Callaway Firm vs. Stiff

Could someone give a brief explanation of the difference between the Callaway shafts labeled "firm" and "stiff."

Many thanks in advance.

In theory, Firm is halfway between regular and stiff

I must warn you. I've owned at least 6 different sets of Callaway irons and "regular" in one set did not necessarily have the same stiffness as "regular" in another set.

For example, I own Apex and Apex Pro irons, both with "regular" shafts, but the Apex Pro shafts are noticeably stiffer that the Apex shafts, even though both are marked as "regular"

Callaway used the Project X shafts which came in 5.0 regular, 5.5 Firm, and 6.0 Stiff.   I've seen the 5.5 also listed as Stiff.  I have only seen the term "firm" used with the Project X shafts but it's possible other shaft makers have a shaft that's in between Regular and Stiff too.

Yep, that's what it is: Project X PXi 5.5

Gracias, gentlemen.

Matrix makes some shafts in a "firm" flex.   I have seen them on their site.   They appear to be similarly positioned between regular and firm.

Some of the Callaway fairway woods from the original Big Bertha and BB Warbird models had graphite shafts listed as Firm.

As per newtogolf and teamroper60 , Firm falls between Regular and Stiff.

In steel shafts for irons, the Uniflex would be called Firm.

I have owned Project X pxi shafts and in my humble experience 5,5 felt like stiff and 5.0 felt like firm to me.

Royal Precision came up with Frequency Coefficient Matching back in the early 2000s.

Anyway, Royal Precision pegged is original Rifle shaft as FCM for regular = 5.0, and stiff = 6.0. But, RP scrambled things up when their Project X came out, and the PX 5.0 (Regular) actually had FCM = 5.5, and PX 6.0 had FCM =6.5.

For Dynamic Gold, the R300 FCM = 4.8, and the S300 FCM = 5.8. (DG shafts, however, are about 10 grams heavier than PX counterparts).

(History note: Royal Precision had financial problems and got bought by True Temper in 2006. Former RP designer Kim Braly now sets the pace for KBS shafts.)

I remember when Project X made its debut. You had many golfers complaining that the 5.5 felt "too stiff." Over the  years, I've read comments that it is a "feel thing" and the construction and design of the Project X is what made it feel "too stiff" at 5.5.

A lot of guys can handle 5.5 in a conventional Rifle shaft, but not in the Project X. It's just not to their liking. I tend to think that moving down to 5.0 was not the answer although that is what many did-- the Project X just did not fit their swing or likability factor in terms of feel.

FWIW.