You are smart to be careful with this, especially with the high-pressure 40S&W.
When you find the minimum O/A length for the specific brand and cartridge you have
, a caliper is a snap to use.
You can get a decent caliper for ~$30 shipped. That way you can check your new ammo if you want.
I think when you have the slightest doubt about the safety of a round, you MUST ditch it 100% of the time. (With the 40SW, 200% of the time.)
100 rounds of top-notch ammo is about $110 mail-order if you have to foot the bill, and that's worth it, in my opinion, to avoid the low low low risk of a ka-boom.
Good luck, and may you never have to fire unless you are at the range.