2400kt, Bottled, Regulated

[aPpYe]

Getting over a ton (literally) of energy from a 13ci tank is a fine result.  Superbly done!

Huh!  I hadn't thought of it that way before.  2,340lbs total!  I'm gonna start telling people that!

Unfortunately, I think you are confusing "knee" and "downslope" with the shape of your shot curve, those terms have nothing to do with the velocity plot in your last post.... They mean how the velocity relates to the hammer spring preload AT CONSTANT PRESSURE....

If you think that your setpoint pressure was reached at around shots 12-15, since I see no sign of a slight increase in velocity at that point, that would indicate you are likely operating on, or close to, the plateau of the curve at 1200 psi.... If you were on the downslope, the velocity would increase dramatically below the setpoint.... If on the knee, it should increase very slightly, or the shot string should at least extend below the setpoint for a few shot before the velocity drops off....

No confusion, really!  The post was supposed to show what is happening once I transition below set pressure. I was looking for thoughts on whether I was closer to the plateau or the downslope.  I thought I had included that thought (being on the plateau) in my last post.  I guess I edited it out...  I tend to read over long posts like that and start rearranging things before posting.

I am still confused about the whole knee/ssg relationship though ... I was hoping to see the string extend past the set point by a few shots, and was actually more worried I was going to see an increase, since I am so far below the plateau (920fps) with no SSG installed and everything else the same...  I am definitely at this gun's highest power level with an SSG and a small gap though.  Is this the "false knee" you were taking about before?  The graph suggests that I am still well up on the plateau, and set pressure is reached at shot 10... Again, this is just one string though, and averages over several strings would be more accurate.

If I want to be over 900fps with an SSG at this set point, I would either need a heavier hammer or spring.  I did remove material from the hammer when I was hunting down drag a couple weeks ago ... I think I am going to leave well enough alone for now though.   I could try a stiffer spring, but I don't want the cock to be uh ... any harder ... um yeah...

[rsterne]

Judging by the shape of that shot string, I would say that you aren't going to get much more velocity without a big decrease in shot count at the pressure you are running....

Bob

[aPpYe]

Yep.  I am not really after that so much as I am after an understanding of how this works... Why is it that having an SSG lowers where the knee is?  Without the SSG installed, the plateau is at around 920fps.   If I were to dial that down to 885fps (the same velocity as the plateau I am shooting at now) I would likely be well into the knee of that curve, right?

As it appears that I am indeed on the plateau, I may shoot another string this evening at something less than max power, both to find the "sweet spot" (where velocity stays consistent a few shots below set pressure), and to see just how efficient this really is if I am truly tuned to the knee...  I would expect even better numbers.

Aside, I am waiting until this evening because I find that this Caldwell Chronograph (with the infrared light kit) is much more consistent if I shoot in the dark with no artificial lighting, be it florescent, incandescent, whatever.   Sub optimal lighting definitely played a factor in the wide ES I was pulling my hair out over a few weeks ago.

[rsterne]

It has not been my experience that the SSG lowers the knee, but it can certainly decrease what you SEE as the plateau and knee.... I found that increasing the preload gave gradually more velocity WHEN OPERATING WITHOUT A GAP, and eventually you could get back to where your plateau was without the SSG.... however, if you had less preload that that, trying to get back to your original velocity required that you reduce the gap to zero, and then the efficiency goes into the dumper.... Once you get the velocity with preload back to where your original plateau was, then backing out until you have a small gap should put you back on the original knee.... but with improved efficiency....

Bob

[aPpYe]

Well, I guess I am satisfied with this gun, as I have been spending a lot more time SHOOTING it rather than tuning it!  I guess that was the whole point to begin with!

Anyway, I picked up a cheap $1 spirit level, took it apart and epoxied the tube to the bottom of my aperture sight.  What a difference it made to my group sizes!  Before, even with a scope, it was difficult to get below 1" (10 shots) at 50 yards, but now 1/2" is pretty normal!  I was beginning to worry that it was my barrel, and was starting to think about L/W and the like, other "premium" barrels ... Now I know it was me all the time!

Here is what the level looks like ...


Here is a DIY front sight idea I am playing with.  I have been banging around with this one for a week or so.  The hole is 7/64" if I remember right, but I will likely go a bit smaller in hopes of getting a little more precision.  A 1/16" hole was too small for me, so it will be somewhere in between.  I am also thinking of having two holes stacked on top of one another, one for close range and one for further out...  I definitely prefer looking through these over the standard post.  I like to shoot with both eyes open, focused on the target.  I know, this sounds like blasphemy to some folks. 

I also like to shoot left and right handed...


This is a fairly typical group (8-10 shots) at about 55 yards or so ... This is bag rested and scoped, shooting full power with the JSB Heavies picked straight from the tin.  I center the level on every shot.  This one measures .52 CTC ...


With the scope removed, my groups are generally about an inch or so, also an improvement from before...  Again, I hope to tighten that up a little with a slightly smaller front sight.

