Lyman #49 used .401" test barrel for 40S&W?

[LiveLife]

FYI, while responding to another thread for 40S&W 180 gr load data, I referenced Hodgdon load data and Lyman #49 reloading handbook.

What I found was perplexing, with Lyman #49 lead load data significantly higher than Hodgdon jacketed load data.

- Hodgdon load data lists 4.1-5.0 gr for 180 gr jacketed bullet at 1.125" OAL

- Lyman #49 lists 4.3-5.8 gr for 175 gr lead TCFP at 1.125" OAL (but the groove diameter of the 4" test barrel fixture was .401" and reflects the higher powder charge).

I used to think that was due to the lighter 175 gr lead bullet over 180 gr, but when I checked the test barrel fixture details, Hodgdon used 4", 1:16" twist, Winchester SP primer and .400" groove diameter barrel for the .400" jacketed bullet while Lyman used 4", 1:16" twist, Winchester SP primer and larger .401" groove diameter barrel for .401" lead bullet.

That would explain the higher start/max powder charges for the lead load data - with decreased bullet-to-barrel fit, bullet was probably driven harder to obtain proper bumping of the base (obturation) for consistent chamber pressures.

Some factory barrels are over sized but I didn't figure universal test barrel fixture being over sized. BTW, I did some more looking around Lyman #49 for other calibers test barrel groove diameters:

380Auto - .355" / .355" sized lead bullet
9mm - .355" / .356"
357Sig - .3553" / .355"
9x21 - .355" / .355"
.38Spl - .357" / .358"
.357Mag - .356" / .357"
40S&W - .401" / .401"
10mm - .400" / .401"
.44Spl - .429" / .429"
.44Mag - .429" / .429"
45ACP - .450" / .451"

Now I wonder what implication this would have on our lead bullet reloading in regards to our barrel groove diameter size?

 

[scythefwd]

bds, most barrels out there are .401. Every test barrel will be slightly different, and the results of this are different powder loads. If your interested in what diameter you should be shooting in your barrel, slug it.

 

[243winxb]

40 S&W Groove Diameter

Jacketed makes more pressure than lead? Maybe? The .001" difference in groove diameter is not the main factor. IMO Just a guess. Hodgdon is playing it lawyer safe with there load data & warning?

This data is intended for use in firearms with barrels that fully support the cartridge in the chamber. Use of this data in firearms that do not fully support the cartridge may result in bulged cases, ruptured cases, case-head separation or other condition that may result in damage to the firearm and/or result in injury or death of the shooter and/or bystanders.