GTA
Airguns by Make and Model => Benjamin Airguns => Topic started by: JSR:. on September 07, 2010, 01:45:15 AM
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Ok, I posted a few days ago about my NP AW .22 accuracy problem with pellets shooting good one day but spraying the next one. I replaced the seal, de-burred the compression tube and internals, lubed it, built new bronze breach assembly spacers. re-crowned the barrel, fixed the pellet seating area in the breach, danced around it chanting "now is fixed, now is fixed..." after every intent but no... Vector-2 (that's what I call my black NP) refused to budge. I was going to try voodoo next... Anyways... after shooting dozens of each brand/types of pellets I have at hand (CP, Benjamin, H&N, RWS, Norica, Predator, and JSB) nothing resembling a group (I am shooting at 20yds)... Nothing, I took a small break still thinking on what can be wrong... Went back to shooting a little more before deciding which color candle and what holocaust (sacrifice) might be needed for the Voodoo ritual... Maybe a couple of our small pests crows will do (courtesy of my Mrod .22)...
Back to shooting... Loaded a CP, shoot and bulls-eye. Didn't feel like celebrating on one lousy bulls-eye... I have been there before just to have it spray again... but then the second, third, fourth, fifth, record!!! The CP's started grouping, then JSB, then H&N, then... almost every single one tried before started grouping now... I looked at what changed... and it just hit me... My Caldwell bean bag (rice actually in it) slipped several inches away from me, and I unconsciously just readjusted the rifle to have it rest at the barrel instead of the fore stock.. voila!... instant groupings!!!.
Then it hit me. The breach/barrel area has to be moving during that instant following the trigger pull. If I applied force to the barrel, not enough to break it but to "move it" it didn't "move", but then if I gently try to move it up and down... it moved! Force didn't let me feel it was moving just maybe a few thousands of an inch but enough to cause a whiplash effect to the pellet exiting the barrel. Couple that small amount of play with the mechanical vibrations of the piston and the vibrations and harmonics will travel down the barrel destabilizing the pellet travel (plus the fact that I am a lousy shot just learning to basics of shooting this type of airguns). I checked the detent (Crosman part 28, CRS5177-034, follow the Nitro NPSS diagram at the Crosman site), and it indeed had some thousands of an inch of play up and down. Of course, it may be within the mechanical tolerances for it to work, but it did look like the pin wasn't acting with enough force to hold tight the breach/barrel. So after evaluating several options, I decided to work on extending outward the detent to increase how much it grabbed onto the detent pin (Crosman part 15, CRS5177-033).
Soo... I separated the action from the stock and did the following...(please excuse the photos quality and background clutter)...
First, I needed to make the pin protrude maybe around 10 20 thousands of an inch forward (towards the compression tube) to catch and apply more force in grasping the pin detent on the compression tube side.
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_C.jpg)
Removed the detent pin by first removing the pivot sleeve. I placed the action in a vise and carefully pressed the pin "in" while removing the pivot sleeve with a brass punch and a small hammer...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_pressin.jpg)
Here you can see the sleeve halfway out...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_presin_B.jpg)
Here are the parts as arranged as they are assembled inside the breach
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_A-1.jpg)
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_B-1.jpg)
I kind of eyeballed how much I wanted the detent to extend, so this picture is how it was built...(look inside the sleeve area where I reinserted the detent to find out how much it did extend)
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_E.jpg)
...and this one how much material I need to remove for it to extend a little...(again, look inside the sleeve area. Pulling the detent forward let me know how much material to remove)
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_D.jpg)
This is the detent. I "sharpied" around the area to be removed (barely noticeable in the photo but it is towards the bottom of the detent "valley")
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_F-1.jpg)
Ok, material removal in one of my grinders. This one is for grinding tools for the lathe ideal for "controlled" material removal. A good file will also do...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_G.jpg)
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_G-1.jpg)
Now, for maintaining spring tension (because if not the spring needed to extend more for keeping tension), I machined a small brass spacer to go inside the detent and take up for the extra internal volume caused by the material removal which slid the detent forward. I made it 35 thousand of an inch deep...
One of my material/metal stock bins at home. Found one perfectly matching the inside diameter of the detent where the tension spring rests...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_bronce-1.jpg)
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_bronce_fit-1.jpg)
Machining the spacer...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_bronce_cut-1.jpg)
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_spacer.jpg)
The spacer inside of the detent...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_spacer_in-1.jpg)
Ok, lubing and preparing for reassembly. Notice the two brass spacers previously machined on top left...
(http://i740.photobucket.com/albums/xx43/jsrshaman/Airguns/Benjamin%20NP%20break%20barrel%20fix/breach_assy_ready.jpg)
...and then, my Blackberry lost power so the camera stopped working :-[. No pictures of the final work, but for reassembly just follow the removal process backwards 8).
So far, the NP is still grouping fine!!! I sighted it at 20 yds for CP's but Benjamins hollow's also shoot fine, so do predators ;D . Now it feels like really "breaking the barrel" when loading.
Now, a few caveats... We all know what happens to warranties when you start tinkering with you guns like this, so keep it in mind. Most of this can be achieved with simple tools. I just happen to have most of the right ones. A good metal file, a bench press (or good quality C-clamp), hammer, screwdriver set, and some ingenuity will do. I don't pretend this to be a fix-all to many who like me had issues with their NP's, but try resting you NP barrel on your shooting bag (or whatever) and see if it makes a difference for you. If it does, then maybe this procedure can fix yours too.
