SOLVED: bad barrel - work on it or replace it?

[nervoustrigger]

Hey, thanks Jerry!

Joe, yeah I'm a little hardheaded.  Just ask my wife.  She puts up with me for some reason.  If there's any Italian in me, the gene for dark skin must have gotten suppressed somewhere along the way.  You might accuse me of being Mexican though.  I love tacos.  The skin thing is still a conundrum though 

Just got the rifle back together and am about to start pumping.  I'm praying for no leaks.  Ooooh, the sound of air leaking is like fingernails on a chalkboard. 

[K.O.]

I  can almost hear it because I bet just about every one reading this is silently chanting "one hole group ,one hole group"...

[palonej]

I swear I heard it too Kirby!!!
I find myself holding my breath reading this thread!

[vigilandy]

You guys would think I'm a stalker if you could see how often I check this thread.... 

[K.O.]

I do think it is very possible that the porting of the tank block and smoothing of the flow in the valve will not only improve the shot to shot

consistency of the air charge,

I think it will also change the resonances caused...  think whistling with 1000-1500 psi... and could if harmonics are part of the equation, have

a calming effect by moving the frequency to one that  is damped out more...

I like to learn so will bug you later Jason on the specifics of your last bit of tuning if you do not mind.

Right now I am just in cheerleader mode...

[DD789]

Hey, thanks Jerry!

Joe, yeah I'm a little hardheaded.  Just ask my wife.  She puts up with me for some reason.  If there's any Italian in me, the gene for dark skin must have gotten suppressed somewhere along the way.  You might accuse me of being Mexican though.  I love tacos.  The skin thing is still a conundrum though 

Just got the rifle back together and am about to start pumping.  I'm praying for no leaks.  Ooooh, the sound of air leaking is like fingernails on a chalkboard. 

Maybe your a member of the other hardheaded group that I'm a partially a member of.

[nervoustrigger]

Guys, I really appreciate all the well wishes.  I managed to get in a couple of pumping sessions before going to bed, bringing it up to about 1200psi which is above the regulator setpoint and no leaks so YAY to that.

Kirby, yeah many of the modifications will tend to change harmonics and my experience has been that they have always yielded wonderfully precise rifles so I am hopeful that things will change for the better.  With everything polished up and lubricated properly, that should give much better shot-to-shot consistency as well.  Also, the RVA will allow me to alter velocity over a wide range which gives me a lot of options to find something that works. 

I am also planning to try O-rings or heatshrink on the barrel per your suggestions and see what happens but I am looking at that as more of a fine tuning tool than a magic wand.  First I need to achieve some decent groupings.

I did O-ring the valve stem to see if I can squelch the blow-by out the back of the valve.  My hope is that the blast of pressure as the valve cracks open will cause the O-ring to slide down the stem and plug the gap.  Then again, it may make matters worse if it behaves inconsistently so if my initial results are poor and the ES is wide, I'll go back in and remove it.

But that is not the outcome I am looking for this evening

[nervoustrigger]

Sorry to leave you guys hanging.  I was up late shooting groups and ran out of steam to post an update.

Basically what I was doing was testing with a few different variables like velocity (RVA setting), with and without the LDC, and with O-rings or heat shrink on the barrel.  Obviously there are an almost infinite number of ways to perturb those variables so I just picked a few combinations to test, looking for anything that appeared to improve groupings...or make them worse.  So far, I am not seeing a significant difference in manipulating those things.  The groupings are coming out pretty much the same. 

The good news is that, while it is not grouping <1/2" like I was hoping, it is now grouping more consistently when I shoot 2 or 3 groups with the same pellet.

Another thing, shot count is way up thanks to the RVA.  I did not keep count of it before but last night the needle seemed to practically sit still when I was shooting lots of groups.  Much quieter too.

[K.O.]

So is it still the  AA 10.3 and ultra mags it likes...

 So at the beginning  It was.

 At the end of it all, the best group was 1.0" at 25 yards (Air Arms 8.4gr) and the worst was 3.63" (H&N Baracuda Match).  The CPUMs, despite engaging the rifling, were in the middle of the pack.

so the best has improved and repeatable  to .5"-.75" or so? how has the worst changed I bet it is a lot smaller...

I was hoping for pics of groups again and that you would give a more complete list just cause I can not help myself you feel like you might

spot some thing even though you know its not that way...

the heavy-ish ldc did not have an effect wow...   does it at least change poi?

If It did not change things it almost rules out harmonics you would think having extra weight hanging off the end of the barrel should make

things  better or worse...

Jason I almost feel like I had you chasing your tail after harmonics but at the same time you have to rule them out.

I mean a good leade, no tight spots in the barrel and the pellets show the rifling is good what else would effect the barrel? how else could it be

a bad barrel at this power level?

it is seated well with two set screws and o-rings so we can be pretty sure it s not moving...

