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

[johngibbs222]

My 0.02$ worth is to get to know your components.
SRPs advantages are several.
Nowadays, in many areas, availability is a major issue ie in my neck of the woods srp are more available than lrp, are cheaper so I bought a rake of cases with sr p cavities.
Single base powders tend to fill the case more than similar performance loads of double base powders, the closer you get to 100% fill the better from an accuracy perspective. (I understand it's one of the reasons that Varget does so well in 308 sized cases)
Single base powders, in general, are more consistent and ignite easier than double base powders especially in cold weather so srp are not disadvantaged. There is a corollary to this statement and that is double based powders are more difficult to ignite thoroughly than single base powders so don't use double base powders with srp in medium sized cases if low sds and consistent velocities are what you are after.
There are other differences but they tend to be open for debate whereas it's hard to argue with the statements I've gathered together and stated above.
I bought Peterson 308 cases with srp because I had many more srps than lrps, I use single based Vhitavuouri powders and do not load to DNE levels. In honesty the loads I use do not shade my 30/30 by more than around a 300 fps difference in muzzle velocity with 150 grn jktd, with the 30/30 loaded with LRP and H-LVR or CFE 223 but the accuracy difference is marked ( as you'd expect).
SRP cases are not pixie dust but they do work well with full cases of single based powders, TBH this old man can't brag about the improvement in accuracy as I'm not a particularly gifted rifleman.
So in answer to the question from my mates I always say I got nearly 6000 srps but only 2000 lrps that's why and it seems to satisfy them especially as they get to see how I shoot on the range.
FWIW economics didn't enter into my equation, for the same price per hundred for peterson unloaded brass I could have bought 140 7.62x51 (308) GGG palma 155 grn match ammo.
With all that in mind, I now return to the OP's original question, almost. I compared peterson srp loaded with 43 grains of N150 and Speer 168 match BTHP using Magtech srp v Federal brass with the same load of N150, same bullet and Magtech LRPs.
Going from a 80 year old memory, my Magnetospeed sporter chrono said the federal loads were between 25 and 50 fps quicker than the Peterson, most of the variance was from the Federal loads, the Peterson ones were remarkably consistent. Ambient temperature was around mid to high 70s and the range is at sea level almost.
As I indicated at 100 yards not a great deal of difference using my 20" barreled Browning BLR 81, I wouldn't like to call which was better. No pressure signs that I could see.
When I reloaded them in my LEE hand press I could FL resize them both reasonably easily. FWIW the Federal have over 10 reloads each the peterson brass was on its first outing. After each load the full cartridges drop into and out of my hornady headspace gauge with a little headspace showing.
For interests sake, before loading I fitted a bullet in each of the cases to the stated COAL and measured the potential capacity of both cases, IIRC the federal was about 1 grain wt of water smaller at 47.2 grains of water, a figure I recorded to use on my software to predict pressure.
Here's a vid of that measuring procedure .
Once again, IIRC, pressure prediction for both loads was in the low 50K range which suits me just fine, the velocity predictions again using my erratic memory were both around 2500 +/- and the actuals were about 50 ish higher.
I apologise for being a little vague on this issue but I no longer use those bullets, I've settled on 130 grn barnes tsx and 178 grain cast gas checked. They are quite a bit faster and quite a bit slower respectively.

 

[VarmintBob]

Velocity tells you what your peak pressure is. There is one SAAMI spec for a cartridge. That defines how much pressure you can "run" unless you decide you want to exceed that spec. There are two differences when choosing between small and large primers. It will take more powder to equal the velocity of a large primer load when using a small primer load. Peak pressure is proportional to the square of velocity. You can't cheat that fact. The other thing you find is that you get less firings with large primers since the case head will stretch to the point of not holding the primer with fewer firings than with a small primer. You can cheat this a bit by using Federal LR primers which have a 0.0005" larger cup diameter. So the only effect of using more pressure with any given primer is fewer firings with the case as long as your case end of life is defined by the primers not sticking in the primer pockets. None of it is magic.