[aPpYe]

Hi All,

I figured I would just ask here ... I have been loving this gun, especially since I put the level on the back of the sites.  It is really, really accurate!  The SSG made it efficient as humanly possible, and I am happy with every aspect of the gun.

... And now I want to modify it again.

Where do I start at getting a longer main tube?  I want to enlarge the plenum and further increase efficiency or maybe even bump it up into the 20+ fpe range.  I briefly looked around the internet and all I find for 2260 main tubes are those that have the roll stamped lettering.  I would prefer it to be either completely blank or with only the laser embossed lettering.  I also want a drop in part that I don't have to machine, other than drilling the extra valve retaining holes.  Would a discovery tube work?  Is there anything I can order from Crosman that will fit the bill?  I am hoping to keep the ~1200psi reg setting, but I may see what I can get with ~1400psi

[dmeguy]

Don Cothran makes excellent 22xx stainless pcp tubes in various sizes. I also see Roy at Mountain Air sells various sizes.

I'm running a Don Cothran 2250 tube at 1500 psi getting 23 fpe with 18 grain JSB's.

[Gipper]

Baker Airguns sells Disco tubes for $20 plus shipping. 

Gipper

[aPpYe]

I like the baker prices.  Would a disco tube already have all the correct machining, ie, breech mounting holes, transfer port in the right place, etc?  I guess I could either plug the gauge hole or of course put a gauge in there.

I can't tell if the "Tubes for Crosman 2200 Series" tubes on that site are roll stamped or not.  It looks like the 16 5/8" tube would just about double the plenum size.

Of course, a disco tube would what, quadruple it?  Anyone know the plenum sizes of these tubes in cc or ci, assuming a regulated HPA setup?  I read somewhere that at some point, plenum size can be too large for a regulator to maintain consistent PSI ...  I am using a Ninja HPA regulator, and this gun is .177 if it makes any difference...

[nervoustrigger]

Plenum too large?   Much ado about nothing.  Not saying the effect isn't present but it is of no practical consequence.  The idea is, if very little air is used, there may not be enough pressure drop to allow the regulator's seat to open and top off the pressure.  Therein lies the answer.  If the pressure barely dropped, the next shot will not be starved of air.  Also, a regulated rifle set up properly, running near the knee of max velocity, will hold a tight ES just as an unregulated one will do over a wide pressure range.  A super tight regulated pressure isn't as critical as it might seem from intuition.

[Gipper]

Yes the Disco tube would be ready to go...No drilling required.


Gipper

[aPpYe]

Plenum too large?   Much ado about nothing.  Not saying the effect isn't present but it is of no practical consequence.  The idea is, if very little air is used, there may not be enough pressure drop to allow the regulator's seat to open and top off the pressure.  Therein lies the answer.  If the pressure barely dropped, the next shot will not be starved of air.  Also, a regulated rifle set up properly, running near the knee of max velocity, will hold a tight ES just as an unregulated one will do over a wide pressure range.  A super tight regulated pressure isn't as critical as it might seem from intuition.

Makes sense to me!

Yes the Disco tube would be ready to go...No drilling required.

Methinks a new Disco tube is going to be arriving at my doorstep in the near future!

[aPpYe]

ORDERED!!!

[Gipper]

I am in the process of building the same rifle, but mine started life as a Disco.  Mine is together but I need to make a forearm for it.  I went with an RAI AR15 buttstock setup,  850 PSI Ninja bottle and the standard QB bottle block.  I used the stock hole positions but added a 10/24 set screw on top and back further from the end of the tube to add additional safety.  The position of the top set screw will also allow me to drill for a pin and use that screw to hold the pin if I decide to up the regulated pressure later on.  I am waiting on a breech riser from Baker and need to add an LDC.  I also removed the gauge and block and replaced with an aluminum piece drilled out to 5/8".  Valve is stock for now as far as I know (bought used), I have the poly tube transfer port and I chopped the barrel to 18".  As she sits she is shooting 8.4 JSB's at 755fps.  When finished I would like to add at least an additional 100fps to that

[aPpYe]

...850 PSI Ninja bottle and the standard QB bottle block...

So you have your bottle hanging way out in front of that long disco tube?

I have been running mine at 1200psi, and getting about 900fps with the 10.34 grain jsb's (24" barrel) ... Depending on what I have to work with and what efficiency numbers I can achieve, I am hoping to get 900-950 with the monsters or even the beasts.  I dunno how possible that is without increasing pressure beyond 1400psi, which is as high as I want to go with the 1.8k burst disks.  Maybe 1500psi.  I don't want to blow efficiency out the window though, so I plan on staying on the knee of whatever curve I get out of the pressure I ultimately decide on.

Anyway, &^^&.  I did not think of this.  Since I got a disco tube, I am going to have to get a gauge block and adapter, or at least a plug.  Once I have the part in hand, I am going to see how feasible it is to turn the bottle around so it feeds the gun through the guage port.

