by B.B. Pelletier
Announcement: Dammion Howard is this week’s winner of Pyramyd Air’s Christmas Big Shot on their facebook page. He’ll receive a $50 Pyramyd Air gift card plus another $50 in goodies!
Dammion Howard (left) shows off some new airguns he found under the tree this year!
Happy New Year from Tom & Edith!
One nice thing about watching a TV program is that it only takes an hour or less to view. You have no sense of the man-weeks of work that go into a short production on screen. Sometimes, the same thing happens in the world of airgun blogs.
I won’t say I’ve been dreading today’s report; but from past experience adjusting the HOTS on the Whiscombe rifle, I knew it might take longer than anyone could imagine to get a good result. It’s easy to say, “Adjust the HOTS for optimum performance with a certain pellet.” Actually doing it is where you discover if it’ll be easy or hard. The report I have for you today was very hard.
I allotted several hours to the actual testing and adjusting that would have to be done. And with my past experience with the Whiscombe, I knew shortcuts the average shooter wouldn’t think of. Let me lay the groundwork so you understand what’s happening in this process
The Whiscombe harmonic optimized tuning system (HOTS) consists of a weight that can be adjusted in or out along the axis of the bore. A jacket around the barrel is threaded to receive this weight. The threads on the weight are very fine, and one turn of the weight moves it a millimeter in either direction. One complete turn of the weight constitutes 1mm movement of the weight.
Besides the weight, there are two other metal parts. One is a short collar that locks the weight in position after it’s been adjusted, and the other is a much longer cover that encloses the entire HOTS from sight. This longer cap doesn’t need to be removed from the weight to make adjustments, just provide access room for the special wrench that moves the weight.
Here you see the HOTS mechanism. The threaded weight is turned in or out of the barrel jacket by the wrench. Once the weight is where you want it, lock it down with the knurled collar on the barrel jacket. Then, install the long cap, and the job is done.
Where to start?
The problem is always the same: Where do you start adjusting the weight? The simplest way is to start right where you are — with the HOTS in the last position it was set. Shoot a group at that setting and go from there. I had that data, of course, from the earlier part of this test, so that’s where I began. Because the last transfer port is still installed in the rifle, the Beeman Devastator pellet still develops about 772 f.p.s.
When I shot a group at this velocity in the earlier test, 10 shots went into a group measuring 1.073 inches between centers. I was looking for a group somewhere near that size this time, too. It might be a little smaller or larger; but if it was a quarter-inch group, there was a problem with the results of the last test. The same care was taken with each shot; to do any less would have skewed the results or made them unreliable at the very least.
The first group shot in this test, shot with the same HOTS setting, measured 0.953 inches between centers. That’s 0.12 inches smaller than the group from the last test. I would call that in the same ballpark and therefore a confirmation that the last test was sound.
Ten Beeman Devastators at 25 yards went into this 0.953-inch group with the original HOTS setting. It’s close to what the gun did in the last test on the same setting.
Adjusting the HOTS
Whiscombe says that there will be several sweet spots throughout a one-inch movement of the weight, which is approximately 25 full turns. He also says that one spot will be better than the others, and that’s the one to look for. He just doesn’t tell you how to find it, other than by adjusting the weight one turn at a time. But my experience told me that the sweet spot was probably not where the weight was at this time, so I turned it in (toward the receiver of the gun) four full turns and shot a second group. This is where my experience with the Whiscombe was supposed to pay off.
I wasn’t going to waste my time shooting 10 shots if the first 5 were spread out. Why bother? I wanted a tight group, and if inside 3-4 shots — or even 2, on one occasion — there was already a large separation, it was no use going further. I turned the weight in 4 full turns and shot another group. This group teased me with the first 5 shots in less than a quarter-inch, but the final 5 expanded that to 0.977 inches. Can’t be certain because of measurement errors, but no improvement at all.
At 0.977 inches, this group is slightly larger than the original setting. Obviously, the HOTS isn’t adjusted at this spot.