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radar · Silver Status Member

Incredibly cool stuff rsterne and Gipetto.
I know I'd rather have a 9mm Disco mod than an apparently delicate, high tech Benji Rogue that depends on a battery and microchip to function, and can't even be refilled with a hand-pump.
Please, no offense to Rogue owners. They are cool, but I hate the idea of electronic regulators on a gun. I only want stuff that is more-or-less permanently "off-the-grid" when it comes to shooting. (I know I need to buy or make ammo, but still...)

-Rob

domer_pyle · Senior Member

They should have left the adjustments manual like the M-rod but with easier to read knobs instead of hex screws. And also not make it look like it's from some futuristic military action-shooter. I'll never own one but they do look a bit goofy, and illuminated screens and computer parts belong in your pocket when hunting, not as part of a rifle lol

rsterne · Moderator

I spent a bit of time in the shop today.... it sure felt good to be back out there.... I tried a 1.75" long 0.045" wire hammer spring, and also the same length from 0.051" wire.... The lighter one wasn't as good as the 2.00" long one I tried previously, and the heavier one was only marginally better, peaking at 736 fps.... but it was VERY difficult to cock.... So far (with the stock hammer) the best spring is the 2.00" long x 0.045" wire one....

I had a few 132 gr. cast bullets that had been sized to 0.357", and tried them out.... They were VERY hard to load, I actually had to tap the bolt closed.... They only hit 540 fps (85.5 FPE), probably because of the tight fit.... I will have to get a smaller sizing die to use with this barrel if I want to try anything other than the EunJins....

The next project is to make a new hammer with rear cocking knob and the ability to accept longer/stiffer springs....

Bob

SMP · Silver Status Member

Nice

....I'll bet you've been just itching.

I think I asked this before but are you using a bullet lube?

? on the new hammer. Are you going heavier or just redesigning to facilitate a longer spring?

rsterne · Moderator

No lube.... just a wipe on the sizing die when required....

The hammer will be cylindrical (ie no "waist", and therefore heavier).... It will have a shaft threaded into it which will protrude through a hole in the RVA adjusting screw and a knob on the end for cocking.... but it will also have a cocking pin hole so could be used either way.... The shaft will also act as a spring guide....

I have some 0.360" OD springs that are 2.5" long (similar to a QB spring)so I will likely make it to fit those as well.... I may need two different shafts/spring guides....

Bob

rsterne · Moderator

I got some time in the shop today, so I made a rear-cocking hammer for this gun.... The hammer is cylindrical (ie no waist) and the same length as a stock Disco hammer.... It is drilled deeper for the longer hammer spring, and also drilled and tapped 10-32 for the spring guide / cocking rod.... The hammer spring is 2.5" long x 0.360" diam, and I have 2 wire sizes, the smaller being virtually identical in spring rate to the hammer spring in a QB78.... I installed a stock cocking pin so that the hammer can be used in self-cocking mode if desired....

The combined weight of the hammer, cocking rod, and knob is 90 gr.... which is 50% heavier than a stock Disco hammer.... The hammer alone is 59 gr.... and the total weight can be adjusted by changing the weight of the cocking knob.... The barrel of the adjuster is made from aluminum, and the screw is made from a 3/8"-16 stainless SHSS, shortened, drilled, and two flats ground on it for an adjusting wrench....

The range of adjustment allows me to set the preload from zero, uncocked.... all the way to coil bind, cocked.... The knob is easy to grasp and the hammer is not difficult to cock even at full preload.... although with the heavier spring I'm sure it would be a bear to pull back.... I doubt that spring (which is twice as stiff) will be necessary anyway.... There is already a mark on the hammer from the sear, so before I install it I am going to harden it.... It is 1045 steel, so will harden easily by heating to a dull cherry and quenching in water.... Once it is hardened I will be conducting more tests to see if I can get this gun over 100 FPE.... if only for a few shots....

Bob

radar · Silver Status Member

I cut an aftermarket (OK, hardware store) spring to be at no preload, uncocked, with an otherwise bone-stock .22, and it gives me just over 300 fps. I was surprised it didn't valve-lock at 2000 psi. I need a better spring guide though, as it sometimes crooks and binds before coil bind preload, like even just adjusting it up from no-load. So for now I took it off. (In fact, the screw is trimmed to just below binding length so it cannot lock up the spring.)

