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nervoustrig

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Viewing 20 posts - 1 through 20 (of 2,129 total)
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    nervoustrig
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    United States
    Accuracy: +110

    All those fasteners for the rail and only 2 per ring cap…I presume you mean the scope is slipping in the rings.  But whatever the case…

    Before resorting to a more aggressive approach, borrow or buy an inch*lb torque wrench.  Clean all surfaces with a clean-evaporating solvent like paint thinner (stoddard solvent) to remove any residual oil from manufacturing or human hands.  Then torque the base screws to ~30in*lbs and the ring screws to ~15in*lbs.  Then test it to see if it still moves (tip: place a piece of masking tape on the tube right where it meets the edge of one of the rings…if the scope slips, it will be easy to recognize right away).

    If that fails or if you want to move on past it, some guys have had success with applying rubber cement to augment the grip.

    And if you want to go all out, lap the rings to improve contact with the scope tube.  Most of these extruded aluminum rings have fairly poor surface contact.  See an example https://www.gatewaytoairguns.org/GTA/index.php?topic=109966

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    nervoustrig
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    United States
    Accuracy: +110

    Apply some heat from a heat gun or a propane torch to soften the threadlocker.  Unscrew it while hot. 

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    nervoustrig
    Participant
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    United States
    Accuracy: +110

    A hole like that is usually an atmospheric vent for the regulator but that is an unlikely position.  Does it hold air?  If so, shoot it.

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    nervoustrig
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    United States
    Accuracy: +110

    Well I’m beginning to think the problems were somewhere in the barrel assembly, not with the liner itself.

    Top group at 30 yards shot yesterday, shooting between the wind gusts.  Right at MoA.

    Bottom group shot today to see if the first was a fluke.  Fairly calm conditions.  A bit under 0.8 MoA.

    That represents about all I can do consistently with an accurate rifle…supported forestock but shouldered (movement from pulse and respiration).  Not cherry-picked.  And actually those two are somewhat better than I could have even hoped with the beater scope I threw on it, with a thick reticle and only 10x magnification.

    I’m not celebrating just yet.  Definitely needs more testing and experimentation but this little bit tells me it can be tamed.

    For anyone interested, here’s a detailed list of my observations from disassembly and reassembly of the barrel:
     
    1.       The O-rings supporting the liner inside the barrel allowed some free movement.  Somewhere in the ballpark of 10 thousandths of an inch.  So although the ends are well supported, my thinking is it can give rise to violent vibration along its length.  In other words, neither supported nor free-floated…a no-man’s land somewhere in between where vibrations are unpredictably additive or subtractive.
    -> Applied a strip of electrical tape across the series of O-rings.  Takes up the free play and simultaneously keeps them positioned while inserting the [now snug] liner into the barrel.
    2.       The steel adapter piece (forward of the brass inlet) had an O-ring on the ID that was flopping around in the groove, doing nothing to seal to the liner’s OD.
    -> Custom fitted an O-ring (a modified -010 with its thickness and OD abraded down for a snug fit)
    3.       The outer collar on the barrel was fastened about 40% of the way forward of the receiver.
    -> Relocated it to its intended position next to the receiver (where its locator pin indexes to the shroud adapter).
    4.       The shroud and air stripper were loooooong overdue for a cleaning.  Caked heavily with gunk.
    -> Neither degreaser nor mineral spirits would cut it.  Had to scrub it free with a Scotch-Brite scuff pad.  Honestly the most tenacious buildup I’ve ever seen.
    5.       Applied just enough torque to the barrel nut to snug it up.  Do not want any undue forces trying to turn the liner into a banana.

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    nervoustrig
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    Accuracy: +110

    Qball, thanks for the added detail about your preferred setpoint.  The owner currently has it at 100 bar so I’ll definitely try at least a couple of higher levels to see how it responds.  A quick pulse of HPA does seem to work nicely in most cases…one of the things I like about PCPs retrofitted to a PEEK poppet and lightweight hammer. 

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    nervoustrig
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    United States
    Accuracy: +110

    Start as coarse as needed if it has a major burr or if you are wanting to flatten the ends.

    Like Dan, I’ll usually carry it out to 600 grit or so.  Just depends on what role the spring plays.

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    nervoustrig
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    Accuracy: +110

    Qball, thanks for the suggestion about the state of tune.  I have not yet tinkered with the knobs and dials, just confirmed it’s producing a consistent velocity.  I’ll get a baseline at the present tune with the barrel & shroud assembly corrections/tweaks and go from there.

    I had failed to say it is a Crown with a 500mm barrel.   

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    nervoustrig
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    United States
    Accuracy: +110

    Okay thanks guys, that’s right along the lines of the info I was looking for.  

    Paul, thanks for the confirmation on the dimensions.

