The load data I have with my Lee dies has a warning that reads "DO NOT use reloads in Glock
or simular guns with chambers that do not fully support the cartridge due to the intrusion of the feed ramp" I have a S&W Sigma V .40 cal wondering if I can reload for it using this data. I dont' understand this warning. A round fits completly in the barrel. Otherwise I don't know what to check for.

thats lawyer talk meaning buy factory ammo so we can sue someone

copperdaddy: This refers to the unsupported chamber issue. Some manufactureres like Glock use essentially the same barrel as their 9mm chambering bored to .40 dimensions. Further, Glock increases the diameter of the chambermouth to enhance feed reliability. This leaves you with a significant area of the casehead that is unsupported, particularly over the feedramp; referred to as the 6 O'Clock position. If the casehead is fatigued on the first firing and then the cartridge is reloaded and on the second or later firings and the previously bulged casehead should index right over the feedramp, you have the potential for a Ka-Boom event. There are other Forties besides Glock that also have unsupported chambers. One thing I recommend also is to avoid very fast burning powders. The .40 S&W has a naturally occuring fast pressure peak and fast burning powders tend to exacerbate the issue.

I believe the Sigma has a supported chamber but I suggest you confirm this with a call or e-mail to S&W.

Most 40S&W data sources I have seen use the same disclaimer.

Do a web search for Glock Kaboom for the horror stories.

If you want to check, field strip your pistol. Hold the barrel muzzle down and drop in a loaded cartridge. Look at the amount of brass in front of the extractor groove visible. If there is much more visible at the feed ramp than elsewhere, it is called 'unsupported'.

An 'unsupported' chamber allows more brass flex, causing more work hardening and reducing the life of your brass. The fear is that when the brass fails there, it dumps high pressure gas into the frame and blows it up in your hand. Keep your reloads light and don't push your brass too far.

FWIW, I load 5.4-5.5 grains (6.0 is max) Vn340 behind a 180 grain JHP and get 5 loadings without a problem. I then chunk that brass.

The Sigma has a supported chamber. Just rack back the slide and see if the feed ramp is part of the barrel or part of the frame. If it is part of the barrel it is a supported chamber.
Peter.

Yep,
I'm one of the guys who has personally had a "KaBoom" with a .40 cal Glock. I posted pictures and a complete description over on Glock Talk a while back.

Long story short. I was using remanufactured 180gr ammo. (Remanufactured, as in reloaded by a company with a manufactures license…. Not Joe Bobs hand loads.)
Case ruptured at the 6:00 position (over the feed ramp) and blew the extractor out of the slide.

The frame and slide were checked for cracks and then rebuilt with new internals.

Bottom line.... Use brand new brass only in Glocks……. or buy a lot of insurance.

Or don't push the envelope for your .40s&w loads. Or don't buy a Glock in .40s&w if you are handloading hot.
I load for a 4006 & a USP & have never had any problems using handloads in brass fired several times. i never shoot reloaded ammo from anything. You just don't know how many times brass has been used or abused. Roll your own or buy new factory in the high pressure stuff.