Author Topic: How is my tune  (Read 407 times)

josh9465

  • Newbie
  • *
  • Posts: 6
How is my tune
« on: April 05, 2019, 07:47:10 AM »
Hi
I have a Weihrauch HW100 .22 with a Lothar Walter barrel 600mm in length.

I set my reg at 120 bar.  I attained a maximum plateau velocity of 895fps by winding in my hammer spring to maximum.

I then set my velocity to around 860fps because that’s between 3-5% of the max plateau velocity.

So how did I do at tuning my HW100.

Over 42 shots 3 mags:
Ave Vel 861fps
ES 13
Min Vel 852
Max Vel 869
SD 4.2

« Last Edit: May 04, 2019, 11:22:48 PM by josh9465 »


  • Perth, Western Australia

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1818
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: How is my tune
« Reply #1 on: April 05, 2019, 07:54:08 AM »
The string looks great, and you followed the correct method.... I can't tell you what the efficiency is, without knowing the volume of the reservoir and the fill pressure.... and the pellet weight....

Bob

  • Coalmont, BC

josh9465

  • Newbie
  • *
  • Posts: 6
Re: How is my tune
« Reply #2 on: April 05, 2019, 03:36:21 PM »
Hi Bob

Cylinder is 255cc

Fill pressure was 200 bar

Pellet weight is 18.13gr.

How do you work out efficiency.
  • Perth, Western Australia

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1818
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: How is my tune
« Reply #3 on: April 05, 2019, 04:04:39 PM »
Calculate total FPE while on the reg.... 860 fps w/ 18.1 gr. = 29.7 FPE x 42 shots = 1249 FPE....

Calculate total air used in std. CI....

Reservoir = (255 cc / 16.4) = 15.5 CI.... Pressure drop is (200 - 120) = 80 bar.... (15.5 x 80) = 1243 CI....

Efficiency = (1249 / 1243) = 1.01 FPE/CI.... That is "low, but acceptable".... Anything under 1.0 is not great....

My guess is that you are getting some hammer bounce.... You can try decreasing the velocity a bit more and see what that does to the shot count.... and recalculate the efficiency.... It should increase.... If you can't accept less FPE, then you will have to increase the setpoint pressure and retune for the new, higher plateau.... minus 3-5%....

Bob
  • Coalmont, BC

josh9465

  • Newbie
  • *
  • Posts: 6
Re: How is my tune
« Reply #4 on: April 05, 2019, 05:05:39 PM »
Thanks heaps. It took me several days going through the forums following your instructions on tuning.

I’ll try you suggestions.
  • Perth, Western Australia

josh9465

  • Newbie
  • *
  • Posts: 6
Re: How is my tune
« Reply #5 on: May 04, 2019, 11:22:05 PM »
Ok I did a retune. How did I do? Does it seem Im getting hammer bounce from the jagged results?

I got an efficiency of 1.107 and extreme spread of 19 over the 45 shots.

My maximum velocity was 913fps using JSB 18.13gr so I set my velocity 872fps, which works out to be roughly 4.5% of the max velocity.

I have a slight upward trend.

« Last Edit: May 04, 2019, 11:23:49 PM by josh9465 »
  • Perth, Western Australia

josh9465

  • Newbie
  • *
  • Posts: 6
Re: How is my tune
« Reply #6 on: May 05, 2019, 12:04:35 AM »
Seems to like 880fps

  • Perth, Western Australia

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1818
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: How is my tune
« Reply #7 on: May 05, 2019, 08:49:23 AM »
The 880 tune looks good.... The slightly slower tune is not hammer bounce you are seeing, but tiny variations in hammer strike causing velocity differences due to being a bit too far below the plateau velocity.... every gun is a bit different.... your gun likes 3.5% below instead of 4.5%....

Bob
  • Coalmont, BC

Alan

  • Administrator
  • Hero Member
  • *****
  • Posts: 2494
  • Set the example... Don't be one!
    • Mobile Amateur Radio
Re: How is my tune
« Reply #8 on: May 05, 2019, 09:40:23 AM »
This thread brings back memories of my college physic class. If memory serves... Depending on the projectile—sectional density, ogive, etc.—there is a dip in the drag coefficient hovering around 850 to 880 FPS. This is also the range where I've found accuracy is at its best. Thus, if accuracy is one of the requisite factors, it would seem to me that a bit of inefficiency could be tolerated, if one tune was a bit more accurate than another one.

Comments Mr. Sterne?
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

  • Member 2000+fps Club
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1818
  • Mozey-On-Inn and see what Coalmont has to offer!
    • Mozey-On-Inn
Re: How is my tune
« Reply #9 on: May 05, 2019, 02:50:34 PM »
Accuracy trumps velocity or efficiency every time.... Where the dip in the drag is depends somewhat on the projectile shape, of course.... Accuracy vs. velocity is often a matter of barrel harmonics....

Bob
  • Coalmont, BC

josh9465

  • Newbie
  • *
  • Posts: 6
Re: How is my tune
« Reply #10 on: May 05, 2019, 02:55:46 PM »
Thanks for your help.

I think I was getting better accuracy with the slower velocity.

But I’ll keep testing.

Who would have thought pcps could be so fussy.
  • Perth, Western Australia