 

[VenatusDominus]

Velocity tells you what your peak pressure is. There is one SAAMI spec for a cartridge. That defines how much pressure you can "run" unless you decide you want to exceed that spec. There are two differences when choosing between small and large primers. It will take more powder to equal the velocity of a large primer load when using a small primer load. Peak pressure is proportional to the square of velocity. You can't cheat that fact. The other thing you find is that you get less firings with large primers since the case head will stretch to the point of not holding the primer with fewer firings than with a small primer. You can cheat this a bit by using Federal LR primers which have a 0.0005" larger cup diameter. So the only effect of using more pressure with any given primer is fewer firings with the case as long as your case end of life is defined by the primers not sticking in the primer pockets. None of it is magic.

Velocity is actually proportional to the average pressure (pressure over time), not to the peak pressure. A load that produces a lower peak pressure but holds it for longer can produce more velocity than one with a higher peak pressure that is sustained for less time, all else being equal. It is the area under the time-pressure curve that produces velocity. Different powders produce different shaped pressure curves, I can load both H1000 and Bullseye in the same cartridge to a peak pressure of 65K psi and get very different velocities.

 

[nwhunter]

I have not tried this in a rifle.
But I have tried this in my 400 Corbon 1911.
Corbon themselves went from large pistol to small pistol primers at some point in time.
I can tell no difference between the two in both velocity and pressure signs.
But I finally switched to large magnum pistol primers, and they show less pressure signs with the same loads and velocity.
But I don't know if this even compares to rifle primers at all.

 

[Wilderness Blacktail]

Velocity is actually proportional to the average pressure (pressure over time), not to the peak pressure. A load that produces a lower peak pressure but holds it for longer can produce more velocity than one with a higher peak pressure that is sustained for less time, all else being equal. It is the area under the time-pressure curve that produces velocity. Different powders produce different shaped pressure curves, I can load both H1000 and Bullseye in the same cartridge to a peak pressure of 65K psi and get very different velocities.

Exactly. Open a reloading manual that shows pressure, pick a bullet weight combo and note all the different velocities of the various powders with same bullet. All will be close in pressure but velocities may vary by 150-200fps, more in some cases.
In addition every bullet reacts differently and ole Saami is yet to list the bullets I mostly shoot lol.
As an aside, Saami spec is not something I worry about too much. In many cartridges I love its based off of actions that were weak when made and brass of the same ilk. Newer cartridges based off the same case will show much higher CUP/PSI ratings and that is what I go by. What is reasonable and safe to expect in this particular rifle/case combo.

This post, and my various searches, is to find out if the so often repeated info regarding small vs large primers is true and to what degree, or what part has been found to be true.

 

[Wilderness Blacktail]

Here's a vid of that measuring procedure .
Once again, IIRC, pressure prediction for both loads was in the low 50K range which suits me just fine, the velocity predictions again using my erratic memory were both around 2500 +/- and the actuals were about 50 ish higher.
I apologise for being a little vague on this issue but I no longer use those bullets, I've settled on 130 grn barnes tsx and 178 grain cast gas checked. They are quite a bit faster and quite a bit slower respectively.

Thanks for that. Thats a sweet rifle! I used to have a Lightning BLR in 7-08. I want it back! Lol
I had good luck with the 150GMX in a 22" savage 99F. Lowest impact velocity was on a small deer at 2300ish.

 

[Wilderness Blacktail]

Do

I have not tried this in a rifle.
But I have tried this in my 400 Corbon 1911.
Corbon themselves went from large pistol to small pistol primers at some point in time.
I can tell no difference between the two in both velocity and pressure signs.
But I finally switched to large magnum pistol primers, and they show less pressure signs with the same loads and velocity.
But I don't know if this even compares to rifle primers at all.

Did the cases take the same amount of firings?

 

[Wilderness Blacktail]

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.

Thank you.
Care to elaborate on any case life difference?

 

[nwhunter]

Do

Did the cases take the same amount of firings?

I haven't noticed a difference, just that magnum primers seem a little tougher, as they don't flatten as much.
Granted I only load warm loads for this caliber.