BAM B51 - Part 2
A look at the "Chuntsman"
by B.B. Pelletier
Well, a very interesting day. You will recall that yesterday I checked the pressure in the BAM B51 and used a hand pump to add another 100 psi. I wasn't sure that it was needed, because the gauge I used yesterday was different than the one I used to fill it initially a week earlier.
Out to the range
I packed up all my gear - rifle, targets, pellets, bench bag, carbon fiber tank, a pump to back that up, chronograph and skyscreens and shooting bench - and drove to the range. Got there, set up everything and decided to chronograph some pellets first. First shot with .22-caliber Beeman Kodiaks didn't trigger the skyscreens, but the sound it made was similar to a blowgun being fired, as in very quiet. That's never a good sign with an unsilenced PCP. Next shot registered 383 f.p.s. I knew for sure something was wrong.
Heed the warnings
There are warnings all over the internet not to exceed 3,000 psi with these BAM pneumatic rifles, so I thought the gun might be suffering from valve lock. But how could that be, when I just told you I had topped off the gun to 3,000 psi? As I've mentioned before, small pressure gauges don't always read correctly and some guns can be severely affected by being overpressurized just a few hundred psi.
I dry-fired the gun several times, hoping to hear the report increase as I shot. It didn't. It became quieter! The gun was out of air! I refilled it from the carbon fiber tank, and it seemed that it was almost empty. You can tell that because you can hear the inlet valve in the rifle pop open when the air pressure in the fill hose overcomes the pressure in the gun's reservoir. I thought it did at about 200 psi. Again, I took it back up to 3,000 psi and then back to the chronograph.
Use a cheaper pellet
This time, I used Gamo Hunter pellets because they're cheaper. I wanted to establish that the rifle was operating before shooting my more expensive Kodiaks. First shot was 407 f.p.s. - well under expectations. Second shot was 206! The gun had run out of air once more. Several dry-fires after that shot confirmed my fears.
Between the evening before and the morning I went to the range, this rifle may have become a leaker. I'm describing what happened so you can relate to this problem if you ever have it. I hope those of you who are thinking of getting into precharged pneumatics are paying attention to this.
What to do?
Okay, I may have a leaker, and a fast leaker at that. I could just stop right there, but now I will to try to solve the problem. When a rifle goes from holding to leaking overnight, as this one seems to have done, the problem is often because a stray piece of dirt or debris in the reservoir has gotten on the valve seal. If I could get the rifle to hold air, I would shoot it without a pellet repeatedly, hoping to blow the dirt out. But I can't seem to do that.
I filled the male Foster fill nipple with Crosman Pellgunoil and then filled the rifle to 1,000 psi with my carbon fiber tank. I was hoping that the Pellgunoil would be blown into the reservoir and perhaps get on the seals, where the dirt would be floated off. This is a very long-shot proposition with about a 10 percent chance of success. It won't fix an O-ring that may have sprung a leak. However, when I tried to fill the reservoir the pressure gauge went up too fast for the rifle to be empty. The Pellgunoil was gone, but no air seems to have flowed into the rifle.
Do NOT add Crosman Pellgunoil to a precharged pneumatic airgun as mentioned in the paragraph above. I have learned that someone once received a petroleum specification sheet with the Pellgunoil they bought that indicated it was straight 30-weight non-detergent oil. If that is true, it is very dangerous to introduce petroleum oil into a vessel containing compressed air. It can form a fuel-air mixture and become explosive. I believed that Pellgunoil is a synthetic product with a high flashpoint, but there is a good chance I AM MISTAKEN.
It turns out I may have been wrong about the rifle being out of air. It may in fact be valve-locked, after all. At the range I wasn't able to hear the fill because of some noisy compressors, but in my office at home I did hear well. Air is not escaping from the rifle anywhere. And the reservoir didn't get warm as I filled it - a sure sign the gun is not accepting air. Add to that all the warnings about over-filling this model and I think I may have the problem.
Here's what I am saying. If the valve in the rifle I have cannot function with even 3,000 psi, then I may have caused valve lock by pressurizing it to that level. Either that or the inlet valve is stuck and refusing to open for some reason. The few low-powered shots I did get at the range have me wondering.
Here's my plan. I'm going to stand the rifle in the corner and attempt a dry-fire every day or two. If I ever get one with air coming out, I will continue until the sound grows loud. I will do that for a week. If that fails to work, then, with Pyramyd Air's knowledge and permission, I will disassemble the powerplant and see if the valve stem deflects down under any kind of hand pressure. If not, I'll use a rubber mallet and a long piece of hardwood to rap out the excess air that's in the reservoir.
When there is something additional to report, I will tell you.