XS60C PCP Repeater project

[Yarp]

Coffee.... The drug of choice for voluntary insomniacs the world over.

[stalwart]

Guys, what would you think of a 60 that had the punch of a .25, but could also run 14.3gr CPHPs (and other fat ones) for plinking or pesting?

I've built quite a few guns with Marlin Micro Groove rimfire barrels, and they shoot well. I want to try one with bullets like these: http://northamericanarms.com/accessories/cb-accessories/cb-parts/cbb250.html , and I'm looking into other options. The NAA bullets will fit in a PRod mag, no problem.

I went straight to the Math Guy, and got this: "950 fps is 61 FPE, so at decent efficiency (boresize ports) that’s 61 CI of air per shot.... The FD-PCP tube is 7 CI x 69 bar = 483 / 61 = 8 shots.... I think there is a good chance to get 1 full PRod clip from 3000 psi down to 2000.... and you’d have something nobody else does.... a 60 FPE .22 cal bullet shooting repeater..."

I have had good luck with Duplicolor bed liner, shot thick and at low pressure for a nice texture, but it only comes in black. I just tried Rustoleum's tan, and got decent results. Here's a pic (including a trace of my mortal enemy...lol... bastid.) before I screw it all up with a local terrain camo job.

I'll post a pic of the finished job, if I don't embarrass myself too much.

[Yarp]

formidable

[avator]

Eric,

  I've found that if you do a thick base coat of bedliner and then cover with a nice, even top coat of whatever color paint you choose, a lot of the texture remains.

Good Luck.

[Chako]

This is really cool, it took me forever to read those wonderful 21 pages in this thread.  How much is it for the cheapest repeater?

[stalwart]

formidable

Well put.

Eric,

  I've found that if you do a thick base coat of bedliner and then cover with a nice, even top coat of whatever color paint you choose, a lot of the texture remains.

Good Luck.

Thanks... I think I'm going to need it... Yours looks great.

This is really cool, it took me forever to read those wonderful 21 pages in this thread.  How much is it to just mill the magazine slot and shorten the bolt?

YGPM

[stalwart]

As the MG barrels will be longer, there can be an added 1.3CI to the tube. Yay!

I have no experience with this yet, so I'm wondering if I put the adjustable port bolt in these, will they be a decent tune in both modes.... or, will they have to be tuned either for the pellets or bullets, and the off tune mode's efficiency lived with? After all, it's only air... unless you're the one pumping...   Any guesses?

If needed, I could go MG in the adjustable single, and find out... right after I finish a pistol run and a few rifles. Give me some time.

[RMM]

As the MG barrels will be longer, there can be an added 1.3CI to the tube. Yay!

I have no experience with this yet, so I'm wondering if I put the adjustable port bolt in these, will they be a decent tune in both modes.... or, will they have to be tuned either for the pellets or bullets, and the off tune mode's efficiency lived with? After all, it's only air... unless you're the one pumping...   Any guesses?

If needed, I could go MG in the adjustable single, and find out... right after I finish a pistol run and a few rifles. Give me some time.

When you presented an 8 shot monster .22 I was also wondering about a tune for each pellet.  I'm still in the experimental stage and learning as much as possible about PCPs and airgunning in general but my first thought would be tuning for a bell curve for one pellet, that curve will not work for another pellet of smaller or greater weight, an assumption mind you.  I'm hoping myself one of our forum experts can field this question in layman terms. 

 

[rsterne]

OK, guys, here is the deal.... In an unregulated PCP, making a drastic change to the pellet weight (like from an 18 gr. pellet to a 30 gr. bullet) will shift the curve.... If you tune it for the pellet, the fill, peak, and refill pressures for the bullet will all be lower (and the power down compared to what could be achieved), as the dwell will be way too short for the much heavier slug.... If you tune for the bullet, which takes a LOT more hammer strike, then when you use the pellet you will start off with the first shot the fastest (probably supersonic) and the rest declining.... The only possibility I can see, without a drastic hammer spring preload (or maybe spring) change would be to tune for the bullet, and then restrict the airflow (like with stalwart's bolt restrictor) to drop the power for the pellet.... I'm not sure exactly what the shot string would look like with the pellets, it might be basically flat for a few shots and then drop off gradually, but it should at least be usable.... I have the ability to do this on my Disco Double, but have never used the bolt port restrictor in that way.... It might work just fine.... Hmmmmmmmmmmmmm....

Bob

[RMM]

OK, guys, here is the deal.... In an unregulated PCP, making a drastic change to the pellet weight (like from an 18 gr. pellet to a 30 gr. bullet) will shift the curve.... If you tune it for the pellet, the fill, peak, and refill pressures for the bullet will all be lower (and the power down compared to what could be achieved), as the dwell will be way too short for the much heavier slug.... If you tune for the bullet, which takes a LOT more hammer strike, then when you use the pellet you will start off with the first shot the fastest (probably supersonic) and the rest declining.... The only possibility I can see, without a drastic hammer spring preload (or maybe spring) change would be to tune for the bullet, and then restrict the airflow (like with stalwart's bolt restrictor) to drop the power for the pellet.... I'm not sure exactly what the shot string would look like with the pellets, it might be basically flat for a few shots and then drop off gradually, but it should at least be usable.... I have the ability to do this on my Disco Double, but have never used the bolt port restrictor in that way.... It might work just fine.... Hmmmmmmmmmmmmm....

Bob

Thanks a million Bob and I think part of my problem was porting (restricting and or increasing) a given air charge (valve dwell)  but as I see it now it's just slowing down the charge when it can't be done with dwell to get the pellet down and out the barrel efficiently and effectively.  Corrections are definitely in order.   

[rsterne]

A heavier pellet, working at the same valve dwell and reservoir pressure as a lighter one, will not have moved as far down the barrel at the instant the valve closes.... The air between the valve and the pellet will therefore be occupying less volume but at a slightly higher pressure (moreso if the plenum volume is small).... This adds to the efficiency, allowing greater FPE to be developed by the same amount of air.... There are a bunch of interrelated things happening, and if you go wayyyyyyyyyyy too heavy the FPE will drop, not increase.... but understanding that will help you understand why a heavy pellet needs more dwell to take advantage of a given barrel length.... If you increase the hammer strike to get that dwell, you gain even more FPE, but then the gun is no longer tuned to work properly with a lighter pellet....

Bob

[RMM]

A heavier pellet, working at the same valve dwell and reservoir pressure as a lighter one, will not have moved as far down the barrel at the instant the valve closes.... The air between the valve and the pellet will therefore be occupying less volume but at a slightly higher pressure (moreso if the plenum volume is small).... This adds to the efficiency, allowing greater FPE to be developed by the same amount of air.... There are a bunch of interrelated things happening, and if you go wayyyyyyyyyyy too heavy the FPE will drop, not increase.... but understanding that will help you understand why a heavy pellet needs more dwell to take advantage of a given barrel length.... If you increase the hammer strike to get that dwell, you gain even more FPE, but then the gun is no longer tuned to work properly with a lighter pellet....

Bob

Got ya.   I will now go back and tune my Bobcat for JSB Exacts 18.13 and use the CPHPs 14.3 for another plinker project.  While I got ya on the phone what's a good starting velocity for the 18.13s??

[rsterne]

I guess it depends on your port sizes.... but as long as you keep the 18.1's under about 960 fps they'll hit what you aim at, even at 100 yards.... That's probably a little ambitious for a Bobcat, so whatever gives you a decent shot string at the pressure you are using.... Remember, my Bobcat is tuned as a Grouse Gun.... 18.1's @ 710 fps (20 FPE) using a bstaley setup to get 16 shots.... The best string I got with those pellets was 7 shots averaging 900 fps (32 FPE) with some port work done.... All my strings use a 4% ES....

