PP700 adventure started(Artemis PP700s-a)

[Kid Shelleen]

I’m still trying to figure out how to reduce the extreme spread on this gun but did find one thing that has been throwing me off.  I filled to 150 bar and the hammer spring is at about two full turns out from fully tightened.  As I shot the string, I noticed much higher velocities when I waited 60+ seconds between shots instead of the average 20 seconds between shots.  I then started making notes when I waited longer and when I shot sooner.  There was as much as a 100 fps or more difference between shots.  I began purposely waiting about 60 seconds between some shots and also waiting only 20 seconds between shots and noted each shot.  In the string below the W prefix is when I waited about 60 seconds between shots and no prefix I waited only about 20/30 seconds.  I’m guessing the first 619 and 429 fps could be the gun settling in or it could be the time it took between filling the gun and taking the first shot (high fps) and shooting the second shot within 20 seconds (low fps).

619. 429. 479. 475. 453. W616. 551. 434. 499. W521. 481. W544. 474. 477. 479. W568. (110 bar). 468. W536. W521. 466. W559. W536. W587. (100 bar). 479. 473. W545. 481. 496. 502. W546. 498. W584. W576. W589. W606. 501. (50 bar) W586. W578. W565. Error. W540. W494. W467. W442 (30 bar).

Not counting the first two shots, the shots where I waited only 20/30 seconds averaged around 482 fps. and the shots where I waited about 60 seconds averaged around 563 fps.. Almost 81 fps difference between the two.  I know very little about how a regulator works so any information on why I’m getting this difference when I wait longer between shots will be appreciated.  Does it have something to do with the plenum?  Since I did the 20 second and 60 seconds shots, it may be a little hard to tell when the shots fall of the regulator but if anyone has a decent guess, I’d appreciate that too.  Also, can anyone tell if my hammer strike is still too light, causing a rise in velocity when it goes of the regulator.  I’ve already increased it by one and a half turns (CW) and the pull is up over 4 lbs. now.

[sawtoothscream]

If the weather isn't &^^& tomorrow I'm going to the range,  very new to tuning so probably need some help from you guys .      Really need to get some lights for my Chrono so I can do this In. The basement

[nervoustrigger]

Mike, that behavior points to regulator creep.  That is, the pressure slowly creeps up following the shot.  A well functioning regulator will have settled within just a few seconds after the last shot but some may take a minute or even several minutes.

You said "the hammer spring is at about two full turns out from fully tightened".  I take that to mean you have quite a lot of hammer spring preload, therefore as the regulator creeps up in pressure, you have plenty of hammer strike to open the valve with authority, therefore the shot is a considerably higher velocity.  If instead the hammer spring were adjusted lighter, what you would get is a lower velocity relative to shots taken in quick succession.

Anyway, this creeping behavior seems to be an inherent limitation with some designs but it can also simply be a result of a slight scratch in the mating surfaces of the valve.  To be clear, the scratch may be either in the seal at the end of the regulator spool (generally a plastic like Delrin / acetal), or in the mating face at the aperture of the valve body (metal).  So on occasion I have fixed such regulators by sanding and polishing the the offending face.

[Wayne52]

I’m still trying to figure out how to reduce the extreme spread on this gun but did find one thing that has been throwing me off.  I filled to 150 bar and the hammer spring is at about two full turns out from fully tightened.  As I shot the string, I noticed much higher velocities when I waited 60+ seconds between shots instead of the average 20 seconds between shots.  I then started making notes when I waited longer and when I shot sooner.  There was as much as a 100 fps or more difference between shots.  I began purposely waiting about 60 seconds between some shots and also waiting only 20 seconds between shots and noted each shot.  In the string below the W prefix is when I waited about 60 seconds between shots and no prefix I waited only about 20/30 seconds.  I’m guessing the first 619 and 429 fps could be the gun settling in or it could be the time it took between filling the gun and taking the first shot (high fps) and shooting the second shot within 20 seconds (low fps).

