In the quest to understand what is going on....and why, I started measuring my ammo. First measurement to interest me was bullet diameter. What a bag of snakes. No body makes bullets the same size, it seems. Having measured my bores in the 58s and the 2008 I found that the OEM CZ barrels i have are as much as .006 inches OVERSIZE. Most of my ammo is 308 and some is 309 and others are 310. But none of it is suitable to be fired thru a .006 oversize bore. Not, at least, with the expectation of any accuracy. And I have enjoyed that accuracy.
First of all we need to get a bore that is closer to the diameter of the bullets we will be firing. In my case I found 2008 barrels that are perfect in bore diameter and even a trifle tight. But most of the ammo I see is 308 so I will be fine in that regard. But just a proper fitting bore isn't the entire story. And my getting basically the same results in group size even though I have been firing three different size bullets kinda proves that. Given that none of the ammo was actually a proper fit I still think I should see some sort of improvement. NADA!
I went to the SAMMI spec and started measuring my brass. I was inspired by observing my cartridge wobbling around inside the chamber and proving to my untrained eye that the brass was too small for the chamber. My trusty calipers proved the rattling theory. the Russian ammo is much undersize. maybe that is military strategy for ensuring that the troops can fire filthy ammo but I think that is backing into a simplistic theory. My 6.5 Swede is supremely accurate and the bore is tight and the chamber is also. The 7.5 mm Swiss is supremely snug as well. But the 58 ammo is at least part of the problem. Stumps don't lie and neither do my calipers. Curiously I had forgotten to try my Sellier Ballot ammo and when I slipped a round into the chamber of that 2008 I got a surprise. It fit snug and had zero wobble. And that SB ammo has a thin neck but the calibre and brass dimension are spot on though the bullet is 309 and that bore is .3055. Still, that ammo did not perform better than the Russian stuff in my OEM barrel as i recall and I will write that up to the bore.
OK, so bore and chamber and ammo are all required. Trigger would be nice. Ammo also needs to be consistent as well as have the correct dimensions.
Well, I can't install the CNC FCG till I get the barrels installed and they are in transit. I have one but there is safety in numbers. Stay tuned.
