2400kt, Bottled, Regulated

[aPpYe]

I am thinking I might exchange my chronograph for the one that comes with the indoor lighting attachment.  I only had a chance to play with it once so far and only for about 20 minutes.   Today it is supposed to rain all day so I don't know if I  will get the chance today either!

Anyway, i have not yet had the chance to plot a graph.  I do know that when I had the RVA all the way out, the heavy pellets were at about 790fps, and they got up to about 895fps when I went maybe 3-4 turns from the point where I felt the spring start to engage.  I then turned it way in, not counting the turns because I was in a hurry, to a point where cocking the gun was very difficult, and I got a couple at over 920fps.  This would mean that the knee is in there somewhere, right?

My goal is to be able to adjust the lighter pellets down to maybe 750fps, while still being able to achieve an efficient 875-900fps with the >10gr pellets and a few turns of the RVA.

[rsterne]

Not necessarily.... If the velocity is still increasing at 920 fps, you may not have enough hammer strike to reach the knee.... That is unlikely, however, but is the reason you have to test it to know where the knee is.... ie the optimum velocity for the pressure you have....

When you adjust the RVA for lighter pellets at ~ 750 fps, be aware that when you reach the setpoint, the velocity will start to INCREASE below that, just like in an unregulated PCP....

Bob

[aPpYe]

Not necessarily.... If the velocity is still increasing at 920 fps, you may not have enough hammer strike to reach the knee.... That is unlikely, however, but is the reason you have to test it to know where the knee is.... ie the optimum velocity for the pressure you have....

It may start increasing above 920, but I don't think so.  After getting 895fps, I saw very minimal gains turning things in after that.  I saw maybe 900-905 after a few turns in beyond 895.  I don't know that I would ever turn the RVA in so far as I did when I saw 920...  It was almost impossible to cock.  I am thinking optimum velocity for this may be about 890 or so, with the spring I have currently.  I guess I will find out tomorrow, unless I can figure out how to get this chronograph working indoors...

When you adjust the RVA for lighter pellets at ~ 750 fps, be aware that when you reach the setpoint, the velocity will start to INCREASE below that, just like in an unregulated PCP....

Are you referring to the increase in velocity I would see once I drop below regulator pressure, due to the vastly increased plenum (the bottle) size, or some other increase that would happen with even lighter spring pressure?  If so, I am not sure I follow...

What I am after is two power settings, one for the heavy pellets at ~875 or so (biased toward power and perhaps 50 yd FT) and the other for light pellets biased toward high shot count and maybe 20-30 yds.

The idea would be to record the amount of turns it would take to get various lighter pellets to the velocity I am after...

[rsterne]

The very first post in this thread should explain it....

http://www.gatewaytoairguns.org/GTA/index.php?topic=74919.

Graph it out, you don't need to use a computer, graph paper will do.... You will see the plateau, knee, and downslope instantly once you do that....

Bob

[aPpYe]

I see.  You were referring to the slight increase shown in your downslope tune.  This is good to know!  I have been considering trying to get away with the higher efficiency of the downslope, and now I will definitely be tuning the heavier pellet right to the knee.  The slightness of the increase means I would likely be okay with it when plinking with the lighter pellets.  Thanks for the info!

In my case, regulator creep refers to the fact that I have ~1450psi output when I have a full (~3000psi) bottle, and maybe ~1400psi when the bottle has a ~1500psi fill, correct?  I am confused, because I would think that the downslope line on your graph would move in the opposite direction, as slightly higher output pressure should equate to slightly higher velocity.  What am I missing here?

Anyway, the weather let up a little (well, my brand new Caldwell Chronograph did get a little wet!) and I had a chance to record some velocities.  All numbers are three shot averages, and I made sure the bottle always had over 2000psi in it.  Of course, this was before I read your regulated tuning post, so I guess they could use some slight adjustment.  Extreme spreads were generally no more than 5fps (which I am ecstatic about!), so I just did some redneck math in my head to come up with the number.

I changed to measuring "turns out" instead of "turns in" as I noticed that that the point of initial spring engagement moves around a bit as the spring rotates inside the gun.  When I turn the RVA all the way in, it stops at the same point every time, so I will likely be putting a little stamp or scratch in the knob to mark this...

