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

A history of airguns

This report covers:

  • Recap
  • Tune in a Tube
  • But the rear sight…
  • The rifle is fixed!
  • Breech seal shim
  • Pivot bolt locking screw
  • Accuracy
  • Air Arms Falcons
  • RWS Hobby
  • Then I read…
  • Michael’s rifle is accurate
  • The big surprise!
  • Next

Today was a long time coming — much longer than I anticipated. But I learned a lot about problems with the Diana 27 that I have never encountered before, and I now believe I can tune one with ease.


Just so you remember, I am tuning reader Michael’s Winchester 427 that is a Diana 27 by another name. It looked good on the outside, apart from missing things like the rubber button on the butt and a locking screw for the pivot bolt. The rear sight was a kluge of backwoods “repairs”, but that didn’t impress me until the very end of the job. In fact, I will tell you now that I should have started there first. It was the main source of the rifle’s issues.

The inside of Michael’s air rifle was a different story, with surface rust everywhere. It must have been stored in a humid climate most of its life. Fortunately, surface rust comes off easily with the liberal application of Ballistol and steel wool.

The tune went well except for the piston seal. That was where I learned that the seal is held on by a blind pin — read about it in Part 4. I replaced the entire piston with a new one from T.W. Chambers in the United Kingdom. For Diana 27 parts they are the best source I have found. I will drill out the old piston pin and fix that piston as a spare — perhaps to rebuild my own 27 one day.

And the new mainspring is strong! The old one is probably still good, but Michael sent me a new one, so I installed it. I’ll send the old one back to him with the rifle.

Tune in a Tube

Tune in a Tube (TIAT) grease is miraculous. For those readers who live in places not served by Pyramyd Air, TIAT is Almagard 3752, a red grease with a very high tackiness. You will have to buy a 14 oz. container, where Pyramyd Air sells a smaller applicator that’s good enough for 5 or more spring guns. It’s also much handier to use because of the needle applicator. Use a little on the mainspring, spring guide, inside of the piston and on the piston rod to quiet the powerplant. Use a little more on the ball bearing trigger to keep the three balls inside the black inner cage during assembly — that’s detailed in Part 6. I applied it one time and all these parts are still well lubricated — despite the rifle coming apart at least three more times.

But the rear sight…

In Part 7 I discovered that the same person who cobbled the rear sight had also drilled one of the rear sight mounting holes directly through into the bore. I discovered it because I could not get the rifle to stop detonating on every shot, despite having done the tuneup correctly. However when I inadvertently held my hand over the breech to feel for air loss, the blast that came out of that hole nearly poked a hole in the palm of my hand!

Many readers advised me to get a gunsmith or machinist to drill and tap the rear hole for a slightly larger screw, rather than doing it myself. They were right about that. I’m not the guy to do that kind of work. So I contacted a good gunsmith and set it up.

So last Friday I disassembled Michael’s rifle one more time, to take just the barrel to the gunsmith. I even removed the cocking link from the barrel so there were no extra parts to get in his way or get lost. And then I had a thought.

I had purchased an all-metal rear sight from Chambers and told Michael it could be his, or I would install a Mendoza rear peep sight on the rifle — his choice. I have a Winchester 425 that’s missing its rear sight and I would use the Chambers replacement if Michael wanted the peep. He wisely chose the replacement rear sight, so I held it over the barrel to make certain the screw holes aligned. Then I thought — what the heck — and I screwed the sight to the barrel. To my utter astonishment, the screw hole that I thought was completely drilled out had threads after all and held the screw tight. Apparently it is only messed up right at the top, which is all I’m able to see with a loupe.

Diana 27 rear sight
The new all-metal Diana rear sight is an upgrade over the original one that’s largely plastic.

The rifle is fixed!

With that screw tightly in the drilled-through hole, the barrel is now sealed and Michael’s rifle is fixed. No need to take it to the gunsmith. So I assembled it for what I hoped was the last time.

Breech seal shim

I have been on the Chambers website many times, looking at all the parts they have for this Diana. Over the course of the time we have been doing this report, I purchased many parts for the gun — including a breech seal shim that I never knew existed. It’s a thin steel ring that fits beneath the new synthetic breech seal and raises it just a little. This is the first time I even knew this part existed, but it went into Michael’s breech!

Diana 27 breech shim
The flat steel shim (left) goes beneath the new synthetic breech seal. I had never seen one of these before doing this job!

Pivot bolt locking screw

Since I was buying from Chambers anyway, I went ahead and bought the locking screw for the barrel pivot bolt. As you can see, its head fits neatly into a cutout in the head of the bolt, preventing it from moving. Once you have the pivot tension adjusted properly, fit this small screw head into a slot and the pivot bolt will never move.

Diana 27 pivot bolt screw
The pivot bolt locking screw (arrow) prevents the pivot bolt from turning and loosening the barrel.


The rifle is back together and, believe me, I did shoot it many times to assure myself that it wasn’t going to detonate. Now let’s see what she does downrange. I’m shooting for accuracy first because TIAT needs time to spread around and settle in. I expect some velocity loss because I have seen it in other lower-powered spring-piston rifles. But the tradeoff is how smooth it shoots. And it does speed back up over time. So, I will just test accuracy today.

