Does anyone have any thoughts or other information on these historical firearms? Can they handle modern 9mm?
The Finnish gun went into production in 1935. Unsure about the Swedish model, but its called the M40, so probably 1940. Both were still first line service pistols in the 1960s.
The Lahti is bulky and beefy for a 9mm Luger pistol. In general shape, it resembles the Luger, particularly the grip frame.
The bolt is enclosed in the slide, somewhat like the Ruger Mk I pistol in appearance (although more square than round, and mechanically much different due to the locking mechanism. I picked the Ruger as an example over other "bolt inside slide/barrel extension" guns because it is better known.)
The mechanism has an accelerator, described as being similar to the M2 Browning .50BMG, to assist cycling function, particularly in very cold weather.
I looked at the take down instruction in Small Arms of the World, and they don't seem all that complicated to field strip. Actually simpler (fewer steps)than a 1911. Kind of like a Luger, but not identical, obviously.
Lock the bolt back, operate the takedown lever, pull the bolt back just a bit to relieve spring tension, then slide the entire top (barrel & slide assy) forward off the frame.
I do not own one, nor have I shot one, but I have handled some at the shows. They seem...solid, and are probably better guns for service use than a Luger.
Standard "modern" ball ammo should be fine, and would be the preferred ammo. Unknown to me if they will feed anything else. Likewise, unknown to me how long they would survive if fed +p or +p+. I would not use +p ammo in them. Despite how strong they look, no gun is better than its weakest part, and the Lahti is a 1930s design, produced for a given load as all military pistols are. Shooting anything else is uncharted territory.
My personal opinion is that if you need +p or +p+ 9mm Luger, what you really need is a different cartridge. However, this opinion is not the majority these days...
Lahtis are neat WWII era pistols, much better than contemporary Italian or Japanese designs, Arguably better than the Luger, possibly the P.38, depending on your parameters.
Hope this helps...