At the risk of sounding pedantic in the light of pretension and self-praise (not trolling for an argument here, either), it's worth noting that the good shooting results above -- both the notable and apparently everyday and pedestrian -- were achieved with custom barrels, except for the Walther. Custom barrels are relied on for better results than factory barrels and the results above demonstrate this very well.
No pretension or self-praise here. It appears I ruffled some feathers with my previous remark. I apologize for my poor phrasing, it was not directed at you, I was just expressing a general frustration. One could show 999/1000 groups sub 1/2", then some punk will pipe up that the one group over means the ammo/rifle isn't "consistent". Makes a feller want to pull his hair out. Perhaps I do have a cavalier attitude towards 1/2" groups, I can only shrug and say (in a very relaxed tone) it takes no real effort on my part to bang out those long strings of sub 1/2" groups at 50 yards. And I do mean bang them out, a friend watching me shoot commented "Holy $h!7 you shoot fast!" Again it's *shrug* "yeah, why waste time?" Once the sight picture is good, send it. Rimfire accuracy is an equation, once all the correct variables are input the result is the desired accuracy. It can be difficult to find the solutions to achieve the desired accuracy at times, this is where I see most people falter. I would love to give everyone who thinks they aren't a good shooter the opportunity to shoot my custom 455. With some brief coaching on rest setup and hold technique, I'd eat my hat if anyone couldn't bang out 10 in a row sub 1/2" with it.
Tuners can help bring improved results with a rifle. As Rabid writes, "A key component of rimfire accuracy is appropriate use of a tuner." He goes on to say "I shake my head every time I attempt to shoot a naked barrel rifle for accuracy anymore these days. To further complicate matters, I have little faith in the quality of factory made barrels (as even a couple Anschütz made barrels I've had were not satisfactory)." I would add and point out to readers that while a tuner can bring improvements in shooting results, it's possible to achieve good and consistent accuracy with good rifles that don't use tuners.
Of course it is possible, I never said it wasn't. Of the 9 rifles I have on the 1/2" challenge list, only one of them was done using a tuner. My point is that achieving that good and consistent accuracy without a tuner is much more of a headache. I can load a rifle up with a lot of ammo I know is capable of good performance, just to see the results suck in that individual rifle. It becomes an exhaustive process of trying so many different types of ammo trying to find something that works, when I know that with a tuner most decent ammo of SK Std+ quality and up will shoot the majority of their groups sub 1/2" without the hassle.
Tuners are a relatively recent innovation and development in the pursuit of rimfire accuracy. They have only been around for about 30 years, and for at least a third of that time they were the purview of a relatively small group of the most serious of shooters interested in experimenting with muzzle devices (MD's) to gain more accuracy. Rifles could be and were accurate before the introduction of tuners. When MD's became more widely used, they made already accurate rifles even more accurate. The key is having a good quality rifle with a good barrel and using good ammo that shoots well in that rifle. It's not necessary to have a tuner to achieve good results, but for someone wishing to compete and get the best possible results, a tuner is necessary to be competitive and a tuner will make a good rifle's results better.
On the bolded point, it is not necessary, in my experience, to have to use ammo that shoots well in a rifle without a tuner in order for it to shoot well with the addition of a tuner. If the issue is a harmonic mis-match of ammo to barrel (not that the ammo itself is just crappy), the tuner very effectively mitigates this factor.
The key is a quality barrel and good ammo. A tuner will not make a modest rifle/barrel shoot like a top quality rifle/barrel even when the best ammo is used. To illustrate, a typical CZ barrel with a will not be competitive with the best factory barrels. And a tuner will not make poorly shooting or inconsistent ammo into something that it can never be, and that is good ammo. In other words, a tuner is not a "magic" solution to turn an average rifle into a really good one or average ammo into really good ammo. There's no free ride to the best accuracy.
Would a tuner make a stock CZ 455 shoot better? Unlikely. It would be beneficial to first ensure that it is bedded properly, has a good trigger, and reliable scope and mounts before considering a tuner. For more on this, see h t t p s ://www.rimfirecentral.com/forums/showthread.php?t=829186.
Yes and no, maybe? A tuner won't fix a barrel with serious issues, that's a given. If the barrel shoots well generally, but is prone to "flippers" (you know, 4 in one hole then a flier patterning), again a tuner won't resolve the flippers. It may only reduce the severity of them (1/2" spread vs 3/4"-1" spread). It will also tighten up the shots that do group together. A properly setup tuner is never a detriment to a rifle, but it's value is ultimately linked to the quality of the platform it is attached to in the first place.
According to respected CZ smith, djdilliodon,
No doubt about it tuners will work. Is it worth using on every gun? No it's not. On rigs that are accurate it is worth trying to get that last bit you can for that little bit of an edge. With factory barrels imo, it's a waste of money and time for the most part. Some factory barrels are of match quality (hey even a broken clock is right twice a day) but majority of them are not. Tuners also work best with longer barrels. In .900"-.920" OD I have found that 24" length is about perfect. Thinner barrels you can go shorter and achieve the same results but of course some rifles that won't happen. All rifles are individualistic even when built the exact same way.
Given that there is very little consensus, and a great deal of controversy surrounding how tuners work and how to use them, I won't get into this too much. DJ's observations reflect limited testing with tuners (most of his customers wanted PRS rigs, and would not be using a tuner). Barrel length/diameter is irrelevant, tuners will work well on them all. What barrel length/diameter dictates, is the design requirements of the tuner to place a certain amount of weight at the correct distance past the muzzle. Shorter, stiffer barrels require less weight at a lesser distance beyond the muzzle. Longer, thinner barrels require more weight at a greater distance beyond the muzzle. Clearly, tuner design is not a "one size fits all" proposition. The Harrells tuner is thought to be ideal for barrel diameters and lengths currently in vogue in competitive benchrest, given it's adjustable weight head, and what that head actually weighs.
And before readers take it as a given that BBM ammo can be relied upon to shoot well, I bought a case of it and tried it in eight different rifles last spring and summer. In none of the rifles I tested it with, including no less than six that shoot very well, did the BBM ammo perform well. Half-inch or smaller groups at just over 50 meters were few and far between. My case of ammo may well have been a poorly shooting lot and I was quite disappointed in it. In any event, don't assume that all BBM can shoot well.