old benjamin 347 with low pressure after repair

[cmhobbs]

Hello, folks!  Long time, no post.  Recent events in life have brought me back to my airguns!  While taking some inventory, I pulled a Benjamin 347 out of the cabinet that had a "stuck pellet" note on it.  So some history and a question:

I bought this rifle in a non-working condition.  Got a repair kit from Pyramyd Air (PY-A-624) for models with a soldered valve.  Took this dude apart (what a chore!) and got the new guts put in.  It shot great for maybe 50-100 rounds and then a pellet got stuck in the barrel.  Pressure seemed to drop over time dramatically.  Into the cabinet it went for probably a year or more and I just pulled it out, cleared the pellet, ran a cleaning pellet through it and it seemed to shoot just fine.  Dropped a real pellet into it and it got stuck again.

I don't detect any leaks and it seems to generally operate just fine, it's just not holding pressure.  It does make a quick sucking puff noise when you extend the pump handle all the way out but it's always done that after I repaired it and I assumed that was the rifle drawing air in but maybe I've done something wrong.

Anyone have any idea what might be going on?  Should I pick up another repair it and undergo that crazy process again?

Thanks!

[happymecanic]

What material were your new seals made from? I rebuilt my Benji 310 with teflon seals and had to keep it pressurized with 4-5 pumps for a few days for the seals to ''seat'' well. I seem to remember some tuners recommend to give the new front seal a tap with a wooden dowel and hammer to help seating it.

Also I need to cock the gun before pumping, otherwise pressure doesn't build up. HTH.

[cmhobbs]

Hey, thanks for the reply!

I'm pretty sure they were nylon and/or rubber.  Here's the kit I used:  https://www.pyramydair.com/product/benjamin-sheridan-repair-kit-fits-some-pre-1995-multi-pump-guns-w?a=624

I tried cocking it before pumping and that seems to have worked once but it failed a second time.  I do wonder if perhaps it's also a pellet issue.  The pellets getting stuck were crosman's hollow points (a variety I typically avoid but they were gifted to me).  I fired a crosman match pellet and a jsb match pellet with no issues.  Same weight.

I figured the seals would be set by now but just in case, I went ahead and cocked it, pumped it 5 times, put the safety on, and put it in the cabinet.

Couple of questions while I'm thinking about it:  what's the typical range for number of pumps on these and how far should they shoot?  I know they're not going to be as hot as my modern airguns.  Is there also a modern version of this particular rifle?  I'd like to shoot this one sparingly due to age so it'd be neat to have a twin model I could play with a bit.

[Back_Roads]

 Not in .177 but in .22, and some have been converted to .177 in the short time they have been on the market. https://www.crosman.com/

[cmhobbs]

quick followup:  i kept about 5 pumps in the rifle for just over a week and that seems to have resolved the issue, thankfully.  i suppose i'll store it with a couple pumps in it from here on out.  thanks for the info!