Thursday, January 15, 2015

How Lawrie Amatruda Makes Polyurethane Seals.

I received an email from Lawrie Amatruda last week showing how he makes polyurethane seals for air guns:
“I don't know if you have heard of me, my name is Lawrie Amatruda, I am in England UK, I read your great Blogs a lot, I hope you don't mind if I share with you my simple way of making flat section polyurethane seals, I am not an engineer, I'm getting to an age where I would like to pass on any helpful knowledge that I have to aid other DIY airgun enthusiasts to resurrect their old guns , I worked out this method some years ago after not very successfully trying to machine them on my lathe, I do lots of resealing of vintage and antique Co2 and pneumatic airguns for guys here, I hope the pictures are self explanatory.”
“…I believe that obviously from all the information you are giving the collectors around the world the knowledge to restore these older airguns for the next generation, the chance to do the same to their treasured collectables, after all we are only looking after them for future collectors to enjoy. Thank you for referring others to me here in the UK, although I am slowing down a bit now, because of my age, so I am fairly selective with the work I take on, mostly the vintage and antique Co2 and pneumatic airguns”.

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Thanks so much for this hard-won knowledge Lawrie!

Sunday, January 11, 2015

Benjamin Trail Nitro Piston Pistol--Part 2

Revisited the plunger spring.  Went another coil longer.

60% moly grease on the plunger.

The stock plastic bushings were really close to 1/16" thick.   I went hunting and sourced these 3/8" x 5/8" x 1/16" thick bronze thrust bearings.  They came from the local Ace Hardware store.  They were in the Hillman fastener section.  Hillman #58008-B.  Don't remember exactly what they cost, certainly less than a buck each.

These will probably be just dandy, though ideally there would be more surface area against the breech block.

So I kept looking.  McMaster-Carr part #5906K531.  1/4" x 5/8" x 1/16" ran me all of about 96 cents each.    They'll need drilled out for the pivot bolt.

A letter J drill bit is about 0.003" larger than the bolt diameter. while this did work, a slightly larger drill bit would've made it substantially easier to install the pivot bolt.  Lining up the bronze washers was a real trick with so little clearance.

Still have room to go larger in OD to fit the counterbore, but I've run out of easy to find commercial offerings.  This'll do.  

Put it all back together and shot I forget how many pellets at the target--twelve or thereabouts.  Better than the last target, but I don't know how much to attribute to the thrust bearings.  This pistol doesn't exactly lend itself to being "benched" for accuracy.  It does feel better now when snapped shut after loading.  More solid, substantial.  The biggest improvement came from fixing the plunger spring to improve the breech lockup.   I think it's a pretty good shooter now for around $75 and I have the novelty of a pistol with a gas strut.   For the money, I still find that the CO2 powered Crosman 2240 has more going for it--more potential accuracy as well as a huge cult following and aftermarket component upgrades.