Question from a new PCP user

Jump to latest Follow Reply
A

Aslap

Member
Mar 2, 2023
86
29
Pittsburgh, PA. USA
I put together a Crosman 2260 that I moved over to PC using the SafePak adapter. I have a 13ci bottle on it and the regulator is set for roughly 1500 psig. I had my son hand pump the tank to around 2500 today and I took it out to shoot it. It's a 20 cal using a Lothar Walther barrel that was a CO2 gun in it's previous life. Very accurate. I'm using the H&N 13.6 grain Barracudas. A previous testing session before I had the gun all together was giving me around 860 FPS. I did not use the chrony today because of weather conditions. The valve is your standard 2400 that is using a bit lighter spring and I have the ports opened up and the valve exit has been angled up. I've also changed the cocking from the little pin thing to a pull back handle threaded directly into the hammer. I have different brass weights that I can use to alter the hammer strike. I have a stronger hammer spring in the rifle also.

Today was a test to see how many shots I could get from a bottle-indicated 2500 psig until I reached the regulator drop off at around the 1500 psig mark. I had probably 40 shots out of it and the bottle gauge was showing around 1000 psig. I was seeing no difference in POI from my first shot to the later shots when the bottle was clearly below the regulated output. I was also getting some of the burping noise with each shot.

So the question is, since I'm still seeing shots with the bottle showing the drop below the regulated pressure that are apparently still at the same kind of velocities that I had when the regulator was at it's 1500 psig reg point, I guess that I am not getting the full pop out of the valve, right? Could need more hammer hit but am I thinking right about this? Next test will be with the chrony to get at the actual velocities across the string as I watch the bottle. I'm going to get the GX CS2 compressor in the next week or so to keep from using the hand pump. Any tips or advice or anything you can think of would be appreciated. This is a fun project! I'll have to post a pic of the thing. Looks right out of "Mad Max".

Tony
 
  • Like
Reactions: maxtrouble and orangeokie
The burping is the hammer bouncing and opening the valve more than once. You should focus first on minimizing that because it complicates the process of tuning. Without getting into mechanical fixes like SSGs or buffers, the simple fixes involve increasing reg pressure or decreasing the hammer weight. You really need to use the chrony to determine your reg setting. Manufacturer calibrations can be way off and your observations may be explained by the fact that the reg is really much closer to 1000psi. When it falls off the reg you’ll typically see an increase in speed (due to the valve opening longer at lower pressure) then a gradual decrease and increase in burping. If it drops straight off thats a sign that you have too much hammer for the reg pressure. The goal is to be a little under peak hammer for your reg pressure (to minimize bounce and maximize air use efficiency), so it’s a matter of finding the pressure that gives your desired speed along with a hammer strength that gives a slight rise in velocity when you drop off the reg. A bit of a juggle when you can’t incrementally adjust the hammer but that’s the way it goes. Congrats on your crafting! It sounds like you’re not too far off from dialing things in.
 
  • Like
Reactions: maxtrouble and SteveV
Upvote 0
weevil said:
The burping is the hammer bouncing and opening the valve more than once. You should focus first on minimizing that because it complicates the process of tuning. Without getting into mechanical fixes like SSGs or buffers, the simple fixes involve increasing reg pressure or decreasing the hammer weight. You really need to use the chrony to determine your reg setting. Manufacturer calibrations can be way off and your observations may be explained by the fact that the reg is really much closer to 1000psi. When it falls off the reg you’ll typically see an increase in speed (due to the valve opening longer at lower pressure) then a gradual decrease and increase in burping. If it drops straight off thats a sign that you have too much hammer for the reg pressure. The goal is to be a little under peak hammer for your reg pressure (to minimize bounce and maximize air use efficiency), so it’s a matter of finding the pressure that gives your desired speed along with a hammer strength that gives a slight rise in velocity when you drop off the reg. A bit of a juggle when you can’t incrementally adjust the hammer but that’s the way it goes. Congrats on your crafting! It sounds like you’re not too far off from dialing things in.
Click to expand...
Weevil,

Thanks for the reply! I figured it had something to do with the hammer but did not consider a lighter hammer. Would a lighter hammer spring or a stronger valve spring help to tame the burp?

The regulator is the standard kind you see on the small bottles that is set to around 850 psig. I made up an ASA that had a slide check and a gauge so I could play with the regulator pressure. One 0.020” shim took the regulator pressure up to the ~1500 psig number. At least that’s what my ASA gauge told me. So I’m kind of stuck with that pressure. My original work was done with the rifle having a .22, 24” Crosman barrel on it. I was just using the SafePak volume and I was pumping that to the roughly 1500 psig level. With 14 grain pellets I was getting 960 FPS and I seem to remember that the burping was less - maybe. I shot some 21 grain slugs and hit 30 FPE with those. Only 2 shots out of the SafePak alone. I was surprised that the .20 didn’t get me higher velocities but that barrel is only 16”.

