ScopesAndAmmo.com Store Logo

+ Reply to Thread
Page 1 of 2 12 LastLast
Results 1 to 10 of 20

Thread: Home Stretch Now!

  1. #1
    Senior Member Doc Sharptail's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Up The Escarpment
    Posts
    320

    Home Stretch Now!

    Probably a good idea to break this up a little- that's a lot to wade through on the other thread...

    Finally got some replacement o-rings in for the fill yoke on my 3K tube, on the 20-78.
    Tore into the gun tonight, and found that the rough valve stem was binding up pretty badly. The dancing valve spring probably didn't help matters... Thanks Todd! (Spent 2 hrs lookin for my replacement valve- I had put it in the factory 20-78 tube so it wouldn't get lost )

    At any rate, I pulled a Todd, and rebated the brass base of the valve stem enough to tightly seat the end of a new spring. Did side-cuts again on the valve front- not as long as the first- I left enough at the front to engage the first couple of spring coils. I opened up the former piercing pin hole to 5/16" to compensate.

    Back to the 16.1 gr Predator, as I'm almost out of the Heavy Exacts.

    1800 PSI:

    1.) 743.0
    2.) 742.5
    3.) 755.0
    4.) 744.0
    5.) 749.8
    6.) 747.3
    7.) 744.6
    8.) 738.4
    9.) 732.3
    10.) 721.4

    I think I found the sweet spot, right off the bat, for a gun with an un-modified hammer.

    I'm not going to type all this one- it's too long:

    2000 PSI:

    1.) 684.7
    5.) 707.1
    10.) 731.3
    15.) 739.7
    20.) 717.8

    Fastest on that string was shot # 12 @ 741.1 Un-modified hammer strike becomes apparent here.

    2200 PSI:
    1.) 567.0
    2.) 653.3
    7.) 656.7
    10.) 677.6
    15.) 723.9
    20.) 746.3
    25.) 727.7
    30.) 697.8
    Fastest on this string was shot #19 @ 749.4 fps.
    I don't think I'll be taking it over 2200 PSI- shot #1 sounded like a long bbl'd .177 @ 500 fps

    Now to investigate shimming the hammer spring. This gun is loaded with potential.

    I'd still be scratching my head, if it wasn't for the input of Todd and Bob and all you other contributors. I owe you guys a cold one- and I don't even drink Doors always open if you end up at the home of the Jets!

    Regards,

    Doc Sharptail
    Last edited by Doc Sharptail; Apr 02 2013 at 03:17 AM.
    "Ain't No Half Way"

    -S.R.V.

  2. #2
    Senior Member SeanMP's Avatar
    Join Date
    Thu Dec 22 2011
    Location
    Just south of "Out There"
    Posts
    911
    YAY! .....I see a curve! Looks like 2200 is a good spot for that rifle. And your getting the shot count that I was expecting.

    Your absolutely right there is all kinds of potential in that rifle. The next step I would take is add a small amount of spring preload until the beginning of the string is where you want it and then flatten the high end of the string with a port restrictor. Usually I use 1/4" teflon rod drilled with #drills. It used to be listed at Fastenal but it's not now. You can still get it on special order. Or PM me if you want such a beast.
    Sean

  3. #3
    Moderator rsterne's Avatar
    Join Date
    Wed Dec 7 2011
    Location
    Coalmont, BC
    Posts
    1,266
    Looking good!.... yes, a bit more hammer spring preload.... assuming you want that extra velocity.... or you can fill to 2100....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  4. #4
    Senior Member Doc Sharptail's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Up The Escarpment
    Posts
    320
    I need to bench with the Predators. I've been suspecting for a while that they are a bit velocity finicky.
    As for the velocity I'm getting now- I'm not sure that it's enough to properly expand the Predators. I don't think I'm far off the mark though. It's gonna be a busy spring and summer for me. I'd also like to do work-up with the exact heavy.

    If anyone hears more about 3K tubes, I'm in the market for another!

    Sean: p.m. sent.

    Regards,

    Doc Sharptail
    "Ain't No Half Way"

    -S.R.V.

  5. #5
    Moderator rsterne's Avatar
    Join Date
    Wed Dec 7 2011
    Location
    Coalmont, BC
    Posts
    1,266
    Some information about the expansion of Predators here.... http://www.canadianairguns.com/showt...ansion-Testing

    Just make sure you look at the right set of data for the IMPACT energy you expect to have, starting from your muzzle velocity and degraded for your expected range....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  6. #6
    Senior Member Doc Sharptail's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Up The Escarpment
    Posts
    320
    Finally got some time to work on the rifle again tonight.
    I shimmed the hammer spring by dropping a plastic nut and a thin washer into the the spring pocket on the rear of the hammer.
    This contraption mikes to .1875". By the feel of the way the gun is cocking, I'd say it's very near to coil bind. Solved the bbl side play issue while I was at it- the plastic bbl band had split at the bottom.

