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Education / Training Diana 27S: Part 3

Diana 27S: Part 3

by Tom Gaylord
Writing as B.B. Pelletier

Diana 27S
Diana 27S.

Part 1
Part 2

A history of airguns

This report covers:

  • SHOT Show
  • Odd-sized breech seal
  • Grainger
  • Velocity with Air Arms Falcon pellets
  • Fooled around
  • WHAT!!!?
  • On with the test — JSB Exact Heavy
  • Chronograph error
  • Cocking
  • 27S
  • Cocking behavior
  • Firing behavior
  • RWS Hobby
  • Summary


I’m at the SHOT Show today. Today is Media Day At The Range, so I’m looking at all the new airguns that are on the range in Boulder City. Yesterday I went to Sig Range Day, so tomorrow I will have a report on both events. The show opens on Tuesday, so the Wednesday blog will be my first report from there.

Today we look at the velocity of the Diana 27S we are testing. If you recall, in Part 2 the breech seal failed and I couldn’t test the rifle. I replaced the seal with a temporary leather one and the velocity jumped from the mid-300s to the high 600s. I said then that it was the largest velocity increase I have ever seen from just replacing a breech seal. I expected a gain of 60-80 f.p.s. Several readers made similar comments.

Odd-sized breech seal

When I measured the old seal I expected to find numbers that were even, numbers that made sense! Instead I found the old seal’s material diameter (the thickness of the ring) was 2.4mm. The inside diameter was 8.3mm and the outside diameter was 13.1mm. Okay, where is the camera — I’m on Candid Camera, right? I expected a ring with a thickness of 2.5mm, an ID of 8.5mm and an OD of 13mm. Who would make something common like an o-ring with such random and odd dimensions? The ring wasn’t designed for Diana. Diana selected the ring from what was available and designed their airguns to fit.

Apparently, though, someone did design a ring like this because when I went to Grainger looking for one, there it was — 2.4mm by 8.3mm by 13.1mm! The reason I was so skeptical is because when it comes to measuring things I’m a cut-three-times-measure-once-and-then-hire-somebody-else-to-do-the-job kinda guy. But, listening to all of you guys with skills, I figured I could at least give it a go — might provide some fodder for a funny blog!


So I placed an order with Grainger for 25 o-rings. I have about 6-8 Dianas that need these seals, and the way I love these guns more can come at any time. The rings arrived last week, and, with considerable trepidation, I installed one in the 27S. Then I set up the chronograph and fired the first tentative shot.

Diana 27S breech seal
The new o-ring/breech seal from Gainger fit perfectly.

Velocity with Air Arms Falcon pellets

Okay guys, we will start the velocity test with the Air Arms Falcon dome pellet. Ten Falcons averaged 689 f.p.s., for an average muzzle energy of 7.73 foot-pounds. Remember — the magic number of 671 f.p.s. is the velocity at which the energy of the pellet in foot-pounds is equal to the pellet’s weight in grains.

The spread ranged from a low of 672 to a high of 710 f.p.s. That’s 38 f.p.s., which is high.

Fooled around

After that I shot some more Falcons and got a string of three that measured 320, 309 and 310 f.p.s. — WHAT!!!?


Right after installing the new breech seal and shooting the gun at velocities in the 690s, I suddenly got one at 374 f.p.s. And that is when it hit me. The new breech seal DOES NOT add 300 f.p.s. to the velocity of the rifle! I had shot through the chronograph in such a way that the first skyscreen was triggered at the wrong time. I know that because I can now do it anytime I want.

It isn’t common but I have seen this phenomenon before. If the muzzle of the gun is too close to the first skyscreen (with Shooting Chrony chronographs) you will get a reading like this. In the case of this Diana 27S I also have to point the barrel slightly downward by a few inches at 3 feet to make it happen every time. That is what happened in the last test, but I didn’t catch it until today. It was just the way I was sitting that made it happen. Apparently the Diana 27S is just long enough to put the muzzle in the exact right spot for this to happen.