Once I get the compressor I can fool around more with the hammer/valve issues. Thanks again for the insight.

Tony
 
Upvote 0
In my experience, a lighter hammer has a more significant effect (on bounce) and lost power can be recovered some by using a stiffer hammer spring (another tricky dance!) It sounds like you are the tinkering type so it many be possible for you to fabricate a stop spring guide (SSG). Otherwise, if you can’t tune the reg, you’ll simply have to settle on a hammer weight that provides an acceptable compromise between power and lack of bounce.

Dropping down to a 16in barrel will certainly have a substantial effect on power. Possibly also with the shorter barrel, the extra air released by bounce is no longer contributing to the projectile (because it has already left the barrel).
 
Upvote 0
HeyU said:
What's wrong with the compressor you already have? I bet the compressor you have cost alot more than the 1 your getting. So keep getting that return on your investment.lol
Click to expand...
Hey - Nothing wrong with the current "compressor". The problem is the old man who has to operate it!

Weevil - I may be stuck with the Crosman hammer on this one. I will try a lighter hammer spring and maybe a stronger valve spring to cut the bounce, Is there any place that shows the construction of the SSG? I might be able to make one. I'm probably also going to go back to the 24", 22 cal barrel. Easier to find pellets that's for sure!

Again, thanks for the tips! I'll up date when I get more info - and the compressor!

Tony
 
Upvote 0
I finally got the GX CS2 compressor and it looks to be very good. Can fill my 13 ci bottle from 1000 to 3000 psig in under 5 minutes! Sure beats the hand pump.

A refresh - this is a Crosman 2240 conversion using the SafePak tube insert with a standard Crosman 24" barrel in 22 caliber. The regulator on the 13ci tank was brought up to 1500 psig by using a 0.020" shim under the regulator spring pack, I had made up a regulator pressure monitor with a slide check to check the regulator pressure as my son hand pumped the bottle to 3000 psig. God love him! The indicated pressure on the gauge was hard at 1500 psig. I understand that these cheap gauges have some variation but the gauge on the hand pump and my regulator gauge appeared to be at least close.

I have changed the cocking on this gun to be a straight back cock with a rod coming through the end cap. I did this to eliminate the small cocking pin that always gave me trouble in the high rise breech I'm using. I can add weights to that rod to initiate a harder or softer valve smack. I have a commercially bought "Magnum" hammer spring. The valve was modified by me to relieve the transfer port in the valve and the outlet port on the valve and the barrel inlet port have been opened up a bit. I use a poly transfer tube. I don't remember at this point just what kind of valve spring is in the valve. I checked the whole thing using my highly calibrated Kleenex around the breech to see that there is no visible blow out of the breech. With this set up, I notice none of the air "chatter" that I was hearing with the shorter 20 caliber barrel.

I had to make two graphs because I'm not good enough with Excel to do everything on one graph. First graph is the overview graph and shows the various pellets and the pressure decrease as the shot count went up. Total shots for this test is 60. I also can't figure out how to get the picture in the body of the post.

Second graph blows up the chart to better see the pellet velocities.

I doesn't appear to me like there is any regulated pressure/shot happening anywhere. For the first 8 shots on the 14 grain pellet, I used my different weights going up to a 2 oz weight and there was no difference in the overall dropping of the velocity from shot to shot so the velocities are just using the Crosman hammer. So, I'm not sure what the next step would be. The above conversation hinted that a lighter hammer might be required but I think ("think" being the operant and, in my case, dangerous, word) this is saying that I'm not hitting the valve anywhere hard enough. So maybe a lighter valve spring or somehow an even heavier hammer spring/heavier hammer?

Thanks for any and all suggestions, critiques, or comments.

Tony

Pellet Weight v Velocity Full Graph.JPG


Pellet Weight v Velocity.JPG
 
Upvote 0
I did bring the regulator back to the stock 850 psig setting. Same thing happens - steady decline in velocity with each shot. I'm wondering if the regulator is actually regulating. I locked onto a number when I was pumping the cylinder but I don't know what might be happening as the regulator is on the gun and shots are being taken. I also added just a 0.005" shim and while I got more velocity, the downward velocity trend continued

I have a 6" length of 0.050" diameter SS tubing connecting the bottle to the SafePak. Could this be causing some kind of restriction so that the reg is actually still at the regulated pressure but the valve is seeing less due to the restriction?

Tony
 
Upvote 0
Where would I check to find this vent? I thought maybe something was leaking so I opened everything up into the rifle and pumped the bottle to 3000 And it’s still there after 6 hours. That might not be a valid test if the leak was after the regulator.

I can’t find the numbers from my initial post so I don‘t know if the regulator was working at that point.

Very odd.

Tont
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu