GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on January 21, 2015, 10:06:15 PM
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As part of the development of the Millennium Pumper and the valves that Mike (CarsonRatSniper) is going to be selling, I decided to test something I have wanted to do for a while.... The poppet in a Disco has a 5/32" diameter stem, and one of the mods typically done is to slim it down to 1/8" or a bit less to get more flow through the throat in the valve.... MRod rifle stems are readily available, cheap, and have a 1/8" stem, plus the head is a smaller OD, which should result in better flow as well.... They are a harder material, and therefore should be easier for the hammer to knock open, and the smaller stem where it penetrates the valve body will reduce the closing force at any given pressure by 36%.... The combination of those things should mean that less hammer strike is needed to open the valve for a given dwell.... The sum of all these reasons was compelling, and the conversion was very easy.... The Disco valve body is drilled 5/32", while the MRod stem is only 1/8", so a bushing was needed.... Readily available K&S brass hobby tubing was perfect for the job, with a 5/32 OD and 1/8" ID.... a short length, glued into the valve with industrial strength CA glue did the job.... I ground a bit off the end of the MRod poppet to make sure the stem was the same length as the Disco one, and I gave the poppet end of the valve spring a little squeeze with a pair of pliers to tighten it up to fit the seat on the poppet better, and the conversion was done....
I needed a baseline to see if there was an improvement, so I checked one of my test mule .25 cal Discos today to find out where the knee of the curve was when tethered at 1800 psi, and then pulled it apart and installed the MRod poppet, no other changes.... The valve is basically a duplicate of what I designed for the Millenium Pumper, with 0.219" ports.... The gun has a stock Disco hammer, but the valve stem has been shortened a bit to increase the travel, and the hammer spring is one of the heavy Disco springs I used to sell, 1.75 long x 0.040 wire.... so, nothing fancy in terms of hammer strike.... I tested with 25.4 gr. JSB Kings....
Original results (Disco poppet with stem thinned to 0.115):
Max. preload (just shy of coil bind): 978 fps
1/2 turn out: 975 fps
1 turn out: 951 fps (knee)
2 turns out: 909 fps
So, the knee of the curve was at 1 turn from maximum preload, in other words that hammer and spring setup was JUST enough to max. the gun out at 1800 psi....
With MRod poppet (stock 0.125 stem, cut to same length as the Disco one):
Max. preload: 999 fps (56 FPE)
1 turn out: 997 fps
2 turns out: 995 fps
3 turns out: 990 fps
4 turns out: 973 fps (new knee, 53 FPE)
5 turns out: 935 fps
6 turns out: 873 fps
Just by changing the poppet, the gun gained 20 fps, and the knee of the curve moved down 3 turns in preload (24 tpi, so that is 1/8 less)....
So, using the MRod poppet in a Disco valve is a clear winner.... It has a bit more power, and a LOT easier to open.... The stock Disco hammer will do the job, and without any magic spring, at 1800 psi.... even with the big ports, throat, and running a .25 cal. barrel.... Being able to create lots of dwell without major hammer changes will be a real advantage when using this valve in a .30 cal or larger.... and will really help when running more pressure as well....
Bob
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*Those* are the poppets I'm using in the Millennium Valves!
;)
This first run of guns will have the bushing since we made them for the Disco poppet, but the individual valves I am selling + all future runs of Millennium Pumpers will have the rear of the valve drilled for the 1/8" stem from now on.
Mike
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Mike,
I got 75.00 burning a hole in my pocket...can't wait to get the valve.
Joe
P.S. Nice write up, Bob.
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Pretty KEWL to incorporate improvements as the build progresses.... and really nice to manage it before the first gun is shipped.... It just keeps getting better and better.... *grin*.... This will be a case of the Production Millennium Pumpers being better than the prototype....
Bob
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It will also have another way of identifying the first run of 10 guns in conjunction with the serial number.
;)
Next week as soon as the poppets are delivered I'm tearing down my .25 Challenger and installing a Millennium valve along with the Mrod poppet, a tapered valve spring and doing the 5/16" transfer port mod to the tube and barrel/breech on the mill.
My Challenger shoots at 70 ft lbs with a modified BOSS valve and a 5/32" stemmed delrin poppet.
That valve has a .250" throat and a 3/16" exhaust port.
