Snowpeak Interesting P35-25 tune

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JimD

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Mar 27, 2021
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I've been chasing a slow leak in my P35-25. Yesterday I replaced the 3 O-rings in what I call the front end, the part before the regulator. A day or two earlier I replaced the O-rings behind the regulator. Still seems to leak about 50 bar a day. I was thinking of degassing it again but decided to shoot it some to see if the pellet preferences are still the same and to have a little fun with it. I learned some interesting things about the tune.

This gun has an Extreme Airguns added volume plenum and slightly larger ports and passage between the ports. I have tuned it to a little over 50 fpe a couple times but I took out the shim on the hammer spring yesterday which decreased hammer force a little. I'm wondering if the leak might be from the poppet and have a ballon on the end of the barrel right now to check that theory.

When I started shooting I was about 230 bar. Limit is 250 for these guns. First 5 shots with the MKII heavies it likes were about 750 fps with the first spot a little lower at 727. I'd turn the spring up a little if I could. I also measured the sound of three of these shots with a phone app and got 80.3db, 83.7 db, and 78.2 db. I then shot some cast pellets (still shoot poorly), FX 25.4s (shot pretty well at about 850 fps), SPA 25.93 (poor at about 835), H&N FTTS (20 grain, 925 and very inaccurate, curiously these were pretty accurate before I added the plenum), and a lot more MKIIs and original Heavies. After 38 shots I was down to 145 bar. The next half dozen were almost all over 750 fps and the magazine after that averaged about 770 fps. The peak I got was 790 fps. That was two shots before I looked at the gauge again and it read 110 bar. The velocity fell to 734 after a few more shots. The gauge read 100 bar.

So I have about 38 shots, I think, on the regulator with a 230 fill. Probably 40 with a full fill to 250 bar. To me that is OK for ~45 fpe. But the interesting thing is the 20 shots after that. They are if anything a few fpe more powerful than the first 40. ES goes up including them in the string from about 18 to about 41 fps. But that is OK for plinking or even hunting. I was shooting a 30 yard challenge target as I did this and the POI didn't change much. It was too windy to be precise about the POI and I was also using its normal 4-14X scope so I wasn't set up to see small changes in POI.

60 shots at around 45 fpe is a lot for a little gun with a 450mm barrel. You could even argue I should fill it to ~140 bar for hunting and take advantage of the slightly higher fpe once it is effectively unregulated. I don't think I've ever used 20 shots in a day hunting with a rifle. If I hand pumped still I would also like being able to get some useful shots and only fill to this relatively low level. I plan to fill it up close to 250 bar still but if I pull it out of storage and see a pressure under 150 bar it's nice to know it's still usable.

Retuned P35-25 in new stock.jpg
 
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Pretty standard off-regulator bell curve for guns tuned well below the plateau and knee, ie: partial valve lock while on regulation. Coming off regulation means the valve starts operating unregulated, and with such a state of tune you're at, you'll see behavior similar to unregulated rifles with a slight increase in fps as the valve is easier to open and creates more lift/dwell, compared to whats seen when on reg, and then a slight fall as you reach the plateau for that given pressure, for an extended period of shots.

Most would say your tune is ideal for those wanting maximum shot count and good efficiency, where as for maximum consistency given conditions such as reg creep, it would be better to either lower the regulator set point or increase hammer preload to get the tune a bit closer to plateau, where when coming off regulator you see less of a bell curve and more of a drop in fps.

If shes shooting good and doesn't experience reg creep commonly, or those effects don't bother you if present, then I would rock with the current tune.

-Matt
 
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My reg is at about 140, maybe 145 bar. I am max'd out on the hammer spring. I've had it up a little further, maybe 150 bar, but I had to shim the spring to get enough force to open the valve.

It's most accurate pellet post installation of the bigger plenum is the JSB Heavy, preferably MKII. Regular heavies are pretty accurate too. That causes my "struggle" to get them up to speed with the little P35. I just tested penetration today and got more than my Avenger shooting 25.4s significantly faster. Similar fpe. So I think I'll stick with the heavies but I may reduce the diameter of the poppet once I find a new one or two to have on hand if I mess it up. But even if I can't get them moving faster it is a decently powerful 25. I find the fact that the velocity stays about the same for 20 shots or so after it goes off reg interesting and attractive. Adds more useful shots.
 