    Of course, I just had to shoot it

    I started off with the 16 gr Predators at 2200 PSI.

    1.) 968.9
    2.) 951.6
    3.) 952.8
    4.) 948.2
    5.) 969.2
    6.) 969.3
    7.) 973.3
    8.) 962.6
    9.) 957.9
    10.) 951.9

    I switched to the JSB Exact Heavy, without refilling the gun. (I was trying to cut the noise back a little)

    11.) 967.4
    12.) 980.1
    13.) 961.3
    14.) 1008
    15.) 989.4
    16.) 983.6
    17.) 659.8
    18.) 114.1

    Test halted. I didn't want to end up with a pellet lodged in the bore...

    In all honesty, this is quite a bit more than I was hoping for. I'd like to tone the predators down a little- to the mid 8's. I was a bit taken aback by the sudden drop at the end of the string.

    I think I'd like to try backing off on the hammer spring pre-load a little. The need for an RVA is becoming increasingly apparent. Before I do any of the above, I'd like to get the gun out, just to see how the Predators print at 25 yds. I may be in for a bit of a wait~it's -20 C here as I type this.

    I added a couple of extra layers into my rubber-backed office carpet cardboard trap. I recovered what I could of the ten Predators...



    I think a couple collided in the carpeting- it happens a lot when I'm shooting over the chrony. I'm at a bit of a loss to say exactly which ones piled up on each other. There was much flaking and pieces of lead trapped in the carpet fibres. At any rate, I do have them expanding

    Regards,

    Doc Sharptail
    "Ain't No Half Way"

    -S.R.V.

  7. #7
    Senior Member sholo's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Slightly north of "out there"
    Posts
    354
    I shimmed the hammer spring by dropping a plastic nut and a thin washer into the the spring pocket on the rear of the hammer.

    I think I'd like to try backing off on the hammer spring pre-load a little. The need for an RVA is becoming increasingly apparent.
    Before I got my RVA, I use to adjust preload by simply adding/removing small S/S washers on the cocking block spring guide. IIRC, they were 1/8" washers - perfect OD for hammer spring, but too small ID to fit on spring guide, so I would put 4 or 5 washers together, clamp them in a brake line flaring tool and drill them out to correct size all at once. A bit of sanding with 800 grit s-paper to smooth out the rough edges/burs and you're good to go!

    Add a couple to guide, shoot over chrony, then add more if necessary. At a thickness of .060" per washer, you can tune velocity to pretty much whatever you want


    HTH,
    Todd
    Todd

    Don't sweat the petty things, and don't pet the sweatty things!

  8. #8
    Senior Member Doc Sharptail's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Up The Escarpment
    Posts
    320


    Bought some "Carbon" drill bits. They cut like nobody's business in the rear tube cap. Also put my new "Vermont" taps to work- both holes are 10 x 32. Found a piece of blue plastic, and cut off a bit, and dropped it into the set screw hole. Seems to work...




    Neither hole is straight. I intentionally tried to angle the adjuster screw with a center-ward slant The set screw is off kilter too. I did these by hand, and it shows. I still have to figure out a way to rebate the "inside" part of the tube cap. I'm thinkin time to break out the diamond cloth again...

    Regards,

    Doc Sharptail
    Last edited by Doc Sharptail; Apr 10 2013 at 03:34 AM.
    "Ain't No Half Way"

    -S.R.V.

  9. #9
    Senior Member Doc Sharptail's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Up The Escarpment
    Posts
    320
    I tried putting the "RVA" into the gun last night. I'm beginning to understand that this won't be a simple endeavour.

    It works, sort of, with the rear cocking pin out of the rifle. Not too sure I want to get into all those other associated mods~ eg: cock on closing, or cut a rear bolt notch, and pin/spring and detent the bolt handle.

    Back to the hammer spring pre-load washers for the time being. Re-located the washer system to the spring guide shaft. What's on there now mikes to .1652". I ran out of steam, and did not get to shoot...

    I'll try tonight, and see if I've cut back on the power a little.

    Regards,

    Doc Sharptail
    "Ain't No Half Way"

    -S.R.V.

  10. #10
    Senior Member Doc Sharptail's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Up The Escarpment
    Posts
    320

    Chart wizard works. just have to find how to imagize it...

    Regards,

    Doc Sharptail
    Last edited by Doc Sharptail; Apr 11 2013 at 01:55 PM.

+ Reply to Thread

Similar Threads

  1. Target shooting competition- at home...
    By AirGunEric in forum Airgun Target Talk
    Replies: 0
    Last Post: Nov 11 2012, 09:11 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts