I think I know what's happening but wanted those more savvy to try and clue me in. Tuning the new Snowpeak M60B I'm having and issue with the hammer spring and velocity. As I bring the hammer screw up in tension (any amount at all like 1/4 turn) the velocity drops instantly. This is with the reg set at 120, 125, 130, 135, 140 bar etc. I know tension is CW and not reverse threading as the screw works into the rifle and cocking gets harder. Right now I have the hammer spring all the way out to get any results at all I like by only adjusting the reg to more air. I think the valve spring might be pretty weak or the hammer is bouncing and dumping too much air when increasing HS tension . Anyone either have this rifle or a better clue what's happening?
Snowpeak PCP "Super Tuners" weird situation. M60B
- Thread starter MACTEN
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I'm having the same issue with my Bullshark. My reg is around 140 bar and anything past 2 turns on the hammer spring drops velocity. I have a plenum on order to see if that helps.
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At least you can put an internal one in the tube.. This one does technically have a plenum but it can't be very spacious as it's the path from the regulator located above the bottle attachment point that travels to the valve located at the breech end. Might be the multiport valve like Hatsans use that causes it be be a lot less efficient.
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It seems like these Snowpeaks max out due to the weight of the hammer. The SA plenum kit comes with a brass spacer that adds a little mass to the hammer.
I would think if it was the weight of the hammer the increased HS tension would show an increase in velocity as well though.
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I'm probably just being power hungry because I'm making right at 24 fpe with 13.43 KOs but I'd like to squeeze a little more out of it if I can.
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That behavior usually indicates the hammer is overdriving the valve stem, causing the hammer to strike the back of the valve body. As a result, it rebounds and dwell is drastically reduced. As mentioned above, more weight will help but it sounds like an extreme case so if you can’t get to the velocity plateau, it may be necessary to modify the valve and/or poppet.
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Maybe I should just leave it alone. I was trying to get some more shots from the 480cc bottle (still filled to factory 250 bar) But, 70 shots at average 46 fpe 25.4 JSB's and 9 es with 2 point something SD might be as good as it gets un-modified)
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The highest regulator setting my P35-25 can support - I can balance against the hammer spring - is about 135 bar. That is with the barrel port, transfer port and the path between them drilled out to 85% of bore size and with the spring shimmed almost to the point that I cannot cock the gun. The hammer spring will not support a higher regulator setting. I got confused when re-tuning it and kept turning the regulator up and wasted a lot of time and air. Every time I turned the regulator up the velocity fell. I think that is pretty much what you are describing. It was a bit frustrating. Then the light bulb went off and I turned it down and started again.
I think you need to turn the regulator down to get to the point where a decrease in the hammer spring will decrease velocity. There should be one. My 3 P35s arrived with the regulator at a setting where this was possible. If you can get back to the stock setting I would do that and then try small changes from there.
You can probably raise the spring force a little by shimming the spring. I opened up the hole in a #10 washer a little and that helped. If it's a little too much (gun won't cock) with the spring turned all the way in you can turn it out until it will cock. The other way to shim the spring is to put a spacer into the hole of the hammer where the spring goes. That gives a little more force on the valve because it effectively increases the hammer weight. The plenum from South Africa includes a brass spacer for this purpose. It is in my P35-25. I tried the washer first and the brass spacer definitely did a little more.
A 177 or 22 cannot have the barrel port, at least, as big as my 25 caliber. The pellet would fall into it. So there will be more restriction. I'm not sure what that does to the maximum regulator setting the spring can support. I'm thinking it will be be the same or less.
There is also another way to reduce the necessary hammer force. You can reduce the poppet diameter a little. Most of the resistance to the hammer is the air pressure in the plenum pushing on the poppet. If it's area is reduced the hammer can open the valve more readily. That is not my idea, Mike suggested it in the thread I started on my P35-25. It seems more complicated since a reduction in diameter (area) will also cause the valve stem to protrude more reducing the hammer throw. So you might have to reduce the stem length to compensate. I got to about the power I wanted without doing this and I'm a little nervous about messing with the poppet but the idea seems very sound and Mike reports success in his P15 (predicessor of the P35 with rear cocking).
I've also thought about trying to change to a pin style pellet probe. I am not sure how to get the stock one out but I haven't really tried. I think that would allow a little more airflow. I think I could make it out of 304 stainless steel tubing/rod without use of a lathe.
I don't know why SPA seems to have used a somewhat weak hammer spring in at least my P35, sounds like other guns too, but I worry it might be due to their choice of the plastic in the poppet. If that is true and you jack up the regulator and the hammer spring it might cause the poppet to fail. May be safer to use Mike's approach to reduce the poppet area to increase flow and decrease the necessary hammer force. Or just live with the fact that SPA guns are not easily tunable to really high power levels (the barrel length on the P35 is also pretty short at 450mm and that doesn't help power but is nice for weight and handling). I got my 25 to 47-48 fpe on pellets and 44 with slugs which is at least currently OK with me.
