Impact 'puff on the cheek' leak

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MonsterMaxx

MonsterMaxx

Member
Jul 27, 2017
352
5
South Carolina, United States
Thought someone else might run into this problem so I figured I'd share it and the solution.



My Impact has been back and forth to FX several times now fixing leaks and upgrading it. Recently got it back and pretty quickly I got the 'puff on the cheek' leak again. Thought it was a breech seal so I ordered some, changed it and went to the field on Saturday. Only to have it puffing again. By the time I gave up and put it away it was getting obnoxious.

This morning I called FX and after a few minutes on hold reached the tech who had serviced my gun. I explained the problem and after some diagnosis he concluded that the pellet probe wasn't going deep enough in the barrel for some reason.

Turns out there's a long rod that connects the block with the pellet probe block. This rod is a turnbuckle (lh thread on one end, rh thread on the other.) It had backed off some and the pellet probe wasn't fully seating. The fix is pretty simple once I knew what to do.

Degas the gun of course. Safe the gun. Take off scope and picatinny rail. The cheek pieces come off. Take out the barrel. Then there's a bunch of screws holding the top plate - loosen these and carefully lift off the long plate, leaving the screws in it. Set aside. Lift the block up off the action and slide the probe end out. Remove the turnbuckle from the block, clean and apply loctite. Reinstall turnbuckle and put the probe and block back in the gun. Close the action. Now adjust the turnbuckle until the pellet probe block is just a hair back from the magazine opening. Mine was so far back I could hardly get to the pellet probe screw. Put it back together. Allow the loctite to cure (24hrs.)

I did one test shot and no puff on my cheek and it's a lot quieter. Once that loctite sets up I'll put it over the chrony.

The tech did say that 1000fps would be too fast for the JSB 44.75gr and that I need to turn it down to around 930fps to keep them stabile.

Yeah, happy!



1571063605_17735818245da48735a699b5.00006610_ImpactWithClague.jpg

 
So the pellet probe set screw was a little loose. I tried taking it out so I could loctite it. Broke the darn tool. Not a run of the mill allen key either, a hardened toolsteel tool. Could not for the life of me get the tip out and ended up destroying the probe block to get the darn screw out. Ugh. IDIOT! Now trying to get a new block from FX. Beware this darn teenie tiny probe setscrew!
 
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Nice lookin' Impact. I especially like the shroud and the LDC. Where did you acquire those?

Also, I had 2 of my Impacts modded for increased power, including the additional plenum yours features. I noticed on my modded Impacts that the original smaller grub screw that holds the pellet probe in place had been replaced with a larger grub screw.

Good luck with getting yours back online.
 
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Since you are going through all those changes, be sure to check that the probe is not blocking the transfer port when you "time" the length of the turnbuckle rod. Mine was not correct from the factory and was actually blocking the transfer port by nearly half. I had to measure and align and "time" everything so it was seating the pellet as far as it could and not restrict airflow, and would also cycle back far enough so it cleared the magazine.
 
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Good thinking. 



Guessing the way to do that is take the probe and barrel out, time the probe in the barrel and use a sharpie to mark the probe. Then 'time' the turnbuckle so it's right when everything is assembled.



?? or am I overthinking this?
Click to expand...

Your not overthinking it, as that is exactly what I do get the ports to match up. Though I scribe the probe with a razor blade where the brass transfer port ends so I have a permanent mark that is easily seen to refer back to when everything is assembled.

If you're into modifying the probe and ports for the best airflow, I started with the probe "timed" open and flush with the back of the magazine/frame area, and then closed cocking lever and scribed the probe seated into the barrel. From there I took the probe and barrel out, inserted the probe up to my scribe line and ground both ports to match each other. Finish by polishing the probe hole edges so it isn't going to cut the o-ring from the new port-matching process.
 
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So I got my Impact parts today. Lined up the back of the probe hole (it's somewhat elongated) with the back of the hole in the barrel. Sharpied it. Put the gun back together and 'timed' the sharpie mark. Finished reassembly. Charged it up. Setup the chrony and loaded a mag.

1010fps from a .30 44.75gr JSB.

1571337387_11950277425da8b4ab3a2ce1.67818968_IMG_20191017_142413.jpg


Second thru 5th were in the high 980s. So yea, it suffers a little from creep.

Decided to take the FX Tech's advise and turn it down some to be in the 930s. Power level 2 was right there.



Sold a friend my pair of PP700SA pistols in a case. So I've got a little $$ to put into the Impact. A 700mm barrel and 580cc bottle are on order (backorder).



Now all we need is a .30 slug liner and some slug experience. Clearly it's going to have the power to sling slugs.



Yes, I'm a happy camper.


 
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