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PostPosted: Sat Dec 01, 2012 7:29 pm 
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Location: Coalmont BC
A short while ago I built a .25 cal Carbine Pumper based on a shortened Disco Tube, the linkage from a Benji 392, and an MRod barrel.... While working on it, I started collecting ideas and parts for a rifle version using a full length Disco tube and a .25 cal choked Lothar Walther barrel.... Instead of having an auxilliary reservoir made from a 16 gr. CO2 bulb under the main tube, this gun would have an internal reservoir and a separate check valve.... After about a week in the shop, here are the main internal parts....

Image

The pump linkage is an extended Billet linkage from Mac1 Airguns.... It is stronger, and 3" longer than stock, although it maintains the same 7.6" stroke, giving a swept volume in the Disco tube of 54 cc.... I wanted to mount the pivot pin as far forward as possible, so instead of shortening the Disco tube I made a threaded end plug to help spread the end load of the pivot pin into the tube.... The smaller stub on the front will mount a barrel band.... The piston is the same as the one I made for the Carbine.... Immediately behind that is a check valve, sealed both sides with O-rings, mounted into two new holes in the Disco tube and secured with high tensile 8-32 low profile SHCSs.... There is a 2.5" long, full diameter, (18cc) air chamber between the check valve and the extended front end on the valve.... The valve extension is 3/8" ID for most of its length, providing additional volume, and enough wall thickness to mount the gauge and a male Foster fitting on the left side just behind the gauge location.... That will enable the gun to be filled from a tank or stirrup pump, both easier than the onboard pump, whose main purpose is for topping up in the field.... Also shown is an MRod trigger with Challenger trigger guard.... Everything will be mounted in a inletted Boyd's Blaster stock from Norm at Discos-R-Us in Nutmeg laminate....

Image

In the second photo are details of some of the parts.... The front plug was pretty tricky to machine.... I had to turn and thread it, mount it in the already slotted Disco tube, and then machine the slot and drill the pivot hole in the proper orientation.... It worked out beautifully, and the tube is full wall thickness at the pin location.... Below that is the check valve.... It is a simple aluminum housing, drilled through, and carrying a shortened check valve pin from a male Foster fitting, retained by a piano wire pin.... I tried one in my Carbine and it functioned perfectly, and the thin pin diameter left room for the screws on both sides.... Beside the check valve is the valve poppet and spring.... You can see how I have streamlined the head of the poppet, and narrowed the stem behind it.... The front of the valve spring has been expanded to 9/32" ID, to match the spring seat ID in the extended valve front end, for additional flow.... The brass part is a custom gauge mount I made from brass pipe fittings.... I used a 1/8" male to 3/8" female adapter and a 3/8" male to 1/8" female, then bored them out for additional volume, and threaded them together and sealed it with solder.... The Blaster stock is plenty deep enough for that assembly, and it added over 3 cc more volume to the valve.... The total volume is now 28.5 cc, slightly bigger than the Carbine was.... The Disco valve has been bored out inside to 0.62" ID, the throat drilled to 0.25", and the exhaust port milled out to 0.203" on a 20 degree angle.... It still needs a little TLC with a Dremel to round and smooth the inside corner.... The porting is 16% larger in area than what I used in the Carbine.... That combined with the longer barrel and slightly larger valve volume should gain a bit of velocity.... I'm hoping for about 10% higher FPE in this version at the same pressures.... With the additional leverage of the extended linkage, the effort should be the same at about 1800 psi as it was at 1500 in the Carbine.... so I have little doubt the peak power of this rifle will be higher....

This project resulted from my joining the Green Forum because of interest in their "Millenium Pumper" project, the concept of which was to bring MSPs into the 21st Century.... There was no concensus of opinion over what it should be like, so I undertook this project as my own interpretation of what could be done easily, starting with mostly Crosman parts and adding a few custom bits into the mix.... There are lots of other interpretations of the idea possible.... this just represents mine....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Last edited by rsterne on Sat Dec 01, 2012 8:00 pm, edited 1 time in total.

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PostPosted: Sat Dec 01, 2012 7:52 pm 
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Looking forward to seeing this completed!

