Benjamin Discovery Power and Accuracy Mods Update

Benjamin Discovery Power and Accuracy Mods Update

Joined: July 27th, 2005, 3:39 pm

June 16th, 2017, 4:36 pm #1

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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Last edited by Mattole on June 16th, 2017, 7:58 pm, edited 1 time in total.
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Joined: July 11th, 2001, 6:08 pm

June 17th, 2017, 2:37 am #2

<font size="3.5" color="#000000" face="Arial, Helvetica">Long ago someone used to offer Disco barrel bands that were fitted with an oring.

I put one on my 22 Disco & it has shot great ever since.

Finally getting my Rapid to come around (post above this one).

Feels good.

Nice post!
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Last edited by Diamondback on June 17th, 2017, 2:46 am, edited 1 time in total.
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Joined: July 27th, 2005, 3:39 pm

June 17th, 2017, 3:23 am #3

Thanks much, db. Yes the "modability" of these little rifles makes them a fun and satisfying airgun to own and play with. The barrel band-o ring combination sounds intriguing!
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Joined: July 11th, 2001, 6:08 pm

June 17th, 2017, 5:02 am #4

<font size="3.5" color="#000000" face="Arial, Helvetica">

Here are some links mentioning the maker:
http://www.network54.com/Forum/79574/message/1237153501
http://www.network54.com/Forum/79574/message/1269187123
http://www.network54.com/Forum/79574/message/1318782621

I remember reading where Mike T of TKO used barrel bands with screws positioned to create upward pressure on the barrel resulting in great accuracy:
Mike T TKO Disco Barrel Band Info
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Last edited by Diamondback on June 17th, 2017, 5:08 am, edited 1 time in total.
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Joined: July 27th, 2005, 3:39 pm

June 18th, 2017, 5:57 pm #5

I tried a mod that I heard mention of here which is to apply a bead of epoxy on the lower area of the barrel hole in the barrel band and the upper area of the air tube hole in the barrel band. Let dry and sand down to where the barrel band will fit snugly onto the rifle. Keeps the barrel from being bent down towards the air tube. It seems to work well!

[/IMG]
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Joined: July 11th, 2001, 6:08 pm

June 19th, 2017, 6:09 am #6

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!

[/IMG]
<font size="3.5" color="#000000" face="Arial, Helvetica">Ok, so after your Disco post I got my Disco out tonight & messed around with it.

I did several dry fires & the stock trigger is not really that bad.

Seriously, I remember it being much worse.

TKO makes it so politically correct.
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Last edited by Diamondback on June 19th, 2017, 6:10 am, edited 1 time in total.
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Joined: July 27th, 2005, 3:39 pm

June 19th, 2017, 2:28 pm #7

Ha - glad to be an instigator.

I could never get past the clunky look of the Disco trigger and trigger guard which was a big reason why I went with the Marauder trigger. Plus all the great feedback from people who had installed the Marauder trigger on their Discovery rifle. After I installed mine I understood what they were raving about.

But I'm glad that you like your trigger just fine!

TKO will be shipping their political corrector to me today. I look forward to being in aural compliance.
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