.25 JSB King Heavy MK1 “33.95” Gr Weight Variation results - 6.36 mm

[bdzjlz]

My JSB months long sorting exercise continues. For those that haven’t followed, earlier this year I embarked on an exercise to sort approximately 25 tins of .25 JSB king Heavy, about evenly split, in both the MK1 and MK2 series pellets, for both weight and head size variance. All will be tested using no less than three different meticulously tuned PCPs under nearly identical conditions.

Now several weeks ago, I reported on the MK2 results in an earlier post. I also have previously posted how the MK1s split out about 60% 6.36 mm, 1% 6.35 mm, with the remaining quantity split about evenly between 6.37 mm and 6.38mm.

I finished sorting the 6.36 mm this morning for weight. Anything that weighed 33.60 Gr or less AND 34.61 or more, went into the misc tin and will just be used up for guests shooting large spinners. The rest were all split out within 1/10th Gr lots. The results can be seen below. BTW, the weight spread variance went from 33.05 to 35.10 - two full grains!

It is always interesting to me how few pellets are actually within a 10th grain of the advertised weight. It is no wonder we get flyers considering the head size and weight variations when shooting straight from the tin.

I will post actual performance result comparisons of all the testing combined, but that is still likely a few months out as I still have a regular job, lol.

 

[Stubbers]

.1 gr variance can result in around 1 fps variance seen at the muzzle (for ~33 gr projectiles), so 2 grains = ~20 fps spread from pellet weight alone, I've proven this mathematically and in practice.

Of course the guys who shoot sub 1% ES strings are weighing and sorting pellets, no gun could do such otherwise, unless your selection from the tin happens to fall within that criteria.

-Matt

 

[bigHUN]

I've been there, done that, a long learning curve until I proof it to myself...
At 110-130 bars and around 900 fps a 2-3 grain weight variation really doesn't matter (.25 JSB king Heavy).
more to be concerned with a pellet head size consistency, because that makes a friction variations still inside the rifling = speed variations still before and at the muzzle.

 

[JimD]

After I bought my one and only pellet mold and discovered my two 25s didn't like the pellets it made one of my investigations was to check weight variation versus commercial pellets I had on hand. That included both weights of 25 caliber JSBs. I was surprised that my cast pellets had noticably less weight variation than either type of JSBs. I concluded weight variation was not the reason my guns didn't like my cast pellets. I think it is just the same reason the SPA doesn't like JSBs and the Avenger doesn't like H&Ns. Guns just like particular brands and types of pellets for no easily definable reason. Applies to cast ones too.

But more to the point, I am not surprised you are seeing a large variation in JSBs since that is what I found too. They are good pellets but less consistent in my experience than H&N Match pellets. But if your guns prefer JSBs there isn't much you can do other than sort them if you want the best accuracy. I do not find that weight variation makes a lot of difference at short ranges, however (through at least 30 yards). I have tried sorting pellets when shooting the 30 yard challenge but I could not see a difference in my scores. My best 4 targets (3 199s and a 200) were all shot from unsorted pellets from a magazine (Carm).

 

[bigHUN]

My .25 Impact MK2 have not seen a shorter then 50 meters - in 3 years, but mostly 100 and beyond... so I cannot argue why some guns don't like certain projectiles especially at those small tiny short distances you people talking about.
But let's get back to basics...let's define what that means "my gun barrel doesn't like this or that pellet"
The rifling is a driver that makes the pellet spin. Either with too fast or too slow RPM.
And we can test it, it is easy.
At longest possible distance that is available to you or you feel comfortable with, make 10 shots each testing speeds. Start with let say 30% slower and increase by 50 fps for each consecutive group up to 30% above the speed you were shooting before.
You record your target ring for each speed group, at the end of the day you will analyze.
You will see that at certain speeds the group of 10' opens up or tightens down.
You actually searching for a optimal RPM of the projectile, and not for fps.
This valid for both the pellets also slugs.

 

[JimD]

I have tried varying velocity before and saw no change in accuracy. But I was not very controlled in my experiments. I would really like my cast 25 caliber pellets to work so maybe I'll try it again. I've also see other simple explanations of why one pellet worked better than another before, however, and those didn't check out. When we pull the trigger and the hammer is released to hit the valve and the gun fires, it sets off vibrations in the gun. Kind of like hitting a bar of steel with a hammer. It rings. The friction from the pellet in the barrel also is an excitation mechanism. So I think it's more complicated than simple spin speed but I'd love to be wrong.

 

[bigHUN]

For example I was trying out some heavier pellets in a new liner. Following first a speed testing process I got into ballpark of per say 900. Here I started the second stage in testing with raising the speed by 10. And I have documented that at 930 the group (size but also the shape) was tighter then at 920 or 940 then started opening up, next up about 960 it was tighter then 940 or 980. I am not negating that has nothing to do with harmonics inside barrel/liner, but convinced that the RPM stabilization down the range plays as well.
This why I like to shoot longer distances especially when I am testing and tuning. At longer distance easier to read the POI. Of course you need optics for that as well, not just to aim but to read the marks.

 

[1a2a3m4p]

Completamente de acuerdo….no es lo mismo disparar un mismo pellet a la misma velocidad en un liner 1:24 vs 1:18….personalmente estoy disparando JSB MKII con 700mm en 1:24 stxs y tengo resultados similares en mis grupos a 880 y a 930…..entre medio de esas dos velocidades pasa cualquier cosa…..eso si a 880 el viento me da mas deriva…..tengo pendiente subir a 960-980 para ver qué pasa…..por otro lado ayer me sorprendió probar el jsb MRS a 1040 fps en liner stxs heavy de 1:16….un verdadero laser en mi PANTHERA….una velocidad ridículamente para probar pellet a…sin embargo, funcionó!!!!! Me queda pendiente bajar a 960-970 a ver si se porta igual de bien…por lo pronto estoy sorprendido con los resultados