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Hot = tighter groups? 452 17HMR

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Here is a wierd one. While trying my hand at the 50yd challenge with two of my fellow 17HMR shooters, I had run out of targets to shoot before the next cease-fire. I started cranking out 5 shot groups on random points on the target. I watched my groups tighten up noticably. I ran probably 6-7 strings as fast as I could rack the bolt and settle the crosshairs on an aiming point. I got the barrel about as hot as a black car in the sun kinda hot. One of the groups was well under the .300 goal :D and one was a maybe, but they weren't on the "official" aiming points. So next time I will take a crack at it after getting the barrel heated up. I am curious if anyone else has had this experience with their CZ? I will qualify some specifics about the rifle:
varmint bull barrel
12oz. trigger
never bedded
total rounds through gun, around 900
barrel last cleaned about 400 rounds ago
shooting both Hornady and CCI 17gr. V-Max
always shot great with everything
This goes right in the face of everything 30 years of shooting and 20 years 'smithing has demonstrated. I have seen plenty of rifles get goofy once they were hot or stay stable, but never one that has tightened up with heat. I do not normally get any cold barrel irregularity or shift of impact that would be noticable. I had been shooting groups for almost an hour at a steady pace, so the barrel was at a stable temperature and then this happened. My friends were just as baffled as I was. So, here is another *** experience to keep me awake late at night tring to solve it. If I can replicate it next time at the range I may consider sending the rifle out for cryo-treatment to see if that keeps it "hot" consistent at normal temperatures. Just figured I would share this and see what experiences others have had.
Mark
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I hadn't shot my CZ .17 HMRs for a while and can't recall their performances at various temperature profiles but the phenomenon is certainly true for my 10/22M-.17 HMR. I have to run at least 2 magfuls to warm it up before it sarts to group right. I can usually shoot it until the barrel gets hot to the touch. When it gets too hot, I let it cool down some. If I leave it to cool to ambient temperatures, the first few shots will be off of the mark until it warms back up again.
 

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Discussion Starter · #3 ·
Ron,
I know what you mean about cold barrel transition, but mine routinely groups really well from a cold barrel, just not this tight. My groups were running in the .350" to .400" range for over an hour. When I warmed things up with those rapid strings, they dropped .050" to .100" off of the groups. This one is right up there with a trans-dimensional portal located in the back of every clothes dryer that devours only your left socks:eek: . We may never know.LOL
Mark
 

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I think sometimes we spend to much time trying to get the X hairs just perfect on the bull. I have done speed shooting where as soon as the X hairs hit the center of the bull I fired. Came out with some good scores & this wasn't with a hot barrel. When you are there, shoot.
 

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Discussion Starter · #5 ·
Farm Boy,
Good point! That was a possibility that my friends suggested I consider. I will be making another foray out to the range for some more play-time and hopefully it will include another 17HMR to intimidate :eek: my CZ into fearing its place in the safe. I have an Accelerator rifle coming from their custom shop to fill my need for speed :D . Time will tell.
Mark
 
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