XS60C PCP Repeater project

[stalwart]

The longest stroke we can have, with the bolt as the cocking lever, is about 35mm... with a separate lever, we can have 62mm... or by moving the valve forward, up to 130mm or so. I don't see the latter happening.

I plan to work with the 30-35mm set up for now, to get a feel for all this. The "through" tube design is pure potential. More than we can ever use.

[rsterne]

So the distance from the sear to the back of the valve stem is about 62mm?....

Bob

[RHytonen]

Your question about maximum power with accuracy will vary barrel to barrel, unfortunately.... I have never found anything heavier than the 18 gr. JSB Exact Heavy that shoots accurately at 50+ yards in ANY of my guns, so that limits you to about 36-37 FPE (950-960 fps with an 18 gr. pellet).... You can probably get a bit more power than that in .22 cal, but if you can't hit anything, does it really matter?....

LW barrels are 23.8" long, although you can custom order longer....
Bob

For perspective, I've read about 1700's and 1800's' airguns used in European (and even American) militaries, to kill (i.e. "effective") at 100 yards using only 800 psi charges (in interchangeable charging "flasks" that doubled as the stock and curiously had the outline -though revolved into both planes- of the PB stocks used even today.) They shot .462" lead ball ammo, traveling at 500f/s, and had 4' long barrels- and this "Girardoni" gun (supposedly used by Lewis & Clarke) had a shot count of 80 (the size of their primitive gravity magazine/loaders) per charge flask! Hence, I guess, my fascination with much longer barrels.

(http://www.defensemedianetwork.com/stories/the-girandoni-air-rifle/
&
http://military.answers.com/military-weapons/the-girandoni-air-rifle-and-the-lewis-clark-expedition)

Especially a later Japanese version reportedly accomplished similar feats using a huge external hammer spring and mechanically extended the valve's dwell with a sort of lever/cam arrangement along the leg of a long (actual) hammer. From the pics it looked much like a flntlock PB.

The point being that modern technology should at least be able to duplicate that efficiency and power usable on larger game. And we can make 3000psi and more. But they had only 800, .462cal. and 4' barrels.
Is there some possible (non electronic) independent control over valve dwell that we might explore?

[RHytonen]

Your question about maximum power with accuracy will vary barrel to barrel, unfortunately.... I have never found anything heavier than the 18 gr. JSB Exact Heavy that shoots accurately at 50+ yards in ANY of my guns, so that limits you to about 36-37 FPE (950-960 fps with an 18 gr. pellet).... You can probably get a bit more power than that in .22 cal, but if you can't hit anything, does it really matter?....

LW barrels are 23.8" long, although you can custom order longer....
Bob

For perspective, I've read about 1700's and 1800's' airguns used in European (and even American) militaries, to kill (i.e. "effective") at 100 yards using only 800 psi charges (in interchangeable charging "flasks" that doubled as the stock and curiously had the outline -though revolved into both planes- of the PB stocks used even today.) They shot .462" lead ball ammo, traveling at 500f/s, and had 4' long barrels- and this "Girandoni" gun (supposedly used by Lewis & Clarke) had a shot count of 80 (but the size of their primitive gravity magazine/loaders was only 22 rounds) per charge flask! Hence my fascination with much longer barrels.

(http://www.defensemedianetwork.com/stories/the-girandoni-air-rifle/
&
http://military.answers.com/military-weapons/the-girandoni-air-rifle-and-the-lewis-clark-expedition)

Especially a later Japanese version reportedly accomplished similar feats using a huge external hammer spring and mechanically extended the valve's dwell with a sort of lever/cam arrangement along the leg of a long (actual) hammer. From the pics it looked much like a flntlock PB.

The point being that modern technology should at least be able to duplicate that efficiency and power usable on larger game. And we can make 3000psi and more. But they had only 800, .462cal. and 4' barrels.
Is there some possible (non electronic) independent control over valve dwell that we might explore?

[rsterne]

The Girardoni was one of the most hyped, overrated airguns in history.... The results they claimed are NOT possible, even with modern technology, using the fill pressures and volumes of the day, or even with increasing those as in the modern replicas.... Here is one example....  http://www.gatewaytoairguns.org/GTA/index.php?topic=49656.0

The "lock" mechanism they used was a rotating cam which had no provision for feedback based on the reservoir pressure, giving basically a timed release of air which of course meant less air with every shot as the pressure dropped, just as seen in that modern replica.... The Lewis and Clark gun no doubt impressed the Indians with it's ability to provide killing power for a few shots on a fresh charge, but as a long range infantry weapon it was a lot of hype....

