Ultra MMC issues

Looking for some clues to help with my Ultra MMC .177. So before I started buggering about with it I had no problems, then I had a leak at the filler probe so I replaced it with one with a gauge. While it was apart I thought I would fit a Lane regulator, the install went fine but when I put a few shots over the chrono it fine for 8/10 shots then it would drop 20ish FPS, next shot would be even lower then back to normal. Worryingly over the course of 30 or so shots this was repeated with the odd pellet not even leaving the barrel. This was about 18mths ago, recently I thought maybe the regulator was faulty (too late to return it) so I bought a Huma, exactly the same issue. I have gone through Lanes very good YouTube videos and happy with all the adjustments for achieving the correct power and its at just over 10ftlbs. So its obviously something I have missed or broken but it is such a simple action I cant see what. Any ideas?

Is it an external reg, or one that is internal and relies on a seal being removed to vent?

External, the Lane one is a model Lancet Mk9.

That's has to be a be a mechanical issue,is the hammer pin/latch loose? Is there something (lost pellet?) in the hammer housing blocking it from a full strike?
Id also check the firing valve.
Also is the mmc mech working correctly? It may be sticking and stopping hammer fall?

I had a similar issue with my hornet and turned out to be a binding/sticking cocking link. When I pushed the button at the front the assembly wouldn’t always return home properly, resulting in a ‘light strike’ from the hammer.

As above, if you cock the rifle pointing at the sky pellets can fall back in to the mechanism, you can usually see them by taking the gun out of the stock and looking in past the trigger.

I noticed with mine that the cocking bar had burrs around in various places and so the cocking button / nob whatever you want to call it at the front of the stock didn't always return all the way forward which would sometimes restrict how hard the hammer would strike and had disappointing results for a Huma regulated gun. Have the gun out of the stock and upside down and cock it (obviously unloaded pointing in a safe direction) then see if the nob returns all the way forward and try pushing the nob back gently and see if it always returns fully forward or sometimes sticks part way.

MMC's are all getting on now and this is just wear and tear and fixable after deburring and making sure it was all behaving as it should it's been fine.

Thanks guys, I hadnt really considered the cocking/trigger mechanism, I will pull that apart and have a look,

I had an issue with my cocking button being hard to cock. Turned out it was because I over tightened the stock screw and the stock was interfering with the rods. Not sure if it lead to a decrease in fps since it was years ago. If its just that its easy fix.

Tancho said:

Thanks guys, I hadnt really considered the cocking/trigger mechanism, I will pull that apart and have a look,

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My brother in law had the same thing and he’d whacked the forend of the stock, cracked it and it was catching on the cocking assembly as others have described. Try shooting it out of the stock to see if it makes a difference.

Also, did you remove the insert/reducer inside the valve body? You need to do this if you’ve installed a regulator. It’s worth reducing the valve tension too by replacing the nylons valve spacer with a thinner metal one.

To get the best from a Lane Regulator on an MMC in .177 you need to do the hammer travel mod, as outlined in his excellent instructions.
Pete.