conflicting load data

[mr. frog]

i loaded some with barnes 185 gr tsx b.t. with 68.5 gr of imr 4350 and a COAL of 3.290. my rifle seems to be a bit short at 3.300 (unless i'm measuring wrong). the barnes site and imr site had conflicting data it seemed, but the oal was different so i'm not sure.
http://www.barnesbullets.com/Copper_Manual4/338 Win Mag.pdf
http://data.hodgdon.com/cartridge_load.asp
does my above recipe seem good to go? also what kind of changes to these numbers would i have with shortening the tested barrel from 24" to 20"?

 

[La Rebel]

1) Your recipe should be a safe load
2) Barrel length does not affect max pressure. It does affect velocity to the tune of about 35 FPS per inch of length.
3) Shorter COAL provides less room for powder as the bullet is seated deeper. Generally if you load the same charge a shorter COAL develops higher pressure.
4) Different sources show different data. Be safe start low and work up looking for signs of pressure. All guns are different, chambers aren't all cut the same. If what you say is true about yours be very careful as less chamber space could result in higher pressures.
I use the QuickLoad program and it shows the max load as 73.3 gr IMR 4350 at COAL 3.290" muzzle velocity for 20" barrel shows 2974 FPS. (24" barrel = 3107 FPS)

 

[noylj]

Actually, for large rifle cartridges, the pressure actually goes down as COL goes down (within normal range) and pressure goes up as COL goes up. For my handguns, I have never really seen any pressure problems even with the bullet seated to touch the lede/rifling/lands (but you may), whereas I sure have seen pressure issues with long loading in rifles.
I can only assume that the referenced URLs gave some indication of the cartridge being loaded? Did the OP start with the starting load (or, as I prefer, the lowest starting load)?

 

[highstandard40]

Actually, for large rifle cartridges, the pressure actually goes down as COL goes down (within normal range) and pressure goes up as COL goes up.QUOTE]

Not always. It depends on the individual firearm and the chamber throat. You will raise chamber pressure by seating deeper, reducing available powder area, and you may also increase chamber pressure by seating long "IF" you have a short throat and get the ogive into the rifling.