HW 55 Tyrolean - Part 7
Time to test the tune
by B.B. Pelletier
Today, we'll put the HW55 back together (finally!) and see how well it performs. You'll recall that I cleaned, adjusted and lubricated the trigger in the last report. This will be the first time I've been able to examine the job with the rifle in the stock. That makes a huge difference in the feel.
You may also recall that I had a choice of mainsprings to try. In part 5 of the report, I talked about how to measure a mainspring before fitting it to the rifle. Well, I was surprised this time. The spring I chose was so close to the internal dimensions that, when it compressed, it became too large to fit and the rifle could not be cocked. The length was never an issue because I couldn't break the barrel far enough to cock it anyway. My initial plan was to remove coils to get the right length, but that didn't take the width of the compressed spring into account. On to plan B.
Plan B was to use a smaller spring that would certainly fit the rifle. And it did. In fact, it's a much better fit than I had hoped to get. It's only slightly smaller than the mainspring I took out of the rifle. I put just a kiss of black tar on the coils to dampen any vibration--so little that the spring now looks dirty rather than black. That's going to give the max power the spring can generate, so let's hope it has what it takes.
The spring guide is Delrin, a self-lubricating hard synthetic often called engineering plastic. That's a modern change from the steel guide the 55 came with; being self-lubricating, it offers maximum velocity without lubricants. It fits the spring very snugly, so all hint of vibration is gone from that part of the gun.
The new spring expands to take up the entire inner space inside the piston, so another vibration cause is gone. When the rifle fires, the spring goes back to its almost uncompressed diameter. That's where the hint of black tar should come in.
The piston seal got a coat of Beeman Metal-2-Metal moly paste. Some of that will burn off with the first hundred shots, but it will also burnish into the compression chamber walls where it'll provide lubrication for many years to come. The last tuner did the same thing, so this gun is probably lubricated for at least the next 10 years. No chamber oil is required. The piston seal fits the chamber very tightly, so compression should remain at its peak for all that time.
This tune will either work well or not, and the only way to tell is to button up the rifle and shoot it. So that's what I did. And the first shot was very satisfying. The gun is now a bona fide HW55! There's no vibration and the trigger breaks as crisp as a glass rod snapping.
I found that the locking lever had been adjusted as loose as possible, but the mechanism was very dry so I lubricated it. That reduced the required effort to unlock the barrel a little, but not as much as I would have preferred. The rifle is still too new and needs a few thousand shots to wear in. The breech seal is in perfect shape and is sealing the barrel exactly as intended.
Cocking is still light and smooth, though the barrel does have to be pressed all the way back for the trigger to catch the sear. On the closing motion, the dreadful "ratchet-y" drag of the cocking arm over the mainspring has been reduced about 80 percent. You can still detect it, but it's a world better than before.
The trigger is HW55-fabulous! I adjusted it to about 14 ozs. That's heavy for a pure target rifle, but good for use by non-target shooters. It still takes getting used to, but it isn't dangerous.
Velocity with Meisterkugelns
Before the tune, the rifle averaged 516 f.p.s. with RWS Meisterkugeln pellets. The extreme spread for 10 shots was 27 f.p.s. After the tune, it averages 546 f.p.s. with an extreme spread of 15 f.p.s. Slightly faster and considerably more uniform.
Velocity with RWS Hobbys
Before the tune, the Tyrolean averaged 598 f.p.s. with RWS Hobby pellets, and the extreme spread for 10 shots was 40 f.p.s. After the tune, it averages 631 f.p.s. with a spread of 15 f.p.s.
Velocity with blue-label target pellets
Before the tune, the rifle averaged 598 f.p.s. with the Chinese-made target pellets I use for air pistol competition The spread was 21 f.p.s. After the tune, it averages 633 f.p.s. with a spread of 19 f.p.s.
In summary, the tuneup turned out very well. The barrel lock still needs to be worked-in and there 's still some drag on the closing stroke, but this rifle has taken a new lease on life. I wouldn't think of opening it again for at least a decade and maybe longer if it holds up.
I'm going to use the rifle for one more test of the new AirForce aperture sight.