Uragan 2, air blast from valving during shot cycle?

[BRAAP]

Received my U2 in .25" 600mm w/carbon fiber stock, shooting JSB Kings @52 ft/lbs, and LOVING IT! Only one thing seems odd leaving me scratching my head.
Since the very first shot, during the shot cycle a blast of air is being released into the stock just above the trigger sear coming out from the valving. To the shooter, this audible "Crack/SNAP" from this blast inside the stock is as loud as the muzzle report with cheek against the stock. I would imagine with the laminate stock the sound wouldn't be as pronounced as with the Carbon stock. I removed the stock to identify this and through dry-firing using a piece of tissue was able to locate where the blast is coming from during the shot cycle. The gun seems to be fine in every other aspect, holds air for days on end, no leaks, performs awesome, laser accurate, functioning great, this blast from the valving during shot cycle is... odd.
What little I was able to uncover in my searching is one other gent in the UK experiencing same issue/feature, he took his to 2 different gun smiths that both said it is normal. Another gent mentioned that some manufactures don't utilize a stem seal. To me feeble mind that would make sense in an effort to reduce frictions that may vary and alter the consistency shot to shot?

Anyone else experiencing this air blast from their U2 during shot cycle?

 

[nervoustrig]

Firstly, you’re correct that an O-ring on the stem is a potential source of a slow first shot as a result of stiction after it has sat idle awhile. From what I’ve seen, not many valve designs incorporate one, and I assume it’s because it’s not difficult to achieve a suitable slip fit that keeps the leakage down to an inconsequential level. For there to be so much leakage to produce a loud pop suggests to me the part tolerances are rather sloppy.

If you really want it addressed, I would recommend seeking out a machinist to assess the fit between the parts and work out a solution. For example if the stem is uniform and healthy so to speak (which is likely), the solution may be as simple as drilling out the valve and installing a close-fitting bushing, or plugging the existing hole and drilling and reaming it the proper dimension. Worst case, maybe have to also make a new poppet assembly.

 

[WorriedMan]

BRAAP,
Just a stab in the dark, search a thread Motorhead did on the Uragan 2, I realize his work was on a .177 but you might find helpful information. Best of Luck, WM

 

[Pfddi]

I think I ran into your problem. I have the same gun except in the walnut stock. Took it out last night after it has been working well and all of a sudden, I'm getting a loud blast directly from the barrel/pellet pusher port. I took the magazine out and dry fired and put my hand in the cavity and can feel the air. As you said it is very loud. I have not take the gun apart yet to review all the seals but I can't see any problems looking from the outside. Did you come up with a solution to the problem?

 

[BRAAP]

I think I ran into your problem. I have the same gun except in the walnut stock. Took it out last night after it has been working well and all of a sudden, I'm getting a loud blast directly from the barrel/pellet pusher port. I took the magazine out and dry fired and put my hand in the cavity and can feel the air. As you said it is very loud. I have not take the gun apart yet to review all the seals but I can't see any problems looking from the outside. Did you come up with a solution to the problem?

Have not a found a solution to stop it, without divulging too much factory has acknowledged this and is apparently normal, not detrimental though has the obnoxious side effect of the very audible blast that sometimes can be felt ever so slightly on the cheek as that air escapes from around the magazine. As I understand the design and what is taking place, any seals that could fix this, could/would introduce gross inconsistencies in shot to shot velocity/power spread.
I did add some sound deadening inside the stock that helped slightly reduce the loudness of this blast.
Personally I feel with as great as this gun is on paper and in function, (LOVE this gun), this oversight on their part is obnoxious enough it honestly should’ve been addressed prior to public release, at minimum incorporate redirection and attenuation of this blast.
As you dig into yours, please do share what you find, thoughts and concepts that may help reduce the obnoxious of this “feature”.

 

[Pfddi]

Thanks for the update! I certainly will. The worst part is that it manifested itself on my wife when she was shooting it! The gun was still shooting fine but I did not put the crony back on it to see if I lost anything as she was really mad at me for ruining her shooting day! (she wasn't too bad - I jest). The gun has been a stellar performer up until this happened. I will try and document the problem visually and audibly once I get it apart and will be happy to ship it off to the factory and post here.