Barrel length effect on load data

[crunchy]

I am going from a factory Rem 700 7mm mag 24 inch barrel to a Benchmark #5 contour 27 inch barrel. What effect will this have on my pet load for the old barrel. Only other thing done was had the action blueprinted. Barrel length increase or decrease max load. Wondering how much less of a charge to start with. Also switched from Rem brass to Norma. Thoughts on what to expect...

 

[bfglowkey]

Well there are many schools of thought but they mostly agree on one thing:

If you change anything in regards to handloads always back down and work your way back up. Normally you would think if you changed brass or primers etc but in this case you have a whole new barrel and different length/manufacturer with its own process etc. You may find your "pet load" is not even valid anymore. It may be close, heck it may be exactly the same if your lucky but its not something to leave to chance. I would back down a minimum of 5% of your current charge and dial it back up in 1% increments. Especially if your load was on the upper end of the load scale. If it was moderate you may have more margin above to play with and be ok trying out the exact same load. One thing to think about is seating depth....were you SAMMI spec on that or recommended by a manual or did you seat it based on your old barrels chamber? You may have to re-measure and if that's the case your talking about at the minimum a seating depth check which could change pressures etc....see how crazy it can get?

Either way you should see more velocity even at similar charge weights due to the barrel increase in length. Free speed is never bad...just don't be surprised if your groups/POI change.

 

[4darkseid]

The longer barrel length should have NO effect on your "published load data" You will probably get a little more velocity with the extra barrel length. By NO means use "More Powder", with out starting low and working up. It is possible depending on the cartridge that going to a slightly slower burning powder would get a few more FPS without increasing pressure since you have more barrel in which to burn the powder.
Stay with the minimum or "Starting loads" until you know how your rifle reacts to them, variations in chamber size, case capacity among things can result in very bad things happening if you start with a heavy or max load.