    When weather conditions improve, I need to shoot some groups with different batches and see what it will do.  I ended up finding a few assembly & fitment issues in the barrel and shroud assemblies that I want to address.   Maybe it will turn around.  Or if it proves hopeless, I’m thinking about lopping off the choke just to see how it responds.  
     

    This all may develop slowly but I’ll update the thread along the way. 

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    nervoustrig
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    United States
    Accuracy: +110
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    nervoustrig
    Participant
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    Accuracy: +110

    A quick scan suggests this one may be useful

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    nervoustrig
    Participant
    Member
    United States
    Accuracy: +110

    Yeah for that reason I’m thinking more likely an O-ring is the culprit, despite the fact O-rings usually have the opposite behavior unless there is a defect in the mating surfaces.  5 years in, it’s due for a reseal anyway so might as well do that.  If you don’t get a new poppet, give its sealing face a careful inspection under magnification to see if it could use a light lapping with the valve with a modest abrasive.  

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    nervoustrig
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    United States
    Accuracy: +110

    The symptom does sound like a leaking poppet except I thought the Mutant was regulated.  Am I misremembering or do you have the regulator set above 150 bar?

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    nervoustrig
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    United States
    Accuracy: +110

    Oh, and just a heads up…if you happen to purchase one, inspect the barrel straight away.  The factory has a track record of smearing the rifling at the muzzle with a piloted crowning tool.  It’s easy to spot.

    Not all barrels will have this damage but for me it was present on 2 of 5 and I have two more right now from an acquaintance.  My two  were scattershot disappointments but group very nicely after removing the damaged portion and recrowning but not everyone is able or willing.  Kinda like buying a new car and having an obstruction in the exhaust, and going home and taking a hacksaw and welder to it.  My justification is that it was less hassle than an RMA.  

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    nervoustrig
    Participant
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    United States
    Accuracy: +110

    Pretty scattered…Diana markets some models.  There’s also Artemis and Zasdar and probably others.

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    nervoustrig
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    United States
    Accuracy: +110

    No preference to a particular geometry in terms of performance…some are more aesthetically pleasing than others, or offer varying degrees of protection from abuse (which should be irrelevant for a precision benchrest gun).  Square/uniform to the bore and burr-free is what I care about.  A simple bevel applied with the brass screw technique can work very nicely:

    As this fly leisurely checking out the target at 30 yards found out…

     

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    nervoustrig
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    United States
    Accuracy: +110

    Bhaur, very impressive results.

    Tuning to a little below the knee does indeed improve efficiency, usually at a slight tradeoff to extreme spread and a little bump just as the pressure falls below the setpoint.  However you have managed a very good result that seems to minimize these potential negatives to a nearly negligible degree.  That is a testament to your careful work with the valve, hammer, and other parts of the gun.  Nicely done!

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    nervoustrig
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    United States
    Accuracy: +110

    The original .25 cal Marauders were fitted with a choked Green Mountain barrel.  Very well-regarded barrels for shooting pellets. The twist rate and presence of a choke do not generally make for a good slug shooter but there are exceptions so you may want to experiment.

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    nervoustrig
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    United States
    Accuracy: +110

    Here's a recent discussion on the topic, including some general bstaley guidance and diagrams from me and some Prod-specific guidance from John (fuzzygrub).

    https://www.airgunnation.com/topic/how-to-maximize-consistent-power-shot-count-on-benjamin-akela-22/

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    nervoustrig
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    United States
    Accuracy: +110

    For anyone interested in voltages and currents, here's what I recorded from mine.


    FX pocket chronograph (PCB marked v2.4)
    —————————————
       Low battery indicator triggers when Vbat < 3.80V
       3.3V regulator is a linear LDO with ~100mV dropout
       5.0V regulator is a buck/boost
       current draw:   81mA @ 5.0V
                    89mA @ 4.0V
                    99mA @ 3.5V
                   114mA @ 3.1V
       Most of the current draw is from the Bluetooth connection.  With no connection to a smartphone, the current draw is <20mA.


    Which reminds me, many of the USB power banks have an automatic cutoff when the current draw falls below a certain threshold.  On the one I'm using, it's at 100mA.  The chronograph pulls a bit less than that (80mA @ 5.0V) so I soldered a small resistor across the leads to draw about 25mA to kick it over the threshold so the power bank will stay on.

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    nervoustrig
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    Member
    United States
    Accuracy: +110

    I agree with clean it and shoot it.

    Virtually every new barrel I touch will get worked with a light abrasive but it’s always a good idea to test it in its original form to establish a baseline.  So for example, if the barrel turned out to be a real stinker, a polishing regimen is not going to be a magic cure.  Something like a bad crown or leade or an irregular bore is another matter entirely.

Viewing 20 posts - 1 through 20 (of 2,129 total)