I just bought a large frame Martini that was converted from .577/450 to .22 by relining. Then it was chambered in .22 K Hornet and the action converted back to centerfire. Anyway, the previous owner fired factory .22 Hornet ammo with .224 diameter bullets in the original .22 rimfire bore. I haven't fired it yet, but will try to obtain some .223 diameter 45 grain bullets for it. Neither have I slugged the bore, but .22 rimfire bores usually measure .221 groove diameter. It probably has a 1/16" twist, so lighter bullets at 40 to 45 grains will be where I start. I have .22 Hornet dies but they are made for .224 bullets. Am I going to need a smaller button for the case neck? I may try at first to fireform standard Hornet cases and then back off the die to neck size only if there is enough room for the case. Before I make all of the mistakes everyone else has made in this situation, does anyone out there have experience loading for a Hornet or K Hornet with undersized bore? What are your recommendations?

Sierra makes 45 grain 223 Hornet bullets. I have some loaded up for an old Winchester Model 54 in 22 Hornet I recently bought, and it has the 223 bore.
As far as the dies go, if it were me, I would use the standard K-Hornet sizing die and see how it goes. The button may get the correct case neck ID to hold the bullet. If not, then its the smaller button you need. You'll need about .002 to .004 interference fit to hold the bullet securely; the case neck ID after sizing should be the numbers I just mentioned, smaller than the bullet OD.
Have a ball with the Martini in K-Hornet. I am a Martini NUT... I have two Martini Cadets in 218 Bee, and two Martini Mk II's in 22 rimfire.

Don

there are lots of hornets out there made up from 22LR's having a 222 bore. the 223 bullets will work fine. after all we're only talking about 1/1000 . it was common back in the late 40's or early 50's to rechamber 22lr's to hornets. at that time there were even 222 bullets available. you can even use the regular k hornet data for loading

I shoot .224 bullets in my .223 bore hornet. Not only does it not raise pressure but I can load mine higher than most - long throat I think. I shoot 55gr Spire Points most of the time but quite happily shoot 60gr spire points too. (1-in-16 twist). Do you know what steel the liner is made from? I believe that lubricating the bullets will save a softer steel barrel from excessive wear. Easier to lube the standard hornet using a wax wad. You could also have an ideal cast bullet rifle.

I fired some standard Hornet loads I had loaded for my Browning A bolt. Primers were flat and I had one split neck in five shots. Also it appears that the necks are narrowed at the case mouth. I suspect that the chamber is a little short or that there is no leade. I'll try fireforming cases with cream of wheat and a tissue plug then trimming the mouth of the case. This is actually a Parker Hale Model CMT2. There is only a Bisley Works stamp on the side of the action, so I don't know if this is a reworked military action or a civilian version. Also the barrel is too small in diameter to have been a military reline (I have one of those also), but I do see a ring at the muzzle that makes me think that this barrel has been relined. If anyone knows about the PH Model CMT2, please enlighten us.

split necks are common in hornet brass, one more reason for the khornet

That is an odd deal. I hear guys talking about split necks on their Hornets and I darned sure know they ain't making it up but as much as I shoot both Hornet's and K-Hornet's, I've never split one (Man, I should never said that. Probably split every other one now ).
I've wondered about that and the only things I can think it might be is the chambers themselves (2 CZ's a Cooper and 2 Anschutz's), possibly the fact that after first firing all I do is neck size, and after 4 or 5 firings I anneal the necks to keep em pliable? Weird!

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Also it appears that the necks are narrowed at the case mouth.

Mine do that all the time. Just a little. For my rifle it's not a problem. The fact that you got a split neck could indicate a generous throat area and the necks may be engaging the radius which may be 'generous' too. It might not be a problem in your rifle either. In mine, it's a benefit as it stops case elongation. If I may ask, what will you be using this rifle for?

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the only things I can think it might be is the chambers themselves

Well, hornets seem to have had a reputation for poor accuracy which is crazy - maybe it stems from the fact that chambers were too generous. My Anschutz (model 1431/32) leaves the neck so large that I can seat the bullet in a paper cup! Not even my 303 Brit leaves that much clearance.

one more thing - if you're not using lil gun for powder - do so immediately - its the super powder for hornets

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one more thing - if you're not using lil gun for powder - do so immediately - its the super powder for hornets

Hell yeah!

I played around a little more with the gun. The cases are definitely too long for this chamber. The case mouth is pinched in. I'll need to trim cases after fireforming. I also discovered that my RCBS case trimmer case head collet won't hold Hornet cases for a trim. Now where did I put that other collet? Also the chamber must be a little out of round as fired cases won't re-enter the chamber easily without orienting them to the firing pin strike.

I was able to load some rounds by decapping with a Lee universal decapper and neck sizing in a .222 die. Because of the out-of-round chamber I ordered a set of dies to resize the case body. I won't expect a long case life from this rifle. The firing pin is a hoot! This gun was converted from centerfire to rimfire and back again..sort of. The flat-faced round pin is probably half the diameter of the hornet primer and would fire either a centerfire or rimfire round of the same size an a .22 LR up to the Hornet. I bought the gun for plinking and light varmint shooting, and just because I like Martinis. This makes my tenth one!

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I bought the gun for plinking and light varmint shooting, and just because I like Martinis. This makes my tenth one!

Nothing wrong with that! This might surprise some folks but I kinda like the 303 Brit!