Wave Pattern POI — How Barrel Tuners Alter Point of Impact
Have a good look at the photos below — this may be one of the most noteworthy target strings we’ve ever published. What you can see is the effect of barrel tuner position on point of impact (POI). You can clearly see that the tuner position alters the up/down POI location in a predictable fashion.
This remarkable 15-shot sequence was shot by French benchrester Pascal Fischbach using his 6 PPC fitted with a CG (Carlito Gonzales) action and a Bukys barrel tuner.
Pascal reports: “After [bullet] seating and load validation, I put the Bukys tuner on, screwing it out 10 turns. According to Carlito, the CG’s super stiff action-to-barrel fit gives a faster vibration modulus that is detrimental below 10 turns [position of the tuner].” Pascal’s procedure was to screw out the tuner 1/4 turn progressively from one shot to the next. He shot one bullet at each tuner position, with a total of 15 shots.
15-Shot Sequence with Tuner Changes
CLICK HERE to SEE Large Version of Complete Test Strip (All 15 shots in a row).
Left Half of Target Strip (shots with 1/4 rotation change of tuner in sequence)
Right Half of Target Strip (shots with 1/4 rotation change of tuner in sequence)
Pascal observed: “Note the point of impact displacement [from shot to shot] tracks clearly along a sinusoide (sine wave curve).” This is indeed notable and significant! This shows how the tuner’s ability to change barrel harmonics can alter the position of the muzzle as each bullet exits, resulting in a higher or lower POI. Pascal sent his results to Carlito Gonzales in Argentina for analysis.
Pascal poses this question to readers: “Guess which three positions Carlito recommends to try?”
Editor’s Note: While this target sequence clearly shows how tuner position can alter bullet point of impact, this, by itself, does not tell us which tuner position(s) are best for accuracy. That will require further multi-shot group testing, involving careful experimentation with tuner position (and powder charge weights). But for those folks who doubt that a tuner can make a difference on a short, fat barrel, just take another look at the photos. The up/down changes are undeniable, and noteworthy in the wave pattern they follow.
Shooting Set-up and Test Conditions:
Pascal did this test at an outdoor range under very good conditions: “This was shot at my home range, outdoors, with four Smiley flag. The range is a narrow cut in high woods. Wind was consistent with readable flags. I started testing the tuner from 10 turns out and on to 15. I recently… found a sweet spot very close to the rearmost position of the tuner, so the rigidity provided by this super long tenon (just short of 70mm) was not a reason to overlook the recommended Bukys tuning procedure.”
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Tags: Benchrest, Bukys Barrel Tuner, Pascal, POI, tuner, Wave Pattern
I would like to see a 5 shot group before the start and after to verify load performance.
I’m strictly guessing but if I remember what I’ve read and if I understood it the three very low impacts could be good. I think you want the points either at the very top or the bottom because those are where the barrel is reversing direction as it whips up and down, but the peaks on the high side are less obvious in these shots.. It has to hit a zero vertical velocity to change direction, so should give more consistent results there. Reminds me of shooting a sporting clay at the top of the arc to take vertical velocity out of the picture. Don’t know if it’s right or not!
I totally agree with the Editor’s Note. POI is different for each linear position of the tuner. No surprise.
What we need to see are 3-5 shot groups at each linear position of the tuner. That would tell us what we want to know; what is the most accurate position for the tuner, or if there really is one.
So…does a particular position on the sinusoidal curve (i.e. high/low POI) correspond to the best grouping? I’ve seen a few of these types of targets, but never heard whether a particular position on the curve actually corresponds to the best grouping.