New to JSB 25.39 monster redesigned, what to expect

[JungleShooter]

What ballistic coefficient (BC) do the MRD's have?

The ballistic coefficient in the HAM list seems really low at 0.039, but at least they do tell how they arrived at it:

● Ballistic calculator: ChairGun

● Drag model: GA

● Method: two velocities: V1 = 718fps | V2 = 653fps

● Range: 30y

● Atmospheric conditions: 244ft elevation | 75-85F | 60-80% rel. humidity





Do you have different BC data? How did you arrive at them?

Thanks! I'm just considering switching to the MRD's, but that would mean pretty big sacrifices.....

Matthias

 

[bigHUN]

I just ordered a small truckload of these MRD's for my L2, the shipping is in my way, and when all arrive I will need to do the investigation game as well.

JungleMan, I assume the POI drop from 20 Meters to let say 50 or 60 Meters - is accurately measurable with a caliper or measuring tape. I will clamp the gun in my Vise and shot 10-15 diablo for each distance and let the Streloc calculate the BC. Now I must be honest I never did this in Streloc before but for my archery tuning I was calculating for a decade+ the two speeds (front and back) by the arrow drop.

 

[Larryt]

JSB official testing shows MRD at 0.050, I have used this always in Strelok and it is damn close on. Have also used the measured drop method and get very similar result.

That said, each barrel, velocity at time etc, do play a role.

For all intent and purposes I use 0.048, which is spot on for me.

 

[NAProf]

Larryt and bunkeru2k,

Thanks for your input guys. I checked everything for leaks. No leaks and no blow by. I am thinking that either my valve isn't working right or I have a different hammer spring. So I got the Huma hammer spring (slightly thicker wire therefore slightly stiffer). I was able to hit higher velocities, but not yours. So I put in the 13 gm hammer and was able to shoot at any velocity I wanted at really small IHS values and PW settings. Was shooting the 25.39 JSB's at 940 fps, the 26 gr JSB Knockouts at 920, and the FX Hybrids at 960. The barrel really liked the Knockout and Hybrids. I am shooting in some HFT matches for the next couple of weeks so went back to the 500 mm barrel and shooting 13.43 JSB Exact RS at around 815 fps. Keeps me below 20 fpe and yields some really nice sub0MOA groups at HFT type ranges.

Cheers,

Greg 

 

[Larryt]

@NAProf - I am glad that you are finding your tunes........ enjoy the lead slinging

 

[Ricochet]

After reading this thread, I tuned my m3 to shoot the redesigns at 950. (STX superior 1:24 700mm) At 50 yards, their good. at 100, they are all over the place. You can watch em in the scope when they come into focus, they dart and dive every direction, No go for me at 100. I saw Michael post video of a bone stock impact on redesigns a while back, poking fine groups at 100 with 25.39 redesigns. Mine will not do that. On a solid concrete bench, sinclair up front, hard bottom rabbit ear protector bag in the back, mild wind.

 

[Bigragu]

@ NAPROF- what has most likely happened is your cocking block, the small black thing attached to your cocking linkage that is attached to that titanium rod, has slipped and since that titanium rod is spring loaded from the front, it has sprung towards the rear.
At the rear of that rod inside the block, that rod is attached to your slug/pellet probe. So if the rod spung back so did your probe and now your transfer ports do not line up.

The fault is the two 4mm grub screws that are on that cocking block. The get loose over time and if you’re not familiar with how all things work, then you won’t take the precautions to prevent that from happening.

You will have to reset the probe’s alignment with the barrels transfer port, and tighten up those grub screws. But you’re not done-

Order two socket head TORX SCREWS- M4 x 6, and one by one, replace each grub screw with those socket head screws. Use locktite on the threads.

With the Torx head you can tighten down with no fear of rounding out the inner corners like you would an allen socket head. If you continue to use those grub screws and they keep getting loose(no matter how much locktite you apply they will loosen up cause you can never over tighten a grub screw of that size), you will end up rounding off the grub screw head and now you’re in as bad a shape as sitting on a public toilet with no TP to be had. Trust me on all of this.

Seems that 99.9% of the time, when velocities suddenly drop substantially on wildcat and maverick platforms, and all things are good(breech o ring still in place, hammer adjustment is balanced with reg settings, and no blockage in the barrel) the loosening of these grub screws are the culprit.

Here is what I’m talking about:

On my personal Wildcat MK2 shown here I’m shouting a 25 caliber 28.4g barracuda hunter Extreme at 1010 to 1015 FPS, with good accuracy, as my transfer ports are perfectly lined up and my tune is spot on.