difference between TMJ & FMJ

[HMdoc]

I just switched over to using Winchester 231 reloading 230 gr 45 ACP. According to the Speer Reloading Manual #13, the min/max for 45 TMJ 230 gr for 231 is 5.6 to 6.2. Using the Winchester reloading catalog, the min/max for 45 ACP 230 gr FMJ is 4.9 to 5.7. What gives? Is there really much of a difference between TMJ and FMJ? By the way, i am using zero 230 gr FMJ bullets. Thanks in advanced.

 

[Dave R]

I believe the only difference is that TMJ bullets have the jacket covering the base. No exposed lead. FMJ usually means the jacket covers everything except the base. I think Speer coined the term TMJ as a marketing term so you'd prefer their FMJs. Which are called TMJs. 'Cause "Total" is better than "full."

Regarding the differences in load data, I think that's normal variation from manual to manual. Some are more conservative than others. I think Speer's manual, overall, is a little "hotter" than the others I've seen.

I saw one .308acp load where Speer's START load was above Hodgdon's MAX load.

 

[Austin Charles]

check out another manual. I don't like speer #13. I alway's take a look at it but hardly ever use their loads. Seems heavy to me.

I like the Lyman's 48th edition. That and I alway's check out lee's.

 

[GooseGestapo]

Sorta what Dave-R said.

The TMJ's are a swaged lead slug that is electro-chemically plated and then again swaged to final shape and size.

The FMJ's have a jacket (swaged metal cup) formed around the lead core. Some have the base open with lead exposed (sort of a reverse of the typical soft nose or soft point bullet to include hollow points).
An exception is the Hornady ecapsulated FMJ's that have a jacket metal disc covering the base opening, making them "Totally" jacketed also.

Usually, you need to use "lead" bullet data for the plated bullets as they develope greater pressures than do typical jacketed bullets.