Benjamin Discovery Velocity

[cj_86]

Just got a new Discovery to play with and first thing I had concerns about is shot count. I was expecting about 20-25 shots per fill (.22 cal) ,but getting only 12-15 before POI starts to drop. After shooting through the chrony it looks like shes shooting a little fast! I was thinking maybe 750-780 fps with Crosman Premier 14.3 pellets and found that its really around 875+fps! The string has a nice bell curve I guess ,but I would rather have reduced velocity with higher shot count.

Discovery is completely stock and with a little research found that people have tried reducing transfer port sizes, reducing hammer weight, and reducing hammer spring tension. Before I start experimenting, I was hoping someone can share some ideas on how they were able to reduce the velocity on a Disco? Transfer port sizes? Hammer Spring mods? 

Thanks,
CJ 

Here is shot string @ 2000 PSI fill:
873
883
885
887
883
882
873
871
865
857
847
843

 

[clgraham82]

Search through these sites (if you haven't already)...tons of info on what you're looking for.

http://www.gatewaytoairguns.org/GTA/index.php?board=12.0 

http://www.marauderairrifle.com/forum/index.php?sid=90ba525d0e9273b42c5148ae49515562

 

[Yote]

Just bought one.PA did the ten for ten #1. 943. 939. 939 935 931. 928. 925. 916 905. And 898. That's from 2000psi down to 1600 psi with a 12 gr pellet.for what it's worth I filled it to 2000 psi and got 32 good shots and another ten while holding one mil dot low

 

[cj_86]

Thanks for the links! I was doing a google search at first but looking through those 2 forums I was able to narrow my searches. Found a good post on GTA about transfer port size that seems good to try for the first attempt with the Disco.

http://www.gatewaytoairguns.org/GTA/index.php?topic=65894.0

*Ok found another good source of transfer port data:

http://www.canadianairguns.com/showthread.php?1075-Influence-of-Port-Size-on-FPE-in-a-Discovery

 

[kiwi-mark]

im fairly new to airguning, but wouldnt you just use a heavier pellet? im considering buying this gun and was planning on doing the mods to increase power n then select a heavier pellet. how wrong am i? someone will know

 

[cj_86]

Using the graph I found online as a reference, I decided to shoot for a .095" port size. I turned a new transfer port out of stainless steel 1/4" rod and drilled the I.D. to 0.093" because that is the closest size of bits I had on hand. Original transfer port size that came with the gun was .140"

Unfortunantly I did not gain as many shots as I was hoping for when looking at the graph. I only gained 6-8 shots vs using the stock port. Oh well more shots is better then zero! I decided to just get over it and just have fun with this Disco. Studying the shot string it seems I can go to a higher fill pressure ,but I don't have a degassing tool in case I lock up the valve.

After moving the barrel band forward I improved the accuracy a little and I am able to obtain 1/2" groups at 35 yards using el cheapo Crosman Premier 14.3 pellets.

Shot string Crosman Premier 14.3 2000 psi fill:
774
770
771
770
777
780
779
769
err
777
775
771
768
766
768
764
756
748
744
740
734
725

 

[John "spysir" Blount]

 Change the striker/hammer spring first, the original discoverys had a different spring which gave the same power but with more shots, the current spring is TOO much.
Not at all sure why they changed as it cut the shot count in half and just wastes air. And for those with no tooling that want a different TP poly tubing like in a refrigerator/freezer works well.
You can also try the bstaley o-ring mod ( drop 3-4 O-rings inbetween the striker and valve) but that works best in rigs with adjustable strikers, naturally you could buy one of those from crosman, the challenger I believe can work. Or any other anti-bounce of your choice for further shot count increase.
If looking for POWER the Don Cothran power valve is THE unit to purchase.

Pertty much any mod for any of the standard crosman rigs 22xx/other will work on a discovery and a 1st gen marauder trigger pack will fit right on ( maybe need a shim). Making it a crazy good carry around light weight rifle.

Change that hammer spring, you'll like it.


John