Small change, BIG difference!

[daved]

And the saga of the Hammerli Pneuma continues :-).  I've been having issues with getting this rifle to shoot consistently, so last night, I decided to rule out one more variable, and did a scope swap.  I replaced the MTC Viper with the Burris Timberline from my S200.  No chance to shoot it last night, but I did tonight.  NO DIFFERENCE!  And not really a surprise, I knew this thing was shooting (too?) fast, but I wasn't quite sure what to do about it.  Well, I finally decided.

When I first tore this thing down, I noted the little hammer spring spacer inside the hammer.  It's basically a bushing approx. 1/8" long and the same diameter as the spring.  I'd considered leaving it out when I put the rifle back together, but decided to keep it as close to stock as possible to establish my baseline.  Well, after the consistently inconsistent results with the different scope, I decided it was time to detune this beast a bit.  For those interested, this is what I chronied after I did my initial "tune".



Note the rather dismal shot count, and how quickly it dropped after just 20 shots.  I figured that was the price you paid for the power this thing has.  But now look what I got after removing just that tiny little spacer:



This is much more in line with the performance I expected when I got this thing.  I've been filling to 3K psi, after removing the spacer, it looks like something around 2500 psi or less is more appropriate.  This also confirms my feeling that the transfer port is too big, I'm thinking it looks like I can increase the power, flatten out the shot curve, AND keep the better shot count by going to a smaller transfer port and maybe increasing the spring preload.  BTW, the accuracy seems to be better at the lower velocity, and it now likes JSB Heavies better than CPH's.  It still tends to scatter Kodiaks, though.  Time to switch scopes back, looks like the Viper is/was just fine.  More later.

Dave

[gamo2hammerli]

Wow daved, you know your stuff.  I wouldn't have the courage to mess around with the insides of a PCP.  That first graph, string 1 and 3 I think lots of airgunners can live with that.  In the 2nd graph all the strings look good with the exception of string 1 which seems like it haven't reached its max power yet....but still do-able.

[daved]

I can't help myself, Stan.  You know the saying, if it ain't broke, don't fix it?  For me, it goes more like, if it ain't broke, you need to take it apart and find out why :-).  Really, PCP's are pretty simple machines, even simpler than springers in some ways.  My first PCP was a Talon SS, and EVERYONE takes those apart, you just about have to.  This thing is showing some serious potential, but it definitely needs some TLC.

String 1 on the second graph is classic valve lock, I need to lower my fill pressure.  Will be doing more testing soon, I'll probably start with a 2500 psi fill instead of the 3000 I'd been doing.  It's a balancing act, hammer spring, hammer weight, transfer port size, and fill pressure.  If it's a $500 PCP, you do that work yourself, if it's a $1000 rifle, it's reasonable to expect that work to already be done.  Now I'm ready to concentrate on the air leaks.  Later.

Dave

[gamo2hammerli]

So inquisitive.....good for you.  For me....I expect a $500.00 airgun to be in the A- zone.  A $1000.00 one to be able to shoot by itself!!!!  heh heh

[daved]

Damn, I knew that Cyclone was good, but I never got it to shoot itself :-)!  BTW, in case you were wondering, I never had it apart, never felt any need to.  I did take the P5 apart, but only to lube it.  It was pretty dry when I got it, typical of all the Diana's I've had.

I'd agree with $500 in the A-zone, but only if you're talking about springers.  Since PCP's seem to start around $500, they need a different scale.  This Hammerli I'm playing with I'd rate a C, maybe C-, the AF guns get a solid B, the AA S400 I had would be an A, and the Cyclone a definite A+.  Oh, and my S200 also gets an A+, if you ever get the chance to ad one to your collection, do so, you won't be sorry!  Later.

Dave

[daved]

The air leak, that is.  Had a major leak at the valve, had it apart last night, polished up the fairly rough valve stem.  Definite improvement, but still leaking.  Took it apart again tonight, made a small tool so I could lap the stem and seat with some silver polish, looks like it's done the job :-).  Still have a small leak at the other end, but need to come up with another technique to remove the filler/gauge, don't want to give it a dunk in boiling water like I did with the valve.  Maybe try heating the tube with a heat gun.  But for now, I can live with it, it's a very slow leak.

Next step, remove the transfer port again, solder it solid (thanks, Dano!), and drill it smaller, somewhere around 3mm to start, I think.  Got the gross issues dealt with, now it's time for some fine tuning :-).  Stay tuned!

Dave

[gamo2hammerli]

By the time you're done with her.....you'll have turned her into a $1000.00 killing machine.  Good job.