JSR:.
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Good machine work, I'm glad you got it shooting well.
Oh, and nice shop too!
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Great article here JSR, Very good information.Thats a great looking shop to Thanks David
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JSR,
You might want to drill some holes in your pivot washers then fill them with moly at assembly. I used bronze for the washers and they have been working great.
Nice shop!
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Excellent work. Gives me 1 more thing to look at when I get home tonight.
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EXCELLENT tip for that not-so-positive barrel lockup. You might be in the brass spacer business with this post. :)
Happy Shooting!!!!
Dave
8)
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This may be the problem with my Summit that I could never scope but shoots fine with open sights. I'll have to look into it, not a thing to loose and give me a project...... Thanks for this post JSR. This should go into the library.
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Thxs! just thought this write-up might be helpful.
Don C., love your idea about the holes in the spacers. I did roughen them up a bit so the lube would stick better, but you approach is much more efficient. Will do shortly, thxs!.
JSR:.
P.D. - thanks for the shop comments ;D. I have been "collecting" tools since I can remember. Got into home shop machining/welding/metal working as per my other hobby, 4x4 wheeling. Not doing much of it for the past few years; went back to school and have very little spare time between work, school, and family matters, but then got into airguns by accident. Need to do some pest control because "changos" (small blackish "Puerto Rican crows") and rats where wreaking havoc with my misses food garden and eating/destroying my two guava trees produce. Darn birds peck on the green guava fruits spoiling them to later come eat when they rot still attached to the tree. Same goes with the banana, avocado, and plantain trees. I love guavas and when in season, take a few for my night walks with my chocolate lab, Archie. Was loosing around two thirds of the production to this vandals. Now they know better... But, back to airguns, Well, I thought I could just get by with one smallish co2 pistol... Ha!... Now I have 4 rifles and saving some pennies for the fifth one. I did own powder burners during the eighties (.22, .25, 9mm, 357, etc.), but retired from owning handguns long ago. Never thought airguns could be this fun... BTW, thanks for this fine forum. Been lurking for a good while now... JSR:.
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JSR, is your Benjamin NP still holding zero now after this mod ?
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Great idea, great write-up and one cool home shop too! Thanks for taking the time to show us this.
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Very nice write up!!! and yea... I hate you for your shop... :)
*(&^ I just want the baby lathe there let alone the big lathe
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Lochlainn,
Yup... it keeps grouping almost everything I throw at it. Now, of course, grouping varies (@ 20yds) from less than half and inch (Barracudas, with a few just going through the same hole), to .75 inches, to 1 inches from pellet type to pellet type (predators, CP's, RWS, Benjamin HPs). Decided to center the scope for predators and crosman premiers as a good compromise being these two kind of kept centered with the same scope settings (groupings of .75 inch for predators and 1 inch for CPs). But I just received a batch of H&N Baracudas and FTT with head diameters 5.51, 5.52, and the FTT with 5.53 and will see which of these the np likes better. I really liked the groupings of the Barracudas best, but this throws out scope settings for predators and I confess of having this thing for it to shoot predators (Barracudas are grouping less than .5" at around 1.75" up-left of center @ 20yds).
Now, I believe I can still have it both ways. I had set the scope turrets zero @ 20yds for predators (and CP's shootable too), but will see if I can readjust from there for the H&N. So I'll just adjust for whichever one of these H&N group best, lock the scope rings and just reset back to zero if wanting to shoot predators. Its easier to remember bringing back the turrets to zero for predators than whatever clicks end being accurate for H&N. I am farily good at calculating distances/working with the mildots so no need to work the turrets for aiming.
Keep in mind though that I am stil learning to shoot it. My other guns are PCP's which almost anyone can learn to shoot accurately with minimal practice. My groupings arent that great, but learning to shoot my np is the other half of having fun :D
JSR:.
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Lochlainn,
Keep in mind though that I am stil learning to shoot it. My other guns are PCP's which almost anyone can learn to shoot accurately with minimal practice. My groupings arent that great, but learning to shoot my np is the other half of having fun :D
JSR:.
I totally agree with you JSR on the learning curve of shooting a springer. The challenge makes you a better shooter in the long run..:)
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I thought that one of the many "perks" of NPSS-ization of these former antiquated springers was to ELIMINATE or drastically reduce this "springer-position" silliness? Seems like there's been a LOT of hype attributed to the NPSS-ization of springers imo. It does help, but if the gun is already in shoddy condition from the factory, aka low machining tolerances and requiring DIY intervention; what's the point of NPSS if other weak-links in the chain keep snapping?
I really wish people would raise my fuss about these issues and quit buying (supporting said lack of QC) them until they (issues) are addressed by Cros/other manufacturers... >:(
JSR,
You might want to drill some holes in your pivot washers then fill them with moly at assembly. I used bronze for the washers and they have been working great.
Nice shop!
Great idea! I too have an idea; what about just milling/turning a shallow "lube-groove" + cross drilling into them. Just like the breach seal O-ring which is grooved into to provide the seal between the breach and the air port? That way either side gets lube and it would hold a lil' more. ;)