by Tom Gaylord
Writing as B.B. Pelletier

Diana 27
Michael’s Winchester 427 is a Diana model 27 by another name. The rifle pictured is my Hy Score 807/Diana 27.

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

A history of airguns

This report covers:

  • Historical baseline data
  • Preparing the rifle
  • Michael’s 427 shooting RWS Superpoints
  • Air Arms Falcons
  • RWS Hobby
  • Discussion
  • Cocking effort
  • Trigger
  • Michael’s barrel is choked
  • What have I learned?
  • A hidden gem
  • Summary

Today we look at the velocity of Michael’s Winchester 427/Diana 27. This will be the end of this report.

I used to think that Tune in a Tube (TIAT) grease increases velocity but now I know from testing that it decreases velocity. Yes, it is a type of grease, but it is so tacky that it slows things down just a little. In rifles of medium power (.22-caliber rifles shooting 750-900 f.p.s.) it can drop the velocity by as much as 40 f.p.s. I haven’t really tested it in a Diana 27 before, so this test will be an eye-opener.

Historical baseline data

The best performance data I have for a Diana 27 comes from my own rifle that still has the mainspring it had when I got it in 1993. Was it the original factory mainspring? I have no way of knowing, so let’s make no assumptions. But for a fact I can say that I have never changed it, so it’s no less than 26 years old, and could possibly be as much as 51-1/2 years old (my Hy Score 807 was made in August, 1967).

My rifle was lube-tuned with lithium grease 20-plus years ago. I now shoots RWS Superpoints at an average of 469 f.p.s. with a 16 f.p.s. spread. In Part 2 of the report on my Diana 27 that I did in 2017, I envisioned tuning it with TIAT to “speed it up.” Since then I’ve learned that the tackiness of TIAT actually slows spring guns down. At the best they remain neutral, but that isn’t common, and in my experience it’s only the very powerful ones that do. The weaker one are always slowed down. Let’s see what Michael’s rifle does.

Preparing the rifle

The rifle has just been tuned, but there’s one more thing to do. A day before testing the velocity I lubed the piston seal with 8 drops of Crosman Pellgunoil. Ordinary household oil would do just as well. I dropped it into the muzzle and stood the rifle on its butt for about 16 hours. That gave the oil more than enough time to run down the bore and through the air transfer port, where it could soak into the new leather piston seal. Leather seals are wonderful, but they must be oiled for best results.

If you remember, I thought I had over-oiled the first new piston seal that I put in the rifle, so I removed it and installed another new one that I left completely dry. I had then put a couple drops of oil on it after assembling it the last time, but it wasn’t much. I didn’t discover the hole in the barrel that was causing the detonations until after that. Okay, let’s test the rifle.

Michael’s 427 shooting RWS Superpoints

Ten Superpoints from Michael’s rifle averaged 409 f.p.s. The spread was 29 f.p.s. and ranged from a low of 393 to a high of 422 f.p.s. That’s 5.39 foot-pounds of energy at the muzzle. It’s about what I expected — and maybe even a little faster.

Air Arms Falcons

The Air Arms Falcon is the pellet in which I’m most interested, because it’s the most accurate in Michael’s rifle. Ten Falcons averaged 432 f.p.s. with a spread of just 9 f.p.s. The low was 428 and the high was 437 f.p.s. At the average velocity this pellet generated 5.57 foot-pounds at the muzzle.

RWS Hobby

The RWS Hobby pellet averaged 448 f.p.s. from Michael’s rifle The spread was 16 f.p.s. — from 441 to 457 f.p.s. At the average velocity the 11.9-grain Hobby generated 5.33 foot-pounds of energy. Based on these results and the target from last Friday I wouldn’t shoot Hobbys in this rifle.

Discussion

The Falcon pellet seems like the best choice to me. And I want to mention that this rifle is smoking on every shot. That’s a good thing, because it means the rifle is dieseling (NOT detonating), as it should. Remember, dieseling is just smoke that signifies some oil droplets have been burned. Detonation is a loud bang that signifies too much oil has been burned.