It looks like your hammer spring guide protrudes into the hammer's spring recess, can you elaborate on this guide or did I miss something earlier?

rsterne · Moderator

The spring guide is also the cocking rod and is actually screwed into the hammer in front of the spring recess and moves with the hammer.... The rod is a bit small for the perfect guide for the spring and if the velocities are inconsistent I may slide a piece of brass tubing over it to increase the diameter and drill out the screw to 7/32" (from 3/16")....

Bob

radar · Silver Status Member

I see.

rsterne · Moderator

I got the hammer hardened and installed today.... It's very easy to cock even at maximum preload on the hammer spring (near coil bind).... The first few shots showed me that it's PLENTY of hammer hit to dump 2400 psi (or more), as the first shot over the Chrony was 835 fps with the 77.8 gr, EunJins (120 FPE).... I progressively backed down the preload until the second shot was the fastest (4 turns out) and then started shooting shot strings all the way down to minimum preload.... At 6 turns out from coil bind, the gun performed virtually the same as it did with the stock hammer running the 0.045" x 2.00" spring at maximum preload.... so between the heavier hammer and the longer, stronger spring I have gained a lot.... At 8 turns out (minimum) the velocity peaked at about 600 fps and at 7 turns out at about 700.... The other results are in the graph below....

The pressure graph is only approximate.... It's slightly different for each setting, but it gives you an idea of what is going on.... At maximum, the first shot was 835 fps and the second shot 809.... but the efficiency was only 0.71 FPE/CI.... At 4 turns out, I got a 3 shot string that peaked at 110 FPE (798 fps) and the efficiency jumped to 0.90 FPE/CI.... From there to 6 turns out, the gun was very sensitive to adjustment, so I shot strings every half-turn.... At 4.5 turns out I got 5 shots averaging 103 FPE (771 fps) and 0.93 FPE/CI.... At 5 turns out it was 6 shots averaging 753 fps (98 FPE) at 0.97 FPE/CI.... 5.5 turns out, the velocity averaged 734 fps for 7 shots, producing 93 FPE at an efficiency of 1.03 FPE/CI.... Finally, at 6 turns out, I got an 8 shot string averaging 715 fps (88 FPE) and the efficiency was 1.07 FPE/CI.... The last string started at 2200 psi, all the others started at 2400....

I'm very pleased with the results.... Basically I can choose anywhere from 3 shots at 110 FPE down to 8 shots at 90 FPE or anything in between.... I'm leaning towards the 5 shot string between 100-106 FPE as the best balance between power and efficiency.... One other thing.... I slipped an O-ring over the cocking shaft, so that I can measure directly the amount the valve opens.... idea compliments of Lloyd.... At 4.5 turns out and 2400 psi (shot #1) the valve opens about 0.060", increasing to 0.090" at 2000 psi (shot #3) and about 0.120" at 1600 (shot #5).... It's interesting to see the "balancing act" of hammer hit vs. pressure in action.... This hammer arrangement answered a lot of questions for me.... It certainly removes the inability of the Disco to dump large quantities of air.... and since I was having the same problem with my Hayabusa (insufficient hammer strike) I now know what I need to do to see some much bigger numbers from that gun as well.... Mr. Green

Bob

radar · Silver Status Member

Looking about done there? You can just go ahead and Fed-Ex me that puppy. I'll give it a good home.

rsterne · Moderator

I still have to try and get some bullets sized for the .308 barrel and try that out.... and I'd like to get a smaller sizing die for the cast .357 bullets I have.... In addition, there is a major addition going on this gun but I'm sworn to secrecy at the moment.... Mr. Green

Bob

maecolis · New Member

This is awesome Bob... And I have to say that this is porn for machinists and airgunners alike... Pardon the drool puddle. Mr. Green

oddtodd · Silver Status Member

One thing good about looking at airgun porn on the computer. No pages to get stuck together!! Twisted Evil

broommaster2000 · Moderator

This kind of airgunporn seems to go deeper then the normal "look what I've done with my stock". Wink