Changing brass

foxyrich

Well-Known Member
Hi,

I have just brought some new brass and changing from Nosler to Norma in 204.

Do I need to retest rounds with increments on powder weights due to brass change, surely the brass is all Sami spec and should not need me to retest?

i was thinking of trying a .2gr lower than my usual load and my usual load to see what's happening!
 
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Cases vary in thickness and volume,
best recheck as pressures can be significantly different especially if you are hot already

just done this with a rem to Norma change
took me a while to find some 300wm Norma brass now it seems to be everywhere!
 
A simple rule of thumb is that you should weigh the new brass as against the brass you worked up your loads in. If it is heavier it will have a reduced capacity. You should also trim the new brass to the same OAL as the brass you worked up your loads in.

Both of these are the two most likely factors to affect pressure. But also will be the thickness of the case neck as against that of the brass you worked you loads up in. Now to complicate matters some "other makers" brass is, in fact, made by Norma!

So Nosler brass may be Norma or it may be made by others instead. Some may know as maybe will Nosler.

BUT AS A RULE OF THUMB ANY COMPONENT CHANGE FROM THE ORIGINAL RECIPE REQUIRES A 5% REDUCTION FROM THE LOAD YOU WORKED UP USING THE ORIGINAL THREE COMPONENTS, BRASS, PRIMER, BULLET.

SO NO, IMHO, .2 OF A GRAIN UNLESS THAT IS 5% IS NOT ENOUGH REDUCTION OR UNLESS THESE ARE MEDIUM POWER PISTOL OR REVOLVER CARTRIDGES YOU ARE LOADING....

SAAMI "SPEC" APPLIES TO OUTSIDE DIMENSIONS ONLY AND NOT INTERNAL CASE CAPACITIES.
 
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Norma make an awful lot of brass for other people.
but it is not the same constituents or made to the same requirements.

NormaOEM.gif
 
there is another picture but I can't find it
brands include Nosler, Lapua, Weatherby, RWS, Sako, etc etc
 
I would say check even different batches of Lapua can have different capacities.

In my case with 24 grn Varget in .223 some are approx 95% full other batch is compressed and I have to adjust my seating die as in compressed bullet needs a bit more pressure to seat it. at correct COL.

They also shoot different POI best check and see what occurs in your situation

D
 
If you don't wish to follow the time tested guidelines mentioned above you can do this: Weigh a sample batch of each makers brass after the cases have been FL resized and identically prepped. (trim, cleaned,primer pockets uniformed if you do such things) Take the average weight of the samples. If the new brass is lighter, carry on. If it's heavier, reduce the charge weight by 12% of the difference in weight.

It's always better to reduce charges and begin anew.~Muir
 
I would say check even different batches of Lapua can have different capacities.

In my case with 24 grn Varget in .223 some are approx 95% full other batch is compressed and I have to adjust my seating die as in compressed bullet needs a bit more pressure to seat it. at correct COL.

They also shoot different POI best check and see what occurs in your situation

D

D. Have you tried using a drop tube when filling the cases? Using the drop tube, the kernels pack better and the compression on seating is less.

https://dl.dropboxusercontent.com/u/12296998/Reloading/Drop%20tube%20looking%20good.jpg

Regards JCS
 
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Checking cases by weight alone is inaccurate, the extra weight may be in the base and have no effect on the internal volume which is the important factor, as someone pointed out earlier batches from the same manufactuer can vary, best way is to seat a used primer the wrong way round, weigh the case, zero your scales then fill the case with water and re weigh the case. This will give you the internal volume in H2O
 
As a rule, any added weight of a cartridge with identical external dimensions will result in reduced case capacity. The formula I gave is pretty common and based on the specific gravity of brass VS the specific gravity of water. Reduction of case capacity effects loading density... which is the ratio of the weight of the powder charge to the weight of water that will fill the powder space in the case. Loading density is a ratio so when you reduce the weight of the water a case can hold by adding brass, you must reduce the powder capacity by the same amount to keep pressures the same. In this case, the specific gravity of water,1.00, divided by the specific gravity of brass, 8.77 equals .114, or 11.4%, or for simplicity, 12%. A reduction in powder charge equal to 12% of the difference in case weights will result in like chamber pressures.

It's far less fuss to just reduce the charge and work up if the new brass proves to be heavier than the old brass.~Muir
 
Looks like I better do some testing then... I currently load 25.0gr of rl10x so will drop it down 1.5gr and work up and see what's best.
 
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