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PostPosted: Wed Mar 29, 2017 11:52 am 
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The valve that is in there is an older 13-XX. It's an aluminum one. I haven't made any volume changes to it from factory. Transfer port sleeve is the standard 13-XX .22 version, and it has not been expanded. There is a lightened poppet return spring in there, and a 13-XX valve stem. I don't think valve volume changes are going to do anything for this build since it's in .177. There's only so much air that can flow through that bbl inlet. Enlarging it won't make any positive changes due to the small bore diameter....

I'm not really a fan of volume increases on these valves- at least with methods that are within my means. The modest gains aren't really worth the effort of drilling them out- even in .22. I think Bob's extended valve body would be the way to go- far safer, and easier on the gun. It is easy to over drill these small valve bodies, and have the valve halves separate at the threads through boring too wide. Ask me how I know :wink: Interesting sound when they separate under pressure :mrgreen:

-D.S.

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PostPosted: Wed Mar 29, 2017 1:11 pm 
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My valve extension was worthwhile in .22 cal past about 7 pumps, and made a 100 fps difference at 30 pumps.... However, in .177 cal, it LOST performance at less than 20 pumps, and only gained 5% at 30 pumps.... It has to do with the ratio of valve volume to barrel volume....

Bob

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PostPosted: Wed Mar 29, 2017 1:24 pm 
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Good to know thanks to both of you!

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PostPosted: Sun Apr 02, 2017 3:52 pm 
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Was poking around the shop on lunch and found some likely candidate roll pins to try in the 13-XX hammer. They're from a P/A roll pin kit, so I won't be too terribly disappointed by bends. Also entertaining the idea of a 13 series hammer spring in there- just for the heck of it... that may increase the life span of the roll pin hammer pin replacements. :rolleyes:

I think I'm going to use the rear edge of the tube when I get to the 2200 build. It may make life a bit easier with either the 2200 or disco hammer springs.

-D.S.

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PostPosted: Tue Apr 04, 2017 12:09 am 
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Oh yes! 8)

Getting close to 2 balanced shots.

With the 13-XX spring behind a 13-XX hammer, JSB Exact 8.44 gr

1st 578.8

2nd 564.2

at 11 pumps with the RVA just shy of 1/2 way in.... took me almost an hour to get there.
This may be the way to go, for the time being :wink:

Interestingly enough ~ mid 540's for 5 pumps with the same RVA position.

More to play around with yet.

-D.S.

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PostPosted: Tue Apr 04, 2017 4:36 pm 
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You should get about the same velocity at 6 pumps (with no retained air) as your 11 pump - 2 shot tune.... You may never get the two shots exactly the same velocity.... and it will vary slightly depending on if you are shooting continuously (in which case the gun will be warm, and constant in temperature).... or if you pump it 11 times and then set it aside to cool (especially if it's cold out).... After cooling, the pressure will have dropped, the first shot will be faster, and you second shot will likely be slower, possibly quite a bit slower, depending on the temperature difference....

I found that my 19 pump - 2 shot tune required 20 or 21 pumps if I was going to let it cool down before taking them.... Of course it depends on how fast you pump, the ambient temperature, and a myriad of other factors.... One thing you might consider is once you find the balance point you like, crack open the pump handle, and let it rebound slightly instead of resting against the valve.... Do NOT open it very far.... The distance it rebounds will be proportional to the pressure in the valve after the last pump (it's the air trapped between the valve and piston expanding back to 1 atmosphere).... Mark that on the tube, close the pump lever again, and let the gun cool.... When you check it again, it probably won't rebound as far.... Try one more pump, and note where it rebounds to, compared to your original mark.... If you are lucky, and the stars align, that one extra pump could be just right to compensate for the cooling.... or not.... try 2 pumps.... Good Luck !!!

This method of using pump arm rebound to measure valve pressure was developed by Steve in NC on the Yellow, to give credit where due....

Bob

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Airsonal;
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PostPosted: Tue Apr 04, 2017 6:18 pm 
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Great to hear you've got two shots so close! Nice fps too for only 11 pumps! That is exciting!

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PostPosted: Tue Apr 04, 2017 8:46 pm 
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After a couple of hours trying to get repeatable, consistent 2nd shots, all I can say is I'm close. Extreme variation is in the 40 fps range (which ain't all that bad), and minimum variation I saw as low as 6.5 fps....

Bob's discussion on temperature has a lot of validity, I'm finding. FWIW, shots are closer together after I set the gun down for it to cool from pumping. I'm not getting the tube that warm- but it's enough to show fluctuating variations over the chrony if I don't allow the gun to cool.(RVA adjustments after tube cooling)

I do need to sit at the bench and see what effect those velocity variations have on p.o.i.
It probably will not amount to much at the ranges I normally shoot at.

That 2100 hammer is gnawing away at the back of my mind... hopefully will get a serious trial with it later this week. Hoping for an hour or so of bench time tonight.