619. 429. 479. 475. 453. W616. 551. 434. 499. W521. 481. W544. 474. 477. 479. W568. (110 bar). 468. W536. W521. 466. W559. W536. W587. (100 bar). 479. 473. W545. 481. 496. 502. W546. 498. W584. W576. W589. W606. 501. (50 bar) W586. W578. W565. Error. W540. W494. W467. W442 (30 bar).

Not counting the first two shots, the shots where I waited only 20/30 seconds averaged around 482 fps. and the shots where I waited about 60 seconds averaged around 563 fps.. Almost 81 fps difference between the two.  I know very little about how a regulator works so any information on why I’m getting this difference when I wait longer between shots will be appreciated.  Does it have something to do with the plenum?  Since I did the 20 second and 60 seconds shots, it may be a little hard to tell when the shots fall of the regulator but if anyone has a decent guess, I’d appreciate that too.  Also, can anyone tell if my hammer strike is still too light, causing a rise in velocity when it goes of the regulator.  I’ve already increased it by one and a half turns (CW) and the pull is up over 4 lbs. now.

I've never tested mine like you have but by the sounds of it the reg is allowing air to leak past it into the valve.  Every now and then I'll put a drop of silicone in my fill probe before filling to insure all the o rings are sealing properly, my guess would be there is an oring leaking but really don't know for sure.  I have noticed when I let my gun sit overnight the first shot is unregulated after sitting.  I have it set right now for a really good 20 shot shot string for hunting and it does a pretty good shot string.  As stated much earlier throughout this thread the orings that come with these guns are very cheap and in all reality I should have probably replaced all of mine with good quality orings from the get go but I was just having so much fun with it I never got around to it.    Eventually I'll take my spare set of orings that came with the gun and match up a good set of Buna N orings for a complete oring set for the gun prior to disassembly.  Being sooo much fun this gun is hard to put down long enough just for an unneeded oring replacement plus the performance of mine has been so good that I find no need of it yet.

It makes sense that adjusting for higher pressures in the reg that less noticeable change in the shot string would be evident because of the better sealing from the higher pressure. 

[bandg]

Jason, do you think that the inherent small size of the belleville springs in this unit could be the cause of the issues many have noted with regulator function?  I have read of some people trying to polish the edges of each individual belleville washer to provide smoother function.  It seems that smaller belleville diameters might "mate" less well along their contact edges, especially the outer diameters, than larger ones might and maybe this is a factor in the noted regulator variability.  Is it possible that polishing all the contact edges and setting them up something like this (((|))) would be more stable for a higher power level?  I haven't had mine down to that point yet but anything that could be done to improve the situation if I do go into the regulator would be helpful.

[Kid Shelleen]

Thank you Jason for the detailed explanation on “regulator creep” and the possibility of scratches on the mating surfaces of the valve.  That sounds like what may be happening and I guess I’m going to have to open the gun up and take look inside.  Thanks Wayne for the information on the O-rings.  Since I’m going to take it apart, it’s a good time to change the O-rings.   Donny, suggested looking at the Belleville stack and maybe changing the arrangement.  I’ll take a look at them and take off any rough edges if necessary or maybe just replace them with some from McMaster Carr.  I’ve used the ones they sell before and they seem to be of good quality.  I’m starting to think the regulator in this gun (my son’s gun) may have several issues because once I got a few hundred rounds in my PP700SA, the regulator settled down and I was able to get a pretty good tune on it.   I got it to where it was averaging 645 fps. with an extreme spread of 35 and an SD of 8, getting about 45 good shots (from about a 160 bar fill).  My son’s gun is a whole different story but a great learning experience.  I just hope I’m not trying anyone patience by asking so many questions.

[bandg]

Questions and discussions are what this place is all about.  Always helpful to me to see both questions to think about and the answers for solutions.  Keep it up.

