American Air Arms Evol 15 Shot Count Drop

[Pfddi]

So I took my Evol 15 out today after filling it to about 260 bar before going out. The pressure for each shot was set at 2000psi from AoA and I have not fooled with the gun. I go out and wanted to sight in some of the JTS 18.1 gr and see how they did. I normally shoot the JSB 25.39s so I wanted to see how these did. I shot 1 magazine and reloaded and the first shot out of the next magazine was 4" lower. I had an immediate WTF, and shot another and it's an inch lower than the last shot. The 3rd one is 3 inches lower. I go look at the reservoir pressure and it's at 1000 psi! No leaks that I could hear and no extra noise on the shot so I am really stumped as to what is going on. I would easily get 35+ with the 26g JSBs so I was thinking I would get a few more with the 18gr. Anyone out there have a similar problem?

Thanks,
Paul

 

[madeintheuk]

Let’s first see if your rifle is leaking. Fill it to 3000 or so, and leave it for a few hrs. See if the pressure drops at all.

 

[IMADMAN]

Just guessing here, maybe wasted air by using a lighter pellet?

 

[Pfddi]

Done. Will report back in a few hours

 

[Pfddi]

@IMADMAN - I thought the same but not that much! I figured I might have to decrease the hammer pressure and possibly the register if I wanted to shoot those pellets, but only 12-13 shots?

 

[IMADMAN]

@IMADMAN - I thought the same but not that much! I figured I might have to decrease the hammer pressure and possibly the register if I wanted to shoot those pellets, but only 12-13 shots?

Yeah, I know you said the report didn’t sound much different, but you might never know. Let us know if any air is lost after a few hours of sitting @ 3000psi

 

[PumaCarl]

What speed were the 18gr pellets traveling at? What speed were they traveling at with the 25gr? If you were getting 35 hot 25gr shots before and only a mag and a half now with 18's, you have to be wasting air. Turn your hammerspring way back and start from scratch. I'm really curious if you find it to be something else. Probably should look at your probe o-ring too, though I would think that you would've noticed that real quick.

 

[Pfddi]

Well we didn't have to wait more than 20-30 minutes. It is clearly losing air! It started at about 2900 and is now down to almost 2500! Good call gentlemen! What's next? I certainly can't hear anything escaping.

 

[PumaCarl]

I would guess it is most likely the fill port. Try putting a drop of silicone oil on it and fill it up a little and see if it fixes itself. That's what I would do first.

 

[madeintheuk]

first place I would check too. Seems to be a bit of a problem if they’re dry.

 

[Pfddi]

Done - a bit hard to get that drop down as it doesn't want to just slide down! Got it back to 3000psi. Back to the wait and will report back. Thank you for the tips!

 

[PumaCarl]

For future reference, all you need is to put one small drop on the fill port before you connect to it. The air filling it pushes it down to where it needs to be. It will either work with a tiny drop or it won't work at all. In which case you would have to change the o-ring there.

 

[Pfddi]

@PumaCarl - Yes, I figured the pressure would certainly move the oil. I hope that does the trick. Do you happen to know which o-ring is required? I have so many spares now that I hope that I have one the right size! I can look at the schematic, but in case you knew off the top of your head...

 

[PumaCarl]

https://5689f0.p3cdn1.secureserver.net/wp-content/uploads/2021/02/E-100-0102-00-C3.pdf

Straight from Tom himself. It's a -04 o-ring.

 

[PumaCarl]

Tom also recommends only using Ultimox 226, which you can find on Amazon, but most people don't have it handy and a drop of silicone has worked for several of us, in a pinch.

 

[Pfddi]

I have the Ultimox incoming already! But I used a drop of silicon oil which - as you said - should let us know it that's what's leaking and I already had it.

 

[pan60]

what type of silicon oil is recomened to have on hand for o-rings?

 

[Pfddi]

I use a light viscosity on the o-rings. For this test, I use the silicon oil I got from Hill that is used in the compressor. I have some that is a bit heavier - not quite a "grease" that I use on other parts as well as a grease itself. It is easier for me to coat the o-rings with the lighter viscosity - thanks to old-age tremors in my hands!

 

[pan60]

i only ask because i seen some onlie i think amazon but everyone i seen said hydrocarbons and flamible LOL i did not think that was rite? one i think 3M said it was mineral oil based so i figured i would ask.
i mostly have used pump guns and i am just getting into the PCP world and was planning on keeping a few things around.

 

[madeintheuk]

Need to use 100% silicone oil if you’re using it theough fill ports and it’s entering the air reservoir. Greased are too viscous to work. Anything other than silicone will combust under the high pressures and speeds of the shot cycle. Tom recommends ultimox for oring lubricants, but this is durning dissasembly, not for “quick fixes”.