I shot from 10 meters off a sandbag rest. I used the artillery hold with my off hand out toward the end of the stock. I shot 5-shot groups because I am getting low on RWS Superpoints that have been the most accurate for me in a .22-caliber Diana 27. The first shot was from a rifle whose barrel had been off several times, plus the front and rear sights. The shot hit in the 8-ring of the bull at 7 o’clock. I adjusted the sight up and to the right and the next shot hit the center. I then finished that 5-shot group. Five pellets went into 0.521-inches at 10 meters. Not too shabby!

Superpoint group 1
Five RWS Superpoints went into 0.521-inches between centers. The group may appear larger because of paper tearing. The sight-in shot is below the pellet.

Not too shabby, but I felt I could do even better. Michael’s rifle hits exactly where it is aimed and inspires extra care while shooting. The second 5 shots went into 0.463-inches at 10 meters. Now, we’re talkin’!

Superpoint group 2
The second group of Superpoints went into 0.463-inches at 10 meters.

Air Arms Falcons

I don’t remember ever trying an Air Arms Falcon pellet in a 27, so this may be a first for me. Falcons loaded easier than Superpoints and went all the way into the breech. Five then shot into a group that measured 0.277-inches between centers. If that one lower hole on the right wasn’t there I would have used the trime in the picture! Michael — your rifle can really shoot!

Falcon group
Five Falcon domes went into 0.277-inches at 10 meters. This was done with open sights!

RWS Hobby

Next I tried RWS Hobbys. They landed in the same general area as the other pellets, but as you can see the group was large and open. Five are in 0.814-inches at 10 meters. They are probably not the best for the 27.

Hobby group
Five RWS Hobbys went into 0.814-inches at 10 meters.

Then I read…

I had read my report on the Diana 27 from 2017 to get ready for this report. But until I got to this point in the test I didn’t read that the rifle prefers to be rested directly on the sandbag! I had been using the artillery hold all throughout this test. Well, Superpoints may be short but I have a brand new tin of Falcons, so I set up the range again for one final test. I shot a 10-shot group with Falcons while the rifle rested directly on the sandbag.

This time 10 Falcon pellets went into 0.595-inches at 10 meters. The impact point shifted lower and a little to the left, but everything is still near the center of the bull.

Falcon group 2
Ten Falcons went into 0.595-inches at 10 meters, when shot from a sandbag rest.

Michael’s rifle is accurate

Michael, your Winchester 427 is an accurate and natural shooter. It isn’t remarkable — at least not for a Diana 27. It is remarkable, though, just because it is a Diana 27. It may be ever-so-slightly more accurate than my own Hy Score 807, but that’s difficult to say. My rifle doesn’t have the tune that this one has, and in this case the tune really does make the rifle easier to shoot accurately.

The big surprise!

Okay, here comes the big surprise. When I told you someone had drilled through to the bore several readers expressed concern about a possible burr in the bore where the hole is. I pushed a pellet through the bore and, indeed, there was a pretty significant burr at that hole. I had all kinds of advice how to correct it if I found a burr, but none of it was anything I wanted to do. So I thought about it for a couple days.

Here is what I came up with. What happens to thin metal (the burr) when you work it back and forth? It fatigues and eventually snaps at the point of fatigue. So I took a .22 caliber brass brush that fit the bore tightly, loaded it with JB Non-Embedding Bore Cleaning Compound and inserted it with a cleaning rod until it was centered on the burr (by feel). Then I worked the rod back and forth many times. At first the rod was extremely hard to move, then it loosened considerably. After I was finished, I cleaned the entire barrel with the brush, followed by numerous cloth patches until they started coming out clean.

I can now run the brush through the bore in both directions fairly easily. The area with the burr can still be felt, but it is significantly smoother than before.

Falcon pellets
Two domed pellets were pushed through the bore. On the right is the pellet that went through immediately after the rebuild. The burr was its highest then. On the left is the pellet that went through after the bore was scrubbed, as described above. It still shows some damage from the burr, but the amount has decreased.

I waited to show this to you until after you saw the groups because after seeing that some folks would make up their minds that the barrel is ruined no matter what the test results looked like. This barrel is damaged, but it is still just as accurate as any Diana 27 barrel.

“Yeah, BB, but how much better would it shoot if there was no burr?” In my opinion — no better. I don’t think you can expect a Diana 27 to shoot any better than what you have seen today.

Michael now has an air rifle he can shoot and enjoy for the rest of his life. If he wants to, he can do the bore brush trick himself and maybe reduce the size of the remaining burr even more. Or he can look for a .22 caliber Diana model 27 barrel to replace this one. I wouldn’t waste my time or money, given how this one shoots, but that’s his call. And, by the way, Michael is reading this along with the rest of you. I never told him any of what you have read today — beyond the fact that his rifle is now fixed.


On Monday I will report on the velocity of the rifle and also more about the trigger pull. Remember — I adjusted the trigger in Part 6, and I got it exactly where I wanted it. The release of stage two is 1 lb. 15 oz. I will also test the cocking effort for you.

I want to finish this report because Michael is anxious to get his rifle back and to experience a Diana 27 in all its glory!