The mag is the limiting factor on a Brno ZK465 build, it is made for the hornet diameter case so fireball and spitfire are out. both of these need to be built on a .222 or .223 action.
like I said at the start of this thread, I was wanting to build a .22 with a bit more performance than the .22 Magnum and it needed to be a centre fire so I could reload for it as .22 magnum ammo is crazy over priced for what it is.
5.57 X 28 was actually the cal I chose to begin with but after trialling the ammo is a lot of different bolt action mags and rifles I found it wasn't going to be an easy build. The 5.7x28 case has a tiny .25cal acp case head diameter so a bolt face bushing would be needed on even a .22 hornet bolt and it would mean making a custom extractor of some description.
Savage actually announced they were making a 5.7 bolt action varmint rifle on their model 25 series frame back in 2011 but it flopped and they pulled the pin on the project for reasons they wouldn't share.
I very nearly ordered all the dies and chamber reamer to build one on a Brno 465 as the cartridge fits the mag and would only require the bolt face and extractor mod with the new cambering.
A 1-14" to 1-16" twist rate would be the best for a varmint rifle build, sticking with the 32gr to 40gr varmint bullets.
5.57x28 is objectively nothing to get excited about, it does a little bit more than a rimfire .22 magnum by pushing a 40gr v-max to 2350fps in a long barrel using a max charge of about 7.8gr of the powders Ive tested in this thread so sits somewhere between a .22 magnum and a .22 hornet.
The 5.7 brass is also much thinner and plagued with split necks and other loading issues of small bottle neck cases.
Subjectively, I think its a kinda cool round but it will never set the world on fire.
That said, believe it or not not everybody needs to be able to shoot past 300 yards or wants the noise of the bigger cartridges. Some of us even use rimfires to that range.. imagine that!
.22 TCM, 5.57X28, .223 Rem
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