-D.S.

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PostPosted: Thu Apr 06, 2017 1:01 am 
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Didn't get a bench session last night.

In the middle of one right now....

Just so's I can make total sense of what's going on~

... change as many variables as possible:

1.) Set the chrony up on the receiving end, rather than the delivery end. In this case, 12 meters.

2.) Change pellet style and weight. Now with the 9.3 gr RWS Super Mag wadcutter.

3.) Lock the RVA nut against the end cap at the halfway from spring contact mark.

Near balance at the 13 pump mark. 1st 551.2 , 2nd, 525.6. Did a 6 series, and except for 2 yanked fliers, all went into .28".
Camera batt is on the charger right now. I'll get some groups up for perusal once the batt cools down from the charger.

Incidentally, just from a quick off the top of my head averaging, based on previous experience, I'm shedding roughly 25-35 f.p.s. over that 12 M - just for those who care about such things...

-D.S.

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PostPosted: Thu Apr 06, 2017 4:04 am 
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Image

That's a total of 16 shots from cardboard box under the forearm rest at 12 meters. I yanked the 2 at left early in the series- I think #3 and #5. Max deviation over this series was 53.2 fps and min was 9.1.

I'm hoping to get out Friday to the gravel pit and see what the discernible differences are gonna be at 20 paces...

As a further point of interest, temperatures.

Ambient in the shop was an even 20.0 C by Greenlee 500 TTH infrared thermometer.
I allowed the gun to cool for 1/2 an hour and took the following readings:

Tube: 21.1 C
Delrin piston head: 19.5 C
Valve (through grub hole on tube side for 2100 frame) 20.0C

After 13 pumps:

Tube 20.0 C
Delrin piston head: 20.5 C
Valve 20.5 C

I need to do a little more work with the thermometer. It would be interesting to see just how warm the tube and piston head become over an extended session of multiple pumps beyond the normal 10 pumps...

-D.S.

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PostPosted: Thu Apr 06, 2017 9:37 am 
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nice shooting Doc... 8)

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PostPosted: Thu Apr 06, 2017 10:28 am 
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In an extended pumping session, the heat produced soaks into the gun, and it can become warm enough to feel the temperature rise.... I have melted a Delrin piston, but that's another story.... :roll:

A 30*C change of temperature will change the pressure by 10% (and the number of pumps by about the same)....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Apr 06, 2017 2:30 pm 
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That delrin is funny stuff. Must be one of the space age polymers- it sheds heat rapidly, but also heats rapidly.
The face on this piston is incredibly thin after being re-worked from being burnt. I don't think it will stand up to much torture testing, and really should switch it out for a metal one. That will come later. I think I want to leave the set-up as is for the time being. There really isn't enough space behind the hammer for powerful springs- until I can come up with a recessed RVA that will allow work with a longer spring. That disco spring was awfully packed-in when it was in there.

I'll pull out the 2200 and see if I can't get it up to shooting. I think it's gonna take a new valve body for that though- the stem seal surface on the inside of the valve is badly corroded.

-D.S.

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PostPosted: Fri May 05, 2017 10:12 am 
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Great project, and good end result! I'm itching to press the checkout button on the 2100b tube and pump assembly myself, next payday maybe [SMILING FACE WITH SMILING EYES]

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PostPosted: Wed May 17, 2017 1:13 am 
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Finally got some time to give this rifle the attention it needed. Work has been really getting in the way lately.

Had a heck of a time getting the 13 series valve out. It had climbed over the valve stop dimples in the 2100 tube. The t.p. seal was wrecked.

Went to a 2100 rear valve section, and an old brass 760 valve front section. The brass mills down nice in cutting for flat top piston use.
Went with 1/4" ice maker tubing under the t.p.. The exhaust hole is cut deeply for the t.p. on the 2100 bbl block. Past experience says two 22-XX seals under the t.p. on that valve rear will work as well.

Back into decent numbers on the low side- 520's-530's @ 4 pumps with 7.9 gr milk carton crosman points.

Toyed briefly with the 2100 short valve stem. Talk about retained air- 4 shots on 10 pumps, none above 300 fps :lol:
Went back to the 13-XX stem in quite short order.

Nice top end with the rva all the way in on the cut down 2100 spring- 840-855-ish at 20 pumps, and no retained air. Not much sense in going 25 pumps- gain is only 10-15 fps.

Now for the sweet stuff. With the rva 4 turns back from coil bound on the cut down 2100 hammer spring, @ 20 pumps, 1st shot 820-825-ish, 2nd shot low 670's to low 680's :mrgreen: I think that's as close to balanced as I'm gonna get!

I'll put her through full paces at the pit this coming Friday, and see how the 2100 rear valve section is going to sit against the valve stop dimples...

If everything stays more or less on a balanced keel, I'll put a p-rod grip frame and trigger on it, and be done with it :wink:

-D.S.

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