Finding the Elusive ‘Sweet Spot’

by Ray Cockayne

Ok so like me you have pawned the wife’s jewellery and bought yourself a tuner for your beloved target rifle, it’s fitted on the rifle and you are now ready to ‘tune’ it. How do you find the ‘Sweet Spot’ that elusive point that magically brings the group size to one small hole at 50M.

Well there are three methods, the first needs a bench rest set up, together with a high powered scope and a chronograph. If you don’t already have this kit then having pawned the wife’s jewellery to get this far you are now going to have to re-mortgage the house.

The second method is BG-o-BG (by guess or by god) simply start with the weight in any arbitrary position shoot a group, move the weight, shoot another group and so on until you run out of ammo or by pure luck see a noticeable closing of the group.

The third method, which I have found to be effective, uses two different batches of ammo and usually gets a result having expended no more than a box of ammo in total.

Before I describe how lets just consider a couple of pieces of information first. In simple terms when a tuner is working it throws lower velocity bullets higher so that they share the same impact point as slightly higher velocity bullets which have a flatter trajectory. The second piece of information I would like you to consider is the graph I produced last year using ELEY’s test facility. Although I used the Starik tuner to do this I believe the graph will be pertinent to any similar tuner. With the tuning weight fully back toward the barrel it has no effect in fact it makes group sizes larger than normal. Moving forward groups diminish then start to increase as the tuner takes effect. At a point further forward is the ‘Sweet Spot’ where the group size is very tight. I’d like to say at this point that I think a number of shooters have mistaken the first area where groups diminish as the sweet spot and have then been disappointed at the results.

All bullet manufactures of top ammo go to extreme lengths to ensure that their ammo is consistent i.e. the variance in velocity is very small, so if we just use one batch of ammo it’s going to be quite difficult to detect the sweet spot especially when shooting using a sling. By introducing a second batch which has a slightly higher average velocity the difference in impact points between each batch at 50M will be marked. I use a batch that is no more than 10 fps faster, for those of you that are not aware the average velocity for batches of Tenex is printed on the box below the batch number, very useful, because that makes our task much easier. As you are aware I now have a BeeSting tuner and this is how I brought it to tune.

On the 50M range, starting with the weight about half of its movement forward from the barrel, probably about mid point on the graph, I shot alternate fast then slow rounds two of each and noted the impact points. At the start the result was normal that is the two slower rounds impacted about 10mm below the two faster rounds. I then wound the weight forward by a full turn again a similar result. Another full turn and although the slower rounds were still below the faster by comparison to the first diagram the group was smaller. This was giving me an indication that I was moving the weight in the right direction. Another turn forward and the group was noticeably coming together, another turn and they seemed to be just one small group. I was now very close to the sweet spot and it was just a matter of fine tuning. Had I gone noticeably further forward then the slower rounds would have grouped above the faster. Job done, simple, it didn’t cost a fortune the house is safe, and all I need do now is get the wife’s jewellery back out of the pawn shop before she notices.

Additionally to this I was shooting with my friend who bought a BeeSting and asked him if he had tried this method, he hadn’t, he’d used the BG-o-BG method. So as my ammo was 10 fps faster than his I gave him some of my ammo to try. Surprisingly his slower ammo shot 10mm above my faster ammo indicating that he had over tuned. As we didn’t have sufficient to do a proper job and as time was pressing we had to stop. He has now picked up a faster batch of Tenex from Bisley and has tuned using an electronic target at 50M on an indoor range. He soon found the point where ammunition from both batches shared the same impact point. He then used a variety of ammunition with different velocities and maker and he was surprised when all held the ten ring.

No problem, came the reply...

Although my friend had independently tested the method I wanted to be very certain that I had indeed hit the sweet spot so once again I called Martin Buttery and asked if I could use Eleys test range, “No Problem”, came the reply. Coincidently I also wanted to know how much improvement I could gain by using the tuner against my bare barrel. So firstly I did a full batch test, for those of you that have never been and done this let me tell you it is worth while and the only way you can be sure you have ammunition that works exceptionally well in your rifle. There were 20 batches available, ten shoots are fired for each batch and the best groups are then isolated and re-tested with a further three groups of ten shots. I had ten batches that gave good groups, smaller than 16mm. After all this we isolated two batches which gave vary good consistent groups. We then fitted the tuner and re-tested these two batches. First I shot using the setting I had found in the field and the groups were a little better we then tweaked the tuner and immediately the results were worse. We backtracked and added a little beyond the original setting the result was also worse, a tweak back close to the original setting and the groups were better than with the standard barrel. One batch group came down to 10.8mm, 4.2mm smaller than the average group without the tuner. The other batch maintained consistently small groups with a marginal improvement.

So to sum up we had shown that the method works and sets the tuner very very close to its sweet spot by independent verification and by use of the Eley test facility.

Reading some of the target shooting forums on the internet I’m aware that some shooters have tried tuners and given up using them due to the difficulty in finding the sweet spot, I hope this will encourage those to fit them again and get them working. To those that have not considered the value of a tuner I suggest you look again because the results do prove they are of benefit, measurably reducing group sizes.

Remember once tuned for a set distance if you move to another, from 50M to 100 yards perhaps, you will need to retune. If you change ammo manufacturer or the velocity changes significantly then you may need to make minor adjustments.

My thanks once again to Eley for the use of their facility.