308 small primer pockets

[stubbicatt]

Guys, I have just bought some Lapua cases with the small primer pockets in caliber 308. No reason really, other than curiosity and experimentation.

I hesitate to even ask, as I know I will be working up loads specific for these cases, and I'm sure I'll figure it out. However, curiosity is killing the 'catt, so here goes:

Anybody know the approximate difference in the amount of powder that will be required to attain similar velocities in small primer cases as would be achieved in large primer cases?

i.e., if I use 43.3 grains of RL15 for my 175 grain SMK load with LR primers, what would be the increase of powder to get same velocity, 44 grains maybe?

I dunno. Once the cases arrive and the snow melts I'll dig out the trusty chronograph and try to make this determination. There is no way to know for sure, but I suspect that the small primer cases, taking a little more powder, at the same pressures, *should* be a skosh closer in ES for more consistent vertical performance at distance, given the same or very close velocities.

Regards,
Stubb

 

[kingmt]

Doubt you find a difference.

 

[capreppy]

Be interested to see your results. The Lapua small primer pocket 308 are Palma cases. Don't know much (if anything at all) other than the 155 SMK is the bullet of choice for Palma type rounds.

 

[oldpapps]

I agree with 'kingmt'.

I see the proverbial hand writing on the wall... Change all primers/primer pockets to 'small', too simplify supply and manufacturing.... Carter did the same thing and we are now saddled with both SAE and Metric sizes.

 

[Slamfire]

I don't have any of the small primer brass but one bud who have used the stuff told me that group size shrunk 20%. Since he is a target shooter I asked him why he was not still using small primer brass, and he said: misfires in cold weather.

That might be a trade off.

 

[gamestalker]

I don't think that primer detonation in a bottle neck case is going to produce significant pressure changes. Unless there is supporting data, I would just load as usual, after a proper work up of course. As with any component change, it is always prudent to re-work the load from the lower end of the published data.

GS

 

[MtnCreek]

At 43 - 44 grs powder, you may be getting toward the upper limits of what a standard SR primer can reliably set off (I'm just guessing here, so take w/ ample salt...). If you have any issues, may think about relegating this brass to lighter bullets/faster powders.

Good luck.

 

[Delmar]

I wonder if the misfire in cold weather could be cured with a magnum primer? Guess I would back the load off and read it carefully as I experimented.....

 

[stubbicatt]

Thanks guys for the input. As far as using a small magnum primer, I don't know, but I would anticipate similar performance to that of a conventional LR primer, and any gains by changing to the smaller primer would be lost.

Again, I've read probably many of the same articles you have read on the subject, and if I stick to extruded powders, which are easier to ignite than ball powders, and stay within max loads, I should still experience reliable ignition and anticipate improved downrange performance. RL15 is a fairly easy powder to ignite, and I don't believe I will have any issues, but one never knows with these things. The purported gains I have read about suggest that the gentle buildup of pressure occasioned by the propellant as opposed to the primer, is supposed to be more linear and more conducive to good downrange performance.

If these small primer brass do perform reliably, I may try another batch necked and trimmed to 243 Winchester, to see how they perform in that chambering.

Anyways, I'll let you know what I find out in all of this experimentation.

This was all prompted by a desire to purchase a new firearm, but upon inquiry, I was unable to find anything I wanted. So, I figured doing some load development might be a good use of my time and attention. After all of this is over in a few months, I may find myself wishing I had bought the firearm. LOL.

Come to think of it, I installed one of those pressure transducer gizmos on the barrel of my 308, and it provides a whole lotta detail on pressure curves etc., which might be very informative. I gotta double check, but I think the program only works on a PC, and my portable now is a MAC.

 

[119er]

A gunsmith that frequents a local range uses the Palma brass w/SP to push his loads farther than the pressure rating of the original large primer case. This is done in custom bolt action rifles for long range target work. Don't quote me but I believe he said that the small primer gives the case head a little more strength and he ups the pressures no more than 5,000 psi over standard max charges. This is professional and unchartered territory for most reloaders and much more consideration is necessary before attempting to try it. Not saying this is true or the reason for SP's but that is what he does and I have no reason to suspect he would use dangerous ammunition in his own or his customers' rifles.

 

[pseudonymity]

That was my understanding as well, that the SP .308 case was specifically designed to handle loads that exceed max SAAMI pressures. It takes a pretty long barrel and pretty high pressures to keep the 155g supersonic at 1k yd.

 

[stubbicatt]

Cool. Since the SP cases are designed to withstand higher pressures, they ought to work well with regular pressures.

It is something to learn, something to experiment with. I look forward to it!

If it doesn't work out, I guess I will have learned that too.

I mean it makes sense to me that pressure created by burning propellant would be more consistent than pressure created by exploding primers. Perhaps it will make a difference.

 

[bigdaa]

Thanks guys for the input. As far as using a small magnum primer, I don't know, but I would anticipate similar performance to that of a conventional LR primer, and any gains by changing to the smaller primer would be lost.

This is what I was chewing over in thinking about the original question.

Have you found loading data pertinent to the Lapua cases with their small pockets?


I checked out LoadData.com and they had a section on Vihtavuori powder that used Lapua cases but damned if they didn't use LR Primers!

 

[bigdaa]

This is interesting reading material on the OP's brass:



http://riflemansjournal.blogspot.com/2010/01/cartridges-lapua-small-primer-308.html

 

[Hummer70]

Be advised the Palma rifles I have examined the fired cases from all hit the primers dead center. Many production rifles have an off center strike of half the diameter of the striker nose (around .030") offset. (Industry recommendation by the way)
I know guys who experienced primer failures using large diameter strikers on small primers where they separate on the outer rim of the primer which will start eating away your bolt face as well as give unpleasant gas escape.