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SMP · Silver Status Member

I am back home and finally got a chance to check the new FTP setup on the chrony. I'm fairly sure I have it adjusted to zero clearance but I'd like some opinions on these numbers.

Shot thru a 10.1" barrel using CP FieldTarget

Stroke # Velocity fps

2 ..... 258
3 ..... 307
4 ..... 352
5 ..... 381
6 ..... 403
7
8 ..... 437
9
10 ..... 462
11
12 ..... 485
13
14 ..... 500

rsterne · Moderator

.177 or .22?....

If the pump arm stays closed after the gun is fired, then it's hitting the valve OK.... If it's really hard to "snap" closed, it's adjusted too long.... You want the pump handle to show resistance about 3/4" from the closed position after firing the gun (ie no air in the pump)....

Bob

AirGunEric · Site Admin

Seems like alot of pumps to get to 500fps- although if it's .22 caliber and with a 10" barrel maybe that's not so far off.

rsterne · Moderator

With a 14" barrel in .22 cal and 14.3 gr. pellets.... FT Piston & Valve and plugged bleed hole.... most guns get to 500 fps in 9-10 pumps.... 14 seems a bit much, even with a 10" barrel.... Did you change the hammer spring to one from a 22XX (lighter) or install a heavier valve spring?.... or is the hammer dragging on anything?....

Bob

SMP · Silver Status Member

It's a .177

I had that previous issue with retained air so I've had the hammer out and thoroughly checked. It was blemish free so I gave it a very fine polish (crocus cloth) and a light buffing with synthetic machine oil. That solved the retained air problem.

The handle is staying closed with a bit of resistance at the stroke end. I don't think 3/4" though so I will adjust it a touch more.

Both the valve and hammer springs are stock.

I thought it seemed a little high but it is an improvement over the stock piston which was at 400 fps at 10 pumps.

The one thing that is notable is there a whole lot more air. It seems like the beyond ten pumps the bang is ferocious and the barrel kicks up a little from the air blast.
edit: replace piston with hammer

rsterne · Moderator

Well you've got something weird going on.... In .177 cal you should be WELL over 500 fps at 10 pumps with a 10" barrel and an F.T.P....

I can't understand how any type of work on the (FT) Piston could have any effect on whether the gun retains air.... The air is retained inside the valve because the valve spring pressure plus the air pressure is more than what can be released by the hammer strike.... Improving the piston can only affect how many pumps it takes before the valve retains air....

Now the Hammer is another matter entirely.... Wink

Bob

SMP · Silver Status Member

Sorry Bob

My mistake read "hammer" not piston Embarassed

rsterne · Moderator

Here are the results from a 1377 I tested - 10" barrel with F.T.P. - 7.9 gr. pellets in .177 cal.... All springs and ports stock....

Pumps - Velocity

1 - 202
2 - 294
3 - 358
4 - 403
5 - 438
6 - 472
7 - 497
8 - 519
9 - 538
10 - 554
11 - 570
12 - 584
13 - 595
14 - 605

This gun started retaining air at 15 pumps....

Bob

SMP · Silver Status Member

Thank you Dr Sterne that is exactly what I was looking for. I'm going to adjust the piston a smidgen and see what happens. Your numbers are what I was hoping for. A decent target punching velocity in 5-7 pumps

SMP · Silver Status Member

I adjust the FTP out a half turn and I felt a more positive stop just before the handle closed.

2 - 320
3 - 383
4 - 430
5 - 464
6 - 492
7 - 511
8 - 530
9 - 542
10 - 553
12 - 567
14 - 582
16 - 585 + 2nd shot 274

As you can see one extra half turn beyond my calculated distance has made a big difference.