So — chronograph users beware. And everybody — a new breech seal should not increase velocity by 300 f.p.s. unless there was no seal to begin with!

On with the test — JSB Exact Heavy

Next up is the JSB Exact Heavy pellet. At 10.34-grains this dome is on the heavy side for a rifle of this power but I have seen excellent results from such pellets in weaker airguns in the past. Ten JSB Heavys averaged 555 f.p.s. from the 27S. The spread went from 552 to 560 f.p.s., so a difference of just 8 f.p.s. At the average velocity this pellet generates 7.07 foot-pounds at the muzzle.

Chronograph error

I got two “Error 2” messages on this string. That message means that skyscreen 2 isn’t seeing the pellet. This is something I am familiar with. Unless the pellet missed passing over the skyscreen it means something has fallen onto the widow above the screen’s sensor. As close as I shoot I knew I wasn’t missing the screen, so it had to be an obstruction. When I looked I saw exactly what it was and was able to clean the screen and get going again.

Diana 27S skyscreen
I shoot with the chrono so close to the pellet trap that stuff sometimes falls on skyscreen 2. There is a smashed lead pellet on the left and a large piece of paper on the right. Remove all the stuff and wipe the screen window with a cotton swab and you’re back in business!


I reported in Part 2 that the 27S cocks with 24 lbs. of effort. That’s more than I expect from a Diana 27, but this isn’t a 27 — it’s a 27S.


The Brits call the 27S the 27 Super, and apparently it was sold to them under that name. They also know of a 35 Super model that I never heard of. Well, looking at both the cocking effort and just the velocities we have seen thus far I think the 27S is more like the Diana 35 than it is like the Diana 27. In fact, the Diana 35 that I tested and tuned last year shoots at lower velocities than this one.

Cocking behavior

The 27S cocks with a slight scraping noise that is common to rifles that have two-piece articulated cocking links. The solution is lubrication, which I will apply when I go inside.

Firing behavior

This rifle shoots with a jolt and a lot of buzz that isn’t common for the other vintage Dianas I have experienced. I will have a look around inside for what can be done and also to see what that anti-beartrap mechanism looks like. But while I’m inside I will lube the rifle with Tune in a Tube in both the mainspring and ball bearing trigger areas. In fact, I am curious to see whether the ball bearing trigger in the 27S looks like the one in a 27 or the one in the 35 that has a few additional parts.

RWS Hobby

This is the last pellet to be tested. RWS Hobby was the speed demon of its day, which was contemporary with the vintage Diana line we have examined. I have found in recent tests that Falcon pellets, though slightly heavier, are often faster, but we shall see.

Ten Hobbys averaged 660 f.p.s., so true to form they are a little slower than Falcons. However, the Diana 35 that I tuned last year averaged 601 f.p.s. with a 26 f.p.s. velocity spread with Hobbys. Today the 27S low was 650 and the high was 671 f.p.s., so the spread was 31 f.p.s. At the average velocity the Hobby generates 6.77 foot pounds.


That’s it for this report. The new breech seal tells us what we need to know about this rifle — it’s in good condition and probably shooting like it did when new.

I would also like to add that today was a big learning day. We learned or were reminded about some quirks of chronographs that I hope will help some of you.

The next report will be a disassembly and examination of the insides of the 27S. And, if it cooperates, I will give it a lube tune and button it back up for another velocity and firing behavior report to follow. So, stay tuned!

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

49 thoughts on “Diana 27S: Part 3”

  1. So, do you think the tune in a tube will drop the speed down to where you want it, and possibly reduce the extreme over all spread?

    And Guys, we see from the photos that even the professionals suffer from the SYC accidents. (Shot Your Chrono.)

    So there is hope for the rest of you that haven’t done it yet, one day will join the exclusive club.

    Just having fun with you Tom.

    Have fun at SHOT SHOW.


