How Good Are CZ Barrels? An Experiment (Pic Heavy)

Leuchtkafer said:
There's too much variance in the groupings to tell when the weight and setting are good with a limited data set. This really complicates the testing process when flying blind on a certain barrel profile with no idea what weight and setting range I should be focusing on. To shoot just the rough course of 25 click intervals between settings with 5 groups at each setting would take 500 rounds. Now do finer testing. Now repeat with 5 different weight combinations. It doesn't take much imagination to see how this can get very time consuming and expensive.
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Lilja has a barrel stiffness program on their website. My working theory is that optimal tuner weight is related to barrel stiffness. I'll never live long enough or own enough different barrels to map the relationship. And we know that a tuner isn't just a weight but a weight at variable position. This means we have a bending moment equal to weight times distance or length. My guess based on my limited experience is that a couple consecutive total weights (as achieveable on a Harrells) may be capable of good tunes which are indistinguishable from one another given all of the challenges of gathering good data. When in doubt I have always went with the lighter weight in the belief that the systems capacity for PC is limited by inertia. So we need enough weight to depress the at rest barrel sufficiently while not so much weight that the rate of barrel rise is excessively impeded. Think of it as the Goldilocks Principle.

OP ... great thread, I appreciate your sharing.
 
Williwaw said:
My working theory is that optimal tuner weight is related to barrel stiffness. I'll never live long enough or own enough different barrels to map the relationship. And we know that a tuner isn't just a weight but a weight at variable position. This means we have a bending moment equal to weight times distance or length. My guess based on my limited experience is that a couple consecutive total weights (as achieveable on a Harrells) may be capable of good tunes which are indistinguishable from one another given all of the challenges of gathering good data. When in doubt I have always went with the lighter weight in the belief that the systems capacity for PC is limited by inertia. So we need enough weight to depress the at rest barrel sufficiently while not so much weight that the rate of barrel rise is excessively impeded. Think of it as the Goldilocks Principle.
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Ken, given how little reliable information there is online about tuners and weights, that's as good a theory as I've seen.

For readers in general, most rimfire benchrest shooters, a group which sees measurable success with tuners at 50 yards, use standard Harrell and Holeshot tuners without added weights. Of course their rifles invariably have barrels with similar dimensions, with lengths from 24 - 26 inches and diameters from the mid-.800's to low .900's.

Barrels with dimensions outside that range may benefit from extra weight. And as Dan Lilja points out on his website, the stiffer the barrel, "the less the muzzle will jump around." At the same time, the less it will respond to a tuner.

Interestingly, when tuners or muzzle devices first began to see widespread use among BR shooters around two decades ago, using extra weights was very common. Some were more sophisticated than others that were sometimes little more than lead wheel weights. Below, an example of what now may appear strange. The image is from a book first published in 2006.



There are some shooters who use Harrell or Holeshot type tuners that are lightened in weight, down from about 8 ounces to 4 - 5 ounces.
 
I was able to get out to the range again this weekend to shoot without the tuner and get some data to wrap up this experiment. I've got over 1500 rounds fired, and have seen enough to asses the performance of this barrel. For whatever reason, it is prone to periodically throwing bad fliers, which I will define as ones that make the grouping go over 1/2" at 50 yards. There's no clearly defined interval in which such fliers show up, and the severity is variable with some groups going over 3/4". It doesn't matter what ammo, tuner/no tuner, this is the behaviour of the barrel. Even if I could determine the exact causation of this, I doubt there is anything I could do to remedy it. It may be possible that firing many thousands more rounds could settle down the barrel, however I am not interested in exploring that possibility when there are more fruitful things to pursue. The following targets conclude this experiment.










Some ammo like Midas + and Eley Match I'd say performed better when a tuner was used on previous days at the range, other ammo isn't showing much difference either way. I didn't tune for each ammo, one setting was used for all. I am disappointed that this barrel didn't turn out to be a good example of tuner use, though perhaps it'll help people realize that if a barrel isn't giving a good performance, one's time and money is better spent on an upgraded barrel rather than a tuner.

Thanks for following along, this barrel is going to be retired as I move on to building out this CZ into my intended project.
 
EugeneM said:
I wonder if you would see an improvement in your groups if you shim the bolt...
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Shim the bolt to reduce headspace? Maybe if I had excessive headspace, but I cut the tenon length to headspace at 0.0415" already, so there's really nothing to gain there. This is just an example of the factory barrel lottery, it's "within spec" for the brand, it's just not on the high end of the bellcurve. No matter, it was a good learning experience and it's onwards to bigger, better things.
 
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