XS60C PCP Repeater project

[airpuffhunter]

congratulations Bob, excellent results

[StevenG]

Congradulations. The fact that this all starts from a $100 PCP is just amazing. Not that there is anything wrong with the FDPCP, love mine, just stunning to see it turned into this.

I am guessing cost is why the Carnivore is not as good? Or is hatsan simply not paying attention?

[rsterne]

The Carnivore weighs 9.3#... what do you think the Grizzly will top out at?

My guess is 7lbs. 9oz.

Nope, too heavy.... It weighs.... *drum roll please*....  6 lbs. 14 oz. 

Bob

[moorepower]

Dumb question Bob, but how much more drop would a .30 pellet have than a .25 bullet of similar weight? At say 100 yds.

[rsterne]

Starting with equal velocity, and talking pellets, not bullets (eg. .25 cal JSB King to .30 cal JSB), the larger caliber has a better BC, and hence less wind drift and slightly flatter trajectory.... That is why they are winning events like the Extreme Bench Rest, which was won with the .30 cal barrel we are using in the Grizzly....

Comparing pellets of equal weight in different calibers is a muggs game, because you can't achieve the same velocity in the smaller caliber in an equal gun.... However, to answer your question, if you started two pellets of the same weight, at the same velocity, the smaller caliber would have the better ballistics.... It would just take some combination of longer barrel, more pressure, or more air used, to get it there in the first place....

Bob

[Kailua]

This repeater project has been a wild journey.  Thanks to you and Eric I have learned a lot.  By they way is that 6lbs 14oz with the stock?

[rsterne]

Yup, complete but no sights.... just weighed it to answer your query....

Bob

[moorepower]

I am sure it is some where in this 46 pages, but I can't seem to find how long the .30 barrel is?

[Kailua]

Yup, complete but no sights.... just weighed it to answer your query....

Bob

Light and powerful that is awesome.

[stalwart]

Yup, complete but no sights.... just weighed it to answer your query....

Bob

Light and powerful that is awesome.

Not to mention agile, and stout.

These results have confirmed, to me, that these rifles are deserving of even more development. This is something I have believed for a long time... we are nowhere near done yet.

[RHytonen]

I assembled the prototype Grizzly this morning, and conducted some tethered tests at 1800 and 2900 psi.... Here is what the gun looked like during this testing....



 I didn't seal the tube to the receiver at the transfer port, so it blows a big slug of air out the slot in the bottom on firing.... This was expected....

Bob

Did you mean "tube" - or valve?
i.e., was the through tube just inserted without glue, or what?

Just trying to understand...

Rod

[rsterne]

The .30 cal barrel is 25" long, plus about 3" for the Hatsan Air Stripper....

I checked the maximum velocity with the regulated setup this morning, and after a bit of head scratching, combined with yesterday's results, I decided that the setpoint was more like about 1900 psi, and the performance was a little less than I wanted, with more shots than I needed.... Soooooooooooo I drained the tank, pulled the regulator apart and added a 0.010" shim, which should add about 300 psi, bringing the setpoint up to ~ 2200.... I then reassembled the gun and ran through the preload settings to chart out the maximum velocity with the three pellets, and what preload settings were required.... While I was doing this, I also measured the valve lift by using an O-ring on the end of the spring guide as I mentioned earlier.... Here are the results....



Notice that the extra pressure moves the position of the "knee" of the curve up about 2 turns compared to the 1800 psi graph published earlier.... pretty much the 200 psi per turn I predicted earlier.... Next, take a good look at the Lift curve.... I'm sure you will be surprised at how little the valve really opens.... I allowed 0.200" of room when I built the Grizzly, knowing that I have never seen a PCP require that much lift when operating efficiently.... Sure enough, with pellets, any lift about 0.090" doesn't increase the velocity but just wastes air.... For the bullets, that occurs at about 0.100".... The throat in this valve is 0.266" in diameter, and a third of that is 0.089", so once again, you certainly don't need to allow more than half the throat diameter for maximum valve lift.... Maximum power levels at 2200 psi were 102 FPE for the 44.8 gr. JSBs, 107 FPE for the 49.4 gr. Daystates, and 121 FPE for the 6.8 gr. Bob's Boattails.... The Grizzly is solidly in the 100 FPE class at 2200 psi, even with pellets.... 

Based on the above data, I filled the tank to 3000 psi, topped it up after a few minutes of cooling, and set the preload to 2 turns in from zero.... I shot a string with each pellet, and the pellets were shooting a bit hot (the Daystates were right at 100 FPE for 12 shots) and not very efficient, but the bullets were virtually perfect.... I then repeated the strings with the pellets with the preload reduced by a turn, to just 1 turn of preload, and plotted the three strings on the graph below....



All three pellets produced usable strings (2% ES) over two magazines.... The 70 gr. BBT bullets averaged 110 FPE over 14 shots, ending at 1880 psi, for 0.90 FPE/CI.... The 50 gr. Daystate pellets averaged 94 FPE over 18 shots, ending at 1960 1900 psi, for 1.07 1.01 FPE/CI.... and the 44.8 gr. JSBs averaged 92 FPE over 17 shots, ending at 1950 psi, for 0.98 FPE/CI.... Note there is a slight bump in the velocity with the 70 gr. and 50 gr. just below 2200 psi, which indicates that they are operating right on the knee of the curve, and the strings extend about 200 psi below the setpoint, with the last usable shot taken at right about 2000 psi.... The pressure graph shown was using the 50 gr. Daystates.... It would be an easy matter to tune whatever pellets ended up being the most accurate in your gun for slightly higher or lower velocity with the corresponding change in shot count.... ie more power, fewer shots, and vice versa.... Overall, I think that having a regulator setpoint of 2200 psi suits my goal for the gun better than 2000, although using the lower pressure you can tune down a bit and get three magazines with the pellets.... Don't forget, I still haven't sealed the tube to the receiver at the transfer port, so I'm getting a pretty large blast of air out from under the magazine with every shot.... In addition, I haven't experimented with different hammer springs.... so I'm sure there is more efficiency lurking in the Grizzly, yet to be found....