Does anyone know of a larger bolt handle I can find?  I suppose I could find the right thread hardware store bolt and wrap something around it...  Cocking would be much easier if I could fit more than one finger around it.

[Gipper]

...850 PSI Ninja bottle and the standard QB bottle block...

So you have your bottle hanging way out in front of that long disco tube?

No I cut my tube back.  I am not sure exactly how long it is as I simply made sure I had enough tube to utilize a crosman forearm if I wanted to instead of making one myself and enough tube to cut it again if I managed to screw it up!!  As it is now the 18" barrel extends about 1/2" beyond the bottle. The breech riser should give me enough room to do a a shroud or LDC.  Your numbers are more inline with what I am after and I figured a higher reg set point was going to be needed but I built this rifle with parts I had on hand.  Max power for me is not the main goal but a nice balance of power and shot count.  I started this project after buying a PROD that I have been less than thrilled with in terms of shot count.  Small tubes are very unforgiving when it comes to balancing efficiency and power...at least for me.  The larger capacity bottle allows me to be less than perfect in my tune and still have acceptable shot counts and Power.  If I could get 40 or so shots out of a fill in the 18-20 FPE range I would be more than happy.

Brian

[aPpYe]

Your numbers are more inline with what I am after ... The larger capacity bottle allows me to be less than perfect in my tune and still have acceptable shot counts and Power.  If I could get 40 or so shots out of a fill in the 18-20 FPE range I would be more than happy.

I see ... I am able to achieve the numbers I have now, largely because of the longer (24") barrel I think.  Also, you are mentioning 40-50 shots at 18-20fpe.  I am guessing you are unregulated then? 

The regulator plays a huge part in shot consistency...  Currently I am getting around 130 shots at 18fpe (jsb 10.34) on a fill before velocities start to drop.  I am hoping to either increase my shot count or power.  Probably going to go for power first to see what I can get, maybe even see what 1400-1500 psi can do with the larger plenum.  I guess I am going to be running through more tins.  I go through FAR more pellets when tinkering than I do when the gun is "done" ... I have been working on the same 500 tin of heavies since March-April (bought a foreclosed house in the mountains and have been brushcutting) and still haven't finished it.  This will change in a hurry!  The brushcutting has to get done first though. After all I need to actually have a house to keep my guns in.

Once I have the parts, I am going to see if I can make 13.43 Monsters (maybe even 16.2gr beasts!) go 950fps, and with any accuracy.  Do I NEED the power?  *(&^ no!  Do I WANT the power?  YES!  One can dream ...

[Gipper]

Your numbers are more inline with what I am after ... The larger capacity bottle allows me to be less than perfect in my tune and still have acceptable shot counts and Power.  If I could get 40 or so shots out of a fill in the 18-20 FPE range I would be more than happy.

  Also, you are mentioning 40-50 shots at 18-20fpe.  I am guessing you are unregulated then? 

My Ninja bottle is regulated at 850PSI.  I just have not done a shot count on it at its current reg setting so have no idea what to expect at this point.  Mentioning 40-50 shots at those power levels was just a ballpark figure of what I would be content with, not an estimate of what I think I will get. 

As far as the gauge block and gauge goes I would eliminate them if you can.  There is no need for the gauge and the block itself can be a restriction at higher power levels.  I am also fascinated with the new heavy .177 pellets available and plan to build a rifle to toss them heavy suckers at  higher speeds but have a Bam B50 I am going to use for that endeavor.

Brian

[aPpYe]

My Ninja bottle is regulated at 850PSI.  I just have not done a shot count on it at its current reg setting so have no idea what to expect at this point.  Mentioning 40-50 shots at those power levels was just a ballpark figure of what I would be content with, not an estimate of what I think I will get. 

As far as the gauge block and gauge goes I would eliminate them if you can.  There is no need for the gauge and the block itself can be a restriction at higher power levels.

I forgot about your 850psi bottle.  If you are just shooting at 755fps, you should get hundreds of shots, assuming a 3000psi fill and your bottle is the typical 13ci...  I am not sure if you will be able to achieve 850fps with 850psi though.  I know I was able to touch the high 800's with 1000 psi using the standard 2400kt tube, but it was not as efficient as the 1200psi I eventually went with.

As to eliminating the gauge block, I am unsure if that is possible.  Something needs to seal off that hole at least, and I really like the idea of mounting the bottle from it.  I am glad you mentioned the restriction though.  I was looking around and it seems that the PROD "GAUGE PORT ASSEMBLY" (1700-104) fits into a disco tube, and is much more open.  I wonder what the almighty Bob would say ...

...And here I was originally thinking I was gonna get away with twenty bucks and a tube swap!  Let the nickeling and dimeing begin.

[Gipper]

No doubt costs can add up but the beauty is you can do it in stages and enjoy the rifle in the mean time.

Brian