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Perfect Plinkin' Pistol, PPP, Mods stage I

May 21 2011 at 10:35 PM
Daysailer  (Login Daysailer)
Crosman Forum Member
from IP address

This topic is also posted on the Crosman AirPistol Owners Forum.

After lots of googling....
After lots of searching 'n studying....
Even more pondering......
Then posting some questions....
More study...etc...etc........

It all comes down to eventually you gotta get out the tools and do sum-thin.

Bought a new 1377 at local discount chain, Bi-Mart. 2010 model with three screw plastic coverplate.
Chrony'd it first day....and again after 350 shots.. The numbers were consistant from new to broke in by 2-3 fps.
Kind of surprised me how consistant it was from the beginning. (results posted below)

My goal was to improve simple plinking power at 3-5 pumps. Hoping to gain one pump worth more power, over stock.

Started doing the 'poor man's' mods that I found, shown in these threads;

Hindsight, I should have started with the valve tip shaving first, but did it later in my sequence, so some informational insight was lost.
Just finished and here are some numbers for ya'll.

RWS Basic pellets, weighed 7.1 to 7.2gr.
F-1 Chrony, indoor, with stickup 3 bulb LED closet lights set on screens. End of muzzle to 1st screen = 18"... NO errors recorded while doing any of these tests.

Column 1, stock 2010 1377, Brown, consistant day to day fps results from 1-350 shots. 5-5 to 5-13-2011
Column 2, piston rod stiffening, Filed valve tip to improve valve/pump cup fit to reduce headspace. Added .031" thick washer shim 'tween piston & pump cup to make up loss of valve length and readjust pump stroke length. Put in a lighter valve spring. Consistant day to day fps numbers, from 360- 575 shots. 5-14 to 5-20-2011
Column 3, added small 'o'ring(A012) shim/spacer between piston cup holder and pump cup, to take up the space created at the piston cup holder joint & the piston cup. First 50 shots 5-21-2011.

Pumps - 1 - - 2 --- - 3 --- Total FPS gained
2 ----- 296 - 299 - 324 = 28
3 ----- 350 - 366 - 397 = 47
4 ----- 391 - 413 - 449 = 58
5 ----- 424 - 444 - 488 = 64
6 ----- 455 - 471 - 519 = 64
7 ----- 470 - 496 - 541 = 71
8 ----- 491 - 509 - 559 = 68
10 ---- 518 - 541 - 588 = 70

Extreme spread on todays tests, for each 5 shot string were within 2.1 (5 pumps) and 6.3 (6 pumps) most in the 3-4 range.

(used my 2009 1377 with over 2500 shots as a Chrony test constant to verify each days tests were within 3-5 fps of this pistol's known consistant preformance. )

Without getting to my stage II mod, "reduce valve volume", I have more than exceeded my realistic goal.
It is also interesting to note the gain per pump increase through the middle of the pump count range. From 4 - 8 pumps gain from each additional pump was amazingly similar.

Many many thanks to all who have posted thier insights, methods, thoughts and just plain chewed on these ideas on the forums before me. Nothing here is new, just rediscoverd !

See threads linked above for picture clairifcations, and a couple on this forum;

This message has been edited by Daysailer from IP address on May 21, 2011 11:10 PM

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