    • Ian,

      Depending on the amount used, TIAT can slow it down a bit and usually reduces the spread. There are times where the speed will actually increase though. With the reduction in vibration and the lubrication, everything works more smoothly. My Tomahawk went from a mule eating briars to a thumper.

  2. BB,

    Glad you got things figured out. Great on the breech seal.

    I cover my chrony eyes (same as yours) with colored electrical tape when in storage. (colored tape will not leave a “goo” like black can). I keep it mounted to a tripod and covered with a dish towel (rods removed). I also made a 1/8″ aluminum wrap around cover to protect the front from a direct hit.

    Have fun at the show! Maybe you could get some video making tips from some of the fellow reporters that you know while you are there in person.

    Good Day to you and to all,……… Chris

      • R.R. and Chris,

        1/8″ Aluminium, Lexan etc…Lol!

        You will need 1/4″ inch steel plate backed by 1/2″ Neoprene (or similar) to keep the shock from a .357 slug away from your Chronograph(s)! I have thrown out my Chronograph parts bin from all my shot up Chronographs. Doing BC measurements with multiple Chronographs down range; even with brick/steel plate/and shock absorbing material in front of them doesn’t help with .458 510 gn slugs and larger, Lol!

        LabRadar winds up being cheap in comparison and does a way better job than all the other consumer Chronographs!


  3. Ah, chrono/ muzzle position anomaly! That brings a bit of satisfaction after those kind of figures.
    Interestingly a friend of mines 27S nudges 9fpe in .22 cal. Consistancy is very good although I’ll have to ask him for the exact figures again.. It is stiff to cock and smokes like a small bonfire. This is serious power for a 27S and there should be no difference in power between the S and regular 27 at factory spec.
    The 35S has a near identical stock to the RWS45. That is the mid 80s euro market RWS variant rather than the more widely seen Original or Diana 45 branded RWS in the U.S. (although it shares the same action). I believe “our” RWS45 was marketed as the Crosman Challenger 6100 in the U.S. It’s a cracking air rifle!

    • Drew451,

      I have a RWS45 that I purchased in the USA in the 1980s and it was branded as RWS45. Back then the only places that I knew about where I could get adult air guns was from Beeman and from a local gun shop that stocked quite a few. I don’t remember which place I picked mine up from, but it wasn’t marketed by Crosman and it says RWS45 on the gun.


  4. B.B.

    I have never had any luck with the “Shooting Chrony” any model. Either there is to much light or not enough.
    Just get the FX chrony, it works SO much better that the ones with screens….
    So much better!


        • Yogi,

          The only way I will ever likely get the oportunity to try one is if someone decides to let their’s visit RRHFWA for a bit. There are no budgetary allowences for a second chrony, most especially when the one is doing just fine and unless I shoot it, will likely do fine for the rest of my life.

        • Yogi,

          Welcome to my bandwagon! I’ve been praisin’ the heck out of this thing since I got it. I don’t think it’s going to catch on too quick with this group though.


      • BB,

        You should try the FX. It’s reliable, super portable, easy to use. You can set it up on a small tripod or just put it right on the end of the barrel with a couple of rubberbands or ponytail elastic bands. So far in my early testing I haven’t noticed any difference in accuracy with it on the my Aspen, .22 shooting at 28 yards anyway. Surely PA would send you one to test for the guys here that don’t want to spend until they see one reviewed by you.

        I have been monkeying with chronos since the 80’s and they all were too cumbersome to use outdoors, in my opinion, so mine never left the basement. The FX radar can be used anywhere, except in the rain, at any time, day or night. I think you will find it a game changer and since you are already a huge proponent of using a chronograph with airguns would be able to get others to take the leap with this product because of its ease of use.


    • Yogi,

      After the frustration of dealing with a Chrony that was ridiculously light fussy and the lighting kit from Chrony is way overpriced!

      I ended up mounting one of those battery powered “led light pucks” (about $4 each) over each of the sensors and have not had an error since.

