XS60C PCP Repeater project

[stalwart]

Ready when you are, Rod. LMK what length trigger job you want, and I'll set one set aside.

Been doing gas ram striker (GRS) homework... and, as usual, it looks like the best way is the most expensive. Although there are plenty of smaller (easier to mount, and cheaper) rams made, the N Forcer has something no one else does: It can be recharged to any pressure needed. All I need is a Nitrogen tank, regulator (for well over 400psi) and fittings. Ouch.  I'm currently looking for a regulator system that goes high enough.

So far, the best price I've found for a regulator that will go over 500psi (over 40# spring force), is $400. I won't need it for GRS, but, it would allow me to recharge springer rams to custom pressures (at some point, all these tools have to pay for themselves).

[student1946]

The gas rams you are talking about are,correct me if I'm wrong,much smaller than any PCP reservoir.You can probably charge them to whatever pressure you wish with very few strokes of any pcp hand pump with the proper adapter.Lots of used ones out there,some for less than 200.00.Not so much fun for charging air rifles but ok,I would think for gas rams.I used to have a Beeman pump for my RX1 and it was puny next to even a Marauder pump.Not much work to pump below 1K.Just a thought.

[tominMPLS]

Eric, did you really mean #4000psi and not #400psi?  Something sounds wrong to me!

Glad to see you are keepin' on keepin' on!

Take care,

Tom

[rsterne]

Something to watch RE gas rams.... some of them have a maximum operating speed (ram speed).... I found one beautiful little miniature ram that looked great until I got to where it said maximum ram speed was 1.6 m/s (just over 5 fps).... The hammer in my Grizzly is travelling about 14 fps at impact, and depending on the hammer weight and stroke, you might need even higher ram speeds.... I don't know what the N-Forcer specs are in that regard.... but I can tell you that a 19mm OD unit with a 25mm (1") stroke is big and heavy....

I would agree, you can easily charge a gas ram with air from a PCP hand pump, but it would be air, not Nitrogen....

Bob

[stalwart]

Tom, the pressure needed to create 40# of force, in the MF19 N-Forcer, is 400psi. Yeah, still kickin'

Bob, I wrote CS about speed and price... we'll know soon. And, the MF19 will fit in precisely the same space as the 40mm tail set up... no stock mods needed.

We'll have a ton of striker weight, even without moving the mag forward (always an option).

The gas rams you are talking about are,correct me if I'm wrong,much smaller than any PCP reservoir.You can probably charge them to whatever pressure you wish with very few strokes of any pcp hand pump with the proper adapter.Lots of used ones out there,some for less than 200.00.Not so much fun for charging air rifles but ok,I would think for gas rams.I used to have a Beeman pump for my RX1 and it was puny next to even a Marauder pump.Not much work to pump below 1K.Just a thought.

I looked into the comparative compressibility of air and N, but started getting lost in the math right away. Found no simple charts or ratios.

[rsterne]

Air will work fine, Nitrogen is preferable because it is dry and doesn't leak through seals as easily as air.... All that means is that the oxygen in the air might leak out a bit over time and you might have to test the pressure and top it up.... after a few years?.... Nitrogen and air both act as ideal gasses (and essentially the same as each other) until you go above about 3000 psi, so not to worry....

Because you will only need about 10# of uncocked force on the ram, your pressure will be really low.... like 150 psi?.... The problem is that at really low pressures, the rate change with compression is higher (less constant force), more like a conventional wire spring....

Bob

[stalwart]

That's really good new$.

Between the fine and extremely wide adjustability of the system, and the reduced (or eliminated?) bounce, I'm intrigued. Given that anyone can supply the psi needed to go from mild to wild, I'm now thinking of a fixed position ram, with a fosters sticking out.

[QVTom]

Bob, how is the rate of compression higher at higher pressures?  Is the ratio not fixed?  Explanation below.