Once again, if it sounds too good to be true, it probably is.... Any attempt at using a (constant) timed or measured (by volume) release of air from a reservoir that is dropping in pressure, without some sort of feedback (self-regulating) mechanism that changes the dwell inversely to the pressure, will produce the first shot the most powerful and then decreasing power after that as the pressure drops.... The common solutions to this problem are currently the "strike open" self-regulating valve, a regulator before the valve so that it sees constant operating pressure, or electronic control over the dwell as used in the Crosman Rogue....

It is commonly suggested to use a "dump valve" to release a precisely measured amount of air, much as is done in MSPs, but that is a terribly inefficient method as much of the air released is wasted after "Elvis has left the building".... With your engineering background, you would probably enjoy wading through what we refer to as the "Geek Gate".... http://www.gatewaytoairguns.org/GTA/index.php?board=164.0 .... There are many threads there with huge amounts of data and discussion that you may find very enlightening.... and in which you are welcome to partake....

Bob

[stalwart]

So the distance from the sear to the back of the valve stem is about 62mm?....

Bob

From the sear (trigger group back on Gen1) to the face of the block... roughly 2.5".

What's the most length we want the stem to protrude?

[rsterne]

It depends a bit on the caliber (and bullet weight), but about half the throat diameter is roughly the maximum usable lift.... at the low pressure end of the shot string.... I have a 0.160" limit on my quarterbore Disco, and the only time it gets there is with what is basically a dump shot.... If you allow 0.200" maximum you should be fine for up to .30 cal, you might want a bit more for a .357 with boresize porting.... However, running such high lift REALLY wastes air....

Bob

[stalwart]

Given that I can provide access through the mag slot floor, what is keeping us from putting an adjustable valve stem in these?

What could you accomplish with only that and a quality pre-load adjuster?

[rsterne]

Not sure what benefit an adjustable valve stem is, unless you are doing a bstaley mod, on an unregulated PCP.... If you limit the travel to reduce the power, then on the low power settings you end up with a "start fast, reducing velocity" shot string as the pressure drops.... Self-regulating valves depend on increasing lift and dwell to counteract the dropping pressure to produce the usual "bell-curve" shot string....

In a regulated PCP, then you could use variable lift to change the power instead of doing it with preload.... I have a feeling that for low power settings you wouldn't get the increase in velocity below the setpoint that you get using preload, the velocity should drop immediately below the setpoint if you were limiting the lift.... On the other hand, that would mean you couldn't tune to get a few extra shots below the setpoint like you can with the preload set on the "knee" of the curve....

Bob

[stalwart]

The single shot, big bore, proto receiver. 30mm stroke, 40mm tail.

I'm going to bond the receiver to the tube. There is nothing to be gained by keeping them separate, and with the valve bonded to the block, this eliminates 3 screws... which allows retention of quite a bit of striker weight. It'll be stout.

[rsterne]

Anything besides glue holding the receiver to the tube?.... I'm just thinking of recoil working it loose....

Bob

[stalwart]

Between having plenty of surface area, and the fact that any loads would be pure shear... I'm confident it will hold. Before I put any of this up for sale, I'll dupe the surface area in a defective receiver, and sledge hammer it to destruction. If I see anything I don't like, I can always resort to a press fit.

The R trigger group mount/stock mount would act as a block, too.... but I seriously doubt it could come to that.

[rsterne]

Have you given any thought as to how you are going to mount the stock once you cut it off even with the front of the receiver for a bottle?....

Bob

[stalwart]

Yes, but have not decided on anything. I left a wide band around the tube at the front to use, if I need it.

[RHytonen]

.....I have never found anything heavier than the 18 gr. JSB Exact Heavy that shoots accurately at 50+ yards in ANY of my guns, so that limits you to about 36-37 FPE (950-960 fps with an 18 gr. pellet).... You can probably get a bit more power than that in .22 cal, but if you can't hit anything, does it really matter?....

