The SAGA of a 56 T/H

A Guest Blog by Stever Herr

PROLOGUE by Hector Medina (Editor)

As humanity moves along in its "progress", it is more and more clear that the only thing that is constant in the UNIVERSE, is: change.

The modern world has brought a number of inconveniences (like worldwide running Flu's), a number of disasters (like Global Warming), and a lot of veritable Tragedies (The continuous State of War since the beginning of the 19th Century).
BUT, it has also brought serious marvels; some of them, undoubtedly, double edged swords that can cut either way.
Among those marvels is the Internet and the level of communication that we can have now with people we have not ever met face to face. And, yet, the commonality of passions, the willingness to suspend (or lower) the "offense" level, and the usage of a "lingua franca" (English), allows us to work; share knowledge, ideas and experiences; and grow together with people that are hundreds of miles away, or thousands, it really doesn't matter.

And that enriches our life. Yes we can cuss the internet for the amount of garbage that we receive on the EMail everyday, but we also have to be grateful for the genuine and wonderful communication opportunities it affords us.

This FOUR PART SAGA is the result of one of those opportunities. A veritable "meeting of minds" that resulted in some fantastic experimentation and some solid science being made.

And so, without further ado, I yield the floor to the Steve Herr, the Gentleman from Pennsylvania, noting that it was a privilege and a pleasure to work with such a fine mind in these experiments.

Part I.- HAYWIRE!

​A 56TH Gone Awry
About 7 months ago I purchased a Diana 56TH in .177.  This was my first Diana with the sliding action design and I was anxious to give it a try.  After much reading and correspondence with Hector Medina, I tore into the rifle, going over everything from top to bottom.  The sled mechanism was polished up, T06 trigger disassembled, polished, relubed and set to a mere 8.2 oz pull.  The powerplant was replaced with an AGT 22mm skirtless design from Tony Leach, and the sled tension was tuned for best groups on target.
While I was very pleased with the results, I was seeing some fliers that concerned me.  It was shooting extremely well, don't get me wrong....but the fliers weren't going away.

After much work to try and resolve this issue, I turned my attention to the factory crown.  The factory crown had been machined at a slight angle, see attached picture.  When looking at the crown you could see that it was deeper and wider in the area of 1:00 O'Çlock to about 7:00 O'Çlock. You could also see that the grooves were blocked off along the edge in the area hi-lighted in yellow with only 5 of the 8 grooves being visible. 

​I finally decided to hand lap to see if I could improve on the crown, and help with the issue of occasional fliers. Using a brass hand lapping tool from Brownells, I went to work.  After the hand lapping, I was now able to see all 8 lands.  However, the crown was still angled.  If there is a lesson to be learned here, hand lapping will not correct a crown that is not square to the bore.  In fact, it may actually make the angle worse.
Here is the crown after Hand Lapping.

N.E. I have often seen barrels that are referred to as having been "drilled off-center". MOST of the times, this is what happens. Yes it LOOKS off center, but it is almost impossible for a modern airgun barrel to have an off-center bore.

​After hand lapping I returned to the target to see if there were any improvements.  At 32 yards it was quite apparent that not only was the problem unresolved, but it had actually gotten worse with groups beginning to scatter.  As the title of this article indicates, this rifle was going HAYWIRE!!

After many hours of experimentation to try and resolve, I reached out to Hector to see if he knew of anyone who could re-crown a barrel square to the bore.  I was pleasantly surprised to find out that this was a service that he performs in most of his builds, and that he would be willing to look into my barrel in detail. 

We also discussed the heavy factory muzzle weight, and the tendency they may have in contributing to fliers.  He suggested some options for replacing the factory muzzle weight.  The options offered were a Harmonic Reducer or a more simple design called a Harmonic Tuner.  I said that I was open to his suggestions and would go with whatever he recommended.

A short time later my rifle was completely stripped down and the bare barreled action along with the barrel shroud was on it's way to Hector.

After evaluating the rifle, Hector began the process of re-crowning.  Here are a few pictures showing the step-by-step process.    Hector continued to machine the surface until the entire internal edge was the same depth and square with the bore.    If you look closely you can see how the crown was squared up nicely.  ​

N.E. Crown as received

N.E. After 45 mins of hand-work, you can STILL see how lop-sided the crown was cut.

N.E. After many more passes, we have reached the point where everything is even all around.

On the final step, Hector added a taper around the outer edge, the end result being a nice target crown.

Hector's next step was to verify that the barrel would shoot.  In order to do this, Hector utilized one of his own powerplants, tuned to the desired level that I would be shooting the rifle (11.4 fpe), and using the same pellets that this rifle seems to prefer...JSB Exact 8.44 (4.53).  He also installed one of his stocks and a scope for the testing.
At 35 yards in a seated position (not benched), Hector confirmed that the rifle would offer up nice uniform groups rather than the scattered groups I had been seeing previously.

N.E. It was a bit windy that day and so, some lateral dispersion was allowed.

It was a HUGE relief to hear that Hector was able to save the barrel on my 56, and seeing the more uniform groups returning on target was extremely encouraging!
A job well done!!!
After the recrowning, Hector moved to the next part of the project, that being a suitable replacement for the heavy factory muzzle weight.  I will cover that in another write-up.

​
Steve