      This is not the one I am using (mine are oval and have more leds) but it shows the led “chips” that provide a better (broad) light than the led “bulbs” that put out narrow beams.


      • Hank,

        Don’t have the space for a light studio or want to carry additional junk to the range. Glad a buddy has the FX. All the others are just a waste of money IMHO!


      • Vana2,

        LabRadars are manufactured by a Canadian company and work even in the dark of night. Give you multiple down range velocity readings (actually way more than the screen five recallable ones are in the data) to calculate actual BC profile!

        Just sayin’ Hank!


        • Steve over at Airgun Nation uses the LabRadar I believe. You can see the info on the chronograph as he shoots. Pretty cool device, but maybe a bit pricey for casual shooters.

          • Geo,

            If I shot a lot, tuned a lot or bought and sold a lot,… I would have it in a heartbeat.

            That said,… even if something exhibits good BC at range,… it still has to perform (group) well at the same ranges. So,… only part of the overall equation.

            I have the Shooting Chrony, same as BB,… and use the same method he uses. 500W Halogen shined at the ceiling (indoors) and works great. No sky screens. I do like Hank’s idea of LED chip lights though.

            As an adder,…. I will lay a yard stick atop the barrel to insure straight/level shooting through the eyes.

            So far, so good. But,… there seems to better units out there now. I always shoot chrony separate to target (grouping). If ever pressed for time,.. I would combine, but never have. Indoor is just more controlled.


  5. Hi BB,

    Hey that is a bit of a relief that is was the chrony and not the o-ring. I can’t wait for the accuracy.

    With all due respect, you do need to upgrade that chrony. Maybe it is time to try a sawed off shotgun on it sometime ;-)?

    You have the newest play PCP the newest crossbow and the newest compressor…What about that chrony?

    I can recommend the airchrony, I think I use it almost every day and it has never failed me ever. Design is simple and tough. Also works well for firearms as it measures up to 6500 FPS.


    But there are also the megneto and the FX radar, but I never tried those. The airchrony is especially designed for airguns.

    Best regards,


  6. Jeez Tom your rear sensor module is starting to look like mine… a little beat up. It’s strange as you would think you would either hear he rear screen and metal frame being clipped or at least seem some plastic flying but when I went to clean my sensors as I do regularly I was surprised to find the damage….lol

  7. BB

    Really glad that worked out. Bit of work on that thing and you ought to have a very nice rifle.

    I think the slightly higher cocking effort compared to a regular 27 is a consequence of the frictional losses from the articulated link and anti-bear trap, not different internals.

    The S models were usually advertised over here in the U.K. as simply S models. But influential 1980s airgun writer John Walter used the “Super” word in a series of widely-read books. Some importers may also have picked it up as a marketing thing – especially as the S models were expensive compared to the standard, and the competition.

    As well as the 27S and 35S, there was also a 25DS. The 25D was a 25 with a ball-sear trigger. The DS additionally had the full S package of angular stock, articulated link, and ABT. They appear to be quite rare, at least in the US and U.K (maybe they were more popular in Germany, given the 7.5joule limit?). I have a feeling that (70s looks aside) the 25DS is a very good classic era Diana springer.

    • I think the range was referred to as both “S” and “Super” by various sources before Walter. The Super moniker pre-dated his book and guns dated around 77/78 were stamped as such in the UK anyway. But as you know M&G liked to mix things up and I have seen pics of some stamped S. The 1980 full range catalogue uses both “S” and “Super” for the series.

  8. When discussing the Model 50 underlever, in the third edition of his book (1984) he says “though the LG50 received the angular S-type stock in 1976, the introduction of the safety (and the true 50S) was delayed until 1980-81”.

    Now if the ‘D’ signifies diopter, might the ‘S’ signify sicher – in spite of the other changes made as well? But, on the UK market, we have the happy coincidence that it can also stand for super.


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