Primers: small -vs- large. Fact -vs- theory.

[Tommie]

Like most of us, I "know" small primers with small flash holes are superior (accuracy wise) to large primers in smaller sized cartridges. I've read countless articles on the subject. But now that I think of it, most of it boils down to very plausible theories or anecdotal accounts. Only once have I come across a true head to head test and in that particluar case there was no measurable difference in accuracy.

What are the facts?

 

[TAJ45]

I asked a very, very experienced B R competitor and serious high volume colony shooter that same question some years back. His answer was:
about .030". Absolutely of no consequence to me personally. However, do not negate the strength advantage of a small primer when pushing for a higher velocity node for competition, therefore longer brass life and safer shooting.

 

[Laurie]

There are not too many cartridges where you can do a comparison - 7.62X39mm (Yes really! Remington made some under the Peters name many moons back - I've still got a box or two, but never got around to a side by side test.) 6.8SPC (Remington is LR; Hornady SR and I think SSA made both at different times.) I did get around to a side by side test in a UK-legal manually operated AR-15 with a Krieger match barrel, and couldn't see any difference in MV, ES, or group size, at least with one bullet / powder combination that the barrel liked.

It's 308 Win where there is the main opportunity to make worthwhile comparisons thanks to standard and Lapua 'Palma' brass. Fortunately, there is no difference in spec between the two types from Lapua - same weight, neck thickness, capacity etc subject to the usual lot to lot differences.

The Palma case was developed at the request of the US Palma Teams not primarily to reduce group sizes, but to reduce ES / SD MV values as a large spread there affects the bullet's POI in elevation terms at long ranges and the standard Palma comp loadings with the mandatory 'less than 156gn' bullet are ballistically marginal at 1,000 yards. Exhaustive testing by the Palma teams showed a 40% or so ES reduction over large numbers of