[Kid Shelleen]

Sawtoothscream.  You probably have heard about home made lights for your chrony before but here are a couple I tried that work and are cheap to make.  Use one of those large chrome, spring clamp, shop lights (the ones that are about 12 inches in diameter.  It's cheap and it works great.  I had to try different power bulbs to get it to read correctly but in my basement environment, a 60 watt bulb, 42 inches directly above the chrony, worked good.  If you have any exposed beams in your basement you can clamp the lamp on the beam, mount the chrony on a camera tripod and adjust the tripod up or down to fine tune the amount of light getting to your chrony.  When I was still living in California, I had another chrony that I made an extra “diffuser” for (just some soft bendable plastic) and mounted a battery powered round LED “Puck” light on the center of each “diffuser”.  Depending on the power of the puck lights, you may have to adjust the length of the supporting rods to get the correct amount of light.  I got these ideas from other posts.

[nervoustrigger]

Jason, do you think that the inherent small size of the belleville springs in this unit could be the cause of the issues many have noted with regulator function?  I have read of some people trying to polish the edges of each individual belleville washer to provide smoother function.  It seems that smaller belleville diameters might "mate" less well along their contact edges, especially the outer diameters, than larger ones might and maybe this is a factor in the noted regulator variability.

Yeah, I suppose if the perimeter of the Bellevilles had really bad burrs or irregular burrs, that could cause issues with the consistency of the setpoint.  Can you comment on what you have observed or read?  I haven't removed the reg on mine so I can't comment on these specific Bellevilles, however if they are similar to the various ones I've gotten from McMaster and Zoro, I kinda doubt it is a factor.  I grabbed my assortment and examined a few different sizes and while their edges reveal they are punched, they either use extremely close-fitting punches and dies or they do some sort of deburring...or both.  Dragging a fingernail across the punched edge indicates it is somewhat sharp but there is no perceptible burr on the mating faces.  Even if there were a very slight burr, I suspect the effect would be swamped out by the axial pressure on the stack but I'm just speculating. 

However if their ID is not a close fit to the regulator spool, I can see where that would be a problem.  Meaning if they fit it closely, they stay concentric and the stack maintains a consistent height and therefore a consistent spring rate.  But if they are a sloppy fit, they can slide radially relative to each other and potentially cause the stack to vary in height as it cycles.

Having said all that, when the time comes that I open mine up, if I find them to have burrs, you can bet I will smooth their faces on some 400 and 600 grit.

Is it possible that...setting them up something like this (((|))) would be more stable for a higher power level?  I haven't had mine down to that point yet but anything that could be done to improve the situation if I do go into the regulator would be helpful.

Actually, quite the opposite.  Yes, the 3 nested (paralleled) washers will produce a higher spring rate which would allow you to increase the setpoint but that would only be advisable if you can't reach your desired setpoint.  The stack has only the travel of two washers which would make it subject to greater nonlinearity.  So for example, I would prefer this arrangement of 10 washers (( )) (( )) (( over this arrangement of 9 ((( ))) ((( unless I could not reach my desired setpoint using the preload adjustment screw located inside the trigger guard.

[Rallyshark]

I’m still trying to figure out how to reduce the extreme spread on this gun but did find one thing that has been throwing me off.  I filled to 150 bar and the hammer spring is at about two full turns out from fully tightened.  As I shot the string, I noticed much higher velocities when I waited 60+ seconds between shots instead of the average 20 seconds between shots.  I then started making notes when I waited longer and when I shot sooner.  There was as much as a 100 fps or more difference between shots.  I began purposely waiting about 60 seconds between some shots and also waiting only 20 seconds between shots and noted each shot.  In the string below the W prefix is when I waited about 60 seconds between shots and no prefix I waited only about 20/30 seconds.  I’m guessing the first 619 and 429 fps could be the gun settling in or it could be the time it took between filling the gun and taking the first shot (high fps) and shooting the second shot within 20 seconds (low fps).

