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Old 04-29-2015, 10:03 PM   #1
Rdsail
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Join Date: Feb 2013
Location: Richmond, VA
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Default High efficiency Mrod .25 Valve

Specs:
Tport: 0.156 Barrel Port: 0.156 Valve: Throat: 0.210 Valve Exit port: 0.167

Intake: I opened it as mush as possible and still have material to hold the spring. Also drilled two hows to allow outer flow.

Now The pictures:








Here is the mod to the shroud holder:




There has been a significant power gain. I'm topping out at 980 with JSB kings and I could add more hammer if I want to. But I brought my hammer down to about ave of 890. My shot count increased significantly and my efficiency went from to 1.304.

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Old 04-29-2015, 10:07 PM   #2
Rdsail
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I did a test to compared the FPE difference by just changing the pellet weight

I tethered the gun to my scuba tank. The pressure on the thank was 2350-2400. I figure I kept the pressure constant and took the average of 8 shots on each pellet. I figured it would give a good reference. It would have been nice if the tank had the pressure at 2600-2700 psi. This is close to the peak of my shot string anyway.

JSB Kings 25.4g @ 903 FPE 46
HN Cudas 31.02g @ 846 FPE 49.3

If I remember correctly (I could not find my notes on the pellets test) when the gun was stock I only got a 2fpe gain between the pellets. But I'm not positive on this.

It is a shame that the Cudas don't group well. Group I got was around 1.5 in compared to .5in with the JSBs. It might be acceptable for hunting. Also the gun in quieter with the cudas

It is actually shooting a little faster than what my chart above but off by 4 fps . If I assume that they are using the same amount of air, the efficiency on at that psi would go up from 1.453 to 1.558. This is a rough estimate but it should be some what close to that.

If I assume that the increase of speed is linear between the two pellets, My gun with the current set up maxes out at 975 with the JSBs (53.6FPE) then the Cudas should somewhere around 910fps which will mean 56.9 FPE. not bad with the size ports that I have.
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Old 04-29-2015, 10:10 PM   #3
Rdsail
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So once I sorted out the accuracy problem, I decided to increase the power to Average of 911 fps with kings. I'm using a 12.5# spring with 2.5 turns of preload here are the results. The gun is much louder and my efficiency went down a lot but I don't really care too much about that it is a hunting gun. Getting 16 shots at 2% spread is mostly my goal.

Here are the numbers for the KINGs. Average: 912 fps : 46.9 fpe



Then I tried at the same Setting with HN cudas 31g Average: 839 fps : 48.5 fpe



Also did Shot the cudas at maximum power with my current set up. The results where a high of 925fps at 2800psi that would equal to 58.9 FPE. I could easily reach 60 fpe by just increasing the t port and barrel port size or by adding a little more hammer. My porting is still conservative.

I'm not sure if the lost of efficiency was do to the combination of the heavier spring and increase power. I it is surprising how much louder the gun in from 895 setting to 910 which is the biggest sign of wasted air. I could have reduced the power but my curve gets larger. I'll be happy when my LCD comes in.

Now for accuracy:

All groups from 40 yards.

This would be my average group of 5 with the magazine: (never mind the shots on the upper left Those where the cudas. They do not group as well)


One of the better groups of 5 with one flyer with the magazine


This is my best group so far this is a group of 3 @ 40 yards. I did not shot more because I did not want to mess it up.

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Old 04-30-2015, 03:49 AM   #4
Bob La Londe
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Very nice. I am glad you chose to share that here.
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Old 05-03-2015, 01:57 AM   #5
Bob La Londe
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I've been wanting greater efficiency (and more power) out of my .25 (gen 2) so I copied much of your work here. I have a 10# spring rather than a 12.5. My first shot with hammer throw at zero and preload at zero was 951 FPS with 25.39 Kings. I started cranking down the hammer throw until I got a shot around 905. (about 6.5 turns) Then for the next 10-12 shots the gun shot like it was regulated. 905-903-904-902.... I was amazed. When I refilled the gun though my first shot was really slow. Down around 850. And then it stared to climb. It wasn't back up in the speed range until shot 9 or 10.

Both fills were to 3000 PSI.

I'll need to do some more experimentation, but it looks like my best shots are from about 2800-2200. Since I already have a screw on bottle on this gun it just might be a good candidate for a high pressure bottle and a regulator.

I wish I had a big bottle I could tether to so I could play with adjustments at different pressures. My little bottle only fills this gun twice before I have to throw it back on the pump.
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Old 05-05-2015, 09:23 PM   #6
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Ok... I cranked up the gun today,and fired some 31.02 grain H&Ns. Fastest shot from 3000 PSI was 908 FPS.

