Small vs large rifle primers. Looking for empirical data from same brand cases

Wilderness Blacktail

Wilderness Blacktail

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Ok for those who have shot both large and small rifle primers of the same cartridge, same brand, and in the same rifle....

Was there a noticeable difference in amount of pressure you could run in one versus the other??

Ive read many times srp is better because it withstands pressure better and thus produces faster loads. I always took that to mean the head was stronger so if you looked for traditional case/primer/bolt pressure signs youd get more powder in before seeing them

In further reading it seems that it may only be due to the case head pockets withstanding more punishment before pockets loosen.
In that case are you seeing the same dots/lift/sticky ejection at the same powder charges but the SRP just last longer?

Or is there more to it than that?
 
Im curious what will come from this site in the next couple days.

For myself I bought my first box of srp in 2019 and was expecting great things. I figured id get great accuracy, low ES and SD, better speeds and a bag if chips.

I got everything but the speeds and the bag of chips. The cases -NOT SAME BRAND- pressured up a grain sooner and with corresponding velocity deficit.

My scientific brain said buy the srp in brand X and lrp in brand Y and then you'll know something. And I may at some point when I feel like spendin a bunch of time n money just to know this one thing.
 
In my 260AI, I have used both SRP & LRP cases. My 6.5x47 only has SRP brass with the small Euro sized flash hole, on 20 cycles and primers are just as snug as new brass.
You do not increase pressure because you are running SRP brass, what occurs is that with the same pressure running in both, you get more firings in SRP brass than LRP brass. I measure my loads over a Pressure Trace.
The reason is simple, the web of a SRP case has more metal surrounding the primer pocket, this results in longer resistance to expansion, that is all, no magic there, just simple physics.

Cheers.
 
Wilderness Blacktail said:
For myself I bought my first box of srp in 2019 and was expecting great things. I figured id get great accuracy, low ES and SD, better speeds and a bag if chips.
Click to expand...
Why would you expect better speeds?
Pressure gives you speed, same volume cases give close speeds, primer size only changes start pressure and how much there is, it doesn't change max pressure unless volume is different or charge weights are different.
What is the expectation of a "bag if chips"?

Cheers.
 
Just so we are clear here, a primers sole role is 2 fold, it pressurises the case to aid ignition, and ignites the powder by 'fluffing up' the powder column, if there is room to do so. Powder is difficult to ignite with a lack of pressure, and no, powder does NOT burn the same way in a rifle case as it does when you ignite a pile on the ground.
Either of those 2 things lacking results in poor ignition, often witnessed by hangfires, but also causes other issues.

Cheers.
 
MagnumManiac said:
Why would you expect better speeds?
Pressure gives you speed, same volume cases give close speeds, primer size only changes start pressure and how much there is, it doesn't change max pressure unless volume is different or charge weights are different.
What is the expectation of a "bag if chips"?

Cheers.
Click to expand...
Because the things I read said that. It was a hypothesis going into an experiment and the resulting data did not back up those initial theories. Better?

"All that and a bag of chips" its a saying. Cake and eat it too? The looks, horse power and good mileage? I dunno something like that.

Its neat you gave pressure testing equipment, most folks dont. We have to rely on what the gun and cases tell us still :/
 
Wilderness Blacktail said:
Ok for those who have shot both large and small rifle primers of the same cartridge, same brand, and in the same rifle....

Was there a noticeable difference in amount of pressure you could run in one versus the other??

Ive read many times srp is better because it withstands pressure better and thus produces faster loads. I always took that to mean the head was stronger so if you looked for traditional case/primer/bolt pressure signs youd get more powder in before seeing them

In further reading it seems that it may only be due to the case head pockets withstanding more punishment before pockets loosen.
In that case are you seeing the same dots/lift/sticky ejection at the same powder charges but the SRP just last longer?

Or is there more to it than that?
Click to expand...
Yes, I have tested this in my .308 twice. I used the same manf brass for lrp and srp. But used two different manf brass in total. I even enlarged the flash hole on one test. Enlarging the flash hole did give me better SD and for the most part of the testing I was shooting the exact same amount of powder because I was more interested in SD and Accuracy later on I did deliberately the small Rifle primer brass masks the pressure better at least with the primers I was using, more meat around the pocket, allowing it to give you more shots and Mask the pressure. For me it was SRP and large flash hole.
 

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