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CZ457
@ 09:36 am (GMT) |
Blair HorrocksLittle bit of rimfire mucking around. I have a CZ457 with a stainless .22LR barrel and recently picked up a 'black' .17HMR barrel for it. I pulled things apart yesterday and took some headspace measurements. I don't have a depth mic but I'm happy enough with the measurements I've obtained using my vernier caliper and a 0.061" thick stainless washer.The headspaces are 0.046" for the .22LR barrel and 0.053" for the .17HMR. Both are within SAAMI spec but I wouldn't mind tightening them up a bit. My ammo rim thicknesses would support that (Winchester .22LR 42gn subs 0.040", and CCI .17HMR 17gn VNT 0.048") I'm not keen on machining the barrel because it would remove the nitride finish and makes the barrel 'non-factory', so the next obvious thing would be to shim the bolt. With these rifles being used in competition I figure someone in NZ will have done this and I'm wondering if there's a popular solution. If shimming is it, do folks buy proprietary shims or get them made? If there are no local (practical) solutions, is it legally okay to just import some shims from the U.S.? I do not want to risk landing in hot water over it. Thanks in advance for any info! |
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@ 08:14 pm (GMT) |
Blair HorrocksRe: CZ457Well crikey, a little bit more to my late-to-the-party .17HMR. I shot out to my mate's farm this arvo with a packet of CCI ammo and although conditions were suboptimal with a very hot, enthusiastic and changeable wind, and just a guesstimated range across part of a paddock, I managed to get some indications of some nice accuracy potential - the main one being that my headspace measurements must be ok because nothing blew up.I only put 13 rounds through the rifle, partly due to the conditions and mainly due to the dogs being dicks and shaking the ute (long grass so I was shooting off the tailgate). I was surprised by the velocities though. My barrel is a 20" and has a DPT can on the front (in temporary .22LR mode with just three segment thingies. The 17gn VNT CCI stuff I was shooting is supposed to MV at about 2650fps but I got an average 2755.5fps, with a max velocity of 2798.6fps. That's 200fps than the advertised 17gn Hornady VMax load. I also got a large ES, but at this stage I'll just put that down to 'rimfire stuff'. Shooting factory ammo out of centrefires for about fifty years means I'm well used to underwhelming MV figures, so the .17 results blew my socks off - the one caveat being that I'm generally very suspicious of a data anomaly that hasn't been verified by at least two different measuring devices, and I just have the one Garmin chrony.. |
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