Yes Al's adjuster is a work of art.
Compromise is the solution.....
Make mine (takes about an hour) use that while you while away the hours testing and making Al's
One of the issues you may be experiencing is the spring preload is enough to pressing hard against the valve stem at rest. I have never measured the clearance but I know mine has some slack.
At most I would reduce it to an 1/8" and see what you have for performance
Sean
Haha okay here is some more practical bling
Instead of a muzzle brake how about a choke band.
A 2" long tube that has the ID cut on a taper of 0.005" over it's length. The widest part of the taper is the OD of the barrel and the narrow end is obviously .005" tighter. The tube is installed with the narrow ID at the muzzle.
The tube is heated to light blue on the iridescent oxide scale and the slide into place and allowed to cool. It will shrink the muzzle and give an effective choke.
Take it one step farther and thread the tube so you can install an air stripper as well
Sean
I would think that 0.005" taper might be too much.... but not having tried it don't know one way or the other.... Dr. Frankengun did this to a QB barrel a few years ago.... He made a steel sleeve in which he used a #1 Morse tapered reamer.... He then machined a matching Morse taper on the muzzle.... He heated the sleeve and slid it onto the barrel a bit further than where it normally stopped.... IIRC, maybe 1/10"???.... I think he achieved a total choke of about 0.0008" and drastically improved the groups from what was previously a mediocre barrel....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
Well I can say the build is complete and I will take some pictures the next fine day I have off. This is one amazing QB78D!My intent was to have a powerful and accurate hunting rifle and that is what it has become. I had an opportunity to take out some bushy tailed rats and began to look for spatter on nearby trees..lol. Not many people had luck with CPHP's in this rifle fortunately I did using the power adjuster to keep the fps down until I get a bunch of jsb 18grs to try. This is my first PCP build and I am hooked
For every mile of road, there's two miles of ditch
White seal is for the stock Co2 cap- it will be a tougher fit getting it around the valve and in the tube- so use the black one for the valve. Don't mind the POS seal the factory used- it's probably half disintegrated by removing the valve from the tube. You can lube the o-rings on the barrel- do NOT lube the o-rings on the PCP tube end or the valve with anything but a silicone lube- petroleum by-products in a PCP are bad news.
I'd say I care- but I'd probably be lying...
If you can actually HEAR the air escaping separate from (ie after) the sound of the shot you definitely have a problem with the valve hanging up.... Even with the lightest of valve springs, the air pressure should shut the valve with anything like 1000 psi in the gun.... I'm guessing maybe you bent the valve stem or it's got some dirt/chips making it drag.... On PCPs, I have found them to be relatively insensitive to valve spring changes, but VERY sensitive to hammer spring changes....Following the shot it sounds like i have a load of air traveling through the barrel after the pellet has left.
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
After adding a little more preload to the valve spring this afternoon I pumped to 1800psi and listened carefully as I shot. Valve is staying open too long and I do believe what I am hearing is the echo of all kinds of expanding air coming from the barrel. I also believe what your saying rsterne is true about the hammer spring and I got too excited to add a spacer of 3/16 before trying it without. You know it sounds like i am shooting with a 10ft piece of 2'' pvc pipe on the end of the barrel along with the crack. Now if only there was an easy way to pull that spacer without disturbing the breech seal and barrel o-rings.
See what happens Sean when you show me functional bling?..lol I contacted al and he so kindly provided me with his cad for his power adjuster. I happen to like brass so I added some to my version.IMG_0411c.jpgIMG_0412c.jpgIMG_0413c.jpg
Al's a nice guy isn't he.:)
Nice work on the adjuster, looks real nice.
Al
Ooooo a morse taper. Nice!
I have heard Dr Frankengun has done some amazing stuff but I've never been able to get on his site. For some reason his sight and my Linux don't get along.
Yes .005 might be a little tight but I wouldn't try less than .0035 and if you happened to get more than 0.001" choke you can trim back a little.
Sean
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