Bob

I keep coming back to that statement and wondering (honest curiosity, not facetiously or antagonistically at all) how it is that .22 pb's are accurate at well over 50yards - and the big airguns reach out with 200 ballpark FPE at at 100-200 yards. Seems like we should be able to get distance accuracy with enough power and heavy pellets.
Aero? Most of the heavy pellets are shaped more like bullets anyway.
Power? We're pretty much there too. The .40-.50 cal airguns don't use any more than 3K (-4.5K?) psi, do they? We can make big valves, and the multiple ports thing in the FD PCP Gen II(which I just realized , never having seen it mentioned, in finallly getting around to stripping my new gun)  shows great promise by defeating the "pellet size" limitation of just one big port. What happens if we make those just a *little* bigger (there;s abut a cm betwee them,) and feed it with more valve and rec'v'r. exhaust size...we could even thin the barrel -again, a *little*, increasing the channel that feeds them around the barrel. But first I have to  get rid of the plastic that seems to have sneaked its way into my gen II. I'm not going to get the explosive hammer impact or the valve dwell increase I want, with any plastic absorbing impact, decreasing the stroke (why is that spacer there?) or defeating inertia components. Again, I very much like the way Eric's going with the heavier hammer (striker) and longer stroke. What I want is an "air hog," whose "waste" I can then use to make power and distance (and accuracy) with a much longer barrel and really heavy pellets.  "Big Bore" is the next "Dark Side" (Now let's  make IT affordable too,) And those two little extra barrel ports remind me of what Rotax did with their kart racing rotary valve 2-strokes in the early 80's. The limitation of exhaust port widths that the piston rings could fall into, was a direct analogy to our airguns' pellet caliber (barrel diameter) port size limit.

[rsterne]

I've never found those radial port worth it, they were used in the RWS 850 and the gun worked better with just one large lower port.... Same for the Hatsan valve, it works better if you plug 5 of the 6 holes to get rid of the wasted volume and enlarge the remaining single port.... I've never seen a Gen 2, but I assume that's what you're talking about.... The problem is the wasted volume around the barrel as a "collector", and all the multiple corners.... Any volume between the valve seat and the pellet drops the initial pulse of pressure and wastes power....

If somebody comes up with a pellet in the 25 gr. range that is ACCURATE then .22's will take a big jump in power.... I have my Hayabusa .224 shooting a 41.5 gr. bullet at 100 FPE with good accuracy, and in Holland they are drilling 11mm groups with it at 100M (0.4 MOA @ 110 yds).... so yes, it can be done.... but the velocities are still limited to subsonic....

It all comes down to the limited power of airguns and transonic drag....

Bob

[stalwart]

I've been messing around with this idea: I'm calling it a "V port".

Plenty of plenum could be eliminated by cutting at just enough height to fully clear the bore, and by using a ball end mill... but you get the idea. Both ports are bore size in length (.177), and even wadcutters feed beautifully.

[stalwart]

With the right dia ball end bit, at the right angles and depth, you can achieve 2 slot shaped ports of extremely excessive size.... without the base of the port being any bigger than the red outline. I'll get the flow of this experimental cut, but have a stronger bridge that is still slim enough to impede flow as little as possible.

I'm looking at finding the biggest square exhaust port I can fit into a stock valve. That will determine the barrel port's base size maximum (potential), and I'll see how close I can get to a decent .357 port before resorting to a custom valve body (which would allow port slots as long as we want).

[RHytonen]

With the right dia ball end bit, at the right angles and depth, you can achieve 2 slot shaped ports of extremely excessive size.... without the base of the port being any bigger than the red outline. I'll get the flow of this experimental cut, but have a stronger bridge that is still slim enough to impede flow as little as possible.

I'm looking at finding the boiggest square exhaust port I can fit into a stock valve. That will determine the barrel port's base size maximum (potential), and I'll see how close I can get to a decent .357 port before resorting to a custom valve body (which would allow port slots as long as we want).

Now that's what I'm talkim'bout....

If I had the spare parts, a mill and a lathe, I'd be trying this sort of thing.
I really like the way you think.

I'm just working on the more conservative ideas of others right now
until I can at least afford a second valve...... barrel.......receiver....striker..... LOL

Right now I just need to be able to air it up, with my bad back.

(And, I just thought of something -
They BETTER not put any ~plastic~ in there when they cut me open next month!)
.oO (get it in writing, Rod......how would you check?)

[RHytonen]

I've been messing around with this idea: I'm calling it a "V port".

Plenty of plenum could be eliminated by cutting at just enough height to fully clear the bore, and by using a ball end mill... but you get the idea. Both ports are bore size in length (.177), and even wadcutters feed beautifully.

Beautiful...
I bet NOW the quality of those barrel O-rings is starting to matter...

What are your latest valves looking like? Two ports?