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JimD said:
My reg is at about 140, maybe 145 bar. I am max'd out on the hammer spring. I've had it up a little further, maybe 150 bar, but I had to shim the spring to get enough force to open the valve.

It's most accurate pellet post installation of the bigger plenum is the JSB Heavy, preferably MKII. Regular heavies are pretty accurate too. That causes my "struggle" to get them up to speed with the little P35. I just tested penetration today and got more than my Avenger shooting 25.4s significantly faster. Similar fpe. So I think I'll stick with the heavies but I may reduce the diameter of the poppet once I find a new one or two to have on hand if I mess it up. But even if I can't get them moving faster it is a decently powerful 25. I find the fact that the velocity stays about the same for 20 shots or so after it goes off reg interesting and attractive. Adds more useful shots.
Click to expand...

Your anecdotes completely coincide with my above post!

Reducing the poppet OD a hair and/or moving over to peek would greatly improve the gun and allow you to either achieve a bit more power or run a hair less preload to return to the same tune.

I recommend peek and .025" sealing margin meaning if the throat/seat is .24" you'd run a .28"-.29" poppet diameter.

If you don't have any peek, and are interested and able enough to fabricate a poppet, let me know and I could mail you a piece to play with.

-Matt
 
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JimD said:
My reg is at about 140, maybe 145 bar. I am max'd out on the hammer spring. I've had it up a little further, maybe 150 bar, but I had to shim the spring to get enough force to open the valve.

It's most accurate pellet post installation of the bigger plenum is the JSB Heavy, preferably MKII. Regular heavies are pretty accurate too. That causes my "struggle" to get them up to speed with the little P35. I just tested penetration today and got more than my Avenger shooting 25.4s significantly faster. Similar fpe. So I think I'll stick with the heavies but I may reduce the diameter of the poppet once I find a new one or two to have on hand if I mess it up. But even if I can't get them moving faster it is a decently powerful 25. I find the fact that the velocity stays about the same for 20 shots or so after it goes off reg interesting and attractive. Adds more useful shots.
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The reason I asked is because I know a P15 can’t find the plateau speed at 150b. I can’t remember but I’m not sure it can at 140b. So that puts you starting your tuning at a mystery number. Are you already -2%, 3%? I wound up building a hammer for mine that accepted larger wire and diameter springs. My gun is set around 150b. It shoots 25-26gr pellets at 900fps. I think around 40 shots per fill. String flat as a pancake.
 
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I got 850 on FX 25.4s a couple days ago with a stock hammer spring. That is up because of the plenum and a tiny bit due to my drilling out the ports and passage. They would be a reasonable option too but they aren't quite as accurate.

I don't really know where I am on a tuning curve because I can't turn the hammer spring up any more. I effectively did that with a shim on the hammer spring and got another 10-15 fps. But when it came off reg with that spring setup it went up another 20 fps or so. So my guess is I am several percent under the peak for the hammer spring. My first shot being low also is consistent with me being not insignificantly below the peak based upon prior tunes of this gun. I'd like to be a little less below but with the shim I was using I was high on the first shot so I was probably too high. That shim went in front of the spring in the hammer so it also increased the mass of the hammer. I might try and inbetween shim. I've done it before.

Thanks for the offer Matt but I don't have any way to make a poppet. I am planning to reduce the diameter by putting one in my drillpress and sanding a little off. Crude. That's why I want to have another on hand. I will measure the protrusion of the stem of the poppet first and try and keep that the same. I'm worried the sealing surface may be too narrow and could even go away if I decrease the diameter. I can rig up something to sand on an angle but I don't know exactly what the angle is. But if all I'm risking is a fairly inexpensive poppet I will give it a try, I think.

I'm also sure a heavier spring would allow more power but I do not have the ability to make a new hammer to accept one. I looked and couldn't find any that will fit the gun as is.

750-800 fps on the heavies is not the end of the world. My little Prod won't do more than that on 14.66 grain FTTs. It's taken 17 squirrels for me. So I don't think it's a disaster if I cannot get it up comfortably over 800 but if there is some inexpensive way to do it and have some fun tinkering in the process I'm up for that. It would be more practical to just buy a different gun but it wouldn't be as much fun.
 
