Sunday, December 28, 2014

Benjamin Trail Nitro Piston Pistol--Part 1

Bought this Benjamin Trail pistol at a flea market several months ago.  It looked to be new in the box and after some haggling, I got it for around $50 or thereabouts.   Knew going into it that there have been some "issues" with the pistol--mainly problems with it shooting high.










Here it is with the cocking assist lever installed.






 














 De-stalled.





















Oh, good.  Fiber optic sights. 




















Seems you can't get away from them nowadays.   The bright dots make it very difficult to achieve a repeatable sight picture--at least on a paper target.





















The rear sight is pretty flimsy--lot of play both horizontally as well as vertically. 





































Along with the sights, the long and heavy trigger pull has been almost universally panned.  A longer adjusting screw (It's a 3mm) will take care of most trigger complaints. 




















While digging through the bolt assortment, I swapped out all the phillips head stock fasteners for allens.


















































The grip is aggressive and took some getting used to.  There's a couple rub points, esp right under the trigger guard. 

This has taken so long because I couldn't get the gun to shoot worth a damn.  I shot some awful groups, changed pellets a couple times and shot even worse.  Couldn't get the pellets in the same neighborhood.  I mean I was missing the 8" x 12" backstop at 30 feet.  This thing was a complete dog.  Crosman owes me a quart of paint to touch up the concrete block wall it was so bad.  Since I've got a pile of other guns that are actually, you know, accurate, the Nitro Piston was set aside until my memory faded and I forgot just how bad things were.



















Initially, I had hopes that getting rid of the horrible sights would make thing better.  Used a heat gun to break the front loose.



















Pulled right off after about a minute at low heat.






















An angled flat on top of the muzzle.  At this point I started digging through my collection of pieces and parts to see if anything looked promising.
























This part of my experimentation didn't pan out for me, though it would work with a different rear sight.  This is the front sight unit from a AR2078 --it was a snug fit to the 15mm NP barrel.




















Removed the globe insert and installed a post.























Used an M5 cross bolt to clamp it to the gun.  Note that the proper way to mount this sight is to groove the barrel for a cross pin.  This is virtually identical to how break-barrel pistols used to be equipped with front sights.   The protective hood shields your hand from the sharp sight edges while cocking.   Archer Airguns sells these for about $15 here.  After getting this installed, I shot another group and realized that the grouping problems weren't related to poor sights.





















 Looked at the breech seal next. 

























 Really didn't see a problem.






















 Removed it and found a steel shim.


































Checked my breech seals and found I actually had a new one, so I tried that--with and without the steel shim.  The gun leaked slightly without the shim.   Looked at the spring plunger and found that the tension was very, very low.  I think the barrel lock-up is inconsistent and the cause of the inaccuracy.





















Removed the four screws and pulled the action out of the stock.
























Removed the e-clip at the rear of the anti-beartrap lever.
































Then the return spring and lifted it off.  I see that it's already slightly bent.  Superb.
































Barrel pivot lock screw...
























Barrel pivot.  The shim washers are plastic.  I didn't get to it today, but in my experience, these plastic washers are nothing but trouble for consistent lock-up.   Bronze will be a good replacement material.































Knocked out the roll pin and there was zero preload on the plunger.  Zip.  None.  I actually found this encouraging.













































Found a longer spring of about the same wire size.  It's about 2 coils longer.  If I do this again, I'll make it 3.





























A small nail made for a fine slave pin.  Tapped the roll pin back in.











































The bent anti-beartrap lever is humped slightly in the middle.

















Put it all back together with a cheap  red dot and a muzzle weight from the old TF79 project.
































I can live with this.  Just one called flier on the right.  Fifteen shots with a mix of RWS Super H-Points and Geco wadcutters.   Some bronze pivot washers and an even stiffer plunger spring should make this even better.  Lot of work.  A typical Crosman 2240 or 1377 will outshoot the Nitro Piston pistol all day long with no mechanical effort--or wall painting.

1 comment:

Arturo said...

how did you remove the rear optics?