Question - FPS with 1377, 24" barrel and FT setup?

[JMJinNC]

I'm currently logging 670 fps for JSB Exacts (8.44gr) out of my PC77 with a 24" barrel at 10 pumps. Other mods are Mellon flat top piston & valve and my own spin on the Brutuz seal.

My question to others with a similar setup (24"/FT), does this sound about right or am I losing pressure somewhere?

Thanks - JMJ

[quickster47 †]

With a box stock 1377 and only changing out the barrel to a 24" one I was getting an average of 513 FPS, or 6.14 FPE, using 10.5 grain CPUM pellets so your numbers look good.

Carl

[arkmaker †]

Here are my numbers, so I would say that 670 fps is smoke'n!
Rich

.22 Crosman Premier Hollow Points. Only mods are 14" barrel, steel breech and flow thru bolt.

5 Pumps
395
399
405
399
402

10 Pumps
489
487
488
488
489

[NorthStaR]

What's the in FPE? 

Sorry the speed thing and pellet weight makes my brain melt. Gimme FPE and I know what's going on! 

[1377x]

What's the in FPE? 

Sorry the speed thing and pellet weight makes my brain melt. Gimme FPE and I know what's going on! 

heres a link to a calculator no need to melt your brain
http://www.airgunhome.com/pages/calculators.html

[NorthStaR]

Thanks 1377x! .....I was hoping I didn't have to even use my brain (at all!!!)! 

I'll figure it out when I get out of work! (The firewall blocks that site)

[JMJinNC]

Thanks all. That calculator says 8.4 ft lbs, confirmed by Chairgun app.

JMJ

[millipede]

i was able to get my gun to shoot cphp at alllmost 900 fps with the long barrel and ft piston. of course i had to pump it like a million times to do that. 

[JMJinNC]

I pumped mine up 15x a few times and got shots in the 710-715fps range, but even 15 pumps is a PITA, and the extra air was overwhelming my reflex-action shroud.

At 10 pumps I get decent power and it's still (neighborhood) backyard  friendly.

JMJ

[NorthStaR]

Ah, now I get it! Thanks for the info. Nice number. 

I get 11+FPE with a 20 inch barrel, FT valve and in .22 caliber at 10 pumps.

I wonder if it's a caliber thing where .22 is more efficient like with Co2?
Meaning .22 gets more shots from a 12g than .177 which I find interesting.

Must be a back pressure thing?

[1377x]

i think croshairs has a 1377 with a 13" barrel he got some pretty good numbers also
i thought he would have chimed in by now

[quickster47 †]

I'm currently logging 670 fps for JSB Exacts (8.44gr) out of my PC77 with a 24" barrel at 10 pumps. Other mods are Mellon flat top piston & valve and my own spin on the Brutuz seal.

My question to others with a similar setup (24"/FT), does this sound about right or am I losing pressure somewhere?

Thanks - JMJ

i think croshairs has a 1377 with a 13" barrel he got some pretty good numbers also
i thought he would have chimed in by now

From reading his post, I really think JMJ is asking about 24" barrels.

Carl

[1377x]

From reading his post, I really think JMJ is asking about 24" barrels.

Carl

that was supposed to be 24"
missed the right keys from the looks of it!

[wildeboer]

I think you are are losing some pressure somewhere along the line. My 1377 with flat-top conversion produces around 685fps with 8.44gr Air Arms with a 14" barrel and 12 pumps.
Do a search on longer barrel vs higher speed. Someone did some tests with a 24" barrel and differant pumps. He also had a spreadsheet on speed vs barrel-length.

[wildeboer]

Sorry, i quickly did a search and the 1377 pistol used was stock standard but for interest sake here is the link.
http://www.crosman-air-pistol-owners-forum.com/board/index.php?topic=2522.0