Rod, the tube is just inserted into the receiver, no glue, at the moment.... Leaks were expected on firing.... but I might have had to make changes, so delayed gluing it....

Bob

[RHytonen]

Here are the results, starting from a 2900 psi fill using my regulator....



.... If I tuned it for 14 shots, it would be over 90 FPE with those pellets, over 85 with the 45 gr. and over 100 with the 70 gr.... Those numbers were bang on what I was hoping for.... I'm getting a little bit of a "burrppp" from the gun at this preload, and the efficiencies are just under 1.0 FPE/CI because of the hammer bounce.... Running right at zero, or near zero, preload is always a bit of a problem, I think a different hammer spring (either lighter with more preload, or heavier rattling around loose) would reduce the hammer bounce and increase the efficiency.... However, even the way it is, it's a pretty stellar performer.... It certainly has the new Hatsan Carnivore beat....

Bob

It just gets more and more impressive, Bob!

What would it take to get the BBT's up to 900(+?) fps -
bigger ports, more air (bigger tube,) longer barrel, more hammer travel (lift?) higher reg pressure?

Which do you think would matter the most?

- Rod

[moorepower]

That would make a LARGE hole in a varmint.

[RMM]

I love these EUREKA moments.  Great job gentlemen. 

[rsterne]

The 70 gr. BBT hit 900 fps at 2900 psi with the 25" barrel operating at the knee of the curve (ie relatively efficiently).... and 940 WFO.... so it's already within the capability of the Grizzly, not just in regulated form with the 25" barrel.... Barrel length and pressure are pretty much interchangeable, so in theory, a barrel length of (2900/2200) x 25" = 33" should be able to deliver ~ 900 fps relatively efficiently at 2200 psi.... *listen to that man singing*....

Porting and hammer changes will not be necessary for your build, although you will need a bit more preload to extend the dwell slightly to take advantage of the longer barrel.... There will be TONS of hammer strike available, IMO.... The air tube (plenum) being longer to support the greater FPE won't hurt, of course.... the one on the Grizzly is ideal at ~ 100 FPE....

Bob

[rsterne]

I took the gun apart to chase down the leaks I had this afternoon.... When I was fitting the tube to the receiver, I decided to mount the stock using the lower screw hole in the valve.... That meant drilling a hole through the inner tube at that location, and I didn't think about that being between the two O-rings either side of the exhaust port.... When the gun was fired, some of the air travelled down between the valve and tube and blasted out the bottom.... My solution was to drill and tap the bottom hole of the valve to 1/4"-28 and use a shortened 1/4" bolt fitted with an O-ring as a plug.... The receiver is drilled out to 3/8" for the OD of the O-ring, which flattens against the tube when the bolt is tightened against the bottom of the receiver.... I blind drilled and tapped the center of the plug for an 8-32 screw which will mount the stock.... I think stalwart has an alternative stock mount planned so that he doesn't drill the tube at the bottom between the O-rings.... One of the little things that prototyping teaches you....



I shortened the spring guide by an inch as well, so that when the gun is cocked it won't hit the stock.... I can no longer use it to measure valve lift, but that part of the research is done now, so the spring guide just serves it's main purpose, and acts as a cocking indicator when the gun is out of the stock.... It is now 4 grams lighter, so the total weight of the hammer plus guide is now 102 grams....

The last job for today was to clean and glue the tube into the receiver with some silicone sealer around the transfer port.... This shouldn't be too hard to remove if I need to take it apart, and hopefully will seal up the leak around the magazine.... I'll let it dry overnight.... and hopefully tomorrow I won't have air blasting out on every shot.... except out the barrel, of course....

Bob

[RMM]

A month or more ago I was working with a 60 valve that had a bad valve stem seal.  The pic shows how I fixed it with a -.006 o-ring.  With the Delrin washer in place holding the o-ring the backer block keeps both from blowing out.   

[RHytonen]

The 70 gr. BBT hit 900 fps at 2900 psi with the 25" barrel operating at the knee of the curve (ie relatively efficiently).... and 940 WFO.... so it's already within the capability of the Grizzly, not just in regulated form with the 25" barrel.... Barrel length and pressure are pretty much interchangeable, so in theory, a barrel length of (2900/2200) x 25" = 33" should be able to deliver ~ 900 fps relatively efficiently at 2200 psi.... *listen to that man singing*....

Porting and hammer changes will not be necessary for your build, although you will need a bit more preload to extend the dwell slightly to take advantage of the longer barrel.... There will be TONS of hammer strike available, IMO.... The air tube (plenum) being longer to support the greater FPE won't hurt, of course.... the one on the Grizzly is ideal at ~ 100 FPE....

Bob

THANKS again!

Now, where can I get a PEEK Mrod poppet/stem?


-Rod

[rsterne]

You don't need one.... PEEK is only needed when the combination of diameter and pressure exceeds the ability of the MRod poppet not to extrude through the throat of the valve.... We aren't there yet, nor do we need to be.... A PEEK valve is slightly easier to open because it is harder to compress.... but when used in an application that doesn't require it, it is more difficult to get to seal....

Bob