by Tom Gaylord
Writing as B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9

RWS Diana 45 air rifle
Diana 45 is a large breakbarrel spring rifle.

This report covers:

  • Cause to reconsider
  • More black tar?
  • What is black tar grease?
  • A quick job
  • Velocity
  • Summary

Today’s report is an unprecedented test. I thought I’d finished the report on the Diana 45 in Part 9, but it still bothered me that I couldn’t get the last bit of vibration out of the gun. I chalked that up to the high number of parts in the rifle’s powerplant. Too many things to make quiet.

Cause to reconsider

Then two things happened that caused me to reconsider. First, while at the Malvern airgun show, I saw and shot a fabulous HW85 that had been tuned by Bryan Enoch. It was stunningly calm. When I talked to him about his tune, Bryan told me that he put a thin coat of black tar grease on the mainspring before he assembled the rifle. That caused me to stop and think — because that tune was perfect.

When I returned from Malvern, I shot my new HW35 for the first time and was startled to find that it had been tuned — or at least that’s what I thought when I first shot it. If you’ve been reading this blog for a couple weeks, you know how that story unfolded. It’s still unfolding, as a matter of fact. I still don’t know yet if that rifle has been tuned or is just smooth because it’s power is so low.

More black tar?

These experiences got me to thinking about whether or not I should have put more black tar grease on the Diana 45 mainspring. I did put on a very thin coat, but it wasn’t much. I didn’t do more at the time because I thought I had removed all the sloppy tolerances in the moving parts. The airgun tuner in me wanted my work to stand by itself — not be supported by the crutch of black tar grease. But shooting the gun after it was tuned told me different. Most of the annoying vibration was gone, but not all. Ten percent remained, and it bugged me.

Then, I thought about my Beeman R1 and the incredible Mag 80 Laza tune that Ivan Hancock sent me. It was a drop-in kit that had a buttoned piston (the first buttoned piston I ever saw, and it was only buttoned at the rear) and a new mainspring that was both longer and made from thicker wire. That spring was uniformly coated with a black sticky substance that looked and smelled like tar to me, so that’s what I called it. With the kit installed, my R1 went from vibrating to dead calm.

I later ruined that Mag 80 mainspring in the Mainspring Failure test when I left it cocked for a full month. That’s 735 continuous hours of being cocked. It didn’t lose much power, but it developed a cant that caused some vibration to creep back into the gun.

Fast-forward to the present. It turns out the best tunes I’ve experienced have all used black tar grease. Why didn’t I put more on the Diana 45 mainspring? I still had the rifle, so I decided to do it — which is the main point of today’s report.

What is black tar grease?

Black tar grease is a viscous black grease that is generally used to lubricate open gear boxes. In other words, it’s for gears that are exposed to the elements. It’s very sticky, so it doesn’t fling off the mainspring when the gun fires, and it’s very viscous, which means parts that are coated with it cannot vibrate. If they try to vibrate, the tar holds them still.

There are probably many different brands of grease that qualify as black tar. I wish I had a brand name to give you but I don’t. I’m still using a jar I bought from Jim Maccari several years ago, and I have a couple more applications left before I have to get more. Maccari’s Air Rifle Headquarters was shut down for health reasons, but I see that he’s opened up a limited site, and black tar is available, again.

A quick job

The Diana 45 was a major pain to disassemble the first time, but this time was different. All I had to do was remove the mainspring.

It took less than 30 minutes to gather the rifle and tools I needed, set up the workplace, break down the rifle, grease the mainspring with tar and button it back together. The first shot told me what I wanted to know. The Diana 45 now has zero vibration! In fact, I compared it to the HW35, and there is no more vibration in the 45 than there is in the HW35 that probably develops half the power. The 45 does have more forward thrust when it fires, but all vibration is gone.

The only thing left is to measure the velocity. We know that using too much black tar slows down a gun. Use a lot, and you’ll lose 40-50 f.p.s. on average. But use just a little and the velocity will remain within a few f.p.s. of where it was without it. So that’s what we want to know — where the rifle is now — both in terms of velocity and also consistency shot-to-shot.

Velocity

There are 3 different velocities and shot string spreads to compare — the initial velocity and spread before I tuned the rifle, the velocity/spread after the tune and the velocity/spread after today’s application of black tar.

The pellets I tested were RWS Superdomes, RWS Hobbys and H&N Baracuda Match pellets with the 4.53mm head.

RWS Superdome pellets
Before tune………..After tune………..After black tar
fps/spread……….…fps/spread….…..….fps/spread
735/18………………..800/24……………….788/24

RWS Hobby pellets
Before tune………..After tune………..After black tar
fps/spread……….…fps/spread….…..….fps/spread
793/28………………..890/20……………….858/24

H&N Baracuda pellets with 4.53mm heads
Before tune………..After tune………..After black tar
fps/spread……….…fps/spread….…..….fps/spread
Not tested……………676/46……………….662/29

Some velocity was lost, but not that much. With both of the pellets that were tested before and after the first tune, the velocity is still higher after the tar. I wouldn’t have cared if it dropped back to the earlier mark, because all I was after in this tune was smoothness. And we now have that.

Some pellets shoot smoother than others. Hobbys shoot the smoothest of the 3 I tested, and I find that to be true for most spring guns. Tuned or not, they all shoot smoother with one pellet than with another.

Summary

I wrote this last report both for you and also to remind myself of the importance of black tar grease to a good spring gun tune. When you find something that works, it’s best to stick with it, as I plan to stick to my black tar — pun intended.