Well since the crowd came out with pitchforks in the 1/2" challenge
success thread it seems we need another venue to discuss what makes rifles accurate and tips on succeeding in the challenge. It appears the only desired posts there are those of
success and some mild congratulations to the victor....
So here we go! The ultimate 1/2" challenge target result compilation is here:
http://www.accuratereloading.com/2009/bl50.html
A massive ammo test was performed with an exceptionally accurate Bleiker rifle. I was musing about how rifles can display significant dispersion patterns when using ammo that is not "in tune" with the harmonics of the barrel, particularly light sporter contour barrels. A recent post in the 1/2" challenge thread had a member offering to test ammo from a machine rest and heavy test barrel, certainly interesting! The Bleiker results pretty well tell the story though, with a heavy target barrel and tuner no less. I don't need to see an experiment with a sporter barrel after reviewing the targets in the link.
What is readily apparent from the Bleiker test is that accuracy is an elusive beast even from the finest rifles. It is extremely dependent on quality ammunition with consistent muzzle velocity that is
also "in tune" with the individual barrel. You see how bad it gets at the final target at the bottom of the list. Another brand of benchrest rifle would result in a different order of accuracy results, they'll each show their individual preference and this Bleiker will spit out ammo it doesn't "like" into groups up to 1"-1/4, yikes!
So how does one evaluate where their difficulties lie? Is your rifle simply not capable of 1/2" accuracy? Have you not tried the ideal ammo for it yet? Or are your shooting skills deficient for the task?
My personal experience and the Bleiker results suggest the answer is something to do with the first two options. If you have a "picky" or possibly "dud" barrel and limited access to variety of ammo, you may never get to load the bullets that would give you success. A trip to England to visit Eley's lot testing tunnel? Not in most of our budgets. The "match" ammo available to the rest of us is the leftovers from what has been heavily picked over by the world's top shooters doing exactly this lot testing then buying in bulk the best lots. You may get lots of ammo that nearly give you success but those random bad rounds in the box produce fliers that ruin your day. Target #38 of the Bleiker test is very demonstrative of this and many shooters would think they simply pulled the shots on the one bad group. I mean look at those other groups and my rifle is a frickin' Bleiker, right? It must have been me.....
This Bleiker test makes it very difficult for any shooter to place the blame for all errant shots solely on their own inability to hold steady and trigger consistently. The errant shot is plausibly explained by all the above mentioned factors, it could be due to an inaccurate rifle, a bad round of ammo, a mismatched rifle/ammo combo or a gross shooter error, maybe even a combination of those factors? It is virtually impossible to declare with certainty the exact cause of any one errant shot, so how do yo know what the heck is going on? My thoughts on the troubleshooting process:
Shooter Error: If this is the cause of poor groupings it is either due to a newbie who is slow to grasp the concepts of shot execution or in the case of experienced shooters, mistakes happen. You know when you've messed up a shot, instantly, before even seeing the impact on target. I've inadvertently triggered my rifle while adjusting my aim on target, the curse of a sensitive trigger

. I've done this on the first shot of a group and been able to "chase" the flier by adjusting POA for the new POI and still shot the group in the 0.2's. If it happens mid-group then well, you blew it and you know it. There is also triggering the split second after the guy beside you lets off his centerfire, his muzzle blast knocking you off target. Your "error" here was failing to time your shot between theirs, and advanced technique only those at busy public ranges sandwiched between "tacticool" AR guys at 50 yards have to contend with. Sometimes you "twitch" on the trigger instead of your usual careful squeeze, you know you did it too. Typically the result for me is a group blown out to 1/2"-3/4".
Your occasional shooter errors are easily lost in the noise of dispersion due to rifle and ammo. Only when you have a solid baseline of accuracy for your rifle, ammo and abilities can you call an errant shot that coincides with a personally perceived shooter error. Otherwise you must be handed a rifle/ammo proven to shoot to a high accuracy level and observe if your own performance with it deviates significantly. I surmise an average group size increase of 0.2" @ 50 yards if your technique is inconsistent, but free of the gross errors mentioned above. When compared to the dispersion possible due to poor ammo/rifle combo in excess of 1", my conclusion is that subtle shooter influence is not a major factor in rifle performance until groupings of 0.4" are achieved and further refinement is attempted for IMHO it is at this threshold when it becomes equally plausible that your technique is the reason you are not shooting 0.1's and 0.2's as it is for the rifle and ammo to be almost at their peak accuracy. Assuming of course you have a high end rifle capable of that accuracy. Getting an average production rifle down to 0.3's and 0.4's is often as good as it gets for them and you can feel confident that you're shooting as well as you can. You can be sloppy with a Bleiker shooting Eley Tenex Ultimate EPS and still have a successful target, there is a buffer in the accuracy for your inconsistencies. If you have a CZ only capable of 0.3's and 0.4's then ya gotta be spot on or you'll bump some groups into the 0.5's and 0.6's and fail.
A rifle with issues: Will make itself known after a couple range days where no satisfactory results were achieved despite testing many quality brands of ammo. It won't show any real obvious preference for one particular ammo, they'll all shoot about the same, inconsistently. Some ammo's may perform quite terribly yet you know out of other rifles they do quite well. Some quick tests with shimmed support pads under the barrel will reveal whether or not it can be "tuned" into an ammo. If a dramatic difference is not observed no matter where in the barrel channel the shim is placed and performance in all locations is equally inconsistent the barrel is most likely a "dud" It is a deep rabbit hole to dive into trying to make such a rifle perform, chances are it can't be saved. Been there, done that. Re-barrel with a known good barrel and move on.
Ammo: You'll see a distinct preference for a brand or lot, the rifle comes to life and shoots great. Maybe you get mostly good performance plagued by random fliers, try another lot of this brand. Test, test and test some more. If the best candidate is "almost there" for challenge success now is the time to experiment with shimming the barrel or barrel channel bedding to try and tune in the performance if you can't or don't want to use a tuner. Free floating is just a suggestion, not a rule.
Here you can observe a dramatic difference in accuracy from only switching ammo. Circled groups are SK HV the others Lapua Midas +. There is a 1.51" average improvement by using Midas +. Shooter's intuition tells me this will never be an accurate rifle. The feeling is backed up by an experience base that shows a 2.024" average improvement with the SK HV ammo used in a different rifle (second pic).
Congrats to anyone who made it through that essay...lol. I hope I've clearly illustrated how complex rimfire accuracy is and how people shouldn't be so quick to blame themselves for poor target results, there is so much more going on that is beyond a shooter's control. Test, tweak and troubleshoot. Feel confident you've got the skills to make it happen. You probably do.