Changing from Federal GMM to Lapua LRP brass

[Ransom1]

I've been shooting federal brass for years an am swapping over to Lapua large primer brass for my .308. I have a 175 TMK load with 44.4gr of varget in Fed brass. Just wondering if I'll have to increase or decrease my powder charge for the Lapua brass. Anybody got an ideas?

 

[Blue68f100]

Run a water volume test and see what the different volumes are. A dry weight might give you a indication.

 

[Ransom1]

Federal can hold .4gr more water than Lapua. Sound about right?

 

[Ruger 15151]

No. Lapua 308 brass has a larger volume than federal.

Not sure how your water test was done. Did you compare one of your fired federal cases to a new Lapua case? Individial cases in any brand vary a lot and fire formed cases will hold more volume then a new case sized to SAAMI spec. To get a more accurate test you would need at least 10-20 fire formed cases from your rifle of Federal and Lapua them trim them to the exact length. Then you check water volume and take an average across the sample for each. You will find that Lapua has more volume.

I shoot 44.8 gr of Varget in Lapua brass (large primer) with 175 SMKs in my Remington 700. I would load at least .4-.5 less if I were to load in federal brass.

As always, I am not recommending you use my load. Start lower and work your way up looking for pressure signs in your rifle.

 

[Blue68f100]

Federal use to make a 308-BR brass that had a larger capacity than its std counter part and I believe it also had small primer pockets.