Well, I am not sure where to start, but airgun pellets are 177 caliber and not 172. However, there head size is different from pellet to pellet, even varies in the same batch. Like with the a-for-mentioned Crosman Premiers, or as I call them scrap lead…… The last few batches, or so called die numbers that I have gotten are really bad. There head size was just under .18, you can even imagine what this dose to the accuracy of my tightly choked barrels on my custom PCP rifles. Shot gun time! Is the term that comes to mind!
Your 397 is designed for pellets only while your Daisy, maybe designed to shoot BB’s and pellets. These are actually 18 caliber, and not 177 like the European air rifles. This is why you can’t shoot BB’s out of them, not to mention what that would do to the barrel, if one could. Daisy and Crosman use oversized barrels, but that is really not where you are having your problem, is it?
Anyway, some pellet makers like H&N and many others have different dies that they use, and something they need to replace these dies because they wear out. When this happened you really get a whole new pellet. One short story to make this all seem to make sense, happened to a shooting buddy who lives in the UK, anyway he has a Rapid 7, and had the power bumped up to near 60 foot pounds. Now this gun shoots really tight groups with the 22 caliber H&N Barracuda, this pellet is sold under a couple of different names, but they are all the same pellet made by H&N. Well, mostly!!!!!!!
The thing is every time he would go out and buy a new batch, or box he never knew what he was going to end up with. Some boxes of these pellets were different than the next box. The thing is some boxes had 19 grain Barracuda pellets, while other had 21 grain Barracuda pellets in them….. There where no markings on the tins to tell what weight pellet he was buying. So he would by some and if he got the right 21 grain pellets he would go and buy a bunch more, only to find out that he was still getting both 19 and 21 grain pellets. The only this was, at least in this case the pellets were the same weight in each box, all the 19 were all 19 grains and then 21 grain pellets were all 21 grain in that box. Talk about making on nuts…… The real problem was not only did the 19 grain pellets shoot to a different POI, but they shot very badly is his 1500 dollar rifle……….
I know that this doesn’t help, but at least you may start to help you under stand the problem….
Jim