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saltydecimator

how to finish sbs build?

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so i am real close to adding more holes, but i am still confused how much the puck is supposed to acct for manufacturing variances. at least im assuming thats what it partially does.  i reused the gas tube after removing the "crimp" in it. attached tonys shorty piston, turned barrel down, and ready to start fitting parts. how do i know if my gas tube is too long, not letting piston go far enought into gas block, and getting stuff outta wack?  i assume that out-of-wackness contributes to some shotguns differing recoil impulse?


sbs/perm/shortened gas build


thanks!!!

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How far did you move the gas block seat back? Tromix piston is for a 2.25" move. Assuming you moved it 2.25", you simply fit the tube to allow the gas block to reach the rear of the seat when installed. After getting that fitted adequately and installing the gas block, fit the piston if the carrier will not travel far enough to allow the bolt to rotate and lock in the trunnion when the puck is in the gas block. Nike....

 

There is a lot that will contribute to how impressively or poorly a SBS will run. Gas puck vs carrier fitment can make or break it.

 

Merry Christmas wink.png

Edited by evlblkwpnz
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i guess my question is pertaining tpo puck.... pretty sure i moved at least 2.25.   havent drilled barrel ports yet, (hopefully) obviously... i just dont understand if puck should bottom out in gas block?  maybe im barking up wrong tree....

 

thanks for the above details, i need to pull parts out and stare at em again....

 

so, gas block, can i  use the hg threaded screw hole as a GB retainer type set screw,  and test fire it, then adjust GB fore or aft permanent placement?

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I don't think it would hurt to test it with your baseline ammo using the HG screw as a set screw if the gas block is interference fit with the gas block seat. I am not understanding the fore/aft inquiry.

Edited by evlblkwpnz

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I think he is asking if the gas block should be so far back that the puck is held against the back of the gas plug by contact with the op rod.

 

Evl is saying that if you moved it back exactly 2.25" from its original location it should be dead on. However, you make it sound like you moved it some imprecise distance that is at least 2.25"

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ah right, its imprecise because i added ports, and dont remember where i started from..... buuuuuuut, guess i can measure from one of the cross pin holes... now, thats assuming Ivan installed it in the correct spot to begin with,  ja? 

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Yes, you want the op rod to be reasonably close to the puck. Too far away is not good.

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hahaha whats reasonably close mean?  i over think things, so i assume there is a super sweet spot?  like how some s12 normal length guns recoil differently.  i assume that is related to distance between the puck and the op rod at time of firing.  as in, block too far fwd, puck wont push op rod through full travel, too far aft and the puck slams into gas block and gun recoils more? or too far aft and puck pushes too hard for too long and causes the carrier to impart more energy into rear trunnion?

 

i guess what im asking is, who has the definitive  "description and operation" of this setup?  in aircraft, in our maintenance manuals theres a section that gives the how and whys, as well as a trouble shooting section....

 

basically, i just  want to(know what the hell is going on) believe... haahha watching x files

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Go to sleep thinking about it, you may wake with the answer. That is how I usually find the answers I need.

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That is why the factory op rod is threaded, the 'stroke of the poke' is their final adjustment.

No simple answer, much trial and error.

The system is a free piston, energy is dependent not only on pressure vs stroke, but also on how much velocity the piston has achieved before it hits the op rod.

You HAVE to have some free travel or there is no place for crud to live before binding the piston travel.

 

I would suggest starting  long with the op rod, and grinding to tune for best operation.

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Or you could drill and tap a hole in the center of the gas puck for a 1/2-20 set screw, and adjust the free travel of the puck that way.

 

You need to have a little bit of a gap between puck and op rod to accommodate fouling, but more than .050" or so is probably a bad thing.

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