MDRL Valve Mods

[FuzzyGrub]

My MDRL is a stock Gen I 25 cal Mrod.

I like the low Es of my Synrod, and my goal is the same power and Es, but for 24 shots. Four shots should come from the MM airtube ext, and hoping to get the other 4 from valve mods. For reference, my Stock Gen II is tuned to 860-870-860 for 16 shots with Kings on a 3K fill.

I started with a Gen II valve which has a heavier return spring than Gen I. This helps with lower Es, but limits peak power. Here are the mods to the Gen II Valve:

- Inlet: 0.295"
- Body: 0.495"
- Exhaust: 0.160"
- TP: 0.150"


The Stock Gen I:

- Inlet: 0.275"
- Body: 0.405"
- Exhaust: 0.140"
- TP: 0.140"

As you can see, only minor changes. I made these mods to the valve a couple of months ago. I used a hand drill and a 0.495" reamer for the valve body. The rest were fractional or number drill bits.

My next step is to mod the gauge block to reclaim a few cc of air that the depinger takes up. I just plan to open up each end, but not the middle. I did make a "D" in the middle on my reg gun, but not going through the trouble here.

Gauge Block:
I just used a 5/8" spade bit and drilled down into each end to 1/2" depth. That leaves plenty of "meat" to the gauge block. I rolled up some thin plastic to fit down the existing hole to center the spade bit.

[Bob La Londe]

I put an air tube extension my my .177. I am not sure how many shots it added, but it does add a little more than 30% air volume if you measure it and do the math, While a .177 doesn't have much bearing on what you can do with your .25 in my case it has even less. I did a drill mod to the t-port and the net affect was I had to back off my adjustments to get the same power and a few hundred percent increase in shot count. The extension tube installed very easily, but I may actually take it back off as it makes the gun feel a little nose heavy for my taste. Sorry, I could not be more help there. Some guys seem to like barrel heavy guns so it might be right up your alley.

[FuzzyGrub]

I've had the ext on for some time, but never went back through the tuning process. I figured it was about a 25% air volume increase, hence the 4 shot estimate. I had a slow leak on the res and had to take apart to fix, so time to change the valve and other parts. I have this in a MDRL bullpup stock so the extra weight is not that much of an impact. The gun is still about 10" shorter than a stock Mrod.

[Bob La Londe]

You know I always thought of the bull pups as more of an affectation than a useful MOD (its not like we are going to be using them in close quarters combat) , but you do raise a very valid point. I may have to re-evaluate my point of view towards them.

[FuzzyGrub]

Yes, the attraction of the bullpup for me is making a long heavy gun into a shorter, more balanced one.

Made swiss cheese to the sides of the citrus depinger. Greased and installed everything in the air tube. Now the wait to see if the leak is fixed. Need to do some trigger mods to this anyway. I should be tuning it this week to see if it reaches my goal.

[FuzzyGrub]

I went with the 10lb hammer spring on reassembly. Leak looks fixed so far. Trigger still needs some more tweaking, and going to add 3/4" to lop.

Shot two strings this evening. Its getting there.

2nd String:

857 - 876 - 855 for 24 shots, ave 868. Es 21 or 2.4% of peak

Center 20 shots = Es 16 or 1.8% of peak

Center 16 shots = Es 7 or 0.8% of peak

Center 8 shots = Es 4 or 0.45% of peak

With 3 1/8T Preload, and 2 1/2T throw, the 10lb spring has plenty of room for higher velocity.

[FuzzyGrub]

A little tweak and had 24 shots 850 - 863 - 848, 15 Es <2% of peak