Switching Brass - How much to back off?

[brn2hnt]

Going to be switching from Federal (fired factory rounds I just kept using) to Peterson (long) brass in my 300wm.

Shooting H1000 and Berger 215's.

How much would you back off from your known load to begin working up a load with the new brass?

The internet consensus seems to be that Peterson will have slightly less case volume after it's formed to the chamber as it typically has a thicker wall and lasts longer.

I don't care where I end up speed or powder charge wise, just looking to safely minimize the amount of workup needed because... components right now

 

[InkedElkSlayer]

I shoot 2 300 Win Mags with Berger 215s and H1000.
A rule of thumb, or advise you’ll usually hear when changing something is back off 10% and start working back up in .5gr increments. 10% is quite a bit and should allow for a good safety margin.
If you want a comparison, my 300 with Norma brass (thicker) is 74.0gr. Wife shoots Hornady (thinner) with 75.5gr.
I do not have experience with Peterson brass specifically. Hope it helps, good luck.

 

[wildwilderness]

I would concur with 10% is the safe answer. My experience with H1000 is it can quickly build pressure. A quick ladder test can save a lot of damage

 

[menhaden_man]

Not sure how to interpret the results but you could compare H2O capacity between the two cases. Could at least give you piece of mind.

 

[35WhelenAI]

Not sure how to interpret the results but you could compare H2O capacity between the two cases. Could at least give you piece of mind.

The information shared above with respect to the Peterson cases and a check of water capacity should get you going in the right direction. Or if you have a dense ball powder fill them the same and weigh the charges.

Heavier cases are typically less capacity.

Back off the charge weight with less case capacity regardless, the amount can be debated based on what others have experienced.

 

[EdP]

Shouldn't your current load now compared with the recommended max be a consideration? The point being that if you have a moderate load and zero pressure signs you may not need to back off as much as you would with a load at or close to max. Also consult multiple sources of load data in the process. Does backing off 10% put you below recommended minimum? I would not do that.

You could load one of the new brass with a mild book load. Measure the diameter of the loaded neck and compare with the loaded neck diameter with a Federal case. Then fire form it, resize and compare volume to a resized Federal case. That is pretty easy to do and gives a couple more data points.

 

[4ester]

The books and everyone always default to that 10% number.

If it were me…. I’d weigh your original case….. then the new Peterson brass to see how they would compare.

If you already know where you get pressure with your current brass why would you back off that far? Personally I’d go 5% max, I’d bet the load with the new brass is within 2 grains.


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[brn2hnt]

Shouldn't your current load now compared with the recommended max be a consideration? The point being that if you have a moderate load and zero pressure signs you may not need to back off as much as you would with a load at or close to max. Also consult multiple sources of load data in the process. Does backing off 10% put you below recommended minimum? I would not do that.

You could load one of the new brass with a mild book load. Measure the diameter of the loaded neck and compare with the loaded neck diameter with a Federal case. Then fire form it, resize and compare volume to a resized Federal case. That is pretty easy to do and gives a couple more data points.

This is a good point, anyone have book data for berger 215s?

I know I'm waaaay past SAAMI COAL, but the only free load data I can find is for a 220 Sierra or a 210 Nosler RDF. (both of which 10% off my load would be under their minimum loads)

 

[brn2hnt]

I shoot 2 300 Win Mags with Berger 215s and H1000.
A rule of thumb, or advise you’ll usually hear when changing something is back off 10% and start working back up in .5gr increments. 10% is quite a bit and should allow for a good safety margin.
If you want a comparison, my 300 with Norma brass (thicker) is 74.0gr. Wife shoots Hornady (thinner) with 75.5gr.
I do not have experience with Peterson brass specifically. Hope it helps, good luck.

10% is what I've always heard, but 10% is YUGE.

Even the nosler data for h1000 is only 5% off max loads for the min loads on a 210 RDF.

 

[N2TRKYS]

I don’t change anything when I change brass.