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
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
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
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! ;D ;D ;D
Quote from: NorthStaR on November 16, 2011, 05:42:37 PM
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! ;D ;D ;D
heres a link to a calculator no need to melt your brain
http://www.airgunhome.com/pages/calculators.html (http://www.airgunhome.com/pages/calculators.html)
Thanks 1377x! .....I was hoping I didn't have to even use my brain (at all!!!)! ;D ;D ;D
I'll figure it out when I get out of work! (The firewall blocks that site)
Thanks all. That calculator says 8.4 ft lbs, confirmed by Chairgun app.
JMJ
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. ;)
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
Ah, now I get it! Thanks for the info. Nice number. 8)
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?
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 ???
Quote from: JMJinNC on November 16, 2011, 03:38:08 PM
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
Quote from: 1377x on November 17, 2011, 04:32:02 AM
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
Quote from: quickster47 on November 17, 2011, 01:27:30 PM
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! :-[
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.
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 (http://www.crosman-air-pistol-owners-forum.com/board/index.php?topic=2522.0)
Here i is ;D One of my 1377s has a 24" barrel and the other one is 12 1/2" barrel the 24" gets 700 fps with 10 pumps with a RWS 8.2gr the pistol is getting very close to 700 fps also.
Mike
Quote from: wildeboer on November 17, 2011, 05:50:24 PM
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 different pumps. He also had a spreadsheet on speed vs barrel-length.
I have the data from that study. That data with a stock gun was shooting 474 @ 14" versus 513 @ 24". I'm shooting 670 at 24"(well, 23.5" actually), so 30% higher velocity. If it's linear, the study's 3.9 fps/inch gain would translate to approximately 5 fps/inch in my case.
I'm shooting roughly 710 fps at 15 pumps (40 fps faster), so I'd expect something like an extra 16fps over my stated 670 at 12 pumps, (686 fps). With my longer barrel, I should be getting an extra 50fps over what you get, right? (5 fps/inch x 10").
So in that regard, my question is answered, since I'm theoretically shooting the same velocity as you would at 12 pumps, but my barrel is 10" longer. Either I'm losing some air at the transfer port, or my flat top set-up is not optimized.
I've attached copies of the barrel length study and my collected data.
JMJ
On all my barrel testing, the two lists and charts, I used 10.5 grain Crosman Premier Ultra Magnum (CPUM) pellets. That could be why my FPS numbers are a little bit light.
I pretty much use CPUM pellets for all my initial testing so I have a consistent baseline.
Carl
Quote from: quickster47 on November 17, 2011, 09:22:31 PM
On all my barrel testing, the two lists and charts, I used 10.5 grain Crosman Premier Ultra Magnum (CPUM) pellets. That could be why my FPS numbers are a little bit light.
I pretty much use CPUM pellets for all my initial testing so I have a consistent baseline.
Carl
Yeah but you get a better punch with the 10.5s .
Mike
Quote from: Crosshairs on November 17, 2011, 09:53:36 PM
Yeah but you get a better punch with the 10.5s .
Mike
That too. I also use them because I bought 5 boxes of the them and there is 1,250 pellets in each box. Price was reasonable, $24.99 per box.
For more serious .177 work I use the Skenco NewBoy Senior .177 domed pellets weighing in at 15.8 grains.
Carl