I think you need to turn the regulator down to get to the point where a decrease in the hammer spring will decrease velocity. There should be one. My 3 P35s arrived with the regulator at a setting where this was possible. If you can get back to the stock setting I would do that and then try small changes from there.
You can probably raise the spring force a little by shimming the spring. I opened up the hole in a #10 washer a little and that helped. If it's a little too much (gun won't cock) with the spring turned all the way in you can turn it out until it will cock. The other way to shim the spring is to put a spacer into the hole of the hammer where the spring goes. That gives a little more force on the valve because it effectively increases the hammer weight. The plenum from South Africa includes a brass spacer for this purpose. It is in my P35-25. I tried the washer first and the brass spacer definitely did a little more.
A 177 or 22 cannot have the barrel port, at least, as big as my 25 caliber. The pellet would fall into it. So there will be more restriction. I'm not sure what that does to the maximum regulator setting the spring can support. I'm thinking it will be be the same or less.
There is also another way to reduce the necessary hammer force. You can reduce the poppet diameter a little. Most of the resistance to the hammer is the air pressure in the plenum pushing on the poppet. If it's area is reduced the hammer can open the valve more readily. That is not my idea, Mike suggested it in the thread I started on my P35-25. It seems more complicated since a reduction in diameter (area) will also cause the valve stem to protrude more reducing the hammer throw. So you might have to reduce the stem length to compensate. I got to about the power I wanted without doing this and I'm a little nervous about messing with the poppet but the idea seems very sound and Mike reports success in his P15 (predicessor of the P35 with rear cocking).
I've also thought about trying to change to a pin style pellet probe. I am not sure how to get the stock one out but I haven't really tried. I think that would allow a little more airflow. I think I could make it out of 304 stainless steel tubing/rod without use of a lathe.
I don't know why SPA seems to have used a somewhat weak hammer spring in at least my P35, sounds like other guns too, but I worry it might be due to their choice of the plastic in the poppet. If that is true and you jack up the regulator and the hammer spring it might cause the poppet to fail. May be safer to use Mike's approach to reduce the poppet area to increase flow and decrease the necessary hammer force. Or just live with the fact that SPA guns are not easily tunable to really high power levels (the barrel length on the P35 is also pretty short at 450mm and that doesn't help power but is nice for weight and handling). I got my 25 to 47-48 fpe on pellets and 44 with slugs which is at least currently OK with me.
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When I retuned my P35-25 and got to my current end point I verified that getting the hammer spring balanced against a lower regulator setting increased velocity versus having the regulator too high for the hammer spring to open the valve.
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I have the hammer spring turned out all the way and tuned it with the reg only and am getting low ES and average 46 fpe right now which is acceptable to me. I had thought about getting a SSS and trying a free float but that's only if I decide to go the slug route as I've read these are un-choked barrels. I may have to take the valve out and just take a look at some point and see what materials and spring stiffness it has etc. I like your idea about a pin probe and have thought that would be much better but haven't gone into it yet either.
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BTW, turning my reg up has been the only way to increase velocity at all. I started with it about 100 bar and tried HS tension from 100 bar in 5 bar increments all the way to 155 with the hammer from all the way out to max ,doing nothing but lowering the velocity with every reg pressure increase. Meaning every time I turned the HS in no matter what reg pressure is at, velocity dropped with spring tension increase.
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There seems to be a fairly small range of reg pressure where the hammer spring works as we expect it to. Seems a bit odd to me since my Avenger can have the reg setting from about 1200 psi to 2900 psi but the hammer spring of my P35s is definitely not that flexible. But on my 3, once the reg is set about where I got it plus or minus maybe 1/2 turn at most, the hammer spring will work. If I am close to balanced then turning the spring down decreases velocity and turning it up will increase velocity but only to a point. Once the hammer spring is fully opening the valve no further increase is available that way, the regulator has to be increased. But then you run out of hammer force.
When I got my P35-25 close I had a pretty good velocity and a decrease of the hammer spring force would decrease velocity but my first shot velocity was lower than the rest of the string. I knew from other tuning on this gun that meant the hammer spring was not right for the regulator setting but I could not turn it up, I was max'd out on hammer spring. Turning it down made it worse. So I decreased the regulator a little. An easy way to do that is to loosen the regulator lock nut and then retighten it. The regulator will go down a fraction of a turn. I think I did that twice. That gave me my current setting. The velocity was increased slightly from where I was with a higher regulator setting. I turned the hammer spring less than 1/8th turn down from maximum velocity and I think accuracy was a bit better (but this gun is not so good for accuracy) and I only lost a fraction of a pound fpe. ES for a 20 shot string was about 7 fps. First shot velocity is the same as the rest of the string.
