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PostPosted: Thu Sep 21, 2017 11:46 pm 
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Location: Toronto
I've always enjoyed shooting multipumps and my first airgun was a stock Crosman 2289. One question that always came up was: How many pumps is ideal in a prolonged shooting session? Of course, one pump is best if you wanted to conserve the most energy, but what would be the optimal balance between pumping effort and sufficient velocity and knockdown power at reasonable airgun distances?

So with some free time and some borrowed gear (thanks Anthony), I decided to chart out the number of pumps vs. FPS for two airguns to see what the optimal pumps would be from an efficiency perspective.

The Crosman 2289 is a custom build:
-Crosman 2200 tube (so it's technically a 2200 and not subject to RPAL standards when above 500fps)
-14.5" .177 barrel fits perfectly flush with the end of the tube and barrel band
-Flat top piston and poly tube transfer port

The Benjamin Sheridan 392PA is stock.

Pellets used were .177 H&N Hammer 7.87gr in the 2289 and .22 Crosman HP 14.3gr for the 392PA. Three shots were taken at each pump figure to get an average FPS reading.

Image
(While I know going from 0 FPE to some FPE from the 1st pump is mathematically an infinite % increase, I've used 100% gain as a plug figure to simplify chart scaling)

What is not reflected in the data is the actual bio-mechanical energy spent pumping, which increases incrementally with each successive pump. For instance, the 6th or 7th pump is roughly twice the effort of the 1st and 2nd pump (I wouldn't know how to accurately measure this). The pumping effort also differs between guns. The 392PA with a larger swept volume (but somewhat offset by more leverage from the longer pump arm) takes more effort to pump than the 2289.

Judging from the marginal FPE % gain, it would seem like the most efficient number of pumps to use in this case is 3 or 4 pumps. After the 4th pump, the marginal FPE % gain is only 17-18% for the next pump and steadily declines from there. Unless you absolutely need the higher power output (e.g., hunting), it's not worth it in terms of energy expenditure vs total FPE.

What do you guys think? Do you notice the same pattern with your multipump airguns?

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PostPosted: Fri Sep 22, 2017 10:42 am 
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Yep, pretty much.... It sure shows you when to quite pumping because the gains are not worth it any more.... What number of pumps that is varies greatly with the gun, of course...

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
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Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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PostPosted: Sat Sep 23, 2017 10:04 am 
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Yes, it would seem that manufacturers usually optimize multipumps for an intermediate number of pumps, but most folks like to use the maximum pumps (or more) to get that advertised velocity.

I think that's why most people dislike this type of power plant. When you're pumping 10 times or 20 times to shoot once, it gets old real fast.

Here's some additional data I got my hands on:

Crosman 2200 Magnum (14.3gr CHP):
455fps, 6.58fpe @ 5 pumps
577fps, 10.57fpe @ 10 pumps

S&W 77A (14.3gr CHP):
452fps, 6.49fpe @ 5 pumps
584fps, 10.83fpe @ 10 pumps
647fps, 13.30fpe @ 20 pumps

I mostly shoot my multipumps at 3-5 pumps for that reason. At the lower pump counts, it's effortless to pump up after each shot. In fact, I would say it's easier to do 3 pumps compared to cocking most springers once. This also has the added benefit of not prematurely wearing out the linkages. If I wanted higher fps and power, I use my PCPs. It's unfortunate that most people who shoot multipumps have the mentality of getting the power out of their guns. Multipumps are simply not designed and not practical for shooting at the top pump ranges.

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PostPosted: Tue Sep 26, 2017 9:57 am 
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Location: Toronto, Ontario
TriggerHappy416 wrote:
Yes, it would seem that manufacturers usually optimize multipumps for an intermediate number of pumps, but most folks like to use the maximum pumps (or more) to get that advertised velocity.

I think that's why most people dislike this type of power plant. When you're pumping 10 times or 20 times to shoot once, it gets old real fast.

Here's some additional data I got my hands on:

Crosman 2200 Magnum (14.3gr CHP):
455fps, 6.58fpe @ 5 pumps
577fps, 10.57fpe @ 10 pumps

S&W 77A (14.3gr CHP):
452fps, 6.49fpe @ 5 pumps
584fps, 10.83fpe @ 10 pumps
647fps, 13.30fpe @ 20 pumps

I mostly shoot my multipumps at 3-5 pumps for that reason. At the lower pump counts, it's effortless to pump up after each shot. In fact, I would say it's easier to do 3 pumps compared to cocking most springers once. This also has the added benefit of not prematurely wearing out the linkages. If I wanted higher fps and power, I use my PCPs. It's unfortunate that most people who shoot multipumps have the mentality of getting the power out of their guns. Multipumps are simply not designed and not practical for shooting at the top pump ranges.
I shoot the m4-177 and 1322 and both guns optimal velocity gains are between 5 and 10 pumps. After that, the increases in fps trail off. . When I chronied both guns a month ago, my fps shot up approximately 95 fps on my 1322 from 5 pumps to the 10th pump. The fps increase on the M4-177 was lower. I usually use 3 to 4 pumps at home and at the range, I move up to 10 pumps as I shoot out to 30 plus yards.

Sent from my K00L using Tapatalk

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PostPosted: Sun Oct 08, 2017 2:58 am 
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I had some time to test the Crosman 1322 pistol as well in its stock configuration.

Image

Once again, we see that the additional % FPS gain starts to trail below 10% after the 4th pump. It is interesting to note that 3rd pump has more marginal gains in terms of FPS and FPE than the 2nd, which goes against the trend from the 2 rifles I previously tested.

From the rsterne's previous posts on his multipumpers and others on the net, we know that the FPS vs. Pumps curve is asymptotic with diminishing returns as the pumps increase. Data from these pumpers suggests that pumping efficiency drops off to less than 10% marginal FPS gain after the 4th pump. Multipumps become less pleasant to shoot when people go for the manufacturer suggested max (usually 10 pumps) in the hopes of achieving factory stated FPS figure.

For a prolonged shooting session at reasonable distances, shooting with 3-5 pumps would optimize for efficiency while maintaining a respectable velocity. Also as a side note, I was unexpectedly impressed with the Benjamin Sheridan 392 as it's one of the most efficient multipump designs I've seen so far without modding.

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