[FrankenMauser]

My last post on this matter was in the now-deleted thread where certain members started attacking another member.

I don't feel like typing it all up again. So...

A summary:
I re-ran a test I did a few years ago, with an established load.
.270 Win
140 gr Nosler Partition
55 gr RL-19
Win LR primers
OAL near max, but I don't remember the exact measurement
Sorted and prepped R-P brass, excluding flash hole deburring.

This load averages groups of less than 0.475" at 100 yards with the addition of deburred flash holes in fully prepped, weight and volume sorted brass.
Without deburring the flash holes, the group size nearly doubles.

I had a partial box of ammo, with 11 rounds in it (loaded last year). I put a very mild crimp on 6 rounds with a .270 Win Lee FCD, and left the other 5 as they were. There was no cannelure to crimp in, and only faint marks left on the case mouth from the FCD. There was no apparent bullet "crush", but I didn't pull any of them to double check.

At 100 yards,
the uncrimped group measured 0.862";
and the crimped group measured 1.631".

But, the strange thing about going from uncrimped to crimped, is that FCD-treated ammo likes to create distinctly different POIs within the same group. Where the uncrimped group looks like a normal group, the FCD group looks like it is showing signs of pressure spikes (different timing for the jump to the throat) or secondary pressure waves. Most of my testing results in three distinct POIs for the same FCD-crimped loads, where the uncrimped load prints at a single POI. The FCD groups-within-the-group are consistent, but the aggregate is usually about twice as large as the single uncrimped group. (Just as the group sizes above show.)

I do plan to do some more testing with other variables, but 95% of my testing in .270 Win (130 & 140 gr) and .30-06 (165 gr) shows a decrease in accuracy when a Lee FCD is used.



Before anyone starts inferring that other posters are idiots for crushing bullets with an FCD, I'd like to point out that for many years, Richard Lee advocated doing so, and uses the concept in multiple ways, in some of his propaganda literature. Lee FCD instructions and Lee reloading manual still include statements saying that it is not only possible, but preferable to form a cannelure in bullets that don't have one, or don't have one at that seating depth.
(I have omitted passages that are unimportant, tangential, or a waste of time.)

Modern Reloading: Second Edition. Richard Lee. 2009. "Factory Crimp". Pages 57-58. (Emphasis mine.)

This tool duplicates the crimp found on most factory ammunition. It eliminates the factory advantage. It works so well that you can seat your bullet to any depth and it will form a cannelure in your bullet. It improves accuracy and your ammunition will function better.
....
Most important, it will never damage and render a cartridge useless, as a conventional roll crimper so often does.

Lee Factory Crimp Die instructions, propaganda description. (Emphasis mine.)

The Lee Factory Crimper is so powerful that it will even crimp bullets in place that do not have a cannelure. Now you can seat your bullets to the best depth and the Lee Factory Crimper will form a cannelure in the bullet as it crimps the case.
....
Until now, handloaders had to obtain a uniform start pressure by seating the bullet so that it would just touch or nearly touch the rifling. A firm factory crimp supplies the uniform start pressure for ammunition loaded for different guns and is tolerant to rough handling. Now you can match and exceed the conventional factory accuracy with little effort.

Lee Factory Crimp Die instructions. (Emphasis mine.)

-Bullets do not need a crimp groove as the LEE FACTORY CRIMP DIE will form one while crimping. However, it requires a harder push on the press lever to form the crimp.
-...When the four splits in the collet are closed, maximum crimp has been achieved.

Note that after 2011, Lee stopped using wording that referred to forming a cannelure in bullets, even though the tool's design and the instructions have not changed. Instead, the current literature uses variations of the phrase "a firm crimp".
Lee Precision, Inc. 2012 Catalog. Page 28. (Entire statement included for clarity. Emphasis mine - the Lee website has similar wording, now.)

The Lee Factory Crimp Die crimps the bullet in place more firmly that any other tool. It is impossible to buckle the case as with regular roll crimp dies. Trim length is not critical. Tests demonstrate that even bullets which have no cannelure will shoot more accurately if crimped in place with the Lee Factory Crimp Die.
Factory ammunition is often more accurate and better able to withstand rough handling because the bullet is firmly crimped in place. A firm crimp improves accuracy because pressure must build to a higher level before the bullet begins to move. This higher start pressure insures a more uniform pressure curve and less velocity variation. Even powder selection is less critical. Until now, handloaders seated the bullet to touch the rifling to achieve similar results. This is not always possible nor desirable. The Lee Factory Crimp Die is included at no extra charge with Lee PaceSetter 3-Die Sets. It's just another added value that only Lee Dies offer.