Benjamin 392 Valve Mod - Increased FPS

[Robert 5mm]

I have a Benjamin 392 and I decided to try doing a valve mod job on my own 392 ( purchased 14 months ago ). I had previously purchased a valve off of Ebay for this purpose, it has two o-rings on the pump end - I do not know who added one, maybe Crosman. . I read all sorts of material and I watched  You-Tube videos, but did not proceed until reading the 3 easy to do steps posted by TIMMYMAC1.

1) Using a dremel I cut off two to three threads ( 1/8 inch ) from the male end of the inside of valve.
2) I cut off approx 1/4 inch from flat end of the plastic check valve insert.
3) I did not use a #113 O-Ring - I used the original #112 - so I did not lengthen the valve assembly or do step 3.

I also replaced the outside o-rings with square cross-section o-rings from the O-Ring Store - SN70016 and SN70113
I increased volume on my valve to approx 4.65 from 4.20 CC and eased the air flow restrictions by enlarging the air path.

Then I finally bought a Chronograph: (I do not have before readings – I do still have the original valve but do not want to replace)

Benjamin Discovery 14.3 gr HP pellets
3 pumps – 455 fps
4 pumps – 554 fps
6 pumps – 621 fps
8 pumps – 684 fps (no air left)
10 pumps – 737 fps (a very little air left)
12 pumps – 770 fps (air left)

I did chrono my two Benjamin NP2 Trails with lead pellets : .177 - 7.9gr – 995 fps and  .22 – 14.3gr – 790 fps

[wll2506]

I have a Benjamin 392 and I decided to try doing a valve mod job on my own 392 ( purchased 14 months ago ). I had previously purchased a valve off of Ebay for this purpose, it has two o-rings on the pump end - I do not know who added one, maybe Crosman. . I read all sorts of material and I watched  You-Tube videos, but did not proceed until reading the 3 easy to do steps posted by TIMMYMAC1.

1) Using a dremel I cut off two to three threads ( 1/8 inch ) from the male end of the inside of valve.
2) I cut off approx 1/4 inch from flat end of the plastic check valve insert.
3) I did not use a #113 O-Ring - I used the original #112 - so I did not lengthen the valve assembly or do step 3.

I also replaced the outside o-rings with square cross-section o-rings from the O-Ring Store - SN70016 and SN70113
I increased volume on my valve to approx 4.65 from 4.20 CC and eased the air flow restrictions by enlarging the air path.

Then I finally bought a Chronograph: (I do not have before readings – I do still have the original valve but do not want to replace)

Benjamin Discovery 14.3 gr HP pellets
3 pumps – 455 fps
4 pumps – 554 fps
6 pumps – 621 fps
8 pumps – 684 fps (no air left)
10 pumps – 737 fps (a very little air left)
12 pumps – 770 fps (air left)

I did chrono my two Benjamin NP2 Trails with lead pellets : .177 - 7.9gr – 995 fps and  .22 – 14.3gr – 790 fps

Robert,

The cutting off the threads and the shortening of the check valve is something I may very well do. I have one square washer installed (SN70016) and the other is a bear to get on so I'm using a standard "O" ring for now. I still have reservations about my ability to enlarge the air path without me messing things up.

The removal of my factory valve spring and replacement with Part # 3P6-LC042E16M Lee Spring I bought from McMaster-Carr made the dumping of air complete with 9 pumps (the most I have done) This spring is also a bit thinner and 1/4" shorter - helping with air volume (although very, very, very little).

Once I have my adjustable piston installed and see how much that helps, then the valve adjustments may very well be added. The more and more I'm thinking about my intended
small mods to the 392 ... the more and more I think that I really should do the two valve thread cut off and the check valve mod.

I keep harping on the thought of 8 pumps to get 16fpe, but I very well may need more compression and more volume to get that ? After way to much thought on this subject I'm getting to the reality this gun just may be a 10 pump gun so I can get the full volume to get that velocity and energy with heavy pellets.

wll