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PostPosted: Sat Dec 01, 2012 9:25 pm 
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Very cool Bob i am curious what is it worth


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PostPosted: Sat Dec 01, 2012 9:47 pm 
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In time or dollars?.... :mrgreen:

The Carbine cost me about $400 in parts.... this one will be significantly more, with the Boyd's stock, the LW barrel, the Billet linkage, and the MRod trigger.... The only way these make any sense is as a hobby project to see what I can do.... then hopefully recoup my costs and roll the money over into the next project.... I hate doing things on a production basis, so I have no interest in making several of the same gun.... This way I get to experiment, build a cool project, develop it to it's potential, and hopefully pass it on to someone who will appreciate it and enjoy it as a unique, one-off project rifle.... I haven't had any complaints so far.... and it keeps the wife off my back from having too many guns around I don't shoot.... 8)

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 01, 2012 9:53 pm 
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rsterne wrote:
In time or dollars?.... :mrgreen:

The Carbine cost me about $400 in parts.... this one will be significantly more, with the Boyd's stock, the LW barrel, the Billet linkage, and the MRod trigger.... The only way these make any sense is as a hobby project to see what I can do.... then hopefully recoup my costs and roll the money over into the next project.... I hate doing things on a production basis, so I have no interest in making several of the same gun.... This way I get to experiment, build a cool project, develop it to it's potential, and hopefully pass it on to someone who will appreciate it and enjoy it as a unique, one-off project rifle.... I haven't had any complaints so far.... and it keeps the wife off my back from having too many guns around I don't shoot.... 8)

Bob


I would be interested when you move on from this gun ......

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and it keeps the wife off my back from having too many guns around I don't shoot.... 8)


I know all about that :lol: I have sold off over half of all mine .......


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PostPosted: Sat Dec 01, 2012 11:41 pm 
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rsterne wrote:
In time or dollars?.... :mrgreen:

The Carbine cost me about $400 in parts.... this one will be significantly more, with the Boyd's stock, the LW barrel, the Billet linkage, and the MRod trigger.... The only way these make any sense is as a hobby project to see what I can do.... then hopefully recoup my costs and roll the money over into the next project.... I hate doing things on a production basis, so I have no interest in making several of the same gun.... This way I get to experiment, build a cool project, develop it to it's potential, and hopefully pass it on to someone who will appreciate it and enjoy it as a unique, one-off project rifle.... I haven't had any complaints so far.... and it keeps the wife off my back from having too many guns around I don't shoot.... 8)

Bob



i imagine the full price $
of all the time to simply think, of who to built it ,probably every night before pass out to sleep
than built it ,
and the costum machined parts,,added to that the factory parts,,
a unique model who worth much more than any reputable factory one ,

even the worth of $$$ ,
beleve me the owner is more proud than any price :lol:
its not only unique ,its real well made too

target man

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9 mm cal,discovery pumper
.25 cal,crosman pumper


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PostPosted: Mon Dec 03, 2012 8:55 pm 
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Well, it holds air!.... I got the main tube assembly done and pressured tested to 2000 psi.... I can actually still use the pump at that pressure, and it doesn't seem much harder to pump than the Carbine at 1500.... which means hard, but not impossible....

Image

I made and installed the hammer and the RVA, lengthened the rear of the bolt slot in the breech 0.10", faced 0.030" off the back of the valve and shortened the valve stem about 1/16" so that it is flush with the back of the valve when the valve spring goes coil bound.... Those modifications, along with the changes I made to the cocking slot in the tube and the bolt allow the maximum possible hammer travel, which works out to about 0.8".... No matter how the travel is adjusted, the cocking pin can't hit anything....

There are basically two areas left to work on.... The Lothar Walther barrel has to be machined to fit into the breech, I have to make a chambering reamer and cut the chamber and a groove for the O-ring, make a .25 cal bolt, machine the transfer port and crown, and make a barrel band.... On the Boyd's Blaster stock, I have to cut a hole for the gauge and relieve a few spots for the MRod trigger.... and then the major job of converting the forestock into the pump handle.... The stock will then need final sanding an finishing.... I'm really looking forward to seeing how this new pumper will perform....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Dec 03, 2012 10:08 pm 
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So, are you basically making an Indy?


