Tuners are legal for Standard Rifle class Silhoutte - not for Hunter
(e) Attachments which do not cause any portion of the rifle to exceed the weight
or dimensions as listed herein are permitted provided they do not extend past the
end of the barrel. Sighting devices are not considered "attachments".
This rule would seem to indicate that a tuner, being an attachment that extends past the end of the barrel, is illegal. The rules do not specifically address tuners for Standard class rifles, there are mixed opinions on interpreting this rule. I'd have to try it, but a tuner may also upset the balance of the rifle for offhand hold, and I might not like the feel of it that way.
It's certainly true that all components have to be considered when discussing accuracy. However, the majority opinion re single-shot vs. magazine is that, all else being equal, single-shot is associated with slightly better accuracy. I believe that part of the reason is action stiffness,
If all else is equal--barrels, stocks, optics,, etc., etc.--then a single-shot action will, on average over the long haul, do slightly better than the corresponding magazine-fed action. This doesn't mean that you can't find numerous examples of the reverse seeming to be true (as with your example of a DJ custom vs. a Turbo build), but this kind of small-sample result is not scientifically reliable. As a frequent consumer of RFC, I must say that DJ has certainly got a lot of free publicity for his work on that forum. I wonder whether, in time, he'll get the same treatment that Steve Boelter got.
Perhaps there is this perception as most single shot rifles are purpose built for high level accuracy, and repeaters geared towards hunting, plinking, position shooting, etc, with stocks that are less favorable for bench rest. When a repeater action is re-worked into a custom build and set into a dedicated benchrest stock, is the accuracy potential not right up there with the single shot actions? Sure, one example doesn't form a definite conclusion, if another two 455's and Turbo customs were built, it is anyone's guess which would be more accurate. The factors that I think weigh more heavily towards the accuracy outcome is the individual barrel fitted to the action, and chamber design. Custom gunsmiths are sometimes playing around with several chamber designs to see what works best, most often. To keep building 455 vs Turbo rifles infinitely, the outcome would likely flip-flop with no real trend towards better accuracy. One time the Turbo wins, the next the 455 does, etc, and the difference we're talking about is really minor. dnttech himself says that it is a very, very slight difference.
In honest curiosity, by what mechanism does the property of an action being "stiffer" improve a rifles accuracy? As far as I can visualize this, I agree there is a need for a certain level of stiffness to "control" the barrel under the stress of firing, lest it flop around like a wet noodle, but beyond this "control" level, does additional stiffness actually benefit accuracy? Perhaps we could infer some conclusions investigating results shot from a barrel block rig in which the action is floated, and the job of controlling the barrel is passed on to the block, so action stiffness is of no relevance. I'd have to see what I can dig up here, but I doubt I'll find what I want, which is comparing barrel block accuracy to action in stock accuracy. If it is possible to achieve the same accuracy with the action in the stock as it is observed in the barrel block, with several makes and models of actions, then action stiffness is not a significant concern. Or perhaps it could be found that only the stiffer actions better match the barrel block accuracy. It would be an interesting experiment to try.
no one posting on this thread can claim to be a high level BR shooter and so the human factor is as much at play as it is in every other shooting discipline. As a result none of us here can divorce his shooting results from his shooting ability.
Fair, I'm likely stopping my journey down the rabbit hole just short of getting one of those precision made one piece rests and a free-recoil benchrest stock. My hope is to get a custom build dialed in to the degree where my errors become obviously perceivable, since as it is I'm not getting reliable feedback on my target results, so it's hard to improve my technique if I cannot relate a mistake to a definite target result.
This benchrest arms race madness gets a little frustrating at times, and that is why I enjoy Silhouette much more. It is in this discipline that I can say with 98% certainty that any misses were my fault, and easily determine what I need to work on to improve my results, and that would be my hold and technique, rather than equipment tuning. There is always room for improvement, and I'd have to look it up, but has anyone shot a perfect round? If not, then one may always hope to try and achieve this lofty goal, after all, people bowl perfect games and get hole in ones, anything is possible.