Benjamin 397

[Div Arty]

    Would appreciate a little information on the Benjamin 397.  Have been shooting a Daisy 880, at 20 & 40 yds. with 3 to 4 pumps, at soda can's.  Just for target practice.  I would like to upgrade for accuracy and a better trigger without increasing the report to much.  I would also be adding a peep sight.
     Also is there any problems with Cobra Air Guns, they seem  to have the best price at $130.00 for the rifle.

[Charles/NM]

What kind of info do you want?
I have an old rocker safety .20 caliber Sheridan, two 397's and one 392 rifle. All have adjustable pump rods I made in my machine shop. That really wakes them up.  I have found stock pump rods to be up to 1/8" too short for full compression.  At 3 to 5 pumps all three are loud.  At 6 and above pumps they really bark.  If noise is an issue for you you might reconsider and get a quieter spring piston rifle in the Beeman R-7 power range.  I prefer my pump rifles over my spring piston ones because of the variable power feature of the pumpers.  Of my three pump rifles I prefer the .22 caliber 392 for it's increased power and large pellets.  Those big heavy 14.3 grain Benjamin pellets really smack a tin can or pop bottle lid compared to the smaller .177 and .20 caliber ones.  For long range, over 50 yard, shooting the 14.3 grain .20 cylindrical pellet has the superior ballistics. Probably best you buy one each of the three bore sizes, lol.

[Div Arty]

    Charles/NM  thanks for the reply and the heads up on the pump rods.   Still kicking the models around.  But probably go with the 397.     
           Div Arty

[Trav]

Charles/NM can you give me some details on your adjustable pump rods?  How much difference does it make?  Is it tough to build?  My son has a 392 (actually his little brother does too, although little brother does not know it yet....it is for his birthday).  Thanks.  Travis

[Charles/NM]

My notes are out in my shop, but IIRC my 392 went from 575 fps at 8 pumps with a 14.3 grain pellet to 650 fps with the adjustable pump rod. This is at 4100 ft altitude. I'll check my notes in the morning and post results at several numbers of pumps. It's a significant difference.
To make the pump rod adjustable you cut it an inch from the steel pump rod head where the pump arm linkage attaches to it and make a threaded sleeve to attach the two parts.  I thread the long part of the pump rod to fit the sleeve and drill the sleeve half way thru to slip over the short stub left on the steel pump head and drill the other half to be threaded to fit your new threads on the pump rod.  The rod is 1/4" diameter.  A lock nut keeps the threaded part from moving and the slip fit is held with a set screw.  While I'm at it I remove the pump arm wood and take out the spring that's in the lever. It is in there to hold the pump arm closed with the original pump rod.  That spring makes the rifle harder to pump and you won't need it now since you will be adjusting the pump arm by trial and error to make it over-center tightly just before the pump arm closes. 
Here's a picture that shows what the finished work looks like and the spring that's removed from the arm.

[Trav]

Charles/NM, thanks for the explaination.  I understand from your explaination how to adjust it, but how do you determine proper adjustment?  I would love to give it a try, but I don't think I could get satisfactory results with my limited tools.  I will roll it around in my head for a few days, maybe I can come up with something that would work.  Thanks.  Travis.

[Charles/NM]

I agree that it might be difficult to make the pump rod mod without a lathe. If you have a home shop machinist in your neighborhood he would most likely be glad to make the parts for you. Even without this mod the 392 and 397 rifles are perfectly adequate for lots of fun shooting.   My mod just makes them a little more efficient that's all.
I measure the pump rod before modifying it and add 1/8" for my first try. I use a metal rod to temporarily hold the end cap in the pump tube.  I pump it one time and shoot that air.  Then I open the pump arm about an inch or so and slowly close the pump arm.  I should feel the pump cup hitting the rear of the air valve when the pump arm is 3/4 inch from closing completely.  If it doesn't hit the valve I make the rod a little longer.  If it hits the valve when the arm is too far open I shorten it.  That's why I said it's a trial and error adjustment.  When actually pumping that interference isn't felt because the pump cup compresses as air pressure is built up. 
BTW, I checked my numbers and I was very close.  Actually the 392 went from 572 fps to 650.  After 2 pumps it went from 360 to 375.  At 3 went from 425 to 455. 4 gives 505 compared to 475 stock. You can see that for a given pellet speed I have reduced pumping by one pump.

[kennisondan]

Charles NM.... I am very impressed with your accomplished upgrade and the explanation you furnished... I would like to do the same to my guns... an old benjamin pistol and rifle in 177 caliber... I am gonna add a 22 caliber to my stable, and possibly some other calibers and power sources.... if the 22 were faster it would be much more potent, as it does not seem to adequately penetrate the likes of squirrels, etc. but I have not tried different pellet types... I stuck with the 177 due to the penetration problem... I can shoot a squirrel with the pistol and 5 to 7 pumps, and it penetrates sufficiently to clear the vitals and the animal drops, but stays alive for 30 to 45 seconds or more before dropping from the tree...
it seems the added fps would make it faster to reload... and would be more powerful and effective as well... but it also seems the 22 would acheve the kind of speeds necessary to kill cleanly even in the pistol... I used to load up the leads from 22 shorts in my benjamins and could kill nutrea at close range on the campus I worked on at nite... shots to the rib cage.. I am intrigued with this idea... I imagine that the middle could be cut out and different lengths of the power pump rod could be acheived with the sleeve and a set screw on each sleeve end... I am just sorting it out and that could be the answer for a person without the wherewithal for threading one end of that rod and if it holds for one end, can it hold for both ends ? it seems the turnbuckle idea could also be acheived with opposite twists on the rod threaded ends and inside of the threaded sleeve so that twisting in one direction lengthens both and the other direction shortens the entire thing...like the old turnbuckles on a screen door to keep it plumb, and sqaure.
Just wondering to be sure I understand what must and could be done and to applaud your work.
dk