Any Interest in 6mm ? - Build Thread

[oldpro]

The "jet" is just an 8-32 pan head screw with a hole drilled through it.... I can make any size I want up to 3/32".... I have number drills down to #60 (0.040"), below that I only have 1/32" (0.032") or 1/64" (0.016") but I'm pretty sure that tiny a drill would just break in a steel screw....

Have you ever got your velocity below 500 fps on a bullet where the plateau is over 900 without hitting a cliff (50% adjustment range) ?....

Bob

yes but my piston ratio is higher. You can extend that range and efficiency also by making the pilot hole smaller its to large for your ratio. I would start around .040 this will require a slightly harder hammer strike but your so light now it would probably be a blessing. Bob is it hard to get to your pilot jet?

[rsterne]

I just have to pull the valve and make a new one by drilling an 8-32 screw.... If the light hammer doesn't give me what I want (which I can test without pulling the valve).... then I will try a smaller jet.... A 0.040" hole is only 40% of the area I have now at 1/16".... The last change to the 3/64" vent hole makes it 2.25 times more area than the original 1/32" vent....

While stellar efficiency would be nice, my primary concerns in order are: power, reasonable cocking effort, and then efficiency.... If I can get around 130 FPE with the 6mm at 2800 psi at 1.00 FPE/CI, I would have reached my baseline goal, that should give me about 25 shots on a 4500 psi fill.... Higher efficiency (ie more shots) is a big bonus, of course....

I am still in awe of the easy cocking this valve makes possible.... Are you using a 1/32" vent through the poppet?....

Bob

[oldpro]

I just have to pull the valve and make a new one by drilling an 8-32 screw.... If the light hammer doesn't give me what I want (which I can test without pulling the valve).... then I will try a smaller jet.... A 0.040" hole is only 40% of the area I have now at 1/16".... The last change to the 3/64" vent hole makes it 2.25 times more area than the original 1/32" vent....

While stellar efficiency would be nice, my primary concerns in order are: power, reasonable cocking effort, and then efficiency.... If I can get around 130 FPE with the 6mm at 2800 psi at 1.00 FPE/CI, I would have reached my baseline goal, that should give me about 25 shots on a 4500 psi fill.... Higher efficiency (ie more shots) is a big bonus, of course....

I am still in awe of the easy cocking this valve makes possible.... Are you using a 1/32" vent through the poppet?....

Bob

No but again our piston ratios are different but having been where you are now I know the smaller pilot jet will work wonders. Can you make your jet removable so you dont have to keep pulling the valve? Slot the top so a long screwdriver can reach down and unscrew it. I cant emphasize how much the smaller jet will help but it may take a few trys to get it perfect thats why I would start at .040 then go up if necessary. The one thing you havent played with is the pilot jet and it really is dramatic when its right.

[rsterne]

The screw also holds the thimble in place in the mounting wheel (a loose fit, so the thimble can self-align but without end play).... but once I am that far into disassembly it's not that hard to pull the valve.... and on the unregulated gun it would have to be a L O N G screwdriver indeed.... *LOL*....

Please let me know (via PM if necessary) the size vent hole you are using through the poppet....

Bob

[oldpro]

It depends on the power level but I typically use a .87 mm jet the reason I believe yours needs to be smaller is your ratio is lower there fore less stable and what I mean by that is a standard valve is what I call 100% stable as it has no tendency to blow open under almost any pressure and the further you are from 1/1 ratio the further unstable the valve gets. After many attempts and months of testing I found a 80% of bore between poppets to be ideal for most guns. 75% is good for easier opening but still stable enough to not blow open or go bbbbrrraaappp. Anything less than 75% was unstable to the point one couldn’t put pre-load on the poppet. So your around 66% and I’m amazed you could get it to seal to be honest with such low holding pressure. So with that low of a % I would increase the bleed like you did into balance chamber to control dwell and also decrease pilot to increase hammer energy needed and also increase lock time or shorten dwell. Your pretty skilled to be able to make this valve in shop it’s not easy even on a C&C. The other benefit will be a wider tuning spectrum.

[rsterne]

I wasn't concerned about using the 1/4" small end, since Lloyd's prototype used just 3/16", and the MRod valve I got from you, which works just fine, is 1/4".... It wasn't the jet size I was asking, but the "bleed hole" as you call it, that equalizes the pressure between the exhaust port / throat and the balance chamber.... I started at 1/32", went to 0.040", and I'm now at 3/64" (0.047") and the adjustment range is WAY better with the bigger vent / bleed hole.... I'm convinced that the bigger that hole, the faster the pressure builds in the balance chamber, and the more the valve acts like a conventional valve (with no blowing open).... I don't care about not being able to put preload on the poppet, as I want to run an SSG.... so my requirements are less stringent than yours, where you have to worry about people doing things the valve is not designed for....