Bob

[rsterne]

OK, further to my comments of June 24, above, I pulled out my .25 cal Disco Double tonight, adjusted it for a decent curve with my 50.6 gr. Bob's Boattails, starting from 3000 psi, and peaking after 5-6 shots at 900 fps (90 FPE).... I then tried a 25.4 gr. JSB King and blasted it through the Chrony at 1190 fps.... I screwed in the bolt stop all the way, got a shot at 830 fps, backed it off a turn, filled back to 3000 psi, and the first shot was 999 fps.... I shot an 8 shot string, which ended at 960 fps (4% ES in a linear down trend) that used about 500 psi of air (so about 0.8 FPE/CI).... In other words, first shot fastest, and not very efficient....

I think this pretty much proves to me that you can't just set a PCP up for heavy bullets and then detune it properly for pellets that are half the weight by just restricting the ports.... You need to also back down the hammer strike to dial back the dwell or you will have poor efficiency and a falling shot string with the pellets.... It may, however, be quite possible to have a two cocking positions for the hammer, one for bullets and one for pellets, to obtain two useful tunes....

Bob

[stalwart]

Bob, I can't thank you enough.

Readers of this thread who have done R&D know how much time and energy Bob has saved me on all this. If you ever see me washing Bob's car, you'll know why I'm doing it so cheerfully. 

Ok... The Trans-ammo idea is on hold. Indefinitely. I'll build an MG single for testing, asap... and will be trying the 2 stage striker, once everything else is set in stone.

johninthecamper sent me a bullet sampler, and I'm very impressed. Quality is Top Shelf. We will not lack for good ammo, and the options he can give us are virtually unlimited.

Some numbers I got backstage... I'm getting excited about the .22 Wolverine: "BTW, just ran some numbers.... The 30 gr. NAA bullet should retain 70% of its FPE at 100 yards instead of 50% for a pellet like the JSB Heavy.... and have less than HALF the wind drift (5” vs 12”).... Interesting thread on Wind Drift in the PCP gate.... The NAA bullet can be pushed to 1050 fps (75 FPE) without gaining too much drift.... so whatever we can drive it to will work great, assuming it stays accurate...."

It's gonna be a fun summer!

 

[au hunter]

      Just remember Bob likes 2 coats of wax!   I have been following this thread closely and have needed plenty of aspirin to keep up with Bob (failed  miserably )

              Brian

[stalwart]

Not a problem. Whitewalls, wire wheels, whatever... I'll be whistling while I work.

I tried to get pics, but I'll need some sun to get good relief... I slugged a couple of John's bullets through a MG barrel with stunning results. His dies are true. To quote Brock Samson: "It's freakin' GORGEOUS!".

Edit: Got one.

[AmBraCol]

Not a problem. Whitewalls, wire wheels, whatever... I'll be whistling while I work.

I tried to get pics, but I'll need some sun to get good relief... I slugged a couple of John's bullets through a MG barrel with stunning results. His dies are true. To quote Brock Samson: "It's freakin' GORGEOUS!".

Edit: Got one.

It looks like you've got a good "skirt" engraved by the rifling.  How close of a tolerance is there between the forward part and the lands? There doesn't seem to be any contact at all, no marks along the shaft.  This would seem to indicate that the skirt does all the work of centering the bullet in the bore as well as imparting spin and sealing the air in back of it.  So I'm curious as to how precise the "bore riding" section fits the bore. Personally I'd like to see just a smidgin of contact to ensure that it rides true and is not cocked a bit to one side or another.  Of course, the proof is in the pudding, uh, er, in the shooting and grouping. We'll stand by for the range reports.

[stalwart]

The range reports are a ways off...lol. Got to build a gun.

This pic sorta shows what I can see, but cannot seem to photograph. There is enough contact to scrape some felt tip marker off.

Sorry about the bad pics. I'm taking these under a magnifying lamp. I don't know what I'm doing with a camera... I shoot til I get lucky.

[AmBraCol]

Okeydoke - that looks much better!    Yeah, details like getting a gun built before shooting the bullets are a drag... ;-) :-D