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JSB MK II Heavy Velocity

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"huntjunky"I'm looking for input for velocity capability of the JSB Exact King MK II 33.95 gr. I'm shooting the 25.39 gr @ 917 fps, with good results, and note that for the approximate same trajectory performance, I would shoot the 33.95 gr @ about 850 fps. What velocity are you guys shooting them at?
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900fps out of a modified FX Boss (.25 LW poly barrel)

5 shots, 50M outside:



 
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I Have a cricket .25 with the tube extended on the regulator side, which allows me to shoot them over 920, 925-930 to be exact, and they are absolutely phenomenal at that speed.

I recently put 12 pellets in 9/16'' group at 51 yards, and 10 at 1 1/4'' at 100 yards.

I am very very happy with that, I just cannot get my cricket to shoot the 25.39 grainers well, usually 3/4'' to 1'' at 50 yards 
 
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Thanks guys. I'm working with my Matador Long and this info really helps. I've found an accuracy advantage, w/ the Heavies, of perhaps 25% but didn't want to spend all the time to re-tune the gun for Heavies, if I couldn't achieve the velocity for as good or better trajectory. As wind drift compensation is my biggest nemesis, I like the idea of the heavy's 40% advantage over the 25.39 gr. This, plus the energy and accuracy advantage, with my gun, is well worth the sacrifice in shot count. It sounds like bringing the velocity up from the current 772 fps (which is what they poop out at, with the gun set up for 25.39 gr @ 917 fps), to 850+ will most likely have no adverse effect on accuracy. 

​Just a side note...I ran tests yesterday, for ballistic coefficient on both pellets and the results were somewhat surprising...the Heavies came in @ 0.0460 and the 25.39 gr came in @ 0.0307. This is contrary to the Chair Gun data base that shows the 25.39 gr @ 0.0360. The point is, you gotta like the ballistic performance of the Heavies.
 
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My .25 Wildcat is set up to shoot the JSB Heavy 33.95 grain pellets at 810 ft./s...from a bench rested position at this velocity my Wildcat will put every shot in the same hole out to 50 yards, 1/2" groups at 75 yards, and 3/4" groups at 100 yards all day long. My very best day was two 4 shot groups that measured 1/2" at 100 yards on Mothers Day this year...conditions were 94 degrees, 90% humidity, and dead flat calm. The head range officer watched me shoot those groups through his spotting scope by the way. 

I am sharing this in the hopes of convincing some of you guys that faster is not always better...your accuracy depends on many factors, but two that you can always control is your velocity and pellet weight. And you guys that are shooting these pellets through a rifled barrel that is choked will end up with completely different results than those of us shooting them through FX smooth twist barrels...and to further complicate things different barrel manufacturers use different twist rates, bore diameters, and choke sizes. Some choked barrels are like shooting pellets through a bullet sizing die...

The bottom line is that you must shoot these pellets at various velocity's until you achieve the accuracy/energy combination you are happy with. I mostly target shoot so I go for the most extreme accuracy...whereas others mostly hunt with their air rifles and for hunting a 1" group at 50 yards is good, and 2" - 3" groups at 100 yards is great! Just remember that with skirted pellets, the accuracy is going to decrease in direct proportion to the velocity.

A gentleman who we all know and love, just recently won the 100 yard competition in Arizona with a .25 Impact shooting JSB Heavy 33.95 pellets at around 865 ft./s...there is a reason he didn't shoot them any faster, because he knows that above that velocity out of a smooth twist barrel the pellets begin to do strange things not conducive to winning tournaments. For me and many others, accurate shot placement at lower velocity is more desirable than brute power that can't hit a barn door twice in the same spot!

Best regards, Chuck
 
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Spot on, Chuck. I very seldom see best accuracy, at a guns higher velocity capabilities, whether it applies to my powder burners or air rifles. I concur that the two schools of thought for "best" tune/setup, pretty much break down into either highest accuracy result (typically applied to target shooting or competition) or best compromise between POI accuracy and velocity (typically applied to hunting). The later, in this case, is my current test bed, which requires higher velocity while maintaining a balance of acceptable accuracy to alleviate an excruciating amount of holdover compensation at ranges beyond 100 yards. This particular gun has proven to be capable of consistent 140 yard kills, on prairie dog size animals, if I can deal w/ wind and holdover, correctly. Thanks to all and yes, I am following "some ones" lead not only when I purchased the Edgun but now with the selection of the Heavies over the standard pellets. My 772 fps velocity testing is quite promising as the Heavies are consistently averaging inside 1/2" 5 shot groups @ 50 yards. If I can maintain or improve on this, with a higher velocity...say 850 fps...I would have the best of both worlds. This will involve retuning spring tension, correctly balanced with a regulator adjustment, from the current 115 bar back up to say, 125-130 bar for best efficiency. As I am getting right at 60 shots, before evident POI drift w/ 25.39 gr, I would expect at least 40 acceptable shots, with the Heavies. My goal is 25% improved accuracy, 40% less hold off compensation, the same or slightly better holdover compensation, and an increase in energy of about 20-25% down range. Achieving this, I would feel I have milked out all that this gun is capable of. Next...better start saving for an FX Impact...your killing me Ted. :)
 
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HJ, I think you are going to discover that the JSB 25.4gr are never ever going to give you the long range accuracy you are looking for, whereas the JSB Heavy 33.95 grain will. I encourage people to shoot both the original JSB Heavy 33.95 and the JSB Heavy MKII 33.95 at long range to see what works best for them. The reason is that the original Heavy's have larger skirts which make a tighter seal in barrels with a bore diameter of say .251-.253...in this case you would have blow by with smaller skirts. Conversely, in barrels with a bore diameter of .250 the MKII seem to work best due to their smaller skirts...in this case the originals create too much drag on the way down the barrel and are not near as accurate. So I encourage you to try both and see what results you get. 

You also may want to try cleaning your pellets with Acetone, drying them thoroughly on an old towel, and then lubricating them with some Napier Pellet Lube... I personally prefer the spray bottle which applies a fine even spray. It is available at Napier USA in Shreveport, Louisiana. Here is a link for you to click: http://www.napierusa.com/acatalog/Oils__cleaners_and_protection.html

Good luck my brother...and best regards, Chuck
 
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Marvelous input, Chuck. Yes, I have long since made the same determination, for long range accuracy for "standards vs. heavies" (w/ my guns). W/ the Matador, I have also determined that MK II pellets are way more consistent than the original larger diameter skirt, with originals coming in last between all 3. This is through 950 shots in testing, though only at 50 yard range with the original 33.95. I feel confident in my results as they duplicate your advice. At some point, once I have things setup and tuned, I will run through the same processes I have with the 25.39, inclusive of sorting weight/diameter, clean and lubed pellets and clean seasoned barrel. This testing did not glean as much gains, in accuracy, as I was hoping. Perhaps it will be different with the heavy MK II. It is quite a game trying to shave off that last 1/4"-1/2" off my 100 yard groups. Given how sensitive the hold is, with a bullpup (I've noted that even how many fingers I caress the pistol grip with has some bearing on POI) and getting the right environmental conditions, I may be at the limits of the possible gains. Next step would be to obtain a gun more specific to long range bench and use the Matador for "puffing them up". Thanks for the link and I hope my report along with your input helps others "Be All They Can Be". ;-) Watch for my video post of some longer range scope cam shooting at live targets.
 
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