The valve, IMO, operates best with an SSG with gap, and since I can easily get to the plateau velocity with a small gap, and have to run a big one to get into the more efficient operating range.... there is absolutely no danger of preload and run-away operation.... Now that I have it operating like a conventional valve in terms of tuning.... it is only a matter of finding the right combination of hammer strike, pressure, and possibly vent and jet sizes to optimize it.... There IS a light at the end of the tunnel, and I'm pretty sure now it's not the headlamp of an oncoming train.... 

Bob

[oldpro]

I wasn't concerned about using the 1/4" small end, since Lloyd's prototype used just 3/16", and the MRod valve I got from you, which works just fine, is 1/4".... It wasn't the jet size I was asking, but the "bleed hole" as you call it, that equalizes the pressure between the exhaust port / throat and the balance chamber.... I started at 1/32", went to 0.040", and I'm now at 3/64" (0.047") and the adjustment range is WAY better with the bigger vent / bleed hole.... I'm convinced that the bigger that hole, the faster the pressure builds in the balance chamber, and the more the valve acts like a conventional valve (with no blowing open).... I don't care about not being able to put preload on the poppet, as I want to run an SSG.... so my requirements are less stringent than yours, where you have to worry about people doing things the valve is not designed for....
 I use a .030 and let the pilot jet fine tune it the rest of the way if you use a big pressure orifice it will limit what you can do with the jet and I have found the best efficiency is to try and run as small a jet as your power level will allow. I know I keep hounding you to try it but when you do you’ll see. That thimble jet will have more effect than the bleed hole and it’s reversable.



The valve, IMO, operates best with an SSG with gap, and since I can easily get to the plateau velocity with a small gap, and have to run a big one to get into the more efficient operating range.... there is absolutely no danger of preload and run-away operation.... Now that I have it operating like a conventional valve in terms of tuning.... it is only a matter of finding the right combination of hammer strike, pressure, and possibly vent and jet sizes to optimize it.... There IS a light at the end of the tunnel, and I'm pretty sure now it's not the headlamp of an oncoming train.... 

Bob

[rsterne]

Remember what I said about two steps forward, one step back?.... Well the all MDS hammer I made is too light to deliver maximum power with the valve with the 0.047" vent through the poppet.... Even with putting in a 14 lb/in spring, at 5 lbs. preload and zero gap on the SSG, I can't quite reach the plateau with the 61 gr. bullets, and I'm down about 10% on velocity (20% in FPE) with the 74 gr.... The good thing is that the shot cycle is a nice clean SNAP (although a loud one), with NO sign of hammer bounce.... However, the large vent, which is intended to make the valve more conventional in operation by eliminating (or reducing) the "blow-open" cycle is doing exactly that.... Basically the valve is operating like a conventional valve that is easier to crack, but that's all....

I have no doubt that by making a hammer that is in between the 32 grams I have now and the 59 grams I had before (both with the 11 gram cocking handle installed) I could find, somewhere, the perfect combination.... However, although not uncomfortable by any means, the cocking force is WAY greater with the light hammer, so I think I have gone too far on the (hard to change) vent size.... Before I pull the valve and make more changes, I am going to make an MDS hammer for the unregulated gun, which is working great except for having too large a gap in the SSG (about 5/16").... The valve in that gun has the original 0.032" vent through the poppet, so has a tendency to "blow open" but it looks like a lighter hammer will drastically reduce that tendency, so it may turn out that a light hammer with the small vent is the perfect combination....

It certainly makes sense to try that before deciding how to proceed with another round of changes on the valve in the regulated gun.... especially because changing out the hammer doesn't even require degassing the gun....

Bob

[oldpro]

 Or open the thimble jet up a tad and that should get you back up on the knee

[rsterne]

The thimble jet is the same as always, 0.063", I haven't yet tried smaller.... HOWEVER, check this out....