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I'm pretty sure the slow leak is from the joint of the regulator to the plenum piece. The gun sealed well with the new plenum but I've had it apart since and did not pull the regulator out to get it snug to the plenum piece when I put it back together. It's a bit of a mess to do because the O-rings on the outside of the regulator don't want to let it slide out. I suspect they were also resisting the regulator sliding down when I screwed the plenum back on. So the airtube has to be completely open so you can push the regulator out. That is my excuse. I also moved the O-ring location a little in this area in the current trial. But if that leaks I will go back to the way I had it initially that worked well. Modifying guns turns into a lot more loose ends than just leaving them in stock condition in my limited experience.
 
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I think only tuning rifles is smarter. With 6 I use my 25s the least so I've decided to see what I can do with this one. Trying to make a gun do something not possible with a retune is kind of asking for trouble. But 10-20% over stock seems like a potentially reachable goal.

The guy where the plenum comes from suggested I just put a longer barrel on it. Said he'd make one. But that would take away from the short light character of the P35.

Another reason I like the current tune pretty well is it seems to not waste a bunch of air. At the tune with the shim in the hammer when I went to use the chronograph the excess air would blow it around. Shot count seemed pretty low. Probably too close to the peak. But with this one there is none of that. Gun seems more settled.
 
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+1 to that last sentence on post #9....I love tinkering and modding but it is easy to start digging that hole deep and get lost in it, or have to do things over and over again because of the mistakes and learning that occurs along the way, which isn't always a bad thing, but certainly can come off as tedious, and sometimes expensive. But, I marvel at my fully customized airgun, to me she is a looker, and I can blueprint every little bit of customization that went into it with my imagination, and appreciate both my efforts and the results achieved.

The barrel is a bit short on the p35's, assuming they are 450mm in all calibers that is, 500mm might net a minor 20 fps increase, really depends.

I can't recommend sourcing a peek poppet enough, the only issue is most guys would want the whole gun shipped to them to perform the mod opposed to just shipping you one, everything is so expensive these days as it is.

Aside from that, I wouldn't change anything, not even the tune really, but that is just me.

-Matt
 
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I have a TJ barrel on mine. It might be an inch longer than the stock one. At 150b the guns report is clean. The hammer I built is maybe just a little bit lighter than the stock one. I would have to go into the GTA archives to find all the numbers. Probably 2017 when we were messing with that platform. I even experimented with the valve return spring. Nothing is better than the stock one. Don’t let anyone convince you to try a softer one.
 
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I wasn't really not trying to but I retuned this gun. I proved to myself it was still leaking and decided I needed to put new O-rings in the regulator too. I measured the protrusion of the adjustment screw but that did not get me back to where I started. Velocity was really low again. So I shot until it came off reg so I knew the reg setting and reduced it 1/4 turn. That seems to be very close to my prior setting but probably slightly higher. I might have also found the "bad O-ring" but am trying to leave it alone to see if I did. I went to fill it for some more testing this morning and it was hissing out the fill port. One-way valve O-ring was bad. A piece was stuck to the nut beside the valve. It's held pressure for 5 hours now.

But the interesting thing is the velocity changes even less when I go off reg now. I only filled it a little above the assumed 140 bar reg setting and got 14 shots I think were on reg and 18 I think were off the reg. I did this in several short strings hours apart to try and figure out how much low the first shot is. It varied but was never over 20 fps. Point of impact was at most 1/4 inch low at 30 yards. Ignoring the first shot, my velocity was from 748 to 778 fps. One of the first shots was within this range. 30 fps is a little high for a regulated gun but I was off reg most of the time. The point of impact change in this range was quite small. I hope the gun is not still leaking because I'm liking this tune and would like to just leave it alone awhile.

The fact that the first shot is lower consistently makes me believe I am below the peak velocity for the regulator setting. The hammer spring is max'd out with a 1.1mm spacer added. I'm shooting 5 shot groups at 30 yards with a 14X scope that are 1/4 to 1/2 inch consistently. Seems like a good place to stop.
 
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I agree, I probably replace that O-ring the most. My guess is I nicked it a few days ago when I installed the previous one. I haven't replaced any O-rings in mg P35-22, however.