619. 429. 479. 475. 453. W616. 551. 434. 499. W521. 481. W544. 474. 477. 479. W568. (110 bar). 468. W536. W521. 466. W559. W536. W587. (100 bar). 479. 473. W545. 481. 496. 502. W546. 498. W584. W576. W589. W606. 501. (50 bar) W586. W578. W565. Error. W540. W494. W467. W442 (30 bar).

Not counting the first two shots, the shots where I waited only 20/30 seconds averaged around 482 fps. and the shots where I waited about 60 seconds averaged around 563 fps.. Almost 81 fps difference between the two.  I know very little about how a regulator works so any information on why I’m getting this difference when I wait longer between shots will be appreciated.  Does it have something to do with the plenum?  Since I did the 20 second and 60 seconds shots, it may be a little hard to tell when the shots fall of the regulator but if anyone has a decent guess, I’d appreciate that too.  Also, can anyone tell if my hammer strike is still too light, causing a rise in velocity when it goes of the regulator.  I’ve already increased it by one and a half turns (CW) and the pull is up over 4 lbs. now.

It would seem to me that you definitely have too much pre-load on the hammer spring(too much hammer strike).  As Jason noted, when the reg creep is allowing the pressure to increase, the hammer strike is blowing right through that extra pressure and producing a higher velocity.  As an example: When your hammer strike is where it should be, the pressure increase would result in a lower velocity, because there isn't enough hammer strike to open the valve at the higher pressures.  Does that make sense? 

The "across the pond" folks are always talking about reg creep, which seems to be quite common for them and their lower powered tunes.  I also saw where one of the guys took his belleville washers out and rubbed them on a wet stone to smooth the edges.  Given that the higher power tunes tend to be more resistant to regulator creep, perhaps a higher regulator pressure would work better?  Just get in the ball park of 600-650fps with hammer spring adjustment, and crank that transfer block adjustment screw way down to get your velocity where you want it.  Since the transfer would much smaller, I would think it would be less affected by small variations in the pressure(reg creep).  I'm just thinking out loud here...I could be completely wrong headed on this one too.  Regardless of power level, I know the first 2-3 shots after a fill tend to be throw aways. 

[bandg]

Good points, Jason.  Probably should have been a little more specific in my goals.  I'm looking for maximum usable velocity before accuracy is lost and trying to eliminate those initial throw away shots that Donny mentioned.  I like to be able to pick up a pistol (or rifle or whatever) and have reliable first shot accuracy.  More important for my type shooting than good strings afterwards even though you certainly want that as well.  It well may be asking too much of an airgun to reach this point but if I can accomplish this at the mid 930+ fps velocities I've currently got with the pp700 then I'll be happy.  My thinking on the spring stack was to eliminate these type contact points () as much as possible even if it narrowed the usable regulator range.  That's why I had the straight one (|) in the layout-thinking it might keep edges from clicking or binding somehow.   When I take the pistol down to try the barrel bushing change I'm looking at then I'll go into the regulator and polish the edges and check that spool/diameter relationship. 

As mentioned about the regulator spool diameter, I've used versions of these belleville springs which are almost certainly larger diameter (about nickel size) on some RC truck slipper clutches.  There is a relatively small input shaft that they fit over and you will notice after running that they do become staggered in relation to each other and effect clutch engagement.  That is the possibility that I'm wondering about with the ones in this pistol since it seems they are probably even smaller but they may be well aligned by the spool.  Thanks for the information and maybe I need a shaft liner on the RC clutch to keep those aligned.

[nervoustrigger]

Donny, you are correct.  You can use a high setpoint and crank up the hammer spring to knock open the valve (which will produce a high velocity) and then choke off the transfer port to bring the velocity back down.  However, I will say the restrictor screw on mine isn't tapped deeply enough to have much effect.  To be clear, I'm speaking of .177 cal.  For .22 cal, the restrictor would have a more pronounced effect.  I imagine it would be easy enough to tap it deeper though.