I made an MDS hammer for the .257 unregulated gun, and it works perfectly.... I was able to run a bit of preload on the 11 lb/in spring and reduce the SSG gap.... and every shot was crisp with no hammer bounce.... and I was able to push the gun right up to 185-190 FPE at 3800 psi, which is more than I would ever run it because it would use too much air at that power.... I backed the power down to 950 fps with the 82.5 gr. bullet (165 FPE) and ended up with 1 lb. of preload and 8 turns of gap on the SSG, which gives me a cocking force of just 9 lbs.... If I go to the 100 gr. bullet I need to reduce the gap a couple of turns, and if I drop back to the 73.4 gr. 257420 I have to increase the gap a couple of turns to keep it under 1000 fps.... Between the easy preload adjustment and gap adjustment, I can tune the gun from a "mild" 130 FPE up to about 180 FPE before it becomes an air hog....

With the gun set for the 82.5 gr. bullets I filled it to 3850 psi (all the pressure that was in my tank), with my digital gauge connected to the gun, shut off the tank and drained the inlet side of the gauge (it has a check valve for that purpose) and shot a 5-shot string as follows....

953
948
947
935
911

The ending pressure was 3350 psi (it used exactly 100 psi per shot from the 300 cc reservoir), and the first 4 shots were within a 2% ES.... I know that at 4000 psi at this setting the velocity is slightly lower, so I will have 5-6 shots within a 2% ES when off tether with a  4K fill.... and of course tons of shot when tethered to the regulator within a few fps of 950.... The 500 psi pressure drop over the 5 shots averaging 939 fps (162 FPE) works out to an excellent 1.28 FPE/CI, which I am more than pleased with at that power with a .257....

The combination of my version of the ART/SS valve and the lightweight MDS hammer is a real winner.... The gun is easy to cock, has tons of power, and when dialed back about 5% below the maximum is also very efficient.... I am sure setting the power lower would get VERY impressive efficiency numbers, but what's the point, this is a long range Varmint gun.... This valve has the original 1/32" vent through the poppet, which I am now confident is a better choice than the 3/64" I tried in the regulated gun.... Something in between, like the 0.040" vent I tried briefly, would increase the hammer strike, but now that I know the original setup works well when used with an MDS hammer I think I will just stay with the 1/32" vent.... I would like to get a couple of 8 lb/in hammer springs and run them with more preload, so that I can reduce the SSG gap a bit more.... but for now this setup will more than do the job....

Bob

[oldpro]

 Most excellent!!! So many ways to skin the cat as they say. Thats not much spring force to pop open a 4k fill thats for sure. This should really reach out well to those critters WAY out there. Better start looking for a bigger scope.

[rsterne]

My Monocoque .257, operating at the same pressure, had a 182 gr. hammer with 1.4" of travel, and took 21 lbs. to cock it.... 

Bob

[oldpro]

My Monocoque .257, operating at the same pressure, had a 182 gr. hammer with 1.4" of travel, and took 21 lbs. to cock it.... 

Bob

Thats a crazy heavy hammer and a VERY stiff spring but thats what it took before balanced valves made their way into our lives. Two years ago we were banging highly sprung steel weights into thin valve stems now a mere 2 years later were using forces a low powered 22 would use to operate. Two years from now??

[MJP]

That is crazy heavy hammer and spring, I have not used that heavy hammer on any of my guns. Savage hammer was around 145gr at 800fpe. Did use 50mm of travel though.

In two years we will be using micro switch type bleed valves to actuate pneumatic actions to cycle the guns. 

Marko

[rsterne]

My .457 Hayabusa uses a 237 gr. hammer with 2" (50 mm) of travel to get 550 FPE.... Cocking force is 32 lbs.... I can just get to the plateau (maximum velocity) at 3600 psi.... I think just maybe it is a candidate for a (larger) SS Valve.... the throat is currently 0.406", but I would go to 7/16" (0.437") and enlarge the ports.... I would not have been able to max. that out with a conventional valve.... You can open the valve with a lighter hammer, but not hit the max. with heavy bullets with a conventional valve.... at least that has been my experience....

Bob

[rsterne]

I just tried a couple of Airsoft BBs in the 6mm at 2800 psi.... 1944 & 1963 fps.... So much for the 1650 maximum.... *LOL*.... Next time I have the 6mm upper on the unregulated gun I will try a couple of shots at 3800 psi.... maybe even 4200.... 

Interestly, Lloyd's spreadsheet predicted 1999 fps for the 1.8 gr. plastic BB.... 

Bob

[lloyd-ss]

Bob, this project has become quite a learning experience. The velocity you got from those air soft plastic BBs is quite an eye opener!

