Mrod 25 cal - increase in power is now resulting in the loudest ping!

[mihogan]

Hey guys, I know the mrod isn't discussed much anymore here but I figured I'd give it a shot.

I've had a 25 cal Mrod that had a DIY hammer debounce device in it for a good year. I had it tuned for more shot count, so was getting around 40 shots at 745 FPS with JSB 25.4 grain pellets.

Long story short, the DIY one constantly needed tweaked and was not consistent, so I bought an HDD from Joe Brancato's shop and installed last month.

It comes with a custom hex adjustment screw on the end cap that lets you decrease or increase the spring tension and thus your power.

I decided to try maxing it out and now get 32 shots but at an average of 830 FPS. Love the increase in power! However, the rifle now pings so loud that it's ringing my ears after a while of shooting!

Is it normal for the ping to increase dramatically when the power is increased? I'm not sure if it is that or the new HDD is for whatever reason creating a loud ping... the HDD involved putting a new hammer striker into the hammer so I wasn't sure if that would be the cause.

Part of me wants to just try adjusting down the power back to the mid 700's and see if the ping disappears. But I've got it set just right right now, fully sighted in, and glued the adjustment screw in to keep it from moving on it's own.

You guys ever experience that? If anyone can confirm that happens, then I'll readily decrease power so that I can have a quieter report. Thanks guys!

[AlanMcD]

What you describe is very real - more powerful shots result in a sharper pressure drop at the valve during the shot, creating a more powerful standing wave in the tube and thus a louder ring.  The thing that rings is the actually the column of pressurized air itself, through reflections down the length of the tube - not the tube (although the tube transmits the sound).

If the ping is bothering you, you can install a "depinger" in the tube - it can be one of several designs or shapes, and the purpose is to disrupt the standing wave in the tube.  Many places sell them, including Tim Hill.  You can search on it - some have had good results with simple rolled up vinyl tube too.  The one downside of a depinger is that it will "cost you" some amount of HPA space, as they take up some volume in the tube, so you could loose a few shots form your shot string.

[3crows]

I have the standard Benjamin depinger in my M-Rod Super Light. I am tuned at (currently) 950 FPS with JSB 26.54 grain Hades pellets. The ping is not particularly louder than stock. I have the Tim Hill valve and the Tim Hill short shroud and use a muzzle device.

[mihogan]

Thanks guys for the responses. Good to know... Maybe I'll look into the depinger, or just tuning down... Will think on it. thanks again

Anyone know of a good resource on how to install the depinger? I assume I need to empty the entire tank, take off the fill valve, install depinger, and then reassmble?

[3crows]

Thanks guys for the responses. Good to know... Maybe I'll look into the depinger, or just tuning down... Will think on it. thanks again

Anyone know of a good resource on how to install the depinger? I assume I need to empty the entire tank, take off the fill valve, install depinger, and then reassmble?

Yes, you will need to remove the fill valve assembly cap. You can use a dowel rod to push the depinger in about half length. I am just using the supplied Benjamin plastic/rubber depinger. I have seem more elaborate devices including the one "somebody" installed in my Gen 1 M-Rod. I think the Benjamin piece works about as well and does not seem to slowly move toward the valve as some do.

Are you sure the hammer is not whacking the valve body face? I had to put one O-ring there to prevent a loud whack and I am also using a lightweight JSAR hammer.

[mihogan]

Whoa, it could totally be that! So you put an o-ring on the valve face? How big? If the hammer is whacking the valve so hard to fully depress the valve and hit the valve face, what keeps the o-ring in place?

It honestly sounds like the ping is coming more from the valve than the air tube. I wonder if that is what is happening

[Motorhead]

ABSOLUTELY ..... greater the valve opens / dwells, more noise the valve makes internally similar to what muzzle report does externally.

Factory G2 rifles came with a primitive & so-so effective de-ping sleeve within air tube, something better in terms of an actual de-ping devise does far better.

ALSO:  Hammer spring Vibration / Strum is very common as well with some known tricks to mitigate.

[3crows]

Whoa, it could totally be that! So you put an o-ring on the valve face? How big? If the hammer is whacking the valve so hard to fully depress the valve and hit the valve face, what keeps the o-ring in place?

It honestly sounds like the ping is coming more from the valve than the air tube. I wonder if that is what is happening

The O-rings installed into the rear face of the valve is a well known mod. Just buy a cheap O-ring kit and find the one that fits the ID of the air tube nicely and then slide it down to the valve and reassemble. The O-ring will stay in place, it just does. Some people stack the O-rings in for tuning but I am using a single O-ring to prevent over driving my valve and stop the (loud) whack when tuned for high power from the hammer hitting the valve. I have heard of instead installing a small O-ring on the poppet valve stem. I went with the large single O-ring for the air tube ID. You may have to adjust your tuning once the O-ring is installed as it will likely reduce the power slightly as the valve will not open as wide or as long.

I am guessing you are using the stock (heavy) hammer?

Oh, please note, on the O-ring(s), if your striker protrudes from the hammer face then the O-ring stack needs to be sufficient to stop the hammer before the striker itself whacks the valve body producing a similar loud metallic ka-whack! My striker is recessed into the hammer body but I am using a different striker and hammer assembly and different valve. But, I ran into the same issues with my Gen 1 and it is reasonably stock other than tuned for power instead of long shot strings. (Me, a contrarian, I do not see the point in .25 caliber for other than power, lol).

Supposedly number 211 size O-rings.

https://www.gatewaytoairguns.org/GTA/index.php?topic=197003.0