I would not change the regulator more than 1/4 turn at a time and I would check to be sure the velocity went in the direction you intended. If you turn it up I would turn up the hammer spring too until the velocity stops going up. If turning down you could leave the hammer spring alone as long as the velocity decreases. If it increases you had too much hammer spring for your last regulator setting.
When I got my P35-25 close I had a pretty good velocity and a decrease of the hammer spring force would decrease velocity but my first shot velocity was lower than the rest of the string. I knew from other tuning on this gun that meant the hammer spring was not right for the regulator setting but I could not turn it up, I was max'd out on hammer spring. Turning it down made it worse. So I decreased the regulator a little. An easy way to do that is to loosen the regulator lock nut and then retighten it. The regulator will go down a fraction of a turn. I think I did that twice. That gave me my current setting. The velocity was increased slightly from where I was with a higher regulator setting. I turned the hammer spring less than 1/8th turn down from maximum velocity and I think accuracy was a bit better (but this gun is not so good for accuracy) and I only lost a fraction of a pound fpe. ES for a 20 shot string was about 7 fps. First shot velocity is the same as the rest of the string.
I would not change the regulator more than 1/4 turn at a time and I would check to be sure the velocity went in the direction you intended. If you turn it up I would turn up the hammer spring too until the velocity stops going up. If turning down you could leave the hammer spring alone as long as the velocity decreases. If it increases you had too much hammer spring for your last regulator setting.
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I actually found that the dreamline hs adjuster fits this and was able to get a lot more room for the spring using it a few minutes ago. I was able to get the velocity to go up and peak with it and backed it of from the max velocity of 924 35.4's to 898.. That's not 95% but I don't want to run it in the 800's as usually 25's do do well for me that low velocity (might be different with this one). I think this airgun would benefit from a heavier HS as others have mentioned and a shorter stiffer spring perhaps. Opening up the barrel port and transfer port are also good ideas but i've read this valve on this one is like my old Hatsan's with multiple holes for exhaust. My es is about 11 right now over 60 shots that way it sits at the 898 velocity area. I need to look for more old FX parts like springs ...can't remember length or diameter
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The transfer port on my 25 caliber is just a hole. You get to it by removing the air tube (after degassing). When you screw off the airtube the spring and poppet are right there. Screwing in the air tube tensions the poppet spring. The poppet seats on a stainless steel piece that has the transfer port on the side. It sits in an O-ring and can just be pulled out. The passage between the transfer port and the barrel port is above it. There is an allen head piece under the cocking hardware on the bottom of the gun. If you pull it you have direct access to the port between the transfer port and the barrel port. My barrel port, transfer port, and passage would accept a 3/16 drill bit but nothing larger.
I have not pulled my 177 or 22 apart to check sizes. I kind of think they might all have the 3/16 passage in the block but smaller barrel and transfer ports. Probably also about 75% of the barrel bore. The passage through the block might also be 75% of the bore size. But it would be simpler for SPA to just make them all the same size.
I don't understand how a different HS adjuster gave you more hammer spring force. I am limited by the spring binding up, fully compressed. Maybe you didn't previously have the hammer compressed fully and the different adjuster allowed you to get there? Did the same thing as the shims I used?
I have not pulled my 177 or 22 apart to check sizes. I kind of think they might all have the 3/16 passage in the block but smaller barrel and transfer ports. Probably also about 75% of the barrel bore. The passage through the block might also be 75% of the bore size. But it would be simpler for SPA to just make them all the same size.
I don't understand how a different HS adjuster gave you more hammer spring force. I am limited by the spring binding up, fully compressed. Maybe you didn't previously have the hammer compressed fully and the different adjuster allowed you to get there? Did the same thing as the shims I used?
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Mine is a bottle so getting to the trxfr hole looks different. I' sure there are bottlenecks in there. I didn't get more HS by putting the smaller adjuster but less.. The other adjuster that came in the rifle already has the most power the valve can handle and like was said earlier the hammer is likely bottoming out on the valve body and limiting the dwell by rebounding too fast. By putting a shorter adjuster in there I was able to get less HS and adjust a small amount and see the velocity increase and back it back off of the knee a bit. In my mind (as said before as it makes sense to me now) a heavier hammer could help likely as it would not bounce as much allowing more dwell likely. Same could be done with a longer valve stem and modified poppet.
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MacTen
How is the M60b performing with the dreamline power adjuster? Did you have to adjust the valve any? Just looking for update.
Thanks
How is the M60b performing with the dreamline power adjuster? Did you have to adjust the valve any? Just looking for update.
Thanks
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