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Tuning Michael’s Winchester 427: Part 9

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.


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.


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.


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.

42 thoughts on “Tuning Michael’s Winchester 427: Part 9”

  1. BB——I bought my Milbro Diana 27 3@ years ago at a gun show. It detonated upon firing it, with thick black smoke in the bore. After firing it with heavy pellets, it stopped detonating. However, the bore was filled with a yellowish smoke after each shot. I have shot it at least 1,000x, and it still has yellow smoke in the bore. Grouping is erratic, sometimes nearly 1/2′ at 10 m. It often will put 3-4 shots in a tight group, but then some fliers open the group to over an inch or more. I have tried many different pellets, all with the same results. Since it is accurate enough for tin can plinking, I have not done anything to improve its accuracy. Cocking and firing is smooth, without any noises. What do you think I should do with this D 27 ( besides sell it). ? Thank you——Ed

    • Ed,

      I don’t know anything about a Milbro Diana. I don’t know if it’s the same or has differences.

      I would clean the bore with a brass brush and JB bore paste band try shooting Falcon pellets.

      You don’t mention if it is .177 or .22. I have not found .177 Diana 27s to be as accurate as the .22s, but I have only tested a few.


      • Milbro Dianas were made in Scotland. Milbro got the Diana designs, trademark (in the U.K.) and machinery as war reparations. M&G had to rebuild pretty much from scratch. Milbros were not made to quite the quality of German Dianas. Milbro stopped making “Dianas” in the early 80s (no longer competitive). While Milbro was making “Dianas”, German Dianas were sold in the U.K. as “Original” brand air guns.

  2. BB
    Is a Beeman C1 similar to a 27 as in how they shoot and do they have a leather seal?

    I guess what I’m really asking is do you think it’s a worthwhile gun to get for plinking. Or do they make more power and are harder to cock than a 27?

    • GF1,

      As they are built, the C1 is more powerful than the 27. Now it is not difficult to reduce the power as you well know. If you did not care to cut the spring down, lighter power springs are readily available. There are tune kits for most good quality sproingers to reduce their power to sub 12 FPE. If you really want to you can get kits to umph it up a bit. You can also get custom length springs.

      Pick you up an old gal. Believe me, you will enjoy her. 😉

    • GF1,

      A C1 is quite different from the Diana 27. They have a Teflon (PTFE) seal. Because the breech joint cannot be tightened, I wouldn’t choose a C1. They are harder to cock and are more powerful. Their triggers are not as nice and can’t be adjusted as well.


  3. BB,

    You have turned this 27 into quite a gem. Michael is going to get a lot of enjoyment out of it.

    You should not have much trouble finding a 35 to tinker with. I have seen these for sale quite a bit. Of course now that you have mentioned you are interested in one more will be for sale on the sites, but with higher price tags. 😉

    I have had some concern because the Webley smokes a good bit, even after my rebuild. My guess is it has to do with the leather breech seal. When you lock the breech closed it may be squeezing out some of the oil into the breech. Thoughts?

      • BB,

        It was a minor concern with this rifle because it smokes more than any I have had. After I tore it down and rebuilt it I was less concerned as I knew it had a new ring seal and knew what lubrication had been done.

        Now my Gamo CFX smoked more than this one. One time. It sounded like a .22 LR going off, a jet of smoke came out of the muzzle and a cloud of smoke rose from around the rotating breech. Yes, it was a detonation. It blew out all of the seals. It was effectively dead. Thank goodness for PA and their service department.

          • GF1,

            I cannot be sure. I had sent my CFX to PA for them to install a Nitro Piston. When I got it back I shot it a few times and was coming to the conclusion that I did not like having my CFX slap me side the face every shot when POW! Not only was there a lot of smoke, I could no longer find the breech block handle. It had gone sailing somewhere never to be seen again.

            The only thing I and PA could figure was that the piston seal must have failed and allowed oil / grease to enter the compression chamber. All of the seals in the rifle were destroyed. Fortunately PA was nice enough to remove the gas spring, reinstall my old spring, replace all of the seals AND refund my money.

            They may not have the best prices in town, but they most definitely have the best service.

              • GF1,

                No, there should not have been oil or grease to have been introduced into the compression chamber, but it came from somewhere. I would not have been in the least bit surprised if the compression tube had not been cleaned out when the pulled the spring and installed the gas spring. That may be why they did not fuss about replacing all of the seals.

  4. Not surprised at the Almagard. I recently tried it in a .22 BAM B18 that I detuned a bit (with a lighter spring) for indoor shooting. The result should have been a gun that was in the mid-500’s with mid-weight pellets, but it did considerably worse. Some would not even leave the barrel!

    Really a shame, because (as you note) it is extremely effective at quieting things down. I wonder if it might be effective in a high-powered gun… I do not think it would drag the velocity down as badly as, say, the spring tars normally used.

    Lately I’ve been playing around with polymer sleeving (polyethelyne or Teflon) inside the piston, where it slides on the spring enough to dampen vibration without imposing much drag.

    • Vince,

      Yes — reducing the play inside the powerplant is a better way to reduce vibration. I did it on a Diana 45 a couple years ago. But things have to be done that take away from the originality, like buttoning the piston.

      This 27 shoots plenty fast enough for me.


      • B.B.,

        I know very little about the spring powerplant of airguns.
        I do know a bit about vibrations, springs and systems to passively and actively reduce vibrations.
        Reduction of play = reduced vibrations. A vibration Sink can be used in some instances to absorb/disipate vibrations and in some systems the various vibrations can be tuned out by additive and subtractive timing of the waveforms produced. I get that concept in most mechanical systems but usually it is only a few individual parts or subassembly that are causing the issue. In this spring piston airgun case I guess the spring tube, spring, and piston are the items that effect the smoothness of the shot cycle. TIAT/Almagard on the spring clearly reduces most of the spring’s vibration and perhaps that of the piston or at least a portion of the piston not supported by the seal. If the lube is too viscous can’t it be thined by an appropriate amount of the right solvent introduced nto the spring or into the spring tube? That would also be possible at the start by selecting a different (lower) viscousity grade; if available.
        Or in Vfblovesnancy’s springer case the more powerful spring should be reinstalled to see if the power returns and the shot cycle smooths out.

        The harshness of most/more powerful Springers is exactly what keeps me from owning more of them!


  5. B.B.,

    i can’t adequately express how excited and grateful I am about this air rifle. I spent some of the weekend putting my indoor shooting range vack in place after it has been off to the side of the basement to make room for my working on some guitars. Time to get ready for my Diana!

    As I have commented before, this is one special air gun now, far more special than it was when it was brand new. It is definitely an heirloom and estate sale gun for me, one of only a few that I have genuine emotions about. I might part with others as years go by, but not this one. It will be a rest-of-life shooter.

    Thank you so much once again for all of your work on my air rifle. I will think of your work on it every time I pick it up and shoot it.

    Oh, and especially fine and special swords are named. Especially fine and special air guns should be, too. Therefore, I have named my Winchester 427 / Diana Model 27 “The Gaylord.”


    • Michael,

      I feel the same exact way about the Diana 34P .22 that B.B. kindly reviewed and repaired for me in 2017. Even though I don’t shoot it much, it will remain one of my most prized possessions. I have written a document outlining all the parts of the review and repair. This will be kept with the Diana 34P so anyone after me will know exactly the history of this Diana and that it was tuned by Mr. Gaylord. Every time I look at it I think of B.B. and how it was reviewed in this blog. Now, you are the second lucky person to have had this done, as far as I know. Good luck and happy shooting.


  6. B.B.

    Krytox grease seems to be gaining favor as a recommended lubricant. My understanding is that it does not detonate at all. Wouldn’t this be better in just about all situations? Maybe a head to head comparison between, Krytox, Tune in a tube, and old Moly?



