by Tom Gaylord
Writing as B.B. Pelletier

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

RWS Diana 45 air rifle
Diana 45 is a large breakbarrel spring rifle.

This report covers:

  • RWS Superdome pellets
  • Uh-oh!
  • RWS Hobby pellets
  • Air Arms Falcon pellets
  • Time to stop and think
  • H&N Baracuda Match pellets with 4.53mm head
  • Where we are

Today, we’ll look at the performance of the Diana 45 that we tuned recently. Although a new mainspring was installed, it has the same power as the spring that was in the rifle, so no vast power increase was anticipated. If there’s any increase at all, it will probably come from the new breech seal I installed. The old one was flat and hard, so the breech is probably sealing air better now.

The point of this tune was to eliminate as much vibration as we could. The rifle’s owner, Johnny Hill, did not like the buzz that came with every shot, and I told him that most or even all of that could be eliminated by tightening the tolerances inside the powerplant. At my request, he made a larger spring guide, and he buttoned the piston to take out as much vibration as possible.

Our plan worked to an extent because the rifle is now calmer, but some vibration still remains. I’ve never worked on a Diana 45 before, and this may be as good as it gets — or there may be some secrets about this model that I don’t know. This is as good as I’m able to make it shoot. I estimate that 75 percent of the previous vibration has gone away.

Now, let’s look at the velocity. The 3 pellets I tested this rifle with in Part 2 are the RWS Superdome, the RWS Hobby and the Air Arms Falcon. That’s where I’ll begin.

RWS Superdome pellets

First up are the Superdomes. When the rifle was still in factory trim in Part 3, they averaged 735 f.p.s. with an 18 f.p.s. spread. This time I got 870 f.p.s. on the first shot, but then the velocity started dropping off right away. By shot 14, the velocity was down to 803 f.p.s., where it seemed to be leveling off.

A second string of 10 shots produced an average velocity of 800 f.p.s. The high was 811 f.p.s., and the low was 787 f.p.s. That’s a spread of 24 f.p.s. I think the rifle is still breaking in and will shoot somewhat slower after a thousand shots, but it’s definitely faster than it was before the tuneup. However, there was an anomaly in this string.

At the average velocity of the second string, this pellet produces 11.8 foot-pounds of energy. I do think the average will be less after several hundred additional shots have been fired, but it’ll probably still be significantly faster than the 735 f.p.s. average before the tune.

Uh-oh!

In the middle of the second string, two shots went 509 f.p.s. and 524 f.p.s., respectively. Since the velocity on the very next shot was 804 f.p.s. and never again dropped lower than 787 f.p.s., I eliminated those 2 shots from the string and fired 2 more shots to replace them. But they did give me cause to wonder what was happening.

RWS Hobby pellets

The second pellet I tried was the 7-grain RWS Hobby. Before the tune, Hobbys were averaging 793 f.p.s. with a 28 f.p.s. velocity spread. Now they averaged 890 f.p.s. with a spread of 20 f.p.s. spread from 881 to 901 f.p.s. At the average velocity, Hobbys produce 14.6 foot-pounds of energy at the muzzle.

But there was another single anomalous slow shot in the string that went only 603 f.p.s. I excluded it from the string like before, but now I was really starting to wonder what was happening! I didn’t think it was the chronograph’s fault, though that is something I will have to look into.

Before I move on I would like to take a moment to reflect on what this rifle is doing. The Diana 45 is one of the original Four Horsemen of the 1970s. They were the first 4 to break the 800 f.p.s.”barrier,” ushering in the era of magnum spring-piston air rifles. Back then, the Diana 45 was advertised as getting just over 800 f.p.s. and could possibly be tuned to get up to 860 f.p.s. So, the fact that this one has just averaged 890 f.p.s. makes me feel a little proud. It probably won’t last, but it’s nice to know I can do it. And, yes, I know they probably didn’t have Hobby pellets to use for testing in the 1970s, but we don’t have to go there — do we?

Air Arms Falcon pellets

Next up was the Air Arms Falcon pellet. The first shot went out at 816 f.p.s.; and after that, none of the next 6 shots went faster than 448 f.p.s. I didn’t record a string because I felt this wasn’t the right pellet for this rifle as it is now tuned.

Time to stop and think

These slow shots were beginning to concern me. Especially when I shots 6 Falcons in a row in the 400s. Was the rifle somehow failing? It felt the same every time it shot, but the numbers were telling a different story.

I thought the Falcon pellets that loaded into the breech very easily weren’t resisting the piston with enough force. Perhaps, the pellets were moving before the piston slammed home and not allowing the air pressure to build up. The lighter Hobby didn’t seem to have the same problem, except just one time. And the Hobby fit the breech much tighter.

So I decided to try a pellet that I knew would give a lot of resistance. The H&N Baracuda Match pellet with a 4.53mm head is both fat and heavy. That would surely give the piston all the resistance required.

H&N Baracuda Match pellets with 4.53mm head

Ten shots with H&N Baracuda Match pellets with 4.53mm heads gave me an average 676 f.p.s from the Diana with a 46 f.p.s. spread from 658 to 704 f.p.s. There wasn’t a single slow shot in this string. At the average velocity, this 10.65-grain pellet produced 10.81 foot-pounds of energy at the muzzle. By the way, the average for this pellet (676 f.p.s.) is very close to the “magic” velocity of 671 f.p.s., which is the speed at which the weight of the pellet in grains equals the muzzle energy in foot pounds.

Where we are

We now have a tuned rifle that’s ready for one last accuracy test. That will be done at 25 yards with a scoped gun. Unless something odd happens, I’ll pronounce the rifle finished and return it to its owner with a couple recommended pellets.

For kicks, I might chronograph the accurate pellets after the accuracy test — just to see if I still get a slow shot now and then. If I still do, and the pellets that do it are accurate at 25 yards, I need to look at the chronograph. Velocities can’t drop by 200 f.p.s. and not affect where the pellets land at 25 yards.

I haven’t told you yet, but this test was the first one conducted using the new chronograph Pyramyd Air sent to replace the Alpha model I shot up last week with the Benjamin Bulldog. This one is an Alpha Master that has a removable display and controller with an 18-foot cord, so now I can set the chronograph out on the range and operate it from safety. I’ll report on this chronograph after I gain some experience using it.