by B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5

Boy, do I have some neat stuff to share with you today! Some of it is so neat that it’s prompting me to publish still another part to this test before tearing into the Diana 27 powerplant. Yes, I’m talking about a Part 7!

But let’s do Part 6 first. You may remember that last time I tested the rifle with a synthetic breech seal provided by Vince. I installed the seal and showed you a picture of it, then I recorded the velocities with the same pellets that were used in the new leather seal report (Part 3). Before that, I had replaced the old leather breech seal with one I constructed from an old belt.

You may also recall that several of you felt I had trimmed the new leather seal too close, and you felt it could not seal as well as it would have if it were left standing proud of the breech. You chastised me and instructed me to make the synthetic seal stand proud of the breech. Vince even provided the new o-ring that became the seal, as well as a thin steel washer for extra spacing.


Several readers felt the new leather seal should not have been trimmed this close to the breech. They thought it would have lower velocity than if it stood proud of the breech a few thousandths.

So, the synthetic seal was supposed to increase velocity over the new leather seal.


The new synthetic seal stood proud of the breech face just a little. Several readers felt this was not high enough.

I showed you the velocity of the rifle before (with new leather seal) and after (with synthetic seal standing slightly proud of the breech), and we all saw that the synthetic breech made the gun slower with two pellets (RWS Basics and RWS Superdomes), faster with one (Crosman Premiers) and was an improvement with Eley Wasps, but it wasn’t clear how much.

Several readers didn’t like the outcome of that test and scolded me for not raising the synthetic breech seal high enough. I was instructed to repeat the test with a higher breech seal. Today, we’ll see the results of that work.


When seen from the side, this is how high I originally installed the synthetic breech seal.


I cut a new plastic washer from a peanut tin top. This was installed behind the synthetic breech seal along with the steel washer that was already there.


This is what the synthetic breech seal looked like for this test.

Eley Wasp pellets
Eley Wasps hadn’t worked well with the new leather breech seal I made for the gun. They shot in two different velocity ranges–or so it seemed at the time. The low range was from 242 f.p.s. to 269 f.p.s., and the high range was from 588 to 620 f.p.s. At the time, I believed those low velocities, but I have since learned that a lighting condition on my test range gives artificially low velocities with certain pellets. I can repeat the low velocities at will, yet bring the rifle back to full velocity just by moving the muzzle back one foot, so I now know the low velocity range I reported then was only a lighting trick. The leather seal was actually shooting from 588 to 620 f.p.s.  all the time.

With the first test of the synthetic seal–the one that may have been too low– the average velocity jumped to 598 f.p.s., with a range from 588 to 612. In other words, not much different than with the new leather seal.

With today’s higher synthetic seal, the velocity with Wasps averaged 572 f.p.s.. That’s clearly a drop of 15-20 f.p.s. from either the new leather seal or the first (lower) synthetic seal.

RWS Basic pellets
RWS Basics gave an average of 658 f.p.s. with the new leather seal, and an average of 643 f.p.s. with the first synthetic seal.

With today’s higher synthetic seal, Basics averaged 634 f.p.s.–a definite drop in velocity from the last two tests.

Crosman Premier 7.9-grain pellets
Crosman Premier 7.9-gain pellets averaged 588 f.p.s. with the new leather seal. With the first synthetic seal, the average increased to 605 f.p.s. Today’s higher synthetic seal netted an average of 579 f.p.s, or a drop in velocity from both earlier tests.

RWS Superdome pellets
RWS Superdomes averaged 588 f.p.s. with the leather seal and 586 f.p.s. with the first synthetic seal. With today’s higher seal, they averaged 564 f.p.s.–a pronounced drop.

What about a higher leather seal?
You didn’t stop with wanting the synthetic seal to be higher. You also told me to raise the height of the leather seal to see if that had any affect on velocity. I removed the synthetic seal and replaced it with the leather seal that was used in the earlier tests in Part 3.

Both the steel washer and the new plastic washer were left in the seal groove, so the leather seal now stood very proud of the breech–for a while. After several breech closings, the leather squashed out in all directions and became visibly lower.


After closing the breech a few times the leather seal squashed out like this. Compare this to the height of  the first leather seal shown above and you will see that this one is higher. However, no matter how high you make the leather seal in the beginning, it will ultimately get smashed this low because the breech is tight. Leather cannot resist the smashing force of steel against steel, so it just squashes out until it fits the clearance perfectly.

Eley Wasps
Eley Wasps averaged 587 f.p.s. with the higher leather seal. That’s a small drop from the first leather seal and the first synthetic seal.

RWS Basic pellets
RWS Basics averaged 648 f.p.s. with the taller leather seal. That’s a drop from the new lower leather seal, but an increase from the first synthetic seal.

Crosman Premier 7.9-grain pellets
With Crosman 7.9-grain Premiers the average velocity with this taller leather seal was 592 f.p.s. That’s a slight gain in velocity over the lower leather seal and a decrease from the average with the first synthetic seal.

RWS Basic pellets
Basics averages 648 f.p.s. with the taller leather seal. That’s slower than the lower leather seal and faster than the low synthetic seal.

Crosman Premier 7.9-grain pellets
Premiers averaged 592 f.p.s. with the taller leather seal. That’s slightly faster than with the lower leather seal and slightly faster than with the first synthetic seal.

RWS Superdomes
Superdomes averaged 568 f.p.s. with the taller leather seal. That’s slower than both the lower leather seal and the first synthetic seal.

Before you jump me for not reporting how the taller leather seal relates to today’s test of the taller synthetic seal, allow me to mention that NONE OF IT MATTERS, BECAUSE THE ENTIRE TEST IS BIASED.

Oh, yes, dear readers, the entire test has been biased from the start, and I will tell you all about it in the unprecedented Part 7. Coming very soon! Boy, am I learning a lot about this particular rifle!