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PostPosted: Mon Dec 03, 2012 11:32 pm 
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for just a bit less than $1799.... :mrgreen:

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Dec 04, 2012 1:31 am 
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Joined: Sun Jun 11, 2006 8:43 pm
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Location: Montreal, Quebec.
I see you took my advice on using a full length Disco tube.. Oh rsternie I am probably going to get flamed for this! I should put a copy right on my ideas but my days of building or spending money on airguns are over! Got the mom to take care of because daddy is gone! I have you to build the guns that I can only dream of building! Anyway I took the economical way out and got REAL FIREARMS with my PAL like my friend nick did.. :mrgreen: lol

edit: Yes I am jealous.. 8)

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PostPosted: Tue Dec 04, 2012 7:21 am 
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Location: Niagara, Ontario,Canada
Kinetic_Genius wrote:
I see you took my advice on using a full length Disco tube.. Oh rsternie I am probably going to get flamed for this! I should put a copy right on my ideas but my days of building or spending money on airguns are over! Got the mom to take care of because daddy is gone! I have you to build the guns that I can only dream of building! Anyway I took the economical way out and got REAL FIREARMS with my PAL like my friend nick did.. :mrgreen: lol

edit: Yes I am jealous.. 8)


All those times I told you to get your PAL so you can experience real power.. you finally did it.. Airguns will always be just airguns..


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PostPosted: Tue Dec 04, 2012 10:40 am 
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Location: quebec
rvd wrote:
Kinetic_Genius wrote:
I see you took my advice on using a full length Disco tube.. Oh rsternie I am probably going to get flamed for this! I should put a copy right on my ideas but my days of building or spending money on airguns are over! Got the mom to take care of because daddy is gone! I have you to build the guns that I can only dream of building! Anyway I took the economical way out and got REAL FIREARMS with my PAL like my friend nick did.. :mrgreen: lol

edit: Yes I am jealous.. 8)


All those times I told you to get your PAL so you can experience real power.. you finally did it.. Airguns will always be just airguns..


but they are there to stay and they have theire place for long time ,
even in a real bad general war situation,,

if powder and amunition are back order in an area ,
airgun could make a difference and be very useful,,


back to the millenium pumper ,,,

i hope some one will take adventage of bob's experience :lol:
and produce that size of pumper tube and valve assembly etc,,

alot will make the convertion ,its a waiting item t'l long time

target man

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9 mm cal,discovery pumper
.25 cal,crosman pumper


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PostPosted: Wed Dec 05, 2012 11:09 pm 
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Location: Coalmont BC
I completed the barrel work today.... I made a chambering reamer from O1 Drill Rod, hardened and tempered it, and then used it to cut the chamber to just past the transfer port location.... I then machined in the barrel port and a rebate in the end for the O-ring to seal the bolt.... It will be pinched between the barrel and the breech.... The barrel OD was reduced to 7/16" to fit the Crosman steel breech....

Image

The reamer has a 0.246" pilot that just rides on the lands in the LW barrel.... It has a 2* taper to create the leade, and then the chamber is 0.254".... The chamber is machined to just past the front of the transfer port, with the leade in front of that.... I also did a target crown on the muzzle....

Image

The barrel port is 0.188" wide by 0.219" long at the bore, tapering to a 0.204" circle where it mates to the transfer port, which will be made from a piece of 5/16" Teflon rod.... After finishing the machining, I used JB Bore Paste to lap the bore and the chamber, followed by a polish with their polishing compound.... The results are a mirror finish inside.... LW sure do make a beautiful barrel....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Dec 06, 2012 10:01 pm 
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Location: Coalmont BC
I got the main fitting of the stock done today.... When I ordered the Boyd's Blaster stock from Norm at Discos-R-Us I wasn't sure what I was going to use it for, so I had it inletted for a Disco without gauge.... I had to modify the inletting slightly for the MRod trigger, and I used a 1" Forstner bit to drill the gauge hole.... I also had to grind a small groove in the top left side to accomodate the Foster QD fitting.... The Challenger trigger guard came too close to my fingers on the pistol grip, so I had to shorten it a bit.... Fortunately, it doesn't have a "back end" so that wasn't a problem.... I've cut off the forearm off to make the pump handle, but haven't cut the groove yet for the pump linkage....

