I am gearing up to load some .40 S&W rounds.

The case length is supposed to be 0.850".

The new Starline brass I bought ranges from 0.842-0.847".

Do I need to be concerned?

How short can it be before it becomes a problem?

Thanks,

Dave

I have never in my entire life had to trim an autoloader case because it was over maximum, and the majority were shorter than the minimum trim length.

Don't sweat it.

Ditto what Mike said.

Agree...never had to trim a 40SW, 9mm, .38Super, or 45acp.

Haven't run tests with the .40SW, but did shorten some .45acp cases. As new, they were under the .898" max-limit (but right about at the .893" trim-to-limit). Not all manuals list a trim-to-length; Hornady does but I ignore it unless the batch of cases exceeds the max. They never have, but I'll admit that things that I haven't seen are possible.

BTW: Hornady lists a .840" trim-to-limit for the .40SW...so if you are really "anal" could use that figure. But not on new brass...new brass tends to expand a bit raidialy and end up shorter on the first firing (becasue most sizing dies don't put them right back at factory new specs).

But I wouldn't trim them for the following:

When I trimmed the .45's to .890", I didn't notice much difference (bullet seating adjustmens stayed constant so that the case volume stayed constant; as the case grew shorter the volume didn't change). By .885" was noticing worse accuracy...by .880" it was much worse.

Now that's .013" shorter than the tirm-to-length..get out a caliper and take a visual on just how big a difference that is. I'll agree that it would also have some bullet-pull differences, but serious doubt if Bullseye is going to notice that small differnece in bullet pull.

In a Colt 1911-type the extractor was holds the case against the breech face at least well enough MOST of the time for the firming pin to light off the primer. With the long inertial pin of the Colt-types, the case can be way-way down into the chamber as the pin has plenty of reach.

Not all pistols use this system (most that don't look like a "colt 45" don't). Their firmming pin travel is more limited and the extractor system may not capture the round as it rises from the magazine.

Point being, accuracy was not as good with too short cases as it is with cases that headspace correctly (and both the .40SW and the .45acp are supose to headsapce off the case mouth). Given a strong enough extractor to hold it agains the breech face and a fining pin with enough protusion, the too short rounds will fire...but (1) it strains the extractor (2) it's variable, so accuracy sucks (3)if you by-pass the magazine, dropping one directly into the barrel and letting the slide slam home, it may not fire at all. In that last one, the case doesn't slide in under the extractor as it does in feeding, the extractor pushins it ahead and deeper into the chamber.

SO..decreased seating depoth of the SWC bullets until they were just kissing the lands...the cases were then actaully headspacing off the bullet rather than the case. Accuracy was as good as before...and a mixed magazine of too-short and normal-length rounds grouped together. This becasme my standard seating depth for the long cases as well...it was evident that even the longest cases were not as long as the chamber, but the problem didn't show itself before the tests.

Know it's been a long trip....but here my advice:
Don't trim them unless they grow past the max. length.
Even if they are of vastly differnt lenghts, would segregate out the short ones to use seperatly.
FOR TARGET AMMO: will tend to use the longest seating depth possible (but not so long the bullet is "jammed" into rifling and refuses to extract).