Some test results 1377 mods

[JWL79]

I have been tinkering with my 1377 for some time now and I finally got a chrono. I did a lot of testing with 9 different pellets and got some decent results. I tested each pellet with 3, 5, 8, 10, 15, 20 & 25 pumps. I can post all results if you are interested. I have so far added a stock, FT valve & piston, steel breech, 16" barrel, adjustable trigger, polished the sear and trigger, polished hammer, and made a few valve mods (change port angle & valve stem mod). I am considering cutting a few threads on the Male portion of the valve to gain some space but I don't know if it is worth the trouble.

After messing with the  valve mods I got the following at 25 pumps:
Crosman Destroyer 7.4gr 775.6 fps or 9.89 fpe
Crosman Penetrator 5.4gr 867.1 fps or 9.02 fpe
Crosman ultra mag 10.5gr 677.5 fps or 10.7 fpe

[arkmaker †]

Those look like great numbers JW! Looks like you have done your homework. Is the accuracy as good? I think that the tree rats will be moving out of your area once they know that you have that :-)

[JWL79]

I haven't taken it out past 20 yards but it is a tack driver, nickel size groups usually, dime size if I am trying hard. 10 yards once I  put 5 pellets thru the same hole.

[BillK]

Those are great numbers!  And it sounds like you have an accurate barrel to go along with them.   
IIRC increasing the valve  volume on a .177 is not recommended.  There are some mild gains to be made in .22 but not in .177.  Something about the capacity of the barrel to make use of the additional volume of air from an increased volume valve. 
However pinning the valve is definitely recommended.  With the number of pumps you are using, that valve should be pinned.  It, pinning, will be more helpful than increasing valve volume and will prolong the life of your gun.
It's a "must do" IMHO.  Lots of info here.  Check out Wyoman posts.
Have fun & straight shooting.......  

[onebaddj]

Dang, those look good to me. Your 1377 is a beast of a gun. Nice work.

[The Zen Master]

Those are great numbers!  And it sounds like you have an accurate barrel to go along with them.   
IIRC increasing the valve  volume on a .177 is not recommended.  There are some mild gains to be made in .22 but not in .177.  Something about the capacity of the barrel to make use of the additional volume of air from an increased volume valve. 
However pinning the valve is definitely recommended.  With the number of pumps you are using, that valve should be pinned.  It, pinning, will be more helpful than increasing valve volume and will prolong the life of your gun.
It's a "must do" IMHO.  Lots of info here.  Check out Wyoman posts.
Have fun & straight shooting.......

Do you have any direct links to Wyoman's post about pinning? Just searching Wyoman could leave someone reading for months till they find the info they're after as happened with me when looking for shortening a barrel - I gave up after reading about 4-pages.