Set up time of flight chrono, Interesting findings, 1322, PC77, 2100b

[K.O.]

First the method,

Computer soundcard , Audacity, two microphones

15" muzzle to tuna can on its side (in front of box of old magazines as a backstop)

one mic at muzzle one at can.

D/T=R  (Average velocity)  (can use chair gun or math to find  Muzzle velocity)  (Should be about 15- 25 fps higher)

First the Good

I thought my  brand new stock 1322 was shooting an honest 460 fps Mv.

10 pumps  Av  454.5
12 pumps  Av  483.8
15 pumps  Av  535.7  (wow!)

now the bad

Lightly used  PC77

10 pumps  Av 508
12 & 15 pumps  507 & 505  (Wha da ? , Canadian valve?)

Lightly used 2100

10 pumps  Av  603
12 pumps  Av 621
15 pumps  Oldest (High functioning Autistic 28 year old) son was due home so tore down and did not shoot. (I was set up in living room)

I think I cost myself some 20-30 fps when I accidently  choked the 2100bs barrel, it was worth it,  still hitting or coming very near a quarter size target @ 30 yards very consistently.

853

Did not get to the 853  I put new seals but I think I am only getting about 425 fps or so. Did not have a dished piston and piston just touches face of valve.

I measure valve volume at close to .51 by .51 with my cheap Vernier caliper.  need to do some thinking...

[K.O.]

OH used

Crosman pointed for both .177 & .22

[1377x]

interesting
the 1322 and pc77 numbers look about right if they are not flat topped
the 2100 is low. i was getting 684fps with 8.8gr beeman crow mags and 704 with cphp i think maybe it was destroyers ex

[K.O.]

 I estimated about   650-670 fps Mv before the 2100 had a choked barrel  and my figures here are  average velocity not muzzle.

I figure muzzle velocity is 640-650 or so now but am to lazy to do the math to be sure.  I guess I could use chair gun to have a closer estimate but 

Honestly losing 20-30 fps to the friction of the choke is very acceptable for the accuracy...


I do wonder what is up with the PC77?

[K.O.]

I picked up the PC77 and 2100 used they may have been stored without a few pumps in them and just may pick up some fps over the next few months as I make sure to store them with 2 pumps.

I may bump that up to 5 pumps for a while...


And yes their power plants are all stock...

[1377x]

the choke accounts for some loss in velocity right
and it could probably use a new pump other than that if its holding air the inside seals have to be good
my seal test is chrony 5 pumps than store the gun overnight then run it across the sensors 24 hrs later. if it reads the same then i do it again only leave it for 2 days
if its still showing good numbers then the last test is one week then check the numbers
i was just looking at my disco and i havent filled or shot it since last fall/winter actually its been 10 months today. it still has a 3k fill in it. it feels good knowing the seals are holding up under all that pressure

[K.O.]

The possibility I am thinking is that if they sat for long periods unpumped is that the cups took a relaxed set and are not parachuting as quickly at the beginning of the stoke thus limiting the buildup of pressure a bit?

It is a theory...

Am thinking of pumping up and setting them on an oil filled heater for just long enough to get them warm,

let cool repeat  once  more,

send a few rounds down range,

and test again.

I  do not think they are leaking down at all after sitting overnight but have not chrono tested that yet.

When I got them as a package deal both (PC77,2100) had accuracy probs so it does seem that a frustrated owner not knowing what to look for and fix would also leave unpumped.

they both also looked un oiled when I got them...

they looked like there had been very little use also

their serial #  are  May/December 2011.

reasonable 

[K.O.]

Man sometimes I ignore the obvious,

Bet you can guess which is the 1322 and which is the PC77,

I am thinking headspace is a possability...

from breech side of pin screw to tube ends measurements are .455  and .475,

Hmmm.

[K.O.]

Arggg.................

had post typed and lost it

I realize .02 is only 5-15 fps lost probably

and that does not explain it not pumping past 500 or so fps,

but every bit is a bit of tune...

I read a post that a guy took a look in his recent 13xx and the pump cup and valve were done right no mod needed.

My 1322 is #  March of this year.

It may be that the PC77  may need one of the mods I was planning on when I pick up a steel breech and 14"-16" barrel next year  (1322 first)

http://www.network54.com/Forum/275684/thread/1211140448/1211339438/some+interesting+valve+stuff+for+pumpers+(Pics)

[Davio]

That's some nice looking roll pin replacements you got there!   

[K.O.]

That's some nice looking roll pin replacements you got there!   

I really think they look like how Crosman would do them if they where not trying to meet a price point.

I just noticed an oooops,

in first post I wrote     15" (Inches)  I   meant  15' (Feet)   which if traveled in .025 seconds    15/.025=600 fps

[rangerfredbob]

The possibility I am thinking is that if they sat for long periods unpumped is that the cups took a relaxed set and are not parachuting as quickly at the beginning of the stoke thus limiting the buildup of pressure a bit?

My first 1377 that was made in 1993 has never been stored pumped up at all and it shoots like new, all original still... no chrony but it feels like the rest of my 13XX's do when pumping if not better than a couple of them...

[K.O.]

My first 1377 that was made in 1993 has never been stored pumped up at all and it shoots like new, all original still... no chrony but it feels like the rest of my 13XX's do when pumping if not better than a couple of them...

Thanks for the input...

I am leaning towards it is probably a headspace  issue I was just brainstorming to figure out what is up with the PC77.