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​​​ ​For the following tests a new P1377 American Classic was used. It had the factory 10.25" barrel and was upgraded with our MAGNUM CUP-SEAL VALVE & PISTON KITCrosman Premier 10.5 grain Ultra Magnum lead pellets were used for all of these tests, they produce more consistent velocity and accuracy then lighter pellets. Lighter pellets shoot faster, heavier shoot slower. A stock factory 1377 shoots about 500-535 FPS with 7.9 grain Crosman lead pellets on 10 pumps, the modified 1377 used in the following tests produced over 520 FPS with a much heavier 10.5 grain pellet on only 8 pumps, a lot more overall power with less pumping. Our custom valves and pitons produce the absolute maximum power that can be achieved with 13XX variants and related models.

 What we've been saying for many years is stronger hammer-springs don't always produce more power. The right combination of strength, length, wire diameter, how straight it compresses, and getting the precise amount of pre-load is what produces optimal power and consistency. The "sweet spot" or best overall performance in the following chrony tests was produced with our relatively light .038" WD HAMMER SPRING and 13XX MAGNUM ADJUSTER set back 4 full turns from full spring compression with the hammer cocked. This is where the hammer hits with the minimum force needed to empty the valve completely at up to 16 pumps. This also makes the gun shoot smoother and more accurately, cock smoother and more easily, reduces wear on parts and prevents damage to the hammer pin at low pump-counts. Our .042" WD HAMMER SPRING without the adjuster produces similar performance and benefits but not quite as much velocity, an average of 9 FPS less for each shot. We've always recommended our .038" WD HAMMER SPRING with our 13XX MAGNUM ADJUSTER to get the best performance from all 1377, 1322, PC77, 2289G Backpacker and 1300KT models. For those who don't want the adjuster the .042" WD HAMMER SPRING is the next best option.

 In addition to the standard pump and shoot method, the test gun at 16 pumps with the adjuster set 9.5 turns back (from full hammer-spring compression with the hammer cocked) was able to produce two consecutive shots without any pumping between them at around 540 FPS. That's two shots on 16 pumps compared to one shot at 11 pumps at the optimal power setting, then having to pump 11 more times for the second shot. This setting works well for hunting and pest control where you can make a much quicker follow-up shot. The precise adjuster setting to accomplish this will vary slightly from one gun to the next but is easy to achieve with a little tinkering. Using a shooting chrony makes it a lot easier to balance the shots or you can do simple penetration or POI (point of impact) comparisons to make sure both shots have adequate velocity.

TEST 1 with our .038" WD HAMMER SPRING and no adjuster :


4                340.2
6                415.8
8                462.1
10              490.9
12              553.4
14              580.0
16              617.4    Valve didn't fully empty on 16 pumps.

TEST 2 with our .042" WD HAMMER SPRING and no adjuster :

4                342.1
6                421.6
8                480.2
10              520.6
12              554.1
14              587.7
16              620.6    Valve fully emptied at 16 pumps.


  Indicates the number of turns back of the hammer spring adjuster knob from full hammer-spring compression with the hammer cocked.
**   Indicates the valve did not fully empty after the indicated number of pumps.
   Indicates that two shots were able to fired from the indicated number of pumps without additional pumping before the second shot.

*1    FPS            *2    FPS          *3    FPS          *4    FPS        *5      FPS            *9.5      FPS

4     341.0           4     343.9        4     355.1         4     357.2       4       335.0          4          349.8  
8     465.9           8     481.4        8     479.8         8     485.5       8       467.5          5          392.3
12   554.3          12   543.4        12    567.8        12   563.9       12     563.9         16         537.2
/ 540.4
16   617.4          16   617.4        16    615.8        16   626.3       16     617.8
**     16         542.6 / 543.4