My .25 Mrod Power Tune

[Bullfrog]

My 70fpe Marauder tune. Because seeing is believing....



Shots 1-8 are with 43.2 grain Eunjins. Shot 9 is a Predator Polymag. Shot 10 is a H&N Barracuda.

My shot string was as follows:
2900PSI
841.9
848.7
862.6
868.6
865.6
874.5
862.3
868.5

1025
930.7
2100PSI

It looks like I'd be better off just filling to 2800 next time. When the wind dies down here I'll do some accuracy tests and post some target pictures.

[Backyardsniper1]

Nice power setup. What games are you setup for?

[renowntwo]

Nice work

[PakProtector]

Instead of dropping fill pressure, it may be that you can increase hammer energy to move the peak up in fill pressure. Not an absolute though, it will also increase the peak velocity and you have a nice clip+ string going with not much spread now.
cheers,
Douglas

[ezman604]

WOW....excellent numbers for a hunter. And I WAS happy with 50fpe from mine.
 
But I haven't done the full valve mod yet. And need some heavier pellets to test also. Heaviest I've tried so far are around 28.4gr.
SAFE & Happy Shooting!!!!
Dave
 

[GadgetX]

Thank you !!    Very interesting.  I did not know I should be waiting 30 secs between chrony shots.  Any chance you could tell us what your approx Hammer, preload and valve settings are?  Thanks again !!

Mike

[ezman604]

Any chance you could tell us what your approx Hammer, preload and valve settings are?  Thanks again !!

Mike

Me or Doug??? LOL
As far as mine, I have the A2A hopped up valve poppit with the factory valve spring and factory throat. Using the 10# hammer spring with about 3 turns preload. Hammer strike full CCW and port restrictor screw full CCW. Also using a 0.155" transfer port orifice.

[rsterne]

Good solid 1 clip string with lots of power.... How accurate are the EunJins in your gun?....

Bob

[Bullfrog]

I'm about to go do some accuracy tests right now. I'll post my results.

Thank you !!    Very interesting.  I did not know I should be waiting 30 secs between chrony shots.  Any chance you could tell us what your approx Hammer, preload and valve settings are?  Thanks again !!

Mike

The waiting between shots in controversial. Not everyone agrees with me on this. All I can say is that from my own experience the numbers are more consistent when I wait.

My hammer spring is set to 1/4 turn from full CCW. My hammer stroke is set for about 1/2 turn from CCW (but dont' quote me on that, I was starting at full CCW and just randomly moved the hammer forward a bit to see what would happen).  My velocity port is set to wide open. I am using the factory sized transfer port.

[Bullfrog]

Here are my accuracy test results at 25 yards. Each group was a 4 shot group. I started at 2800psi, shot 8 shots, and filled again. I was shooting on the edge of a windy field off a bipod.

Picture #1 from left to right
Benji Domes; Eujins 43.2s

Picture #2 from left to right
Baracudas; JSB Exacts

The Baracudas surprised me. My experience has been that they don't like high speeds, but that's also based on 2 tins from last year. Maybe those were bad batches.The Benjis were amazing (I've never shot them before). The Eunjins not so much. At slow speeds the Eunjins stack like the Benjis. I suppose that's acceptable body-shot accuracy for coons but I'd rather pop them right in the ear with the Baracudas or the Benjis.

[Bill G]

Yes the Barracudas have always impressed me in the .25 m-rod.  They seem to fly really well up to around 950fps.  In my gun, the barracudas, benji's and of course the JSB's all shoot so well it is hard to decide.  I primarily shoot the Barracudas just for the higher energy. 

Bill

[rsterne]

Your results are pretty typical.... Unfortunately, your gun is tuned for the EunJins at 70 FPE, and although it is showing great accuracy with the lighter pellets at 25 yards, you may find that not to be the case at 50-75 yards and beyond.... unless you detune it to keep the pellets used in the 950 fps range....

Until somebody comes up with pellets over 31 gr. that are accurate at long range.... there seems little point in tuning to over ~62 FPE, unfortunately.... I've been fighting that fight for a long time, unsuccessfully....  In fact, none of my guns like anything heavier than the 25.4 gr. JSB Kings when you stretch the range over 50 yards.... so I'm limited to about 51 FPE for long range work.... 950 fps is two FPE per grain of pellet weight, by the way.... makes it easy to figure that out....

Bob

[Bullfrog]

Nice power setup. What games are you setup for?

My target animals are coons and hogs.

Your results are pretty typical.... Unfortunately, your gun is tuned for the EunJins at 70 FPE, and although it is showing great accuracy with the lighter pellets at 25 yards, you may find that not to be the case at 50-75 yards and beyond.... unless you detune it to keep the pellets used in the 950 fps range....

Until somebody comes up with pellets over 31 gr. that are accurate at long range.... there seems little point in tuning to over ~62 FPE, unfortunately.... I've been fighting that fight for a long time, unsuccessfully....  In fact, none of my guns like anything heavier than the 25.4 gr. JSB Kings when you stretch the range over 50 yards.... so I'm limited to about 51 FPE for long range work.... 950 fps is two FPE per grain of pellet weight, by the way.... makes it easy to figure that out....

Bob

I don't shoot much over 30 yards in hunting situations. When I set up on feeders I usually don't get further than 20 yards away should I have a chance to pop a hog. I'll try some 50 yard shoots just to see what will happen.

[GadgetX]

Good thread. 

Bill - It seems I can get more FPE from the Benjamin Domes (27.8gr) than the JSB Exact Kings (25.4gr), they fire similar FPS.   Any idea why?  The JSB group better at 30-50 yards.  I have not been brave enough to put my chrony at the target yet...

Bull - Thanks for the ~ settings.  I am considering a valve hopup kit from Dave for my .25 MROD.  May try a tin of Baracudas just for kicks.  I can tell you that I tried the H&N Silver Point with no luck at all.  Wanted a hunting pointed pellet, good penetration, but a 4" grouping at 30 yards.  PS - let me know if you ever shot a Gamo Platinum PBA .25 Cal pellet from that AG, I want to have on ear protection.    > 1400fps

Mike

[Bullfrog]

I haven't done any 50 yard testing yet. However, I did make a couple of changes. I didn't trust my hammer stroke to not slip so I broke my gun down and blue-loctited it very heavy. Now it barely turns. Hopefully that will keep it where I set it.

Second, I found a Gaska tank extension and shroud extension sold together for a good price. I added the tank extension but didn't get a chance to re-tune the gun until this afternoon.

I ended up just shooting it wherever the hammer stroke randomly was and it was clear that the numbers were calling for something higher than a 3000psi fill. Instead of lowering my spring tension I simply filled to 3300PSI and here's my numbers with Barracudas:

3300PSI
955.0
936.9
937.3  EDITED TO ADD THIS MISSING SHOT
955.2
946.2
948.8
946.8
953.4
957.9
953.5
947.1
947.2
938.4
934.6
2500PSI

I bet I could turn my power down and get a ridiculously long, flat curve.

[rsterne]

What pellets for that last string?....

Bob

[Bullfrog]

Sorry, I forgot to say. Barracudas.