My own 27 has smoked on every shot since I lube tuned it more than 20 years ago. Cardew showed us that all spring guns of a certain power level diesel on every shot — as long as they are properly lubricated.

I do believe that Michael’s gun will continue to increase in velocity by a very small amount as he shoots it. Perhaps when he has a thousand shots on this tune it will shoot Falcon pellets 10-15 f.p.s. faster than it does now. That’s where I think it will remain for the next 20-40 years, as long as the piston seal is lubricated.

Shot cycle, compared to my Diana 27/Hy Score 807

My own rifle shoots faster than Michael’s, so I wanted to compare the shooting sensations of both rifles, side by side. My rifle shoots smoothly, and, until I tuned this one, it was the smoothest 27 I had ever shot. But Michael’s gun now puts it to shame. Michael’s rifle is dead calm, where mine shudders with some low-speed vibration that is felt through the stock after every shot.

Cocking effort

My own rifle cocks with 17 pounds of effort. Michael’s felt a pound or two heavier, so I measured it on my bathroom scale. If I cock it slowly it peaks at 20 pounds, but if I go fast it peaks at 22 pounds. That’s the new mainspring, plus a piston seal that’s very tight. The seal will eventually conform to the compression chamber walls and speed up because the oil I put in will soften it and make it pliable.

Trigger

I adjusted the trigger in Part 6 and was very pleased with the results. But while shooting for accuracy last Friday I detected a slight bit of creep in stage two. And I do mean SLIGHT!

My own 27’s trigger has no creep and that’s what I wanted to send back to Michael, so I adjusted it once again. This time I got it where I want it with no creep in stage two. Stage one now takes 1 lb. 11 oz. and stage two breaks at 2 lbs. 13 oz. I know that’s heavier than what I recorded in Part 6, but I tested the trigger several times after adjusting it this time and that’s where it is. It feels like just a few additional ounces are all that are required to make it fire, but the trigger gauge tells a different story.

Michael’s barrel is choked

While pushing the brass brush through Michael’s barrel I could feel a choke near the muzzle. I’m pretty sure it comes from swaging in the dovetails for the front sight, but it still has a positive affect on the pellet, every time one passes through that section.

What have I learned?

This tune was more thorough than others I have done on Diana 27s. I literally left no stone unturned on Michael’s rifle. It has given me a desire to do the same to my own 27, so as soon as I fix that piston to accept a new seal I think that’s what I’ll do. I also plan to buy a new synthetic breech seal and shim for my rifle.

If there were any problems with the rear sight on my rifle I wouldn’t hesitate to replace it with a new all-steel one. It’s stronger and has click detents that are sharper and easier to feel and hear.

I will keep my eye out for Diana 27s that have major issues — like the hole in the barrel. These airguns have nearly an unlimited life because of the way they are made, the aftermarket parts suppliers and the low velocity at which they operate. As long as the barrel, spring tube, stock and trigger mechanism are present, there is not much that can’t be fixed.

A hidden gem

What I learned in this project is transferrable to another airgun that’s should be easier to acquire than a Diana 27. The Diana 35 is the 27’s big brother. It’s longer, heavier and is supposed to be more powerful, but if the truth is told, it really isn’t that much more powerful. It’s just harder to cock. In fact, the 35 is too hard to cock for the slight increase in power that it offers. And that’s what makes it such a hidden gem — I think.

Instead of tuning one to the get all the power it has to offer — which really isn’t much more than a 27 — a 35 could be tuned to be just as quiet, sweet and easygoing as the 27! And it should be much easier to find a 35, because after shooting one awhile, few people keep them. They buzz, kick and are just too hard to cock. I think I will go on a quest to locate one.

Summary

This report began as one thing and quickly changed into something else. I was just going to do what I thought was a simple tuneup to a Diana 27, but upon examination of the gun I discovered many other faults that had to be corrected first. The most critical thing was a messed-up rear sight that hid a hole through to the bore. I didn’t discover that until the end of the project.

I have learned a lot about the Diana 27, including several things I really didn’t want to learn. The result is a spring rifle that’s so smooth that I hope some of you will eventually get the chance to shoot it one day.