Author Topic: PC77 flat tops (Updated with crony #s) (Read 6703 times))

Rescue35 · « **on:** April 26, 2011, 07:18:17 PM »

I have a bad habit of cutting metal when I'm bored. That said I was bored today and since I had a disassembled PC77 laying around I played with the valve some. Ended up faceing the cone off of it. Then i grabed some 6061 aluminum round and and made a new piston. Put it into the new PC77 and all I can say is WOW! There is an amazing increase in power. I so need to get me a chronograph. I also can not wait for my stuff from Crosman to show up. I want to see what this thing can do in .22.

In .177 @ 20 yards it is knocking holes in an old steel pan that it used to just bounce off of. I would definitely recommend a flat top piston and valve to anyone wanting more power out of these pocket rockets.

Fun with pneumatics!

Toolmaker · « **Reply #1 on:** April 26, 2011, 07:54:10 PM »

Lets see some pics of your work. We really like pics.

You did take pics, right?

Rescue35 · « **Reply #2 on:** April 26, 2011, 08:45:32 PM »

Quote from: Toolmaker on April 26, 2011, 07:54:10 PM

You did take pics, right?

Just of "Slim" who was hiding under the Hudson, it didn't turn out to good. He is my Guard Snake.

I'll get one with it installed. I almost made it to long. It will work until I make a new one.

Rescue35 · « **Reply #3 on:** May 05, 2011, 07:24:08 PM »

OK. Parts got here early yesterday (5-4) from Crosman. I ordered them 4-14 (I must have gotten caught up in the inventory). I also received my crony from PA late in the afternoon so the PC77 was a .22 by the time it got here. Any way, here are the numbers.

These numbers are with a 14.5" .22 barrel and flat top piston and valve made by yours truly. The second reading is an additional shot without additional pumping. The shot number corresponds with the number of pumps.

1 145.6
2 248.7
3 317.8
4 360.3
5 398.6
6 431.3
7 454.6
8 485.6
9 497.6
10 517.6
11 532
12 553.6
13 558.3 228.7
14 565.4 323.6
15 573.3 365.1 (10.44 fpe & 4.23 fpe respectively)
16 563.4 426.1
17 552.9 Oops...forgot this one and wasn't about to redo it $:-\$
18 529.1 502.6
19 511.8 542.9
20 471.5 555.1 143.1

Here is a picture.

I'll have to put my other one back together in stock form to test it and then make a flat top piston for it for comparison and to see what .177 is putting out.

Future mods include valve work to see if I can get more umph out of it. Lighten the trigger and make a metal breech with decent sights that don't shift. I will also try to quite it (them) down especially the .177. With the flat top it was getting rather loud.

slothart · « **Reply #4 on:** May 05, 2011, 07:44:45 PM »

Are you adding a power adjuster or a heavier spring?

Rescue35 · « **Reply #5 on:** May 05, 2011, 08:41:29 PM »

I'm thinking of lightening the spring in the valve first. That will make it easier to pump and dump more air. After that I will consider either a power adjuster or heavier hammer spring.

slothart · « **Reply #6 on:** May 05, 2011, 08:47:38 PM »

Looking forward to seeing the results...

MountainMan126 · « **Reply #7 on:** May 05, 2011, 09:37:45 PM »

I have been shooting the superdomes in mine , 8.3 gr.
Average is about 597 fps at 10- pumps and around 650 with 15 pumps . Using a Mellon air barrel 18", f/t piston valve and power adjuster .

Mine has much less fluctuation in fps when pumped fifteen times , maybe 3 fps. Where when pumped only 10 times around 7 fps is average . Anyone else notice anything like this?

Ethan

1377x · « **Reply #8 on:** May 06, 2011, 05:08:48 AM »

a lighter valve spring and/or a heavier hammerspring will let you dump all the air past 15 pumps.
i used my stock trigger spring in the valve
for a heavy hammer spring i have read the crosman 2200 hammer spring is a great replacement spring

Rescue35 · « **Reply #9 on:** May 06, 2011, 08:12:29 AM »

Forgot tomention. The string above was using CPHP .22 14.3 grains

MountainMan, I have not tested for consistency yet. Still working on the power, but I will soon.