I did find something that helps. I put a tiny amount of silicone grease in the slot of the screw and it holds the screw on the screw driver as I lower it inside the big nut it resides in. It doesn't make it last longer but it helps getting the silly thing installed.
 
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I shot 10 shots with my P35-177 as it came off the regulator this morning: 885, 884, 880, 881, 879, 874, 873, 870, 866, 865. The pressure gauge was just under 140 bar at the start and about 110 bar at the end. I think the reg is at about 125. I view this as a normal path as you come off reg. Roughly 5 shots before velocity starts to fall fairly quickly.

Yesterday I shot a shot 18 shots while the fill valve was leaking (so pressure was falling more rapidly). I started near 150 bar and ended at about 95 bar. Velocity was: 751, 761, 769, 759, 763, 768, 120 bar 770, 767, 766, 771, 768, 770, 765, 765, 761, 757, 755, 745 95 bar.

I will shoot it again today but I don't know how many shots I'll take. It is around 200 bar right now and I probably will not shoot down to the regulator but when I do I will update this.

What I think is unusual is the velocity stays up pretty consistent with the regulated velocity for so long. By 120 bar I was well off the regulator but my velocity was still 765-770 fps. For another 8 shots. Without the extra leaking I think I would have gotten 20 shots after the regulator at about the regulated velocity. To me that is unusual.
 
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I shot a string that started at 200 bar from my P35-25 starting at 3pm. I was waiting of the peak temperature which was reportedly 86 degrees. I'm trying to make sure I don't get a really low velocity again when it gets hot. I stopped to check pressure every magazine which is every 8 shots. You'll see that scattered in the string. I also looked at the gauge when it seemed to fall of the regulator. 200bar 716, 758, 753, 751, 752, 749, 753, 749, 180 bar, 743, 747, 758, 756, 759, 760, 764, 757, 170 bar, 746, 757, 768, 765, 761, 762, 767, 764, 155 bar, 749, 761,780, 145+bar, 755, 773, 772, 774, 766, 140 bar, 764, 775, 764, 775, 768, 773, 776, 774, 120 bar, 768, 770, 776, 771, 766, 760, 754, 748, 100 bar.

I'm taking the 780 fps as the point I fell off the reg which seemed to be a little over 145 bar. That and the first shot being so low tells me, I think, that the hammer spring is low for the regulator setting (but is all the way up with a shim). It looks like my ES on the regulated part of the string is about 25 fps (ignoring the first shot) which is not very good for my P35s but also not a big problem. Including the part off the regulator would make it about 37 fps which seems to cause the unregulated portion of the string to hit slightly high at 30 yards but pretty much to the same point of impact (maybe 1/4 inch high).

The part that is surprising for me is that I am getting about another 20 shots after it falls off the reg that are pretty flat in velocity and they continue down to almost 100 bar. It seems like the hammer spring setting is working very well in the unregulated area. Much different and better than my P35-177 when it goes unregulated. The 177 regulator is about 125 bar and the 25 caliber is at least 145 bar. So the hammer spring settings are much different.

With a full 250 bar fill it still seems like I will get about 60 ~45 fpe shots. I may try shimming the spring a little more to try and raise the first shot velocity but I also think it may not be as low when the weather cools off. I also wonder if it might raise the regulated part of the string a few fps reducing the difference when it goes unregulated. Always something more to try. But I'm going to try to stop messing with it for awhile.

Any thoughts on the long flat unregulated portion of the string? It seems like a good way for a regulated gun to be tuned (especially if I could make it a little flatter).
 
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First shot looks like a result of potential reg creep.

I already gave my thoughts on the unregulated string, but I'll add another 2c of mine.

The pressure change, valve spring closing force, valve stem closing force, and hammer spring are all 'self regulating' your fps. It certainly doesn't appear entirely flat, it raises from an average of 750~ fps while on reg into the 770's and then back down to 750 before it falls off a cliff outside of your desired bell curve. Any unregulated gun is tuned to self regulate over an even larger pressure differential. All it means is you're not tuned to your plateau, rather quite below the knee. I also don't think the 780 fps was exactly where it came off reg.

-Matt
 
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