I'm going to use the oblong .219" porting in the barrel and the Teflon transfer port to match the Millennium valves .219" exhaust port so I can take advantage of the .266" throat.
I want to see what the Millennium valve will *really* do!!! I might have to put my 1:14 twist barrel back on it for shooting 52gr Bob's Boattail! (That barrel is on the Millennium test upper right now).
;D
You know, looking at your results using the Mrod poppet almost looks like the ideal cross platform setup...Kings 'in the zone' at 4 turns preload out but that may work well for slugs if you go 4 turns back in on preload. A King @ 1000 fps means that same tune should push a 37gr in the mid 800's - that's a compromise I wouldn't mind having.
Mike
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I have a disco .22 and have it apart while refinishing stock. I am in midst of modding the goofy breech screw (which I have stripped twice) to 6/32 and the valve screws to 10/32 HT screws. I am still investigating the tport mod...I have spare and plan to drill it to .161 although I might go to .146 or so to start. Also looking at porting on valve etc.
I figure I might as well do this as well. After a search on parts list I realized there are a number of different parts lists for mrod depending on year. Are the poppets all the same or should I order the latest...or does someone have the part number I need? Also...what size hammer spring should I use and what length? I currently have a .035 spring with a couple coils cut so it is about 1.75" long now and I have diy PA.
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looking forward to trying this myself. i've heavily modified my valve so will see how it compares. Looking forward to see results with you all here.. great thread.
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Mike, I did some testing today with my Monster Disco valve with MRod poppet along the lines of what you suggested above (once again, we think alike!).... First, at 1800 psi, I cranked the preload to maximum, and got the following....
25.4 gr. Kings = 999 fps (56.3 FPE)
36.1 gr. Daystates = 897 fps (64.5 FPE)
41.7 gr. EunJin Points = 853 fps (67.4 FPE)
50.6 gr. Bob's Boattails = 781 fps (68.5 FPE)
I then left the preload at maximum and started increasing the pressure until I found the point where the velocity peaked....
25.4 gr. Kings = 2600 psi = 1078 fps (65.6 FPE)
36.1 gr. Daystates = 2400 psi = 956 fps (73.3 FPE)
41.7 gr. EunJin Points = 2200 psi = 888 fps (73.0 FPE)
50.6 gr. Bob's Boattails = 2000 psi = 793 fps (70.7 FPE)
As I expected, for a given hammer strike (in this case maximum with a stock hammer and a 0.040" wire spring) the pressure where the velocity peaks drops as the bullet gets heavier.... Conversely, for a given pressure, you need more hammer strike to max out the velocity for a heavier bullet.... To take full advantage of the flow capability of this valve with heavy bullets at higher pressures is going to require more spring (eg. the QB spring I mentioned) and/or a heavier hammer.... However, for the Millennium Pumper, which is designed to operate at 1800 psi, the hammer and spring I am using are plenty for anything up to a 52 gr. bullet.... particularly once you dial it back to get more than one shot....
Bring on the new 34 gr. JSB Kings, I can hardly wait !!!
Bob
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Very respectable numbers, Bob. Time to go predator hunting.
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Oh Yeah! ;D
I smell a 2200 psi regged 90ci Ninja Tank from Tim and some 36gr Wicked Monster HP's in my future!!!
Thank you Bob for taking the time...you're R&D is *priceless*!
Mike
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Great results, now I just need to know how you do all that...
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very nice results! I have a couple of mrod poppets sitting around. that might be a nice improvement for my disco but I don't know if it is worth the trouble of taking it apart. it already performs very well
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So Bob, the Mrod poppets are a drop in replacement to the original poppet?
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You need a bushing for the valve stem to seal.
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You need a bushing for the valve stem to seal.
Okay. Thanks
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No, read back in the first post.... You need to bush the back of the valve down to 1/8" instead of 5/32" when you use the MRod poppet, and grind a bit off the end of the stem so you don't lose hammer stroke.... You want the stem to stick out the back of the valve the same distance as the Disco stem, or a whisker less, not more....
Bob
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No, read back in the first post.... You need to bush the back of the valve down to 1/8" instead of 5/32" when you use the MRod poppet, and grind a bit off the end of the stem so you don't lose hammer stroke.... You want the stem to stick out the back of the valve the same distance as the Disco stem, or a whisker less, not more....
Bob
Okay. Thanks Bob. ;)