The force differential of a gas spring is based on the volume extended and the volume compressed.   Fill pressure doesn't change the ratio.  Typical gas spring has a piston rod ~20% of total volume. 

One consideration as you reduce the fill pressure is the the seal drag becomes more prominent.

Tom

[rsterne]

You're right, Tom, not thinking clearly here.... The N-Forcer rams have a 30% increase in force between extended and compressed, so unless you get down to really low pressures where the difference between gauge and real pressures starts to be an issue, that ratio would be maintained.... At 0 psi gauge (and hence zero force extended), the ratio becomes infinite, however, providing the compressed force is enough to overcome the friction of the seals.... At 100 psi gauge, the change in percentage force would be from 1.3:1 to about 1.5:1, would it not?....

Bob

[stalwart]

I'm willing to cheerfully put up with a few more pounds of cocking force, to get past plenty of seal drag... as it is our bounce damper.

[QVTom]

You're right, Tom, not thinking clearly here.... The N-Forcer rams have a 30% increase in force between extended and compressed, so unless you get down to really low pressures where the difference between gauge and real pressures starts to be an issue, that ratio would be maintained.... At 0 psi gauge (and hence zero force extended), the ratio becomes infinite, however, providing the compressed force is enough to overcome the friction of the seals.... At 100 psi gauge, the change in percentage force would be from 1.3:1 to about 1.5:1, would it not?....

Bob

Bob, I have experience with the MF25 but not the 19.  I believe the design is the same other  than the diameters of the rod and housing.  There is some dead space in the back of the housing where the valve is so the piston does not quite displace as much volume as expected.  I'd say the 1.3 is a good estimate.

The breakaway force on the seal is quite stiff, maybe about 4 to 5 lbs unpressurized so I'd expect more under pressure.

Tom

[stalwart]

They got back to me right away. In it's entirety:

"Good Evening,

We test units for seal life at 140 strokes per minute. For a 2" stroke it's 1 million cycles for leakage. We do not test for speed!
1 piece MF19X25 is $43.75 we need to know the pressure to charge the cylinder too
We accept VISA and MASTER CARD

Please note: MF19X125 is $46.95

Thanks,
Lauren ".

So, it looks like we'll have to learn that ourselves.

[RHytonen]

Ready when you are, Rod. LMK what length trigger job you want, and I'll set one set aside.

Short, please. I have small hands (yet played the piano, organ and guitar...go figure.)

Just had a nice talk with Lloyd. He had just one mag of the pair I ordered left (it's coming Mon.)
but is expecting more in 2 weeks or so. He's saving me two more after this, for next month.

I should be done with everything by the beginning of August and then we can start.
The bolt retractor is gonna work!-
I'm using the corkscrews' second (upper, on the gun) pinion gear (-just two teeth of it actually-)
which I was going to discard, and reversing it with a guide-captured push-link from (each of) the main handle(s) just before the 'home' end of their stroke. Simplest I could get it so far.
I have a 1.5" stroke for the bolt (before an 8-9mm retraction.) I want the mag here so I can see if that's enough. If it works with these sloppy tolerances I can think about duplicating the corkscrew's mechanism with much better tolerances, and tweak along the way for more stroke etc..

[QVTom]

They got back to me right away. In it's entirety:

"Good Evening,

We test units for seal life at 140 strokes per minute. For a 2" stroke it's 1 million cycles for leakage. We do not test for speed!
1 piece MF19X25 is $43.75 we need to know the pressure to charge the cylinder too
We accept VISA and MASTER CARD

Please note: MF19X125 is $46.95

Thanks,
Lauren ".

So, it looks like we'll have to learn that ourselves.

There is a German manufacturer of gas springs which the name escapes me at the moment.  They have substantial tech data online and they do have a spec. for maximum rate of extension.

Tom

[rsterne]

I just had a ridiculously simple idea that might reduce, or even eliminate hammer bounce, while making a gun easier to cock.... emulate the forces of a gas ram with a simple coil spring....