I know you might kick my butt for suggesting one more harmonics experiment...

and that is three or four inches of shrink tube on the muzzle end to protect it and a movable weight( about one or two lug nuts worth) with a

set screw and a few groups with the better pellets... this is one that I have actually seen work on a buddies .22 PB...  .75- .5 groups down

to ~.3 groups at 40 yards. I did a search and  even Bob has some weights he has used on disco barrels.

The barrel on these qb79s are larger but that is also a long unsupported portion of barrel

http://www.gatewaytoairguns.org/GTA/index.php?topic=25689.0




the o-rings and shrink tube I just have heard works(is a trick the rimfire bench rest guys try) and did a search to make sure if others had used

it and if it worked (cheap and worth a try)

I thought  of it as more of a fine tuning thing especially with a .5 and >.5 barrel

http://www.gatewaytoairguns.org/GTA/index.php?topic=34014.20

I really do almost feel like I have talked you into chasing a harmonic tale and hope you have not let it stress you and enjoyed the process  instead...

I wish an experienced tuner would jump  in and say things looked to be pointing to harmonics to me also then maybe I would feel better about having made the suggestions... 

Because I am not the one there doing the work...   I am just the one saying I bet we can get .3 or so groups and if lucky a one holer...

but yep the improvements could just from your porting and smoothing flow, the leade work and the extra barrel set screw...

EDit and the RVA would mean less of a blast disturbing the pellet as it leaves the  barrel... If that is the cause...

and I do not have a lot of faith in the weights if a heavy ldc had no effect!


I just can not see that it would be a bad/mediocre  barrel without showing why...

and If it is not a bad barrel then an air stripper is the only other tuning tool I can think of and it did help Bobs .22 group...

and I do not know if you and Andy want to go to that expense and effort because it could be more Tale chasing...

well anyways if you need a stress relief mechanism I  offer to make a kick me sign and tape it to my back for the day on Sat...

I will even post a pic if you want...


I can only think of one other thing and  maybe you are not wiggling your ear just right before the shot ...

[K.O.]

I just can not help myself  how  much adjustability does the rva give you can you back the velocity way down?

I did think of a test to see if something is disturbing the pellet as it leaves the barrel I have not  tried it myself.

The theory is that the diablo shape is self correcting because of the drag so it could be knocked off balance and re-stabilize...

so if you shoot from as close as you can without the muzzle blast itself messing up the target (mounted on card board or something)

say 2'-5' the pellet hole would possibly show signs of yaw...

Man I wish high speed cams where a dime a dozen that would be a very useful tuning tool...




One of my hobbies is making Acoustic lap slides and dulcimers. Part of  the process on the carved top and back ones  involves tapping on the

plate as it is carved hearing the drop in pitch and feeling the changes in liveliness of the top or back plate and the when you add bracing you

tune the bracing the same way.

point is I bet through all of this, part of the learning even if only on a subliminal level, is the small changes that most likely going on in the

feel of the shot cycle, makes me wish I was there... That and I could do the pumping so I feel a little less of a pain in the tush...

[nervoustrigger]

Kirby, as usual you raise some good points and ask some good questions.  I do intend to measure and publish the results of my recent test but I still need to run through some of the poor-performing pellets to see how much they changed.  I'll add the data to my spreadsheet and see if a pattern emerges.

Andy and I were chatting about going ahead and putting the .22 barrel on it since it is about 75% of the way to being a solid HPA rig.  I plan to do a bit more testing with the .177 first though.

I can indeed turn the velocity way down.  In general, the ES tends to climb when doing that but I doubt it is enough to matter at 25yds.  I will say that I was struck immediately by how much smoother and quieter the shot cycle was after tuning the internals so I am becoming less skeptical of harmonics but I'll see if I can try another form of barrel damping before I give up on it.

[vigilandy]

I gotta thank Jason again for helping sort out this rifle.  And KO-- thanks for throwing ideas at him.     

It seems like we're close to the limit of this barrel's ability for whatever reason.  I too am very interested in seeing the effect of the recent work that Jason has done.  If it's making one inch groups at 25 yards... that's about 3x better than before... assuming you could hit a 3" target consistently.       BUT, popping in the .22 barrel is going to make this an AWESOME rifle.   

No tears to be shed over the backup plan.   

[K.O.]

 

 

All the things that actually helped Jason would have done any ways... I honestly do feel that way...

I just got to throw stuff out for those who are just getting into this to ponder...

and the cheerleading well     

[nervoustrigger]

It has been a few days since I've updated you guys so here's what I have been up to.

As I was playing around with the RVA and shooting groups, I noticed something.  At different velocities, some pellets tended to shift their grouping around on the paper pretty dramatically which does point to harmonics.  I had tried a handful of dampers to no avail so I ordered a Limbsaver De-resonator to try out.  Beyond that, Andy gave me the green light to shorten the barrel a bit and see if that takes out enough of the whip to make it group better.

