Affect of freebore on COAL"
Whenever my son gets a new pistol I get to handload some ammo for it.
I always tell him that I need the gun in-hand to do my tests & make sure the load(s) that I typically use, or that I specially assemble, pre-check in it before I actually load anything to be shot.
He used to skeptical but always provided it.
Recently he purchased a 9x19 Kriss Vector SDP & brought it over for said routine.
Lo & behold, virtually none of my 9x19 handloads that we use in our assortment of pistols (largely 3rd Gens, but not limited to) can be used in the KV-90 because, as it turns out, has no freebore cut in the barrel's throat, only some leade from the chamfered rifling. (see pic below)
I generally like to load my rounds on the long side of standard, since they're usually full-power loads, but well short of the SAAMI COAL max @ 1.169".
The S&W 3rd Gens typically have very generous freebores, usually around 0.100", plus or minus 0.020" the best I can measure, & many different bullets I load can be seated longer than SAAMI max before contacting the rifling.
Any 9x19 I handload for us will work in any of our pistols, but not anymore.
Checking a handful of the bullets I commonly use, they all had different maximum COALs (using a technique similar to what
mikerjf mentioned) in the KV-90, because of the different bullet profiles, which I then lower by .008" to add some clearance between the ogive & the rifling, before I make an actual dummy round.
Fortunately he only wants to use the SIG V-Crowns & they had the longest max COAL (1.114") of the ones I checked, which was still below my normal 1.125" COAL.
He was glad I scrutinized the process beforehand.
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Kriss Vector SDP-90 chamber/throat with no freebore
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Typical chamber/throat with freebore between the chamber's shoulder & the chamfered rifling (internet photo).
My S&W 3rd Gens look like this, as do others.
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