Image

The other thing on today's agenda was to make the barrel bands.... The front one (right in the photo) fits on the 5/8" stub on the front of the front pivot block, so the outside of the band is the same diameter as the OD of the main tube.... The rear barrel band is designed to sit immediately in front of the gauge, and clamp the front of the breech in place for extra stability....

Image

The Crosman steel breech's main weakness is the 4-48 screw in the loading port.... There is nothing forward of that to hold the breech and barrel in place.... I would have had the band right up against the front of the breech, but because of my oversized gauge mount I had to have a 1/4" gap between the band and the breech.... The band is made in two parts, the lower one will stay on the main tube, located with a set screw.... The upper half will sit on the barrel, just in front of the breech.... You remove the two clamping screws to remove the barrel and breech from the gun.... When you replace the breech and tighten the screws, it pulls down on the barrel, clamping the front of the breech securely against the main tube.... The top of the barrel band is flush with the top of the breech....

The only major jobs left are to cut the slot in the forearm for the pump linkage and make the .25 cal extended probe bolt.... With a little luck I'll get those done tomorrow and then I can give the stock a final sanding and start finishing it with Watco Danish Oil.... This thing isn't far from initial testing.... I just need Lloyd's MRod trigger shim....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Dec 10, 2012 4:56 pm 
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I tethered my "Millenium Pumper" today, running it regulated at 2000 psi to find out what it can do.... How does over 1000 fps with JSB 25.4 gr. Kings sound (over 57FPE) ?.... I initially set the hammer travel plunger flush with the end of the hammer, which gives me a travel of about 0.6", roughly the same as a stock Disco.... I can increase the travel 5 turns (24 TPI) or about 0.2" from there.... I ran through the entire range of RVA travel from coil bind out 12 turns (16 TPI) which is 0.75" of preload adjustment.... I then increased the travel 3 turns (0.125") and repeated the procedure.... Here are the results....

Image

First comment is that coil bind occurs 2 turns further out on the RVA with the additional 1/8" of hammer travel, which makes perfect sense.... I noticed that at high preload the increased travel actually lost a few fps, and I was wondering if the outside rim of the hammer was hitting the valve, limiting the lift in that situation.... I selected three different RVA settings, and ran the hammer travel through it's range to find out, with the following results....

Image

4 turns out on the RVA is the most preload I can use that will not cause the spring to go coil bound with the maximum hammer travel (5 turns).... You will note that there is a small but definite LOSS in velocity with increased travel.... At 9 turns out, the velocity increases as you increase travel, reaching a peak at 4 turns, and then drops.... At 12 turns out (minimum preload), the velocity increases steeply as the travel increases.... That is as per the expected behaviour, as not only does this style travel adjuster increase the travel, but as the preload is constant, it also increases the cocked spring force, so with light preloads, you're getting twice the bang for the buck, and power increases steeply....

For both the 4 turn and 9 turn out RVA settings, there is a downturn in velocity at 4 turns out.... My assumption is that is the point where the outer rim of the hammer is hitting the back of the valve, limiting valve lift.... It would appear, therefore, that is the maximum travel the gun can make use of without further modifying the back of the valve to allow the momentum of the hammer to carry it further.... Is this worth doing?.... Considering I will never run the gun at those high power levels, probably not.... The efficiency would be terrible at the long dwells associated with that much lift.... At 2000 psi, I would likely not run this gun at over 950 fps even if it was tethered.... That means at least 9 turns out on the RVA at minimum hammer travel, even less if the travel is increased.... A good solution, at least for further testing, would seem to be to set the travel at 4 turns, giving a hammer travel of about 0.77".... This will result in very low preload on the hammer spring.... I may well need to try a shorter and/or weaker spring as I'm running out of room to decrease the preload to allow tuning the gun.... This problem will increase at lower pressures....

I'm going to have to ponder these results for a while to decide where to go from here.... I'll probably do some testing at 1600 psi to accumulate more information before making any changes....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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