Meanwhile I decided that I needed a little change of pace...some probable shot at a successful outcome so I set about with the remaining modifications for the .22 cal setup.  I kept the lower assembly pretty much just like it was, already having a modified valve and hammer and a RVA.  The only other things I did to the air tube assembly was hog out the tank block to get a bit more plenum, upgraded the screws that retain it, and adjusted the setpoint of the Ninja SHP regulator to 1500psi.

I then turned my attention to the receiver assembly...added a second set screw for the barrel, milled out a rear downslot for the bolt, and deburred and polished the inside.  Also polished up the bolt and ported the hollow probe to 0.170".  Got it all assembled late at night and pumped up to about 2200psi in preparation for some chrony testing the next morning.  However apparently the bottle had a weak 1.8k burst disc because a couple of hours later I heard a loud POP and in about 10 seconds, all of my pumping efforts returned to the ether.  Sigh.  Fortunately I had a spare so soon I had it replaced and started pumping again.

The next day at the chrony, a little twisting of the RVA screw to find the peak velocity with JSB 18.1gr:



I was pleased to see a little over 27fpe considering the anemic plenum volume of a QB79.  In the interest of shot count (efficiency), I backed off the RVA just a smidge for a velocity of 800fps and locked it in with the set screw.

Today after work I had a little time to put some lead through it.  After a few clicks on the turrets, here was the first 5-shot group at 25 yards:



That looked promising so I hung a target out at 43 yards and shot two more groups:



Winds were varying quite a bit from dead calm to about 10mph at almost a 90deg angle so effortlessly punching a couple of dimes with mostly horizontal stringing is pretty encouraging.  And with that, it has earned a temporary but rightful spot next to the front door



What a difference a barrel makes.

[vigilandy]

I can't believe you have not given up on that barrel!  If ever I was facing impossible odds, I'd want you on my side.    Until just now I'd never even heard of a deresonator.  Makes me wonder what other tricks you have up your sleeve....   

It's amazing that in stock form, this rifle shoots 22 pellets at 500fps.  That's probably with lightweight pellets. Jason has it shooting 800+ fps with 18.13gr!  And those groups are amazing.


Question Jason -  have you noticed any difference in the quality between the older TF79 versus newer QB79?

[K.O.]

That barrel is stuborn... I wonder if it would stay strait if you toss it into a heat treat and a slow oil quench to change it's modulus of elasticity... 

I wonder if you hung a 5lb weighted wrist band on it if it would still be  a brat...

I had thought about the limb saver but just can not get into it, I mean who wants to have a toilet plunger hanging on their barrel..

I am getting an image of you holding the barrel and shaking it shouting  " I will best you ,you will submit to nervoustrigger!!!"



Those 40+ yard .22 groups are why I would really like to build a 800 fps .22 pumper... and are worth the work you put in...



I  think just to be a pot stirrer I will bring up that it might be affordable and not to difficult to pick up a np 725 barrel and mod it for another

option with the fpe you are getting

Cheers,

           Kirby

[nervoustrigger]

I can't believe you have not given up on that barrel!  If ever I was facing impossible odds, I'd want you on my side.

Think I should change my avatar?

[nervoustrigger]

have you noticed any difference in the quality between the older TF79 versus newer QB79?

Nothing of great significance.  I have yet to pull the valve out of the TF79's air tube but the receiver and barrel seem to be the same as the QB series.  The dovetail adapter on the TF is kinda nice though...gives the scope mount a little more to bite onto.  I've never had any trouble with the grooves milled into a QB receiver but they do seem a bit slight. 

The other obvious difference is the trigger.  The 2-stage trigger of the TF might be a welcome feature to some but that style--a hollow trigger blade which catches after some travel--just feels contrived and fake to me.  I prefer the solid feel of the die-cast trigger blade of a QB.  When the assembly is polished up, shimmed, and lubricated properly, it's a joy to use.

[Tater]

I can personally attest to the lengths Jason will go through to help someone. I still can't believe the amount of effort/help he gave me with a scope issue.

I can't believe you have not given up on that barrel!  If ever I was facing impossible odds, I'd want you on my side.

Me too! And it's already happened!   

[K.O.]

The only modded parts of my 1322XLT 750fps  are larger pivot pin,

stuffed 1377 piston,

old style metal 2200 piston other piston half,

brass tube insert for valve intake passage reduction, on a .135 C.I. + valve

Made of a .3 larger than 2100b valve nose with a bored 2100b exhaust half ported to .22 until the .190 transfer port seat,  that gives way to

 a .220 brass transfer port that connects to an ovalport  in a .22 barrel...

Hoping for an accurate open sight 25 yards...

1322 using a 2100b pump tube  @750 fps 14.3 gr CPHP. @ 15 pumps