Velocity does not increase at all under 7 turns in.  I did not notice any notable differences until I got to 9.5 turns.  Here are my results:

Turns out       Velocity
     7                   932
     8                   929
     9                   929
     9.5                917
     10                 911
     10.5              909
     11                 900
     11.5              886
     12                 879
     12.5              865
     13                 853
     13.5              839
     14                 820

I did not bother to make a graph, but this would put the knee at about 9.5 turns out, correct?  I will have to shoot some groups to see what kind of accuracy I am getting at this velocity, but it does seem a little high, in the transonic region I see so many writing about...

I noticed that as I got past maybe 13 turns, the spreads would widen up quite a bit, maybe as much as 20fps.  This has me thinking that I want to always use the gun with a moderate amount of preload to keep extreme spreads low.

All my lighter pellets ranged from 930-975fps with the RVA knob all the way out and completely removed from the gun.

Based on this data, I am thinking the first thing to do would be to try lowering set pressure a tad to bring that knee (and find it again!) down to a velocity I am more comfortable with, say ~900fps.  Once that knee is at the velocity I want, I can then look at clipping the spring to a length that will accommodate my heavy pellet knee, and allow for lower velocities with lighter pellets ...Does that sound right?

EDIT:  Oh yeah, I have noticed that the hammer seems to be getting jammed when cocking it now, since I had to pull back on it pretty hard when I was cocking it at the heaver preloads.  Have you run into this?  I am going to try putting some grease (or maybe dry PTFE lube) in the tube to see if this fixes things.  Nothing seems damaged when pulling things apart, but it sure is hard to cock now, even with no preload!

[rsterne]

You need to read that thread on tuning again.... When you are tuned on the Downslope, lower pressure results in higher velocity, until you hit the peak of the velocity curve just as if you were shooting an Unregulated PCP.... That is why the velocity may show a slight increase as the tank drops from 3000 psi to the setpoint.... Once you reach the setpoint, then the rise in velocity is sharper and although I only showed about 20 fps in that graph, it can, in fact, be over 100 fps if you are tuned far enough down on the Downslope.... As an example, consider an Unregulated gun tuned for 1000 psi and then filled to 1500.... The velocity would start slow, rise, peak, and then decline.... If you ran that gun on a 3000 psi tank with a 1500 psi regulated output, it would stay relatively close to the velocity it did at 1500 psi until it dropped below that, then it would act exactly like it did without the regulator....

You are definitely on the plateau at 7-9 turns out.... You are on the downslope past 11 turns out.... The knee of the curve is in between 9-11 turns.... That is only a range of 30 fps, about 3%.... so you can tune anywhere in there and get good performance....  The closer to the plateau, the more air you will use.... I would expect that 10-10.5 turns out would produce the best balance between power and efficiency.... If you really need to reduce the velocity 10 fps, then you can reduce the pressure by maybe 50 psi.... I personally would try all the settings between 9.5-11 turns out and see how many shots you can get and pick a setting.... It looks like you are VERY close to what you want, so close it may not be worth resetting the regulator....

You likely bent or galled something at the higher preloads.... Have a look at the hammer cocking pin, and the slot it runs in.... also the bolt handle....

Bob

[aPpYe]

Okay, so I have read and reread that post...  Let's try this again!  It helps me if I look at things at their extremes, here is my take on how I am (shakily) understanding things:

Let's say we have pressure that is so high that the hammer (and spring) is unable to overcome it at all.  This is valve lock, right?  My use of terms may be shaky here as well, more on that in a minute.  Let's say we lower our pressure (or make the hammer heavier, increase spring pressure, install a heavier spring, etc) to the point where the hammer is just barely able to open the valve.  We would have an extremely small amount of air released, and the projectile would barely move.  The more we keep lowering the pressure (or increasing the force with which we strike the pin), the more air is able to escape, and velocity increases with each shot until we reach a peak.  Then velocity falls because we again have less air escaping, this time because the air pressure itself is low enough to cause it not to be able to escape as quickly.

Yeah!  I think I get it now.  The slight increase we see due to regulator creep is the same as what we see as we are getting away from valve lock in an unregulated setup.  If we back the RVA on our regulated guns so far off that the hammer barely strikes the valve pin, we again have valve lock.  This seems right.  Am I using the term "valve lock" correctly?  Also, it is a "pin" that the hammer strikes against, isn't it? 

On to incorrect use of terms.  I have been saying that I use the gun for "FT" ... I assumed that the word "field target" meant plinking out in the woods, making acorns and pebbles bounce around.  This is the kind of shooting that I enjoy ... hiking with a gun in my hands, maybe harvesting an occasional squirrel or splattering an insect or three.  I guess this is just "plinking" ... I did not realize that "Field Target" was an actual discipline that people compete in.  This is not something I have ever done, although it sure sounds fun!  I apologize for any confusion!

