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Prod HDD and TP tune results

May 29 2012 at 7:50 AM
Rick C  (Login rcashen)
YC

I recently tuned my Prod with a HDD from AoA and transfer port re-size. Here are my experiences.

In stock form with the spring and valve stroke maxed I was getting 30 shots ranging from 620 to 665 when filling to 2800 psi. (12.5 - 14.4 ft/lbs) with FTT pellets.

First I installed the HDD, this is not a drop in install it took several tries before I was confident I had it fit correctly, I also had to grind the back of the cocking shoe to allow clip installation after installing the HDD. I used a chrono to verify I was close to the same velocity as pre-HDD (within 10 fps).

The first thing you notice is the velocity of shots at higher pressures are very low. Once the valve starts to operate on a single strike, shots above 2300-2400 psi have much lower velocity than before. So there is no use in filling past, in my case, 2325 psi. Apparently in stock form the gun takes advantage of the double strike to use air above pressures the valve likes. Although I can't image a double pulse does anything for accuracy. Since I fill the prod from a hand pump filling to a lower pressure is good news.

Next I drilled out a transfer port I purchased from Crosman. I use a #43 (.089) on my drill press to produce a .092 hole. I picked this size from the excellent work I've seen in other posts. This size was listed as the most efficient above the stock size. I tried a port drilled with a .094 drill that produce a .098 hole, but I found that made the gun to peaky. I was after constant velocity.

With the HDD installed and the transfer post swapped I began tuning for consistent velocity.

I found with the stroke and spring maxed the best I could get was a 24 shot string with a 45 fps spread. But when I backed of the spring a half a turn I got this nice string.

05/28/12
Prod .22
Pellet H&N FTT
Strok Max
Spring 6.5
.092 TP
24 Shots (6-25)
Average FPS 671.7
Average Ft/lbs 14.7
Max FPS spread 30 fps

No FPS FLBS Pressure
1. 635.9 13.2 2475
2. 634.7 13.1
3. 644.0 13.5 2400
4. 643.8 13.5
5. 650.6 13.8
6. 661.7 14.3 Start String
7. 664.2 14.4 2300
8. 662.0 14.3
9. 678.0 15.0
10. 667.2 14.5 2200
11. 677.4 15.0
12. 677.0 14.9
13. 675.5 14.9
14. 679.0 15.0
15. 678.3 15.0
16. 683.1 15.2 2000
17. 685.4 15.3
18. 683.4 15.2
19. 674.7 14.8
20. 674.1 14.8
21. 671.8 14.7 1800
22. 666.5 14.5
23. 658.4 14.1
24. 660.2 14.2
25. 655.5 14.0 End String
26. 644.0 13.5 1600
27. 638.4
28. 638.6
29. 624.6
30. 616.7 1400

I am very happy with these numbers and gun is a snap to fill now.

Rick C

 
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