[rsterne]

I tried to glue up the 0.047" vent through the poppet and redrill it with no success, so today I made a new poppet for my SS Valve.... I am still using the 3/8" big end and 1/4" small end, but I added a thin (1 mm) O-ring inside against the shoulder of the poppet as a bump stop.... It should never touch, but if the valve was driven fully open (or blew fully open) the O-ring bumper would take the shock instead of either the shoulder on the poppet hitting the inside shoulder of the thimble, or the spring going coil-bound.... It was just a safety measure, but also a way to find out if the valve was opening that far.... As I expected, the O-ring made NO difference, which is proof that the valve is not trying to open more than the 0.19" travel before the O-ring hits.... This was a useful piece of information (and expected), and I plan on incorporating this feature into any future SS valves I make to insure they don't break from being overdriven, or from machine-gunning.... I used PEEK for the poppet, not because it was required, but just because I had some and wanted to try it, and it machines nicer than Delrin....

When I reassembled the 6 mm regulated gun I finally nailed it.... I used the 32 gr. MDS hammer, and the 11 lb/in spring with 1 lb. of preload on the SSG guide.... I was able to easily get to the plateau with all three bullets, and have to run 5 turns of SSG gap with the heaviest and 7 turns with the lightest to get about 3% below the plateau, where I want to operate to get reasonable efficiency.... Here is a graph of the velocity vs. SSG gap for all three bullets at 2800 psi....



I am getting nearly 200 fps of adjustment before the valve falls off the cliff, which is plenty, I will never run it that low.... You will note that there is one additional line on the graph, the dotted black line.... I set the SSG gap at 6 turns, and using the 63.8 gr. bullets I tested the velocity adjuster on the back of the receiver that restricts how far the bolt retracts by moving a pin into the J-slot for the handle.... The reason for the slight increase in velocity when the adjuster is turned in 2 turns is that I had to shorten the nose of the bolt 1/16" because it was pushing the bullets too far forward, which made the 73.4 gr too hard to chamber.... This meant that with the bolt handle pulled all the way back in the J-slot it was creating more wasted volume in the chamber, behind the barrel port, which was dropping the velocity slightly.... It shows the importance of minimum wasted volume between the valve seat and the base of the bullet.... From the maximum velocity setting I have 8 turns of adjustment on the 8-32 screw, which moves the bolt nose from the back of the port to nearly obstructing it.... at which setting the velocity is below 500 fps.... The cool thing about this adjuster is that you can easily try different velocities, to find out if there is an optimum for accuracy.... Of course you should adjust the Harmonic Tuner at each velocity, just to make sure what you are seeing is a true velocity effect, not a change of accuracy due to barrel harmonics....

Once I am sure that there are no leaks, I will remove the "tiny tank" and replace it with my 500 cc CF bottle.... At that point I will be able to test the efficiency at various velocity settings.... These two guns are nearing the end of their development, which is a relief because it won't be long before the Motel gets busy and my shop time disappears once more....

Bob

[lloyd-ss]

Bob, All the effort is paying off and you've ended up with a  lot of versatility in that set-up. Well done.
Are you pretty much using the SSG on 100% of your projects now?
Thanks,
Lloyd

[rsterne]

I design it into every new project.... Sometimes there was so much hammer strike required (as with my Monocoque) I haven't been able to set it up with a gap and still get full power.... but that should be a thing of the past now with the SS Valve.... Over the next couple of years I will be making more of them to reduce the hammer strike on all of my bullet shooters.... Some of them will be upgraded to larger ports and valve throats whereas they were limited in the past because I couldn't get enough hammer strike.... In reality, I think all my new PCP projects will have bore-area porting, because even with regulated guns and lower power, it seems to be very efficient, and you can run a lower setpoint for a given FPE....

I was just thinking this morning how several relatively new technologies have come together to drastically change PCPs over the last few years.... The SSG gave us the ability to eliminate hammer bounce, and reduce cocking force compared to an SSS with gap.... The drop sear triggers on the MRod and PRod supplied us with readily available, good quality triggers, which allowed the use of MDS hammers.... The MDS hammers made the use of aluminum main tubes more practical.... and of course the SS and Cothran Valves drastically reduced the cocking force, particularly in big-bores.... and allow even lighter MDS hammers without excessive spring force.... The balanced valves also allowed the use of larger valve throats and porting in guns with limited hammer strike capability.... unleashing an FPE capability not previously possible in those configurations....

A decade after I got back into airguns, I suddenly feel like there is so much new to learn.... and that PCPs have entered a new generation.... It's exciting to be a part of it....

Bob