I think I am going to remove a shim and see if I can still achieve 900fps with whatever the lowered pressure turns out to be.  I figure I might be able to wring out a few more shots this way... I can always go back.  I know that the knee will always be based on whatever ~10gr pellet I decide to use, and I will just have to live with the slight rise in velocity when using the lighter pellets.

As far as clipping the spring for the lighter pellets, is there any kind of good methodology to follow?  Would it be better to have the clipped side touching the back of the hammer or on the RVA side?  How much should I  clip off to start?  I figure I am safe so long as I start with a length that is shorter than the distance my RVA is backed out at the knee.  It turns out I have an extra spring, as when I ordered my parts from Crosman, the guy on the phone said that the RVA did not include a spring, although it did.  I am also thinking it would be better to remove all spring pressure when I am done for the day, as I do not want the spring to set, just as the springs in spring piston guns do ... Is this really an issue with regulated PCP's?  Is there such a thing as a gas piston hammer spring?  Hmmm... 

As far as the stiff cocking, I am embarrassed to say that I had the barrel mounted off center to the transfer port.  This in turn caused some undue pressure on the tube and things were not quite lined up correctly.  The gun cocks fine now, and I added some dry PTFE lube for good measure...

[rsterne]

Sounds like you got it!.... "Valve Lock" to me, is when you can't get any air to shoot from the gun, the pressure is too high for the hammer strike.... Some use that term for any time the velocity is less than maximum because of high pressure.... I would call an extreme case of that "partial lock", but a small amount is just normal tuning for an unregulated PCP....

I would put the clipped end inside the hammer.... You can bend the end closed if you wish, but I don't think it really makes a difference.... There is NO need to release the preload on a spring, in fact leaving the gun cocked will not normally hurt a spring, and certainly not one that has been "set" (compressed to coil bind) even once....

Bob

[aPpYe]

Hmm... So it seems that if I want to split some hairs, the true sweet spot would be where I can maintain that same 5fps velocity spread for as many shots as possible below regulator set point...  Of course, then I would have to live with whatever velocity I come up with there, and there is just something cool about saying "my gun shoots 900 fps...". Of course, I still have yet to determine what velocity will give me the best accuracy at 50 yards on this gun, and with these pellets...  I did shoot some quick groups the other day and achieved about 1 inch at 50 yards, and that was right at 900fps.  It was getting dark and misty though, there was also a little 5-7mph inconsistent breeze and I was using peep sights.  I guess the real measurement would be to make sure i have a few hours on a still day, put a scope on there and shoot some groups that way...

Anyway, why is it not required to release preload?  Is it because the spring lighter?  Do springer springs compress further than ours do when cocked?  What other factors would make them not as affected by fatigue?

[rsterne]

The spring in springers is often pushed very close to the yield point, and are MUCH more highly stressed.... I don't know what you have read about leaving them cocked, but they lose about 5% after several MONTHS of being left cocked.... After a week, it is less than 1% loss.... and some of it comes back when uncocked....

BTW, while the regulator is probably capable of holding 5 fps, not many regulated guns are better than 1% unless you weigh and measure all your pellets.... because THEY can vary 1% or so.... Unless you are shooting over 100 yards, a 1% ES is more than adequate....

Bob

[aPpYe]

I see.... I did not know that the loss in spring strength was so nominal.  Really all that i have read on the subject are a maybe a few Tom Gaylord articles on "nitro piston" brands, and the lack of spring wear  that is their main selling point.  I was never really all that interested in the articles either, since I never really considered getting a springer because of a bad experience I had with one I considered buying from a buddy several years ago.  I did not know about the "artillery hold" and I couldn't get it group well.  I went through maybe 5 different springers at the time and they all went back to the store for the same reason.

At the time I was enamored with the power claims of the air force condor, but ultimately decided on a CZ-452 ultra lux, which has proven to be ridiculously accurate.  I was really happy when I moved to the country  last year and discovered I could legally shoot as much as I want right off of my deck.  I didn't even have to take off my slippers if I didn't want to!  In was happy until I ran out of bullets anyway.  Then the .22lr bubble had me spending over fifty bucks for 500 rounds...  First thing I did was start reading about the condor again, but the shot counts and bell curves just weren't doing it for me.   The whole artillery hold thing for springers just seemed unreasonable to me.  While i did notice an improvement with my red ryder, accuracy being as bad as it is with that gun, holding a gun that lightly feels unnatural to me. 

Because of these things, my interest in shooting was starting to wane once again, until I saw your qb79 ninja article.  100 shots with no curve seemed too good to be true!  That got me REALLY interested once again, and I have you to thank for that.

As for my 5 fps claim, I thought it was a little tight, but I was not exaggerating.  These were just a series of three shot groups as i backed off the spring a half turn each time though.  Pellets were just picked from the tin, I don't even own a scale!  Spreads only opened up when preload was at ts lightest, though I don't know why.

[rsterne]

5 fps is great if you can get it.... just not necessary unless you are shooting at 200 yards.... 1% at 100 is just fine.... Chrony your .22LR ammo some day and see what the ES is over a box.... you will be shocked.... and yet they still shoot MOA at 100 yards....

Bob

[aPpYe]

Okay waitaminnit.  I can't say I have ever really considered 200yards with an airgun...  Certainly not with my .177 cal...

What kinds of distances have you tried?

[rsterne]

I have a confirmed kill on a Ground Squirrel at 106 yards, mind you on the second shot (.22 cal 18 gr.@ 960 fps).... Carl just posted about hitting a 39" square steel plate repeatedly at 1065 yards.... and pop cans at 700.... Check out the Big Bore gate.... Also, the last gate in the Target Shooting section is the Long Range Club.... N.U.A.H.... which means "Nothing Under a Hundred" (yards).... Pellets at 100 yards are challenging but getting more commonplace.... Bullets at double that is where you really need to get down to about a 1% ES....

Bob

[aPpYe]

Okay so what about actual group sizes at these crazy ranges?  I will definitely test myself, but it am wondering what kind of group sizes I might see with my .177 at various ranges.   

And check this out:

900fps with a 1250psi set point!  I was at about 905fps with the adjuster all the way in and I was at about 895 with 10.5 turns out.  887 with 11 turns!   Cool!   I also removed the ball and seal from the bonnet and filled with everything hooked to the gun.  Perhaps whatever slight increase this provided to flow and plenum size helped keep the velocity up as well.  I am super happy about this!  Time to start cutting my spring...

EDIT: Hmmm.  Look at the differences between these springs:

Neither of them have been clipped.  The short one is what has been in my gun for a few weeks.  The springs were identical when I got them. 

...is this normal?  I am gonna be clipping the short one in a few minutes...

[BigTinBoat]

EDIT: Hmmm.  Look at the differences between these springs:

Neither of them have been clipped.  The short one is what has been in my gun for a few weeks.  The springs were identical when I got them. 

...is this normal?  I am gonna be clipping the short one in a few minutes...

Well it sure looks to me like the lower portion of the spring on the left (longer one) has been "stretched". The upper coils match with the right spring, but the coils at the bottom appear to have a larger gap.

[rsterne]

The shorter spring has been "set".... My guess is that if you take the long one, put it on a rod so that it can't kink, and compress it fully (to coil bind), just once, it will be the same length or shorter than the short one.... That is why I always set my hammer springs before I use them for the first time.... If you do that, they will never change again.... and neither will your preload settings....

Bob

[aPpYe]

... spring on the left (longer one) has been "stretched".

This might be wide angle phone camera tricks...   Not sure.  The one on the left looks exactly as it did when I first got it, which is exactly what the other one looked like.

The shorter spring has been "set".... My guess is that if you take the long one, put it on a rod so that it can't kink, and compress it fully (to coil bind), just once, it will be the same length or shorter than the short one.... That is why I always set my hammer springs before I use them for the first time.... If you do that, they will never change again.... and neither will your preload settings....

Bob

Hmm.  I never thought of that.  And I already cut the short one!  I will make sure to set them with my RVA knob and my "degasser tool," a 4" 10-32 screw I got at the hardware store...  I hope the short one will still get me my 900fps ...  If not it is good that I have a spare...

Speaking of which, I am really glad you suggested that RVA from the challenger...  I can't so easily remove the spring I guess, but I like how closely to complete spring bind it gets to before stopping, and I dig that the knob is also threaded for the degasser tool.  However, it seems to have a hole for a set screw, but that hole is not threaded.  Is it supposed to be like this?  If so, what exactly is that hole for?

[rsterne]

It is for a plastic plug to provide friction so that it doesn't self-adjust....

Bob

[BrokeWinger]

I don't mean to hijack your thread,, I'll apologize for that in advance.

But I have a question regarding pinning the valve. I'm planning some mods on my own 2400kt. I plan to use a HiPac system with extensions. My question; is the single valve screw sufficient If using a HiPac system or do I need to add the two extra screws as well?