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Benjamin Discovery Power and Accuracy Mods Update

June 16 2017 at 12:36 PM
Kevin  (Login Mattole)
YF

Here is the latest shot string from my .22 Discovery after adding the following parts: extended bolt probe, Challenger hammer with recessed striker, and the following products from Magnum Airpower LLC: higher strength valve screws, Magnum Hammer Spring, Compact Power Adjuster, Custom (.150) Transfer Sleeve, and Wide Bore Gauge Port. The valve is an unmodified Disco valve.

Starting Pressure was 2500 psi. Power adjuster was set at 1 turn out from point in hammer spring tension were spring started to bind.

Pellet Weight(gr): 18.13 (JSB Jumbo Heavies)

# FPS FT-LBS
21 841 28.48
20 851 29.16
19 856 29.50
18 862 29.92
17 864 30.06
16 872 30.62
15 873 30.69
14 869 30.41
13 874 30.76
12 872 30.62
11 870 30.48
10 873 30.69
9 ERROR 2
8 867 30.27
7 865 30.13
6 867 30.27
5 870 30.48
4 857 29.57
3 857 29.57
2 847 28.89
1 848 28.95

Average: 862.8 FPS
SD: 10.0 FPS
Min: 841 FPS
Max: 874 FPS
Spread: 33 FPS
True MV: 863 FPS

So the ES is 3.8% over 21 shots which I think it pretty good. This is the kind of velocity and shot count that I was hoping to get from my Discovery. I would call it a done deal, except that Magnum Airpower will be coming out with a customized high performance valve for the Discovery very soon which is supposed to deliver even greater efficiency at higher power levels, which I look forward to trying.

Accuracy mods that I did for this rifle included polishing the crown and leade, cleaning up the barrel port, installing an extended bolt probe, and adding a second barrel band. I shimmed each barrel band using beads of 5-minute epoxy on the lower part of the inner ring of the barrel hole and the top part of the inner ring of the air tube hole. Then I sanded the beads down just enough for the bands to have a snug fit onto the tube and barrel.

Here is a 6-shot group I did just a few minutes ago. The scope was a rather cheap Bushnell Trophy 3-9 and the crosshairs covered the dot I was aiming at so I have no doubt that with a better shooter behind a better scope the group could have been smaller. I am a happy camper with this rifle!

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This message has been edited by Mattole on Jun 16, 2017 3:58 PM


 
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