Barrel Slugging Discovery

[saphelps]

Luger LCP: 0.355
Luger SR1911: 0.451
Sig Sauer P250C 9mm: 0.355
Wife's S&W M&P 9mm: 0.351

These were all slugged and measured with micrometer and most fell within my expectations. I'm casting all at .001 larger, so no extra die expense, a bonus.

Wife's M&P, though, results in a diameter that is .005 smaller than cast. Is this an anomaly that should be brought to Smith's attention, or just load my cast and shoot? Factory loads have shot fine (well they leave the barrel and go bang), just issues hitting the sweet spot and grouping all over the place. I assumed the compact handle and have compensated but she's still all over. Tell her more practice (and just empty 3 mags on the BG) but now I'm thinking more an issue with the firearm?

Can't seem to find a .352 sizing die anywhere.

Anyone else with M&P 9mm that I could compare against on barrel bore size?

[Hickory]

The S&W has a 5 groove rifling.
You might not have a correct reading if your caliper didn't measure groove to groove.

[saphelps]

That's what I thought initially as well. When measuring, I ensured the micro was seated against both highest points and not in the "indent." Two slugs hammered through with same reading. Will run another slug through tomorrow.

[saphelps]

Hickory, you called it and thank you. I had to go back and once again measure, which this time my eyes must have been on, since I did get .355 with both caliper and micro. For now, I'll continue to let wife believe it's the barrel while she trains to "compensate."

[gray wolf]

Seems your question pertains more to your wife's accuracy with the pistol. I say that because while you thought you had an issue with size you don't mention anything along those lines as a resulting problem.
How do you shoot ? perhaps you should fire the pistol and check it's accuracy, off a sand bag would be good.
If you do well and you probably will, then she can see it's not the pistol and then concentrate on her shooting.