Put a positive stop for the spring, possibly an internal one, that prevents it from extending fully.... and have that stop the spring 1/8" before the hammer hits the valve.... Instead of using a heavy spring that has zero preload and let's say 20 lbs. of force when cocked, use a longer spring with a lower rate (about half?) so that the spring when against the stop has, let's say, 5 lbs. of preload.... When cocked, the force, with the correct choice of spring, could be about 15 lbs. instead of 20 lbs.... but when the hammer rebounds to hit the spring and recompress it, instead of hitting a spring that has zero preload (and hence is easy to compress), it hits a spring that already has 5 lbs. of preload.... The hammer impact might not even be enough to recompress it, and if it does, not very far.... The average spring force available to accelerate the hammer is 10 lbs. either case.... Also, in either case, the hammer is being accelerated for 7/8" of travel (assuming it moves 1" from cocked to valve contact, with 1/8" of free play (negative preload).... In both cases, the hammer energy should be the same, or very close....

What do you think?.... With the heavy spring, rattling around, the cocking force starts at zero and increases over 7/8" of bolt travel to 20 lbs.... With the light spring, preloaded against a stop, the cocking force starts at 5 lbs, and increases over the same 7/8" of bolt travel to only 15 lbs.... The spring and stop would have to allow the hammer to move away from that assembly without drag, of course, so that is the technical problem to overcome.... but I think it should work just fine.... The same problem exists with a gas ram anyway, the hammer must not drag on the sides of the ram....

Bob

[stalwart]

Makes sense to me! Given that you already know the forces you are dealing with, your idea would be directed at bounce, therefore efficiency, the new shot count would tell you all you need to know... right? If I get the picture here, your idea would incorporate your existing adjuster?

The GRS setup would only contact the striker (solid slug) at the very tip of the ram. There is just enough room for the ram (in the original stock), before trigger placement becomes an issue... post #438 shows a 26mm set up, to give you an idea.

I'm first going for all the force I can generate with 1" of stroke, to find the limits of that, then that will tell me if we have to use any more of the 2.5" the design can allow us, to get to the .357 I have been pondering for nearly a year. I need to come up with a modular design, so anyone can go up or down in both caliber and power at will (without needing me... I've got work).

[stalwart]

There is a German manufacturer of gas springs which the name escapes me at the moment.  They have substantial tech data online and they do have a spec. for maximum rate of extension.

Tom

If you think of it, please say something.

I'm going to proceed with the MF-19 for now. I have 1 of their 25s in a springer... really like it, and feeling that initial "stiction" is what gave me the idea to put it to use as a damper. My experience with anything like this is HP suspension... and that drag is something you fight to eliminate many times (MC forks especially).

I really need to know just how much weight we can sling around, under control.

[rsterne]

Yes, only the tip of the ram should contact the striker.... The gas ram still has the advantage of a relatively small ratio of force from extended to compressed, which would be very difficult to obtain with springs.... The N-Forcer is only 1.3:1, my example above was 3:1.... However, a stiff, short spring with negative preload has an infinite ratio of compressed to extended force, and is the hardest to cock of all possible solutions for a given hammer energy....

Bob

[stalwart]

The N-forcer has an M6 fill port. Aren't there "probe" style fillers available that fit these? If so, where would I find one? I like the idea of needing no wrenches to top these off.

[RHytonen]

Eric and Bob, would it be correct to say, the XS60 factory bolt probe deposits a boolit (or a pellet, if the 'probe' was almost a caliber thick) about 5mm past the port, when fully extended?
At least that's what  think I'm seeing on my stock gen1 receiver.

In other words, it could be 5mm shorter if it was being retracted to clear the port at the end of the loading stroke?
If it was 5mm shorter, would that be enough to clear the grizzly's mag?
Or would you still need to cut the bolt handle slot's back end a few (guessing about 3) mm?