Hatsan AT P1 PCP air pistol: Part 2
by Tom Gaylord, a.k.a. B.B. Pelletier
Today, I was all set to report the velocity of the .22-caliber Hatsan AT P1 PCP air pistol, when I discovered that there’s more I need to know about this airgun. I’d like to thank those who’ve been waiting patiently for this second report. I stalled for a long time because Hatsan uses a proprietary quick-fill probe. That means I have to undo one of my more universal fill connectors to attach their probe. Thankfully, the threads on their probe are standard 1/8″ BSPP that connect to most air hoses coming from tanks and hand pumps these days (I can still remember when that wasn’t true!), but I was working on both the Condor SS and the twist-rate report and needed a fill device for both of those. In the end, I pressed my Hill pump into service, and it proved to be a great way to fill the AT P1 pistol.
The first problem I encountered was with the 10-shot rotary clip — but I want to stress that it wasn’t the pistol’s fault. It was mine. I tried loading 28.4-grain Eun Jin domes that looked like they fit the clip well, but proved to be too long and jammed the gun.
Because they were the first pellet I tried, I thought the gun might be broken until it dawned on me that the pellets were the problem. Once I changed to Crosman Premiers, the gun functioned perfectly and there were no more cocking or feeding problems.
Rotary clips are sensitive to the length of pellets. If they stick out on either side of the clip, that can cause the gun to jam, as this Hatsan did. So, when selecting pellets for a rotary clip, keep this in mind. I chose the Eun Jin pellet for the weight. I thought it would allow this powerful pistol to develop its maximum power, but I went too far.
Removable air reservoir
In Part 1, I completely neglected to mention this pistol has a removable air reservoir. I saw the degassing tool in the tool kit and knew that it could only be used on the other (hidden) end of the reservoir, but for some reason I didn’t think to mention it.
Of course, the reason for a removable tank is so you can carry extra charged tanks in the field. Each one will give you more shots. I don’t think this is such a great feature after you learn how many shots you can get on a fill, but the choice is yours. At least Hatsan gives you the option.
Shots per fill
This will be the remainder of the report because I discovered during velocity testing that the AT P1 pistol has a very specific power curve. It’s not an inverted bathtub curve — where the velocity rises to the optimum level and remains there for a number of shots before falling back down again. Instead, the velocity rises, peaks and drops instantly. The curve looks like a peaked mountain with no flat spot at the top.
The manual says to fill to 3,000 psi and that there are 35 useful shots per fill. Several readers expressed doubts that the 50cc reservoir held enough air to give 35 powerful shots, and I agreed with them. If this was a target pistol, then 35 shots would be very possible; but at the power Hatsan claims, which is a .22-caliber pellet traveling 780 f.p.s. at the muzzle, it seems impossible to get 35 good shots on so little air. And, indeed, it isn’t.
My first fill was higher than 3,000 psi, and the velocity was depressed for many shots. When it did rise, it did so in a straight up and straight down fashion. There was no group of shots going at similar velocities. This told me I needed to control the fill very carefully.
I also noticed that the pistol fell off the power curve with about 1,800 psi remaining in the reservoir. But I didn’t stop shooting there. I stopped with about 1,500 psi remaining in the reservoir. From this test, I was able to determine that the pistol used about 62.5 psi per shot. I did that with a chronograph and with an accurate pressure gauge on the hand pump. The pressure gauge that’s built into the test pistol’s reservoir reads several hundred psi too low to be of much use.
I know how much air is in the reservoir when I start shooting because that’s what the pump’s gauge reads when I stop filling. I know how much air is in the reservoir when I stop shooting because that’s the spot on the gauge where the reservoir inlet valve is overcome by pressure during the next fill — you can see this when the gauge needle clicks at the opening of the inlet valve.
It took 1.5 pump strokes per shot, so refilling the reservoir went very quick. That’s why I believe the Hill pump is the best way to go, and the possibility of spare reservoirs isn’t worth the effort.
The shot count test
The next test I conducted began with a fill to exactly 3,000 psi on the hand pump’s pressure gauge. I used Crosman Premier pellets, exclusively for this test. I’ll give you the velocity readings and then interpret them afterward.
I’m not going to give you an average for this string because I don’t know which shots you want to consider as the good shots. Clearly, the pistol was slower at 3,000 psi on the hand pump gauge. And, remember, this is with the more accurate hand-pump gauge. The pistol’s built-in gauge was still showing about 2,700 psi at this point. Either way, there’s too much air pressure in the gun because the valve isn’t opening as long as it should, as evidenced by lower velocities.
Let’s say I like 761 f.p.s. for the first shot. If you agree, then the first 5 shots in this string were wasted. At 62.5 psi per shot, the gun was overfilled by 312.5 psi when it was filled to 3,000 psi. Since these gauges don’t read that accurately, let’s round that back to 300 psi overfill and say I need to stop filling the reservoir when the pressure gauge reads 2,700 psi.
If you select a different velocity as the start point of the shot string, then the beginning fill pressure will need to be adjusted accordingly. This is why I am not giving you an average velocity today. I can give average velocities, but before I do you need to know what is behind my numbers, because this pistol operates within narrow limits.
If I take the second reading of 761 f.p.s. as the ending shot in the string, there are a total of 7 good shots in the string. I think that’s probably too restrictive, and I need to expand my velocity variation allowance. If I allow a velocity variation of 74 f.p.s. between the fastest and slowest shots in the string, I can get 16 good shots on a fill and can start the fill at exactly 3,000 psi.
Do you see how I’m doing that? I’m using the chronograph numbers and accepting all shots until the pistol no longer drives Crosman Premiers out the muzzle at a velocity of greater than 700 f.p.s. My choices are arbitrary; but until I make them, I can say nothing about the shot count of this pistol
Well, maybe that’s not entirely true. Whatever I select as the acceptable velocity variation, I can say with certainty that this air pistol can never get 35 useful shots on a single fill. Where I draw the line is my choice, of course. If I want to shoot groups at 50 yards, the variation has to be tighter than if I want to hunt with the pistol out to 30 yards. Do you see how the anticipated use of the gun drives the useful number of shots you’re going to get?
When you change the clip, the gun must be cocked to pull the loading probe back out of the clip. Then, the clip’s axle must also be withdrawn to the front of the gun and held out of the way. That’s a separate brass bolt on the right side of the gun. The clips come out and go back in easily enough when these things are done.
Here you see the bolt probe that pushes the pellet into the barrel (brass pin in the clip recess) and the brass clip axle (the head is a brass knob) that’s been withdrawn to the front of the gun to remove the clip.
This gun is LOUD! I had to wear electronic ear protectors when testing it in my office. And although my office door was closed, my wife, Edith, remarked on the loud discharge when I was finished.
In the next report, I’ll test the pistol with several good pellets and give you some of the velocity data you’re used to seeing. But when I do, you’ll know what’s behind my numbers.