Old Sparky;
First, not bore size but groove size. I first slug the barrel and then order sizing inserts from NOE just under this. I buy two or three of them. I test under size by .003 thou, then polish the up in size by .0001 at a time until I find accuracy. I continue until accuracy or fps falls off. This is where the additional size inserts come in. I now know exactly where the sized needs to be for a given slug in my barre. A different slug may very well require a slightly different size.
So many say their gun can't or won't shoot slugs. Is it that, or just not properly sized. Buying a premade slug for a gun or many guns that preforms at a top level is more like blind hog finds acorn. Luck in the highest order. This will explain why many find one Impact with a given barrel shoots well, when another says his is terrible. One is lucky, one is not. neither have given due diligence to what is usually required for top performance.
Oddly, many think a slug cannot be slightly under sized for the barrel. However, a .0001 or .0002 may show a tiny light around them n the bore but the blow by is insignificant. The friction caused in a barrel with a slug is much greater. It is a balance act. For instance, both being accurate, you may loose 5-10 fps to blow by, yet size up one more .0001 and loose 20-30 fps due to friction. As I said. A balancing act. Something a strictly plug and play shooter will never consider or experience.
More than likely, simply due to not understanding internal ballistics and expecting the manufactures to magically do everything for them. Which of course, is impossible and very naïve.
The FX slug helps in this regard, as it is much more compressible. And why a choke works with them. Chokes are terrible in most cases with typical full bodied slugs. An FX barre has a choke of .005. Not .0005, but .005. HUGE!!! The slug if a full solid slug, unlike the Fx version will have to be sized to the choke. Not barrel. Now you have huge blow by and a slug not perfectly centered in the bore and rattling down the bore until it slams into the choke. Maybe straight, Maybe not. No control what so ever! Which makes a good leaded almost iffy if not virtually useless.
I removed the choke on the Fx Superior Heavy .22 and reaped huge benefits with slugs other than FX Brand.
Before and After pic's.
View attachment DSC02497.1609840027.JPGLast pic, one shot to settle reg, 10 on target. 35 gr slug, 930 fps, 80 yards. (All I have here).
Knife
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. Thanks for the starting point
