Bore friction isn't just a thing for slugs

Thank you for the great information. I don't like .177, too darn small for these old fingers but I do have a couple of guns in that caliber.
I am wondering, would running your pellets thru a sizing die help? I was looking at a contraption designed to flare the skirts-a pellet sizer ( https://www.trrobb.com/product/adjustable-pellet-sizer-177) wondering if it was buying.

I am wondering, would running your pellets thru a sizing die help?

I haven't used one of his sizers but from what I've read from others, it does a good job of what it is described to do. 

I failed to mention in the original post that both the originals and redesigns group well in this particular gun (QB79 HPA conversion) and that's really what I care about.  I suppose if I had a nicely made sizer like the TR Robb, I might try sizing a small batch and do some more testing to see if accuracy improves but I wouldn't be inclined to do it solely for the energy.  But generally speaking, pellets--unlike slugs--don't seem to benefit so much from sizing.  Granted it may help mediocre pellets group more acceptably but far less likely to improve pellets that already group MoA or sub-MoA. 

Hi Peter, for what it's worth I too was curious about the skirt thickness, thinking back on some H&N Rabbit Magnum II pellets a few years ago that nearly required hammer blows to get them through the bore.  But it turns out the skirt geometry of the Monster originals and redesigns are practically identical in this case.  And just as you noted with thick and thin between two batches of Ultra Shocks, I know JSB goes back and forth all the time so I'm not saying that would always be the case, but at least in my example it doesn't look like thick vs. thin plays a role.

Somewhere in May (2021 is now last year) I was running out with previous year batch MK2's (33.9gr) and bought again two boxes
...
Turns out the new production have bigger skirt. That is fine I spent them all during summer time @ BR but definitely no good for scoring cards.

In case you didn't already see it, in May this topic came up on another forum:
https://www.airgunnation.com/topic/25-delta-wolf-problem/

Except the difference being the other way around...with both the originals and redesigns both being the smaller skirts.  Ordinarily the skirts should be approximately:

6.68mm on MKI
6.60mm on MKII

Is the alloy hardness the same between both pellets? Wondering if that is a factor.

That throws out my guess.

Is it possible the faster one has lube on it? Just seems like the skirt is going to crush into the chamber to the same size on each.

Very interesting, Jason

What airgun produced the results you shared in the OP?

If a springer, I think that oversize skirts can also contribute to piston bounce.  I propose that that is the primary cause for velocity loss, then; because manually sizing pellets down first, speeds them up.  That sizing down happens in a springer breech cone, so pellet friction down the barrel after that should be similar to your manually sized pellets. 

The energy loss from doing the work of sizing down the pellet as it is fired, is not very large.  I say this because while the breech "un-popping force" is larger for a large skirt pellet, the distance it travels to overcome that resistance is very short; and energy is force x distance.

If you were using a PCP with a probe load then the initial sizing down is most likely already done on loading.  Suggesting that perhaps increased friction due to longer contact band is the culprit.  Of course that could be the case with a springer too, except that sizing down the pellets manually also lengthens the pellet's band of contact with the barrel.

If you shot the slower pellet un-pre-sized pellet into water to preserve the skirt as much as possible; then did the same for the fastest pre-sized diameter, comparing the contact band at the skirt between fast and slow pellet states might show something.  It is possible that your manual sizing is causing the skirt to "roll over", thus actually shortening the contact band in the barrel.  That would corelate with reduced friction - supporting your hypothesis.  Especially of the larger pellet skirt captured after firing show a much longer band of hard contact with the bore.

Now, if lead was springy then the larger skirt pellets would have "memory" and spring back a little as the pellet travelled down the barrel. I think lead is particularly "dead" as a spring material, so once the pellets is sized down by the breech or your die plate hole, they should behave somewhat similar.  Assuming contact band lengths are similar.

The differences between old and new monster pellets is not just in the skirt diameters, but in the flare angle of the skirt where it contact the barrel bore.  That angular difference would seem to change the friction band length, from my perspective.  The question is, how does the skirt diameter interact with that?  A larger skirt would probably result in an even longer parallel section rubbing along the bore. 

Perhaps you could size down to an even smaller diameter and see what the velocity results are.  I think if you are using a springer, the velocity will drop off if the skirt diameter is not at least above groove diameter.  Whereas, with a probe loaded PCP, sizing down pellet skirts to 0.001" under groove diameter may produce the highest velocity.  Much beyond that, and air leakage will remove gains from reduced friction...

Most interesting, I wouldn't have expected so much loss from just a few thou on a pellet skirt, of all things... Would have thought that it would have been sized down when loading, and shot just the same...
As an aside, if you want a smoother "reamed" hole from a drill, drill it out .030"-.050"-ish undersized, and stone a 45-degree chamfer on the corners of your finish drill, like a reamer.... It will leave a much smoother finish, especially in stainless steel...
Jesse

Jason, nice observations! I shoot both in .22 and the older versions skirts have a small flare where they contact the lands but the Redesigns skirt has one continuous flare up to the head, similar to a slug, so in my thinking, a larger percentage of the Redesigned pellets skirts contacts the lands adding more friction than the older versions. I could be way off base! LOL!

Subscriber, Randall, yes I suspect the bearing surface is quite a bit larger for the Redesigns, both due to its geometry and its considerably larger initial diameter.  I tried getting a picture of a couple of the sized pellets to show how far up on the taper it contacted but it did not turn out good enough to see properly so I didn't include it.  When I get some time I'll see about getting a good side-by-side photo and maybe try a water capture.
 
BTW the rifle is a regulated PCP at about 1400psi.