Another cartridge: 5.7x45 Czech

[GunTech]

After looking at the 7.62x45 Czech as a basis for some new cartridges, here's yet another one that looks promising. This one was designed from the beginning for the AR-15, and has the same bullet limitations as 223. Formed by necking down and blowing out a 7.62x45 check case, making it a fairly simple conversion.

How does it stack up against the 223? I ran the numbers in QuickLoad for this round and the 22-250 and compared them to the M855 5.56x45 round, which is spec'd at 3000 fps from a 20 inch barrel. QL calculated the pressure required as 53,820 PSI

5.7x45mm will throw the same 62gn M855 bullet at 3288 fps at the same pressure from the specified 20 inch barrel.

At the same pressure, 22-250 will make 3297 fps with the M855. Admittedly this is a low opressure for 22-250, and when loaded to SAAMI pressure, the 22-250 does a calculated 3354 fps from a 20 inch barrel.

Still, the 5.7x45 comes within 66fps of the 22-250 and could be fired from an AR-15.

Thoughts?

 

[Nolo]

Too big for an AsR.
I mean, it's the same rough dimensions as the 7.62x39mm round, and is probably pretty close in weight, and it gives increased damage (the same energy, almost certainly increased frangibility) and accuracy, so it's better than that round, but I don't really see the benefits of this round over the .223. It seems too large to me. I don't like to go over ten and a half millimeters width.

 

[HorseSoldier]

What kind of numbers would it be clocking from a 14.5" or 10.5" barrel?

 

[GunTech]

I wasn't looking for a military catridge, but rather a superior varmint round for the AR-15. I just picked the M855 bullet for comarison.

Predicted velocity from 14.5 inch barrel is 2958 fps and 2636 fps from a 10.5 inch barrel.

 

[GunTech]

This round basically falls between 223 and 22-250, a bit closer to the latter.

I need to run the numbers against 204 Ruger.

 

[Nolo]

GunTech, I'm not sure what this buys you for a varmint round, unless you're into sniping capybaras.

 

[GunTech]

Well since 22-250 is one of the most popular LR varmint rounds sold, and this round comes pretty close to 22-250 but can be fired in an AR-15...

 

[Nolo]

Oh, I think I understand now.

 

[Vaarok]

Um, why make it out of the 7.62x45 Czech case when that casing isn't much more than a shortened 6.5 Carcano case with a bigger bullet?

 

[MachIVshooter]

It's an oddball case to base a wildcat on (perhaps the reason you chose it?). Still, I could think of others that would be more available at a lower cost. Have you priced 7.62x45 brass lately? Nearly $1/case.

ASI in Texas does WSSM conversions on AR's. The .223 WSM outperforms the 22-250 and nips at the top .220 Swift loads (some guys have pushed it beyond the Swift, much to the detriment of their chamber throats).