Naturally, the trigger pull will get harder due to the higher hammer spring tension but if the reg creep can't be tamed, your recommendation may be just the ticket to get the ES in check for a lower power tune.

[sawtoothscream]

my results stock

[sawtoothscream]

would like to have those over 600fps as thats hunting legal in NY   

[Rallyshark]

Good points, Jason.  Probably should have been a little more specific in my goals.  I'm looking for maximum usable velocity before accuracy is lost and trying to eliminate those initial throw away shots that Donny mentioned.  I like to be able to pick up a pistol (or rifle or whatever) and have reliable first shot accuracy.  More important for my type shooting than good strings afterwards even though you certainly want that as well.  It well may be asking too much of an airgun to reach this point but if I can accomplish this at the mid 930+ fps velocities I've currently got with the pp700 then I'll be happy.  My thinking on the spring stack was to eliminate these type contact points () as much as possible even if it narrowed the usable regulator range.  That's why I had the straight one (|) in the layout-thinking it might keep edges from clicking or binding somehow.   When I take the pistol down to try the barrel bushing change I'm looking at then I'll go into the regulator and polish the edges and check that spool/diameter relationship. 

As mentioned about the regulator spool diameter, I've used versions of these belleville springs which are almost certainly larger diameter (about nickel size) on some RC truck slipper clutches.  There is a relatively small input shaft that they fit over and you will notice after running that they do become staggered in relation to each other and effect clutch engagement.  That is the possibility that I'm wondering about with the ones in this pistol since it seems they are probably even smaller but they may be well aligned by the spool.  Thanks for the information and maybe I need a shaft liner on the RC clutch to keep those aligned.

I haven't tried shooting mine over the chrony with a full fill after sitting for a while.  I usually do 3 dry fires after a fill though.  When my gun is relegated to back door pesting duty, I too want that first shot to be on point.  I tend to leave it with around 170 bar in it when it is there for pesting opportunities.  I rarely take more than 5 shots in those situations.  In fact, I usually take 1   If I go hunting or shooting, I do give it a full fill(-3 dry fires).  The other day I had gone shooting, and I tried it about 3 hours later with 180 bar in it.  The first shot over the chrony was 900fps, which is exactly where I have it tuned for my pesting pellets. If you are worried about that fist shot variation, then just leave it with 180-160 bar in it, and you should be fine for when you need to just pick the gun up and shoot.  Mine may do okay sitting with the full 200+bar fill, but I don't really have a reason to leave it at that.  When I'm doing a lot of shooting it never sits long after the fill anyway.   

[Rallyshark]

would like to have those over 600fps as thats hunting legal in NY   

That shouldn't be too hard to accomplish Tighten down the reg adjustment a bit, give it a little more hammer spring, and make sure the transfer restrictor is all the way out.  That should put you over the 600fps mark.

[sawtoothscream]

my brother and I went out to go after reds,  didnt work out lol.   He blew his tire in the woods, a redtail was hunting the same area and a thunder storm moving in.   So they decided to stay in today.

anyways sighted at 25 yds and the 18gr exacts performed awesome.   could cover the groups with a nickle easy.        Cant wait to have a good day to hunt with it

[sawtoothscream]

would like to have those over 600fps as thats hunting legal in NY   

That shouldn't be too hard to accomplish Tighten down the reg adjustment a bit, give it a little more hammer spring, and make sure the transfer restrictor is all the way out.  That should put you over the 600fps mark.

will have to look over that diagram and give it a go.   Put lights on my chrono so i can finally tune in my house      thanks

[sawtoothscream]

So where exactly is the transfer restrictor?   Is that the one on the top of the loading port block?   

[Rallyshark]

So where exactly is the transfer restrictor?   Is that the one on the top of the loading port block?

Yep!