Velocity differences between 6.5cm brass brands

Rodney65 said:

I am mot an expert reloader by any meansI load a lot of 6.5cm and have accumulated a number of type of brass. I have noticed using different brass results in big changes in muzzle velocity.

For example my Hornady large primer brass loaded with 41.8gr H4350 147gr ELD-M and 210M primer averages 2572fps with an SD of 14 on the first loading.

Using Federal large primer brass with 41.5gr (0.3gr less) powder and 210M primers is considerably faster at 2702fps, SD 11 although that was on the second loading.

The Federal brass is about 20gr heavier. Neither are annealed. Is the slightly reduced case capacity the reason for the increased speed?

I have noticed that my brass from slowest to fastest is:

Hornady large primer
Lapua small primer
Federal small primer
Federal large primer

Changing brass brands causes the biggest velocity shift I have noticed, much more than different primers or even a small changes in charge weight. I would expect some change but that seems like a lot.

Is this normal? Are the higher speeds with some brands just a free velocity increase? Does anyone else track this or am I just an idiot for having so many types of brass or possibly doing something else wrong?

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Yes, reduced case capacity will increase velocity. To what extent depends on by how much it's reduced.

There does tend to be a significant difference between Hornady brass compared to Federal brass. . . on average. Because there can be significant difference from one lot of brass to another within a particular manufacturer, there can be a big difference, like where Hornady's cases might be at the very low end of capacity and Federal's at the high end of their variance. This why it's always a good idea to actually measure case capacity whenever one gets a new lot of brass or when making a move to a different brand.

So, to your question, "is this normal", the answer is YES.

If I understand your question "Are the higher speeds with some brands just a free velocity increase?"; if you want to put it that way . . . yes. Like Winchester brass is known to have much larger case volume in their .308 brass that allows more powder for increased velocity with a lower pressure threshold. Cases with smaller case capacity may produce more velocity but with a lower pressure threshold.

For my .308 have have numerous brands of cases and have measured their capacity to see what the differences are. . . and I've recorded it all (all but those that just aren't used much, which I've picked up as my shooting ranges).

The best thing to do is to stick to one brand of case until they can't be used any longer. Even when you stick to a brand but get a new lot, it good to check the new lots capacity as it's not unusual to have to make a change in the powder charge. Below is an example from Peterson Cartridge Company's Test Data showing variations in their 6.5 CM cases:

Rodney65 said:

I am mot an expert reloader by any meansI load a lot of 6.5cm and have accumulated a number of type of brass. I have noticed using different brass results in big changes in muzzle velocity.

For example my Hornady large primer brass loaded with 41.8gr H4350 147gr ELD-M and 210M primer averages 2572fps with an SD of 14 on the first loading.

Using Federal large primer brass with 41.5gr (0.3gr less) powder and 210M primers is considerably faster at 2702fps, SD 11 although that was on the second loading.

The Federal brass is about 20gr heavier. Neither are annealed. Is the slightly reduced case capacity the reason for the increased speed?

I have noticed that my brass from slowest to fastest is:

Hornady large primer
Lapua small primer
Federal small primer
Federal large primer

Changing brass brands causes the biggest velocity shift I have noticed, much more than different primers or even a small changes in charge weight. I would expect some change but that seems like a lot.

Is this normal? Are the higher speeds with some brands just a free velocity increase? Does anyone else track this or am I just an idiot for having so many types of brass or possibly doing something else wrong? The Hornady handloads sat for the better part of a year.

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No idiotic tendencies, ....it's a common known and reported on occurrence for as long as reloading and scales have been with us.
Called weight sorting.... seperating brass by brand and then weight sorting that particular brand of brass intoweight categories.
This is done to keep velocity variations low.

The Velocity increase is due to pressure increas of smaller capacity cases... not free velocity, just increased pressure.

In the same 308 case, with the same load of bullet & powder SR primers will usually give lower velocity...depending on powder used by as much as 40 to 50 fps over LR primers, plus larger velocity variations with certain powders, and temperatures....

SR primers in large cases like 308 tend to work good in a narrower range of powders, temperatures, & conditions than LR primers.

Rodney65 said:

I appreciate the feedback. I expect some change but some of the numbers just seemed all over the place.

I would like to be able to load an assortment of headstamps so they get close to the same velocity with a particular bullet but it just doesn't seem achieveable. Some brass gives tighter SDs, some is overworked and is disposable, some I have more of for when I need to load up for a match so I different uses for them.

I am trying to keep tabs on everything by recording velocities and putting them in a spreadsheet where I record the day's weather, powder/primer/bullet/case type and number of loadings.

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I think the best you can do when mixing headstamps is to measure each case's cases volume/capacity (not weight) and that should be a close as you can get for consistent velocities between them. Keep in mind there are other issues going on, like differences in the thickness and the alloy composition of the brass that'll react differently to the expanding gases as well as sizing which will effect pressure/velocity. It's simply best to stick to one headstamp of the same lot at a time. Otherwise, it just get complicated.