Is JSB Heavy MKI now JSBHeavy MKII?

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Drumsnguns

Member
Jun 14, 2016
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North Carolina, United States
I had some old JSB Heavy MKI pellets which I compared to MKII by shooting targets with my Impacts. The MKI's won and significantly with both guns. So I bought 12 cans of MKI from Pyramyd. 

They were delivered in two days and while inspecting for damage, I noticed that they looked similar to the MKII

So I got one of each and compared side by side.....IDENTICAL!!!!! It's like they got the wrong lids put on them. Comparing to the "old" MKI is no contest ...they are entirely different, The head is slightly bigger and the cup is deeper with a smaller base.

So I guess I spent an additional 170 bucks to get more of the same.

Am I missing something here? Can anyone comment?



Thanks

KP

FYI the Impacts are as follows

Impact MK2 w Power Plenum and 700 mm barrel/Slug Liner A. Terrible for slugs but shouts JSB pellets like a laser.

Impact MK1 Gen2 (rebuilt w Gen X valve parts) 600 mm barrel and Pellet Liner A and yes a tack driver as well with JSB
 
The principal difference between the MKI and MKII is the skirt, the MK1 being larger. That caused incompatibility issues with some magazines so they introduced the MKII to address it but kept the MK1 around because some people got better results with it.

Other geometric differences like depth of the skirt cavity, head size, etc. are features that have always waxed and waned with JSB between batches purchased at different times. Even visual differences we see between JSB and the equivalent weight Air Arms-branded pellets flip flop over time. For example the skirts may be shallower on the JSB this month but shallower on the Air Arms next month. I have no idea why they do it unless it’s somehow related to the vetting process for a new mold but suffice it to say these types of geometric differences don’t tell us much of anything.

In this case, measure the skirts if you want to verify your suspicions.
 
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I think that is unusual my .25 MK1 with a Polish Plenum and 700mm slug liner A shoots the NSA 33.5, 36.2 and VK 34 slugs at .5 to 1.25 inches all day long At 740-960fps. It does very well with the 33.95 MKII pellets as well.

Seems like my STX liner on the other hand does not shoot the slugs well but preferred the MKII pellets over the regular JSB heavies. Although I do not have any of the original JSB heavies to re-test and make sure. They did not all fit well in the magazine.

https://www.airgunnation.com/topic/the-infamous-slug-power-kit-on-my-gen1-impact/





36gr NSA slugs Shot three shots but could not see them so dialed in some elevation and shot three more. ;^)

?1

33.95 JSB MKII Best 5 shot group ever with the pellets usually 1+ to 2 inches at 100 yards. No wind at all at this moment.
 
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Same old story from pyramid. I quit dealing with them long ago. If your lucky they will make it right.
Click to expand...

If they're coming out of the tin looking like MK2s, it's coming like that from JSB, not Pyramyd is it not?

I'd be interested in seeing a comparison of these though. I'm planning on doing some testing with MK1s vs MK2s in mine. Seems like Ted reignited the interest in these when he started using them in his new rig.
 
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OK here's what I measured:



MKII's bought back in April 2020

Head Size: 6.36 mm

Overall L: 8.84 mm

Skirt L: 5.05 mm

Cup Depth: 1.63 mm



New MKI, Just purchased

Head Size: 6.36 mm

Overall L: 8.84 mm

Skirt: L: 5.02 mm

Cup Depth: 1.57 mm


Old MKI Age Unknown

Head Size: 6.36 mm

Overall L: 8.93 mm

Skirt L: 5.23 mm

Cup Depth: 2.28 mm

MKII and New MKI side.1603922506.jpg


MKII and Original MKI.1603922623.jpg


MKII and NEW MKI.1603922878.jpg


MKII and Old MKI.1603923586.jpg


So one picture is side by side MKII vs MKI (older) and one picture is MKII vs MKI (new). Can you tell? Pretty obvious the side by side of the underside cup pix. Hope to hear some opinions.
K
 
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I think that this goes way beyond "consistency."...The measurements i made between the MKII's and the New MKI's are statistically the same. The old MKI's are significantly different.

No, what we have here is the same pellet under two different names.

JSB's do differ in weight but not in form too much.



I took several random samples from each of the three tins and though there were differences within each sample they were minimal to be insignificant.

Does anyone have an email to JSB/Czech Republic?
 
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Thanks for the input and email address to JSB guys. I've sent the info to Pyramydair. Hoping they will refund or exchange. I think I'll go ahead and send to JSB as well so they can inspect their QC.

And for what its worth, the pictures from top to bottom:

MKII on left, New MKI on right

MKII on left, Old MKI on right

Cups: MKII on left, New MKI on right

MKII on left, Old MKI on right.
 
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Well, the big lie continues. Apparently Pyramyd Air has talked to either Predator or JSB since they now have this on their web site. 

Please note: The only difference between the original King Heavy and the King Heavy MkII pellets is the outer diameter of the skirt. This dimension on the original MKI pellets are 6.68 – 6.70 mm while the MKII pellets measure 6.58 – 6.60 mm. The appearance of the skirt or back of the pellet can vary.

However, I just got four tins each of Mk2 and Mk1 and ALL the pellets have the 6.60 skirt diameter. Maybe if they repeat the big lie enough times we’ll believe them?
 
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