I have seen in several loading articles (not manuals) a crimp value at the case mouth for say 45 auto of .470 or so.

For example in this recent thread a link to encyclopedia of Bullseye shooting showed .473 crimp.

45 ACP original loads

Encyclopedia of Bullseye Pistol

So where as these values found? I looked and searched but can not find anything. What purpose do they serve?
I just seat the bullets and light taper crimp to smooth it out and shoot them.

If there is one for 45 auto, what are they for 9mm and 40 SW???

__________________
Still Running Against the Wind

I always took it that they were referring to the amount of crimp. For example, if the .45 ACP is .473 nominal at the mouth before any crimp is applied (SAAMI SPEC), then the .470" "value" is a crimp that is .003" under nominal when referring to how much crimp is applied.

It's a way to measure how much crimp you are applying, instead of doing it blindly or just by feel. The measurement comes from the nominal diameter of the bullet + the thickness of the case x2. .451 + .011 + .011 = .473. From here you can crimp down various amounts. .472 would be a crimp geared toward optimal accuracy at longer range, .470 would be a crimp geared toward reliability in an autoloader.

Personally I crimp 9mm to .378 and 10mm (same for .40) to .421.

Of course these values will all vary a thousandth or two based on your components, they are just general rules of thumb.

Look at a cartridge drawing. Those usually are with no crimp and will be the maximum from SAAMI specifications. Check out their #205 .pdf file.

As Dragon said, point of reference. With a .452" cast bullet, it will be a different measurement if you want the same amount of crimp all other things being equal.

Case wall thickness plays a big part in this measurement. You cannot accurately measure wall thickness with calipers. Load a round in several different brands of brass and measure the diameter. If the bullet is jacketed or plated, I doubt you will change it's diameter without using a LFCD. Check the diameter of several. I would almost bet, although I'm not a betting man, that you will find one brand thinner than others, R-P or Remington.

FWIW

Excellent! Thank you all. I have looked in every manual and Googled and could not find this anywhere.

I shall go forth and crimp with confidence

__________________
Still Running Against the Wind

I bought 4 Shooting Star 'premium' mags for a 1911. The "Owners Manual" that was packed with each mag stated, "Best reliability is achieved with an H&G #68 style bullet, seated to an OAL 1.250" +/- 0.002" with a taper crimp at 0.469" ."

It is about the only thing I clearly remember after not getting a new 1911 to work reliably with my cast bullets. Bought new mold, new mags, and followed directions above without any problems. Now all my and Mrs Engineer's 1911s are reliable without any feeding problems. I do use a Lee Carbide Taper Crimp Die -- the only Lee die worth owning.

__________________
S&WHF 366

I use the LFC die on virtually all my ammo. AS to the only one worth owning I and thousands of others do not agree.

__________________
Still Running Against the Wind

Other than 380 and 35Remington, I don't own another brand of dies than Lee except the ones that are designed for a Square Deal B!

Never have had an issue with them. I even use them on my XL650!