1377 Number of Pumps?


June 20, 2014, 09:34 PM
Just purchased a crosman 1377, first airgun in a million years. The manual recommends 10 pumps but some online say 12 is fine. If the majority of shooting gets done at 3-5 pumps for target shooting will the occasional 12 pumps for garden pests adversely affect longevity?

If you enjoyed reading about "1377 Number of Pumps?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
June 21, 2014, 09:37 AM
I'm fairly new to air guns too…but I've done a bunch of research. What I've learned is this: If your owners manual says 10 pumps is the max…pumping it more won't give you any more velocity.

The amount of pressure in the tank isn't the only factor at work when you pull the trigger. A valve has to be opened to let air out of the tank. Too much air pressure at the start can cut short the amount of time this valve is open…leading to lower velocity.

One good analogy I read was that it's somewhat like putting gas in your car. If you normally put 10 gallons in your tank, but then put 20 gallons in, it won't make the car go faster.

June 21, 2014, 12:17 PM
You can also damage the pump linkage due to excessive force needed to close the pump handle

June 21, 2014, 04:17 PM
Thanks guys for the insight. In retrospect 12 pumps probably isn't going to make any significant difference/not worth it.

June 21, 2014, 05:56 PM
You can pump it as much as you want, but returns diminish fast. The first pump providing more air than the second and so on. This is why 10 pumps won't give you twice the power as 5, and it gets worse as go. For example I tested my unmodified gun and 15 pumps only made 17% more power than 10. Each pump puts air in the reservoir and the more air in the reservoir the more resistant it is to taking in additional air. Also the increased pressure pushes back on the plunger dropping the compression ratio so it's only capable of making so much pressure period, so at that point it won't matter how much more you pump you'll get nowhere except make more heat. At the rate of diminishing returns I imagine it peaks at maybe 25% more power at maybe 25 pumps. One drawback to excessive pumping is heat, so if you pump 20x, shoot, repeat over and over you can get the reservoir hot. I suppose it depends on what parts were used making the gun, specifically the seals, but heat is usually a bad thing. Looking at the guts of mine which is newer and has better seals I suppose it could take quite a bit of heat, but why push it. Now rather than pumping the gun more one should consider making it more efficient. With a better plunger with a higher compression ratio that doesn't give under pressure it can get more air in per pump, especially noticeable as reservoir pressure rises. With a nice aftermarket flat plunger setup adjusted properly you could get 10 pumps worth of power in say 6 or 7. And of course you could get 15 or 20 pumps worth in maybe 10-12. There's also the question of how much pressure the gun can take before blowing, but with an unmodified oem setup it would be impossible unless it was defective. Even with a modified setup I cannot imagine it ever being a threat, however some mods involve reservoir work that does weaken it and if done improperly I suppose it's possible.
So, if you like to shoot at a power level of 5 pumps for targets, it would be nice to have a modified pump to bring that down to say 3. And, no, 12 pumps in a stock gun will not harm it, just don't expect a 20% power increase to match your 20+% of additional effort. Another way to get more free power per pump is to get a longer barrel. There are also a bunch of other mods like increasing air flow thru the valve and to the pellet. Google 1322 or 13xx mods, they cover all kinds of things people have tried, and show how much power per pump you get with a stock gun, with this mod, that mod, combo of mods etc. Here's a link to a bunch of links: http://tinyurl.com/13xxmods
Btw, when I said 17% increase in power at 15 pumps I mean ftlbs energy, velocity increase is a less impressive looking 8%.

If you enjoyed reading about "1377 Number of Pumps?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!