6.5 creedmoor

[Brawley_z06]

I’ve been running lapua srp brass and using h4350 at 41.9 with great success and ran across some Peterson srp brass and was curious what I should start at load wise or would it be about the same as the lapua. Thanks in advance

 

[Beiruty]

Drop 1gr and test

 

[STOMP442]

Always start low and work up. In my experience Peterson and Lapua have been very similar but I would back it off at least half a grain and see from there.

 

[Chris Edmondson]

I’ve been running lapua srp brass and using h4350 at 41.9 with great success and ran across some Peterson srp brass and was curious what I should start at load wise or would it be about the same as the lapua. Thanks in advance

Try measuring case capacity of each brand. No matter what, you got good advice to start low and work up.

 

[Chiquita]

Try measuring case capacity of each brand. No matter what, you got good advice to start low and work up.

Good way of doing this?

 

[Chris Edmondson]

Good way of doing this?

I hate measuring case capacity, it's tedious and messy .

21st Century sells primer pocket plugs that help, they prevent water leaking out the flash hole. Here's a link: https://21stcenturyinnovation.com/buy-online/ols/products/primer-pocket-plugs

The idea is the dry case with the plug installed, is weighed. Water is added to the case, using an eyedropper, until the case is full. The problem is the water will have a meniscus so judging whether the case is full or not, is a PITA. I've heard that adding a bit of alcohol to the water will help the meniscus, there may be other methods. Either way, the weight of the dry brass is subtracted from the final weight with the water, that's the case capacity in grains of H20.

For the purpose the OP asked about, this method is probably close enough for govt work.

As far as predicting how different case capacities affect internal ballistics, software like QuickLoad and others are decent indicators. I used the method above when I switched from Starline to Lapua a while back, with QL, the real world results aligned nicely with the predicted results.

 

[Chiquita]

@Chris Edmondson , thanks for the explanation. Sounds like as much fun as standing in the Vegas all you can eat buffer.

 

[bks22345]

One thing to add, make sure they are trimmed to the same length. I’ve always used a fired primer, knowing each one might have a very, very, very small volume difference. Someone one this forum suggested installing them upside down. Light bulb.

 

[Ned Ludd]

Good way of doing this?

Case Volume Determination (pic heavy)

Readers here will see many, many posts regarding determination of case volume. There seem to be about as many different methods as there are posts on the topic, such as using detergent or alcohol mixed with the water, how the primer pockets are sealed, how "full" the case should be filled...

forum.accurateshooter.com

As long as you have a decent analytical balance, it's not that big of a deal to measure water volume with 10 cases and take the average. On the other hand, if I needed to determine water volume for 100+ cases, I probably wouldn't.