Air Arms Shamal: Part 2
by Tom Gaylord, a.k.a. B.B. Pelletier
Air Arms Shamal is an attractive PCP. It was Air Arms’ first precharged rifle.
This report covers:
• Trigger adjustments.
• Discovering the maximum fill pressure.
• Shot count.
• Velocity with various pellets.
• Discharge noise.
In this report, we’ll discover the Shamal’s pressure curve, which will be instructional for all who are new to precharged airguns. As I mentioned in the first report, this rifle didn’t come with a manual; so when I got it, I had to discover the pressure curve on my own. I did, and it turned out the rifle wanted an initial fill pressure of 2,600 psi. That was on the gauge that was on the fill device that came with the rifle — the device that I no longer have. I need to find out where on the gauge of my carbon fiber tank the needle wants to be when the rifle is full. These small pressure gauges are not that precise, so the number could be off by several hundred psi. Also, the gauge on my carbon fiber tank isn’t marked in hundreds of psi. There will need to be some interpolation involved.
More than a decade has passed since this rifle was mine. I’m not sure where it’s performing today. So in all respects, this is a brand new air rifle to me. That will benefit you if you want to look over my shoulder while I do what needs to be done.
Before I get into that, however, I first want to address the adjustable trigger. Shamals haven’t been around for a long time and there isn’t that much written about them. I want this report to serve as an owner’s manual for all who get one in the future.
The Shamal came with two different triggers — a standard one that my rifle has and an Olympic trigger that sounds more adjustable, but which I know nothing about. My trigger has 4 adjustment screws. From the back to the front (holding the rifle on your shoulder) they are:
1. The sear engagement (clockwise to reduce).
2. The first-stage travel (clockwise to reduce).
3. The first-stage weight (clockwise to increase).
and in front of the trigger:
4. The second-stage weight (clockwise to increase).
Trigger-adjustment screws: (1) Sear engagement, (2) first-stage travel, (3) first-stage weight and (4) second-stage weight.
When I tested the trigger with my electronic gauge, the firs-stage weighs just under 6 oz., and the let-off was between 12 and 14 oz. The first stage is long, which I like, and the release is as light as I like a trigger to be, so I’m satisfied with this trigger as it stands.
Discovering the max fill pressure
This is something that has to be done whenever a new gauge is used. I had data from previous tests that told me the fill pressure should be 2600 psi, so I filled from my carbon fiber tank to 2750 psi. That gave me the following velocities with the same 14.3-grain Crosman Premiers I used over a decade ago.
The fill pressure at the end of this string was 1500 psi. This string tells me almost everything I want to know about this rifle. First, the fill pressure I used was way too high. I’ll fill the gun again to a much lower pressure and see where that gets me.
Next, there are just under 20 good shots on a fill — down from what I thought so many years ago. I like the velocity that runs from 780 to 806 — a spread of 26 f.p.s. Looking at the curve for Premiers, I should start with shot 18, although the shot before that didn’t record, so I can’t be certain whether it was any good or not.
If I end the string at shot 34, I’ll get 17 full-power shots close to my desired range. What should the starting air pressure be? That’s solved easily.
I’ll guess that 2350 psi is the start point. I filled the rifle to that pressure and got the following results.
Okay, as the pressure inside the gun has decreased with each shot, the velocity has increased. The last shot was 781 fps, which is as low as I want the velocity to go on the power curve I’m willing to accept. The gun’s reservoir pressure has now dropped to the maximum pressure that will give me a velocity on my desired power curve (781 fps).
The velocity of 781 is at the bottom of the power curve that I have identified for this rifle. Since my last shot was 781, the rifle is now on the power curve. The pressure in the reservoir is now at the highest it can be and still give me the velocity I want. From this point on, as the rifle’s reservoir pressure drops, the velocity will either increase or remain stable. As long as it’s at 780 fps or higher, the rifle is on the power curve I’m looking for.
Now I can find the ideal starting fill pressure for my desired velocity range. All I have to do is start to fill the airgun, again. When the needle stops moving fast, indicating the fill hose is full and the gun’s intake valve has just opened, I stop the fill by closing the tank’s valve and look at the needle. The needle is pointing at the air pressure that is in the gun’s reservoir. I can see on the gauge that this rifle likes a starting fill pressure of 2250 psi!
To confirm that I’m right, I fired one more shot with Premiers. It went 781 f.p.s. Bingo! I’m right at the start of the power curve, with at least 16 more good shots in the reservoir.
I also discovered that the rifle performs very much the same as it did long ago. I’m using a different chronograph, yet the velocities from the late 1990s and today are within a few f.p.s. of one another.
The power curve I’ve accepted gives me an average velocity of 792 f.p.s., which is good for 19.92 foot-pounds of muzzle energy.
I will now test the velocity of other pellets, but I’m not going to shoot long strings and get the averages. I will shoot 2 of each pellet and take the lowest velocity of each pellet as the average for that pellet. While that’s not exact, it’s far faster than shooting whole strings and averaging. I know I’m on the power band for the next 16 shots; and if I use even fewer than 16 shots (4 pellets x 2 shots each = 8 shots), I can be sure that all of them are on the power band. The power band is the place where the velocity of any pellet will vary the least.
Eun Jin domes
This 28.4-grain Eun Jin dome pellet gave me velocities of 592 and 586 f.p.s. Taking the lower number as the average, I get a muzzle energy of 21.66 foot-pounds.
The Beeman Kodiak pellet weighs 21.14 grains and gave me velocities of 683 and 680 f.p.s. That’s very close to the “magic” velocity of 671, where the weight of the pellet in grains equals the energy in foot-pounds. Using the low figure of 680 f.p.s., this pellet gave an energy of 21.71 foot pounds at the muzzle.
JSB Exact Jumbo Monsters
Next, I tried JSB Exact Jumbo Monsters — a 25.4-grain pellet. They gave me velocities of 584 and 611 f.p.s. Using the lower number, that’s a muzzle energy of 19.24 foot-pounds.
The bottom line is that this Shamal is a 20 foot-pound air rifle as it’s operating now. That’s what it was when I owned it in the 1990s. So, the rifle hasn’t changed, but the gauges have changed and so has my perception of the total number of shots that are available. So, this update was important to the operation.
I don’t know what I was thinking when I reported the Shamal as a quiet air rifle before, but it isn’t. It sounds exactly as loud as a .22-caliber Benjamin Discovery running at the same power.
Someone asked about the loading room at the breech, and on this rifle there’s a generous amount. There’s no loading trough, so it’s easier to get your fingers behind the breech with a pellet. And all pellets load easily because there’s no rifling at the breech. Rifling doesn’t start until after the air transfer port, which is deep inside the breech. The bolt nose has a long probe that pushes the pellet past the air transfer port and into the rear of the rifling.
That’s a 28-grain Eun Jin standing on the receiver. It’s one of the longest .22-caliber pellets around. As you can see, there’s plenty of room at the breech.
That’s it for this look. Next time I’ll scope the rifle and head to the range.