From: bruce@faxmail.co.nz (Bruce Simpson)
Newsgroups: rec.guns
Subject: Re: overpumping Crossman 1322
Date: 12 Jan 1996 01:02:31 -0500

On 11 Jan 1996 09:33:40 -0500, tsai@oyster.nacto.lkg.dec.com (Karl Tsai)
wrote:

#In addition, I also found 13 pumps will send the same pellet at over
#470fps and 15 pumps will do it well over 480fps.  This is against the
#claim of the manufacturer that more than 10 pumps produces no increase of
#speed.

There are some mulit-pump pneumatics which do loose MV if overpumped (but
not much).  I think it's all related to resonance in the gas path and
vortexes created by the gas-streams.  In the "ideal" gun the relationship
between pressure and velocity would be far more predictable.

When I first bought my Sharp it sort of plateaued at 10 pumps with the
extra effort being required to squeeze another pump or two not being
returned in extra velocity.  I worked the ports and now the plateau doesn't
occur until 14 or 15 pumps (depending upon temperature, humidity, etc).

There are some multi-pump pneumatics which are fitted with pressure relief
valves (particularly for the UK market where 12ft lbs is a legal maximum in
some cases).

#I fully understand that this is a rather undesirable practice (over-pumping)
#as it stresses the pumping mechenism but am wondering has any of you
#observed similar phenomenon on your multi-pump air guns?  I'm most
#interested to hear from you Bemjimin/Sheridan multi-pump users.

I think that the major damage from over-pumping is a greatly increased
wear-rate on the pivot points for the pumping mechanism.  Even though I
kept these points well oiled on my Sharp, they wore out after about 12
months of 13-pump operation.  I replaced the bushing with a couple of
ball-races and now it's not only easier to pump but it's also showing no
signs of wear even after another three years of heavy use.

The instructions for my Sharp include stern warnings against "over-pumping"
and have a 10-pump maximum.

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