1377x, That was pretty much what I was thinking. Since I have a stock one apart I'll take some measurements and see about making some new springs as I have music wire on hand.

MountainMan126 · « **Reply #10 on:** May 06, 2011, 08:42:07 AM »

I still have the stock springs in mine , and no residual air at 15 pumps. I set the power adjuster to dump all the air while maintaining the least compression of the spring. Which is close to all the way in, but not quite there.

Ethan

Rescue35 · « **Reply #11 on:** May 09, 2011, 06:00:18 PM »

OK, played some more today. I reassembled one in stock form, just like it came out of the blister pack. Then I made a flat top piston and turned down the cone on the valve.

No wind shooting CPHP.177

# Pumps Stock Flat-Top
1 189 186
2 272 298
3 322 364
4 361 417
5 371 451
6 417 494
7 442 518
8 457 537
9 467 563
10 477 574
13 507 611
15 516 647
20 ** 680
25 ** 636

Then I made a lighter valve spring for the .22

5 396 Residual Air
6 428
7 453
8 476
9 493
10 519
11 538
12 556
13 570
14 588
15 588
16 592
17 609 368
18 612 422
19 618
20 626 390

At 626 fps that is 12.46 fpe. It's just cool to break 600.

Rescue35 · « **Reply #12 on:** May 09, 2011, 06:44:05 PM »

Picture of the flat top piston I made today for the .177 and the corresponding valve after machine work.

1377x · « **Reply #13 on:** May 09, 2011, 09:00:50 PM »

nice piston
is it adjustable?

Rescue35 · « **Reply #14 on:** May 09, 2011, 09:39:59 PM »

No it is not adjustable. The first one I made was and it just seemed like cheating. This one was done my way. Once fitted to the handle I checked for clearance with the valve. Faced it down and cut the O-ring grove. Works perfect.

Rescue35 · « **Reply #15 on:** May 09, 2011, 09:59:41 PM »

The lighter valve spring also made it much easier to pump. There is virtually no resistance until the 6th pump. However the hammer will hold the valve open so it must be cocked before pumping...or the air just comes right out the barrel.

MountainMan126 · « **Reply #16 on:** May 09, 2011, 10:19:50 PM »

Quote from: Rescue35 on May 09, 2011, 09:59:41 PM

The lighter valve spring also made it much easier to pump. There is virtually no resistance until the 6th pump. However the hammer will hold the valve open so it must be cocked before pumping...or the air just comes right out the barrel.

I have seen several posts related to a lighter valve spring, this is the first time I have heard about the change is pump force needed. Makes it a little more interesting, not that mine is difficult, but a little less force is less strain on other parts involved and quieter too.

Rescue35 · « **Reply #17 on:** May 11, 2011, 08:24:16 PM »

I've gone back to using the stock hammer spring as with the stronger springs I was having issues with the plastic breech twisting ALOT while cocking and I was not getting any noticeable power increases. I will probably make an rva in the future.

ETA breech link. http://www.gatewaytoairguns.org/GTA/index.php/topic,12575.msg106669.html#msg106669

slothart · « **Reply #18 on:** May 11, 2011, 08:56:29 PM »

if you don't mind me asking, where did you get your stronger hammer spring?
I am looking to upgrade mine, but AC is currently sold out and the other sources I've found are charging what seems a bit high to me. My next stop is the hardware store to see what I can find there.

Thanks

Rescue35 · « **Reply #19 on:** May 11, 2011, 09:43:43 PM »

Not at all. I made it. The best bet is Crosman, try the Benjamin discovery spring. If you want to try to match something up at the hardware store the info in this link will be helpfull. http://www.gatewaytoairguns.org/GTA/index.php/topic,12418.0.html The second post down has the dimensions for several Crosman springs that will fit.

Side Note: Both of these are louder now. Especially the .177

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PC77 flat tops (Updated with crony #s)

Author Topic: PC77 flat tops (Updated with crony #s) (Read 6703 times))

MountainMan126

MountainMan126

MountainMan126