Have a very nice early 340 with a Weaver K6W in .22 Hornet... kinda, more on that later. Just had it to the range and found terrible feeding from the magazine, Will sometimes feed if one round in the magazine, more forget it. It is a factory magazine. Was shooting PPU ammo and had 2 misfires out of 14 rounds, good solid strikes looked like. Oh, BTW, it has been re-chambered to K-Hornet! I'm fine with that, even if it wasn't marked as such but out of the 12 rounds I got fired, 6 split in the old shoulder area when the brass blew out to K Hornet.
I'll be looking for another magazine, does anyone make after market magazines that are decent? The problem seems to be the round is releasing early and popping up to the top of the receiver, sometimes with the case head still stuck in the mag. I reload so I'll try annealing some brass and loading some lighter fire-forming loads. Shame to have so many troubles, I've always had a soft spot in my heard fro the 340 series, maybe because I remember my dad lusting after one in .22 Hornet and never being able to afford the $63 price. This one is pretty handsome, nice walnut and figured stock and I;m sure it will be fine once I get these kinks worked out!

Is it possible the mag was tweaked for the K-Hornet brass? Maybe load load some dummy rounds with the fire formed brass and see if it cycles.

Lee

Yeah, that was my first thought.

Damn, that is brilliant guys and had totally escaped me! I'll load up some k-Hornet brass and see how that goes and I haven't cleaned the bolt so I bet that'll cure the light strikes or at least I'll have my known primers in and I suspect the next range visit will

my found when shooting hornet in the K chamber i needed a strong extractor to hold the case against the bolt face. the lack of a shoulder let the brass move enough to have soft strikes even with rim. bet the lips were tweeked for the K configuration. even so the 340 mags are some of the worst i have ever dealt with. even my 222 has 3 mags and 1 1/2 of them dont work!

My .22 K-Hornet is a different beast, but taught me a lot about managing that little cartridge. It's a 1935-vintage Winchester M54 .22 Hornet converted to K-Hornet by Lyle Kilbourn himself (the "K" in K-Hornet).

My protocol for eliminating split cases upon fireforming is to not fireform the brass at all. I utilize a hydraulic case forming die from Hornady. Without going into a lot of detail it involves water and a big lead hammer. Annealing the virgin brass first is important also. It produces a nicely formed case with plenty of shoulder to headspace on for initial firing, albeit with the shoulder corner angles left a little soft. (Not that that's really critical in my instance as this rifle enjoys headspace as tight as can be.) Initial firing then sharpens up the angles crisply. I haven't lost a case yet, and brass lasts a loooong time- the chief virtue of the K design IMO.

I've often said that if limited to but three rifles, please let one of them be a Hornet.