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Post # 7: Find Your Sweet Spot (13xx Pumper Family)

4/29/2014

2 Comments

 
The saying "your mileage may vary" gets tossed around a lot referring to our guns.  I use the phrase myself.  Whether bone stock right out of the box or highly modified and tuned, there will almost always be differences from one gun to another.

On the pump guns (1322, 1377, PC77, Backpacker, 760, etc.) so many people want more power, more fps, more fpe.  Often right out of the gate I get orders for heavy hammer springs over and over.  Hardly ever does anyone ask for a lighter valve spring.  But we've been over springs earlier, but I am just making the point that there are certain knee jerk reactions that might not be right for the gun (at least not right away).

Some examples:  I have had folks with a stock 1377 or 1322 call to order a heavier hammer spring.  I ask how they are using the gun (targets, plinking, small yard pests, hunting, etc.).  Often I hear primarily targets and plinking but with the occasional bird or squirrel as the target.  I ask how many times they are pumping the gun.  Lots say not over ten (as Crosman advises), but some say 12 to 15 or more.  I ask if they pump max all the time?  Or just as needed?.  So I ask at ten pumps (or whatever their self-imposed max is) is your valve retaining any pressure after a shot?  Most do not know and have never tried to find out. I HAVE to ask this next question!  Why are you wanting a heavier spring to release more air if you don't know if you even can?... when it is likely that your gun is dumping all of the charge every single shot!  So therein lies what I call the "sweet spot".  

You pump your gun higher until you reach the point that after a shot, you re-cock without pumping and see if there is anything left in the valve.  Lets say on a given gun that is 16 pumps. So if that is the case, then why even pump past 15 pumps? If you target shoot and plink 90% of the time with 6 to 10 pumps, then when you think you need more power you will know that 15 is about all she's got (without further mods).

Now there are speed demons out there that will pump the maximum all the time/ every time.  If your piston is stock and you do this repetitively and often then you are going to decrease the life of that piston due to the heat and friction this behavior subjects the piston to.  During a spirited shooting session of repeated maximum pumping just stop for a second and feel the air tube.  Pretty warm, huh? The concern over this is what is behind several mods including "stuffed piston" (reinforced so it will not bend / deform under higher pressures and temperatures... also the pistons made from metals (aluminum, brass) or better plastics (usually delrin) to take the heat and pressure abuse. Some go for Viton o-rings at the piston and the valve outer... because Viton handles higher heat than standard Butyl.

So find that sweet spot!... if for no other reason than to not be over-pumping every time and stressing your gun for no gain.  Hopefully that will be enough for you.  If that sweet spot is not enough for you, then you'll know you need to move on to valve and / or piston mods, spring mods, porting mods, extended probes, etc. etc.
2 Comments
Lewis "Bud" Conboy
5/18/2015 02:53:01 am

I installed your R P valve. I am up to 20 pumps, with no residual air left in the valve. I just read your article on using cardboard boxes for a back stop and sort of a power indicator. I am going to try it to see how much penetration I can get. I might even re-install the stock valve to make a comparison. The only thing stopping me is the honeydo given to me by she who must be obeyed. When I get around to it I will let you know my results. Bud

Reply
heatpumpservices.co.nz link
6/30/2020 03:40:27 am

The more pumping tips and following the effective techniques as well. I know about the site and generating more pump services. The more maintenance and servicing on pumping.

Reply



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    Author: 
    David Grimes

    A serious airgun enthusiast with a particular fondness of Crosman pistols, I learn something almost every day.  


    I am not an overall expert or guru, but I will share some things from time to time that maybe some of you will find interesting.  


    There are often many ways to accomplish an objective. I do not pretend to either know them all or imply that I am always right. 


    Therefore, I reserve the right to be wrong from time to time.  ;) 

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