  7. The thing that stands out for me is the damage the pellet sees from the overbored hole not really seeming to have as much effect on accuracy as I would have assumed. On the other hand, if I get oil in the bores, I find my accuracy goes south. I think how perfect the pellet is in flight is not as important as I thought, allot depends on the power level of the gun, and other factors, whether it will consistantly hit a target where its intended. Sometimes particular ammo will never group well in a given gun, but it may be a small detail like oil in the bore, messing things up, and not something more serious, like a bur.
    Whew. Rob

  8. B.B. and Readership,

    Has anyone tried to build a spring powerplant of multiple Springs in Series?
    My thoughts keep coming back to a mind construct of say, five shorter power springs of varying length separated by anti-torsional disks.
    My theory is that: the varying lengths could be tuned to dampen one another’s primary and harmonic vibration signature. The amount each smaller spring expands on compression may be reduced, thus reducing the spring-slap inside a tighter tolerance power spring tube. It may even allow spring rate variation which might have/be of some use in taming the shot cycle.

    What do you all think?

    Your Darkside Big Bore Uncle…


    • Shootski,

      You are barking up my tree! 😉 That is the kind of stuff I like. I did use a Torrington needle bearing in my TX200 and some vibration washers at the spring end (in the piston) It all worked well. In the end, it got a Vortek HO kit.

      Strut springs can be/are,…. variable wire diameter from end to end as well as coil diameter and coil wind/pitch. From what I gather, it gives a better ride as the spring is being compressed.

      I did a test with 2 needle bearings, one on each end of the spring and compressed it. The total twist was 5/8 of a turn as I recall. Not as much as you would think. Check out the Vortek kits. They use nylon sleeves and special rubber washers. The use a heavier spring to offset the tighter tolerances. It might not be more powerful, it won’t be less,… but it works for smoothing things out even more. Mine did pick up a bit.

      The bearing came from a Riv-nut gun that uses the bearings. Hardened washers on each side of a flat needle bearing.

      Keep us all posted as to any further thoughts on your concept/idea.


    • Shootski,

      The other thought is that car springs are meant to improve things on the compression stroke,… whereas we are looking for improvement on the release stroke. The strut has the internal shock that helps on both the compression stroke and maybe? more so on the decompression cycle.


    • Shootski,

      Which,… maybe?,…. poses the possibility of a gas strut springer???? Now that is something that I have not heard anyone toss out yet. Instead of separating the 2,… maybe the two working in unison is the key?

      Ok,… I am done,…… Chris 😉

      • Chris and Shootski,

        The FWB 300s has a coil within a coil, counter-wound to reduce, hmmm, torsion? But the idea of an air rifle with a gas piston spring inside a coiled steel spring is intriguing.

        Whatever happened to Umarex’ groundbreaking backwards gas spring powerplant?


        • Michael
          The original spring in a FWB 300 is not one inside the other.

          It has two short springs that make a you a full length spring and they are counterwound with a plastic spacer that goes between the two springs.

          • Gunfun1,

            That means, if I am not mistaken, that a single slightly more powerful spring could be replace those two end-to-end springs, yes? I wrote “slightly” because there are elements of that design that are probably not stout enough to last very long in an actual magnum air rifle. The cocking lever, for example, would give out pretty quickly if the powerplant were too strong.

            But getting one with a new blue seal that shoots around 630 up to about 700 might be do-able.

            On the other hand, the FWB 300 and 300s are vintage. One could de-tune a Diana 54 roughly 30 percent and get the same thing, obviously without the awesome trigger, but still, not a bad trigger in the least. Imagine a 10-11 foot-pound 54. Hmmm.


            • Michael
              One of the FWB 300’s I had I modified with a Marconi single spring if I’m saying the name right. Also used a o-ring in the piston rings groove instead of the factory cast iron ring.

              It was shooting in the low 700 fps range with JSB 10.34’s. and it still cocked easy. With two fingers.

              And yes a detuned 54 would be a great gun. Heck they are nice even as they come from the factory with the factory magnum spring. I had one in .177 and .22 caliber. They both shot very well and smooth. But just a little hard to cock.

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