This is the first point of tune and it is now beginning to launch the lower velocity bullets higher. At some point along here would be the point of tune for 100 yards, the greater distance needs the lower velocity bullets to be thrown even higher so that they will share the same impact point at 100 yards with the faster, flatter trajectory bullets, for us at 50m it’s too much.
Then the group sizes drop, as it comes into tune for 50m, the impact points converge and ‘bingo’ we hit the sweet spot. This is giving a group size of 11.1mm on Eley’s rig. I say this very deliberately because the action is so solidly anchored down, the only item that can move/flex is the barrel. This produces larger groups than when mounted in a stock and held by a fleshy lump - i.e. me and you!
The stock and our bodies have a damping effect and group sizes will always be smaller in reality because of that fact. None the less Eley’s computer recorded scores no less than 10.5mm in our ten shot group. Following this, the groups get larger as the barrel goes out of tune for our 50m distance. It would probably be here that it would be in tune for 25 yards, although I have to say that at such a short distance, it would be near impossible to see any gain. Having said that, I did shoot a 7x possible last week at 25 yards. Beyond this point the tuner loses its ability to throw the slower velocity rounds higher. Roughly, from the trend line, we can see that it starts to ‘tune’ at mark 7 and loses its ability at mark 22.
Conclusions? Firstly, go back and look at the group sizes when the weights were close to the barrel -
17mm. These are well above my batch-test results and show that the added weight has made things worse, which gives credence to some of the chat that indicates that some extension tubes do more harm than good. Does the tuner do what is stated on the box? Yes and we have the proof - the sweet- spot produces groups better than my batch-test results. Is it worth having to improve scores? Guy Starik thinks so and he is one of the best in the world but, you must make your own decision.
What’s next? Well, we plotted an almost perfect graph and proved that the tuner works but, in the tuner world, five turns for each increment is very crude and I would like to re-test using finer increments around the sweet-spot. My suspicion is, we will get even better results.
For and against? For - smaller groups, stability on aim, longer sight-base, easy to remove and fit, good tube without the weights. Against - if you do not have a comfortable hand-stop, the added weight won’t help. You will need to benchrest to find the sweet-spot and if Centra gave some instructional guidance it would help narrow the field.
My thanks to Celia my able assistant, Dr Stuart Clarke for his wonderful graph and last but not least, Martin Buttery and Eley for the welcome given and the use of their fabulous new and much improved test facility.
The author wishes to point out that he is in no way connected with Eley or Centra.
Target Shooter 69
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