necking 5.56x45 down to 5mm/.20 cal

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mortre

New member
Is .20 cal considered 5mm? Has anyone tried this? Seems like it would be almost the same thing as .204 ruger, maybe a little hotter. I've been thinking selling off my whole rifle collection and putting together some rifles in 5x45mm, 6x45mm, 7x45mm and 8x45mm. Maybe even go with a system that would let me swap out barrels at home, or base them all off of the Zastava M85 A mini-mauser action (imported as the rem 799). Just so that all of my rifles would be able to use the same brass, primers and for the most part powder. And cover pretty much anything I would want to hunt in the lower 48. And in the end, it just seems like it would would be cool to say "Hey, look at this!" Of course that is long term project.

Does anyone have experience with the Model 799's? Do they have close to the accuracy potential of the Rem 700's?

So what, does that seem like a dumb thing to do?
 
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Is .20 cal considered 5mm? Has anyone tried this? Seems like it would be almost the same thing as .204 ruger, maybe a little hotter.



Yep, .20 cal (5.182mm) is pretty close to 5mm. The .19 cal (5.03mm) wildcats are closer in pure numbers, but the 5mm/35 SMC wildcat, for example, is actually .20 cal.

What you're describing - a .223 case necked down to .20 cal - is actually known as the .20 Tactical. More here:

http://www.6mmbr.com/20Caliber.html
 
I think the 8mm is out of the question, not enough shoulder left to headspace on. The 7mm has been done also but on an improved case, it's called the 7mm TCU. The 6mm or 6x45mm has been around for quite awhile and is a great little cartridge. I think it's a little light for deer but some use it. I shoot a 6x45 for preds.

When you get into the larger bores on the 5.56 case it runs out of capacity real fast.

AWS
 
[quote...What you're describing - a .223 case necked down to .20 cal - is actually known as the .20 Tactical.




The Tac .20 isn't just a straightforward neck down from the .223. The shoulder gets moved back, the shoulder angle steepened and some of the body taper gets blown out.

Simply necking down the .223 to .20 caliber is a .20-223 (some call it the .20 Practical). Performance is close enough to the Tac to call it a wash. But they are in fact two different cartridges.

- DAA
 
Actually I was talking to a custom gunsmith the other day. He has taken the .223 round all the way up to .357 without improving the case. However he was head spacing off of the case mouth as opposed to shoulder.

Also, he was saying he could get over 2,000 fps with a 200 gr. bullet in carbine length barrels. Not a screamer, but sounds like plenty for a thick woods rifle to me.
 
hi mortre, interesting concept. when you say 45mm, are you referring to a 222 case? i have a book, about as thick as a phone book, called wildcat cartridges of the world. it has a over 150 different cartridges that have been messed with for more efficiency, more accuracy, or just so some one got his name in the book! i am a real 222 fan; i have 4 of them. in my opinion, there really haven't been any improvement in 22 cal weapons since it was introduced, if you take all things into consideration. this book shows necking up the 222 to 6mm, 7mm, and 30 cal., with very impressive results for the size of case and powder burnt. i want to build a 6mm/222, looks like an awesome all round cartridge for ranges to 200 yds.
let me know what you think, lee.
ps. the 204 ruger is derived from the 222 magnum case, necked to 20 cal.
 
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Actually I was talking to a custom gunsmith the other day. He has taken the .223 round all the way up to .357 without improving the case. However he was head spacing off of the case mouth as opposed to shoulder.

Also, he was saying he could get over 2,000 fps with a 200 gr. bullet in carbine length barrels. Not a screamer, but sounds like plenty for a thick woods rifle to me.



Seen one before. Basically a rimless .357 Max.
 
Why not just do somthing starting with the 308 Win or 30-06 Springfield? yes they have already been done called 270, 243, ect. Heck a 308 or 30-06 necked to .223 would be a real screamer.
 
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hi mortre, interesting concept. when you say 45mm, are you referring to a 222 case?



The metric designation for the .223 Remington is the 5.56x45mm NATO (like what M16s use). That is what he is referring to.
 
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