In this gun that is:

+7 turns preload.
-1/2 turn (modified hammer) striker length.
10 lb hammer spring.
Lightly ground both ends of stock poppet spring to shorten.

At that tune I could tell the gun could stand to be charged to 3200, but I do not trust the aluminum bottle over 3000 PSI. If I go with a 250 bar bottle I will put a proper regulator on it. Probably set to around 2400-2500 PSI.

Follow up shots were 900, 896, 892, 886.
Next string at those settings was similar starting at 902.

I would bet money that this valve could allow this gun to be adjusted to 6-8 shots at 55FPE. Maybe more if I was will to over charge, or possibly higher FPE instead with a stronger hammer spring.

Now I am getting back to my original goal. That is a long shot string around 900 FPS with 25.39 Kings. So far I am upto 18-19 shots with an almost regulated looking curve on shots 1 thru 15. I've got zero preload and a bunch of hammer stroke turned in and I still can't seem to get past the curve on the top end. So far I've only been shooting a 20FPS spread, but at the end of the string it does start to fall quickly. I've been stopping at about 886-888. Most shots are just over 900. (902-907). Its really close, but I think I need to find a string that starts at or around 890. My last two strings started at 900 and climbed to 907.

Charging my bottle right now. One more half turn reduction of hammer stroke and one more string then I'll post some string data.

FYI: I am really liking my Pro Chrono Digital. I can actually record string data and target shoot at the same time. At my short target range (23 yards) this gun is blowing one ragged hole for whole magazines. Sometimes two. I've blown several holes in my aluminum backer plate. Fortunately I have a big dirt pile behind that.
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Old 05-05-2015, 09:35 PM   #7
Rdsail
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Nice! Looking good. I can't remember what my max power was. I tuned for accuracy and not power. The HN cudas never shot well for me at 40 yards
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Old 05-05-2015, 10:16 PM   #8
Bob La Londe
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I think I have found the point of diminishing returns.

24 shots from 882-903-883. Its a little lower than I was hoping for, but its pretty darn good. I was hoping for about the same spread 10FPS faster. This is an average of 895, and an extreme spread of only 21. SD is 6. That's a little high for the competitive target shooters, but the middle of that string shows less speed variation than my regulated .177.

The setup is 7 -1/4 turns of hammer throw (6-1/4 compared to stock) and preload adjuster just bumped off zero so its on the spring and not on the end of the threads.

1 882 3000 PSI
2 887
3 893
4 891
5 894
6 897 From here to ...
7 898
8 898
9 902
10 902
11 900
12 903
13 901
14 902
15 903
16 900
17 899
18 899
19 895
20 896 ... here looks really good.
21 894
22 890
23 887
24 883 2300 PSI

I definitely think I could regulate at 2400 PSI and get a loooooooooong string at 900 FPS. I'm done working on this gun for a while. Dan, I want to thank you for this valve setup. I didn't do it exactly like you did, but close. I only bored the center of the valve out to 29/64, and I stopped a little short to make sure I didn't damage the valve seat.

I am sure there are guys shooting better powerful strings, but I am pretty happy with this one. I won't change anything until I am ready to spend more money on the gun. It will probably be a while.

FMI: Previous string was 896,905,906-908-903,897,897,895,898,893,890 for 16 w/ 900 AVG, ES 18, SD 5.
3000-2350. 6-3/4 turns striker
(5-3/4 compare to stock)

String before was more powerful at 6-1/4 turns with 19 shots at 902-907-886. Average of 901, ES 21, SD 5. This is the tune I would probably use for target shooting as 1-14 was 902-907-902 and very steady from shot to shot.
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Old 05-06-2015, 01:28 AM   #9
Rdsail
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nothing wrong with that! good power and shot count!
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Old 05-07-2015, 03:43 PM   #10
Bob La Londe
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I need to do another tuning string or two. I took a shot at my 40 yard spinner yesterday when I had some guests, and it didn't spin all the way around. Before it would spin 2-3 times. Somehow my numbers may be off, or I suppose I could have just made a poor shot on the target. I didn't shoot it again, because I was showing off a bit and that wasn't very impressive. LOL.

Also, I was just looking at my first results compared to my last results and it doesn't make sense. I think its time for a fresh battery in the Pro Chrono. The display was a little weak when I shot those last couple strings. (I had forgot and left it on.)
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Last edited by Bob La Londe; 05-07-2015 at 03:49 PM..
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