Couple of left over questions: Walter and Tom

Couple of left over questions: Walter and Tom

Joined: November 17th, 2006, 3:51 am

December 20th, 2010, 12:31 am #1

Walter: Hows the BAM 51 coming along?
Tom: Anything new on getting that QB PCP up and running right?
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Joined: August 16th, 2006, 10:39 pm

December 20th, 2010, 3:43 am #2

I will degas the tube in morning and try and align the transfer port better. I am at 2.5 coils clipped off but no consistancy between my strings...I just am not getting a consistant squish on the ice maker tube with the alignment.. each time I remove the breech its like getting a different transfer port dia.


Its cold but I am going to take the second hammer out to the garage and get cold....I am going to lighten it like Bills only the front behind the cocking pin to same diameter of the skinny middle.....then I will try the stock 59 MM long spring with it...

Today speeds were too low for the hammer spring used

I think the faster lighter hammer might be the ticket this long spring is too hard to cock. if that does not work I am wondering if a lighter valve spring would help

Its holding pressure great left it at 2500 last night and it was right there this afternoon....that delrin stem must have been lapped to the seat

What you think of the port alignment?? can I improve that??

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Joined: October 25th, 2002, 3:46 pm

December 20th, 2010, 4:08 am #3

Walter: Hows the BAM 51 coming along?
Tom: Anything new on getting that QB PCP up and running right?
it seems to start amazing me then the next shot will move a bunch.
makes a new group in a new spot then might return to the first.

Drives me nuts so its on the shelf while I finish up work for other fellas.
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Joined: November 17th, 2006, 3:51 am

December 20th, 2010, 4:10 am #4

I will degas the tube in morning and try and align the transfer port better. I am at 2.5 coils clipped off but no consistancy between my strings...I just am not getting a consistant squish on the ice maker tube with the alignment.. each time I remove the breech its like getting a different transfer port dia.


Its cold but I am going to take the second hammer out to the garage and get cold....I am going to lighten it like Bills only the front behind the cocking pin to same diameter of the skinny middle.....then I will try the stock 59 MM long spring with it...

Today speeds were too low for the hammer spring used

I think the faster lighter hammer might be the ticket this long spring is too hard to cock. if that does not work I am wondering if a lighter valve spring would help

Its holding pressure great left it at 2500 last night and it was right there this afternoon....that delrin stem must have been lapped to the seat

What you think of the port alignment?? can I improve that??

Am a believer in the lighter striker, but havent found it to be best for power. Has helped with shot count, but has always had a bit of a velocity penalty.
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Think youre transfer port, with the right icemaker tubing, should move more than enough air. Steve and others have used an o-ringI tried that, but never got it to work.

Wanted this .177 PCP QB to slow down and give a longer shot count. Strangling off the transfer port did that quite wellbut even this dinky port can earn 16 foot pounds at 120BAR. (ugly sealbut it seals).
[/IMG]
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Joined: August 16th, 2006, 10:39 pm

December 20th, 2010, 4:15 am #5

did you reduce the smaller diameter section as well???


I have some of those carbide insert style bits how fast did you spin it to cut thru the surface hardening???

the two hammers are starting out 1 gram apart one like 57 and one 56 grams
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Joined: November 17th, 2006, 3:51 am

December 20th, 2010, 4:19 am #6

it seems to start amazing me then the next shot will move a bunch.
makes a new group in a new spot then might return to the first.

Drives me nuts so its on the shelf while I finish up work for other fellas.
You probably thought of them.


Not my stock work (have no talent in that area), was bought (used). Air tube has been free floated from the valve on forward. Am guessing the previous owner felt that the tube could expand and contract enough to change the point of impact.
[/IMG]
I did glass bed the air tube from the valve back and set the barrel band to have just a touch of slack on the barrel. May just be chance, but its the most stable POI rifle in the safe.


Edit:

Had three things that needed to be done.

1. the trigger housing bolts onto the air tube with two screws (but you have to remove the parts of the trigger to get to them). If the trigger housing wiggles, the trigger pull varies.
2. can adjust the trigger to end up with a sear-drag situation...which does accuracy no good at all.
3. Cleaning the striker and making sure the inside of the air tube was smooth/polished and the strike moved freely cured an accuracy problem from gunk build up (the only openings in the air tube are right were the striker runs...so whatever dust/filth they pick up just plates itself to the striker).
Last edited by gubb33ps on December 20th, 2010, 4:41 am, edited 1 time in total.
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Joined: August 16th, 2006, 10:39 pm

December 20th, 2010, 4:19 am #7

did you reduce the smaller diameter section as well???


I have some of those carbide insert style bits how fast did you spin it to cut thru the surface hardening???

the two hammers are starting out 1 gram apart one like 57 and one 56 grams
decent string variation ...its just going to take time ...and a bag of orings

I think I have some 007 rings I will try that too....

How high you been cutting your ice maker tube?? I tried 3/16 too high squishs all over

If .125 works I will drill a piece if plate for cutting them consistantly
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Joined: November 17th, 2006, 3:51 am

December 20th, 2010, 4:29 am #8

..it seems to last nearly for ever, even with multiple take downs. I honestly never has measured them. Will just cut and try, not fully assembling the rifle until i can just manage to squeeze the receiver down to full contact by hard 2-hand grip pressure.

Take the time to smooth the inside of the breech where the barrel fits. Don't want to enlarge it. Tightening the set screw often ends up raising a burr in the breech were the set screw exits.

As for the striker...can lose a lot of weight if that's a goal. Yes, did reduce the diameter of the center section. It's round and held from rotating by the two pins, so the sides of the striker can go as well. first cuts were by a TC bit, but once I broke though the hard "skin" (it seems to be case hardened) switched back to HS steel for a smoother cut.

First one i did, I annealed the striker first. Cut nice and smooth. Then rehardned it. Easier to use the T/C bit and switch back to H/S for a smooth cut.

But am not sure a lighter striker is going to get you to 900fps. Was good at extending the shot count a bit once the spring tension was readjusted, but never could get the max. speed from a light striker than can be had with a heavy one.
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Joined: August 16th, 2006, 10:39 pm

December 20th, 2010, 4:38 am #9

Bill cut off that back section as well behind that raised ring at rear....I will make it look like yours first....easier to cut off than put back on LOL

Bills's string
here is my last shot string using 16 grain pellets
2500psi start, 1450psi finish

958.5
962.0
971.3
974.4
979.1
981.1
985.6
982.4
984.2
981.6
980.3
974.3
969.3
960.7
949.7
940.8
925.8
916.8
909.1
986.0
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Joined: March 28th, 2002, 6:54 pm

December 20th, 2010, 7:26 am #10

decent string variation ...its just going to take time ...and a bag of orings

I think I have some 007 rings I will try that too....

How high you been cutting your ice maker tube?? I tried 3/16 too high squishs all over

If .125 works I will drill a piece if plate for cutting them consistantly
striker and factory QB spring. You may have to mod the valve body and fit a wire probe to do it, though. That's the setup I've used to hit 930's with a decent string.

That port alignment seems pretty typical of the PCP tubes, doesn't seem to hurt power.

I spot face or file a flat seat on the valve to make it easier to get the poly tube to seal, and with that setup have been able to use nylon tube,even larger ID and tougher.A counterbore works also.
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