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

[Crosshairs]

Here i is  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

[JMJinNC]

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

[quickster47 †]

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

[Crosshairs]

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

[quickster47 †]

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