.25 Mrod Bolt mod results (pic heavy)

[aceflier]

First off I want to thank Shorty for being a good friend and doing all of this for me. Over the past few months he has really helped me out lots. I also want to state that this is not a stock .25 Mrod so don't expect this from this mod alone. There has been port work and valve work done as well as shorty's spring installed.

Ok here we go. The first picture is of the default bolt and the one on the right is the modded bolt.



As you can see the original bolt takes up lots of space in the barrel port.



This picture shows the modified bolt. Much more room! There was a .25 JSB King chambered in this pic to make sure pellets still cleared the port.



Now for the good stuff. 43.2gr Eun Jin test

Filled to 3000psi and shot a 3 shot string with the original unmodified bolt. 6HS 0HT Here is the avg FPS.



Same 3000psi fill 3 shot string modified bolt. 6HS 0HT avg FPS



That's 55fps increase with 43.2gr pellets! So this mod is a huge gain if you ask me!

I am now ready for some hunting!

[shorty]

Way too cool.

[rsterne]

Very KEWL!.... yeah, that original bolt certainly obscured the barrel port badly.... Although the calculated area around the probe was nearly as large as the barrel port, I guess there were just too many corners for the air to go around.... Well done !!!

What did you end up with for the diameter of the probe?.... I usually use 7/64" (0.109") on a .25 cal.... unless the ports are huge....

Bob

[oneshot61]

Wow.. 9 ft lbs with the probe mod. That's awesome!

[aceflier]

The info I got from Shorty was...

The ports are .187 through

Modified:
Probe diameter - .115"
Probe length - .253"

He lengthened the probe length a little and took a hair off the neck to do so.

[K.O.]

Nice... bet it gets about 4-5 fpe even on a stock mrod..? Bolt Mod  will defanitly be Happening to my  Synrod test mule once I get every thing going.

how much louder than stock .25 Mrod..?

[aceflier]

At full power it is a little louder but still not that loud to me. It's the quietest in my herd.

[Frank in Fairfield]

A Reminder...

This is a Gen II bolt..

[degriz (AKA) Lou Hauburger]

Great info, nice job Shorty. My modded .25 is shooting well but more power is always a nice 

[mobilemail]

So is this issue with the port blocking the bolt strictly on gen2/.25?  Does it affect gen1s?  Does it affect .177/.22 in either gen?

[FuzzyGrub]

Gen 1 25 cal Mrods use a flow thru bolt, not a bolt probe.  The Gen 1 & 2 Mrod 177/22 use a bolt probe.

[rsterne]

If I understand correctly, this 9 FPE gain was on a gun where the valve, transfer port, and barrel port are larger in area than stock (0.187" instead of 0.141").... Please correct me if I got that wrong.... When you increase the flow area by 76% in one section, areas that weren't restricted (or not enough to make much difference) before will then benefit from enlarging.... The same thing applies if you have all the ports bore-size, then retracting the bolt (using a J-slot) so the nose comes completely back behind the barrel port, will give you that last little bit of performance.... Calculating the area is a good guide for where to look for improvements, but sometimes simply looking at a part will tell you what needs to be done.... This is an example of that.... The calculated area around the stock probe in the chamber is slightly larger than the 0.187" barrel port, but just looking in the hole tells you it's in the way.... Kudos to Shorty for recognizing that....

Bob

[aceflier]

Right on Bob. I would expect even more gain from a Retractable probe. I'm in for that if anyone ever makes and sells one.

[3BI5]

With changing shapes and forms the calculated flow area isn't usually the same thing as effective flow area. That can make a big difference.

In a regulated gen2 .25 marauder with about 22cc plenum and 2000psi set pressure this mod made about 10fps increase in max velocity (905fps with 25.39gr JSB kings). 

[Rivers3Plinker]

If I understand correctly, this 9 FPE gain was on a gun where the valve, transfer port, and barrel port are larger in area than stock (0.187" instead of 0.141").... Please correct me if I got that wrong.... When you increase the flow area by 76% in one section, areas that weren't restricted (or not enough to make much difference) before will then benefit from enlarging.... The same thing applies if you have all the ports bore-size, then retracting the bolt (using a J-slot) so the nose comes completely back behind the barrel port, will give you that last little bit of performance.... Calculating the area is a good guide for where to look for improvements, but sometimes simply looking at a part will tell you what needs to be done.... This is an example of that.... The calculated area around the stock probe in the chamber is slightly larger than the 0.187" barrel port, but just looking in the hole tells you it's in the way.... Kudos to Shorty for recognizing that....

Bob

Good point Bob.
Reminds me of modifying engines for performance.
Adding a high flow intake system to a motor that is already exhaust restricted won't do squat.
Once you start modifying you gotta know where the restrictions are at in the system and act accordingly or you waste money and time and get less than optimal results.

[shorty]

I can't take the credit for this mod as it has been done before. Just not any before and after results with this 1 modification with a ported system. Thanks Aceflier.

It really is too cool though. 54 fps increase with 43.2 Eujins......!!!!!! Boy-yaaaa - Bammmmm....

For anyone that wants to try and do this, good luck....

The bolt is hardend. It must be ground and done right. You ain't gonna do it with a file. If you do it on a grinder, you must have steady hands or a jig or your gonna tear it up.

If Hill or Travis is reading, this would be a great aftermarket part for the gen2 - 25 cal. I see it as a 50 to 60  dollar part. That's it... When set-up properly on the lathe it took less than 5 minutes.
Anyone running a Hill or WAR valve in 25 cal should be very interested.

[FuzzyGrub]

FWIW: I have converted Prod 22 bolts to 177 cal by removing handle and spinning in caveman lathe (drill) and using diamond files.  They are hardened and it does take a while.   To do the Mrod 25 cal probe only should be doable the same way. 

[shorty]

It would be so much easier and better if it was just a "cheap" aftermarket part.


Hey Aceflier,
When are you gonna run a string with the 33.95 jsbII ? I bet you will see an increased shot count or maybe a lower fill pressure with the same shot count. You know, your just a few "50 - 70 fps" away from me with .196" porting...  .

Can't have that now...

[aceflier]

I'm tuned for kings and Polymags (I have 7 tins of each)for squirrel season as of yesterday. 925-930 ish. Never ran a full string just 2600-2300 psi 3HS OHT and got 10 shots in zeroing and setting fps. I just shot till the fps leveled out for 3 shots. Will fine tune next week. I don't need that power till coyote season in October. I'm on the fence to shoot 31gr Grizzly or MKII's. (Both do well) Or 41gr slugs.

Forgot to add its still a lazer. 5 shots hole in hole at 35yds.

[Rob M]

im shocked no one is making these commerically available , nice work! will the gen 1 bolt fit the gen 2 ?