1377 and estimated FPS

[mcc1961]

I am building a 1377 carbine with a 24" barrel,FT piston and valve,discovery spring and power adjuster.How much can you guesstimate my max FPS will be at 10 pumps?Here is a pic of the truck bed coating on my stock and pump arm.Waiting for parts so I can get it back together.

[breakfastchef]

Here are some of my numbers. Two of my 1377's are setup similar to yours without the Disco hammer spring or a power adjuster.

14" barrel - 630 to 650 ave. fps at 10 pumps
18" barrel - 630 to 670 ave. fps at 10 pumps

Velocity averages change between chrony sessions.

[JMJinNC]

I'm getting 695fps with 8.44 grain JSB Exacts and 640ish with 10.3grain JSB heavies. Over 700 fps with sub 8 grain pellets.

24" barrel, ft piston & ported valve setup, extended probe bolt, stock springs.

Details in this thread:

http://www.crosman-air-pistol-owners-forum.com/board/index.php?topic=6135.msg62960#msg62960

JMJ

[pirouge]

WoW, I shoot a 1377c carbine with a 16" barrel, I need to look more into that flat piston, I would be happy with a honest 600fps using 7.9 crhp's, I need to look into a crony also.

[0351_Vet]

Custom 1377-10 pumps 670fps with Meisterkugeln 7.0 Grain Wadcutters, very accurate.
MAC1 prepped 12" barrel.  AC Custom flat top piston and valve.