel to dislodge the case, and the cleaning rod head got stuck in the counterbore at the muzzle. I managed to extract both at home without damaging anything.
I couldn't figure out why this had happened, but the conclusion I came to was that it was not modified for the 'D' cartridge. Interestingly enough, my home made drill rounds will not chamber in the rifle, but factory and surplus ammo does.
Based upon the replies, handload for your M24. Personally, if I were you I would measure the size of the bores on all of my Finnish rifles and handload for all of them. It's fun and they will be much more accurate.
I recently asked a similar question, as I'm getting a M-27 that is "F" marked. I thought this link was informative and helpful; http://www.mosinnagant.net/finland/Bowser.asp . Scroll about halfway down the page, somebody has asked about ammo for his 28-30. Bore diameters are listed for various Finnish Mosins.
The com-bloc 7.62X53R ammo I measured bullets were all over the place compared to Finnish Lapua D-166 round.
Com-bloc crap if made after the 1950's was surely made for a light machinegun, many bullets are out of round, and the weight is also all over the place, clearly NOT match quality in any sense of the word.
Finnish assembled Civil Guard Rifles in excellent are all very carefully made.
Why waste time shooting crap that could possibly damage a great investment?
The question was not about quality, but safety. It is "possible" to damage any firearm by shooting it with any ammo. With reasonable care (firearm in good working order and the correct cartridge for the firearm) it is not likely.
A owner of a pre 1939 Finnish made rifle, was asking if current com-bloc ammo was safe to fire in his rifle if there was no D chamber marking.
The cartridges made at that time had 0.3075- 0.30826" diameter bullets. Current imported surplus ammo bullet diameter is at least 0.310" diameter.
Ask any knowledgeable high power target shooter, about using bullets that are 0.002" larger in his National Match M1 rifle, contact Hart the famous barrel maker about shooting over size bullets in his barrels.
Unknow to most U.S. collector, and shooters that in the pre war years it was very common for SAKO, and Lapua to mark the bullet diameter on a cartridge boxes.
You book I suggest you read is, Suomalaiset Sotliaspatruunat 1919-1945, [Finnish Military Cartridges 1918-1945] written by Mika Pitkanen and Timo Simpanen. This is by far the best Finnish small arms cartridge book ever written to date. Over 300 fact fill pages explaining EVERY military cartridge used in Finland!
They just printed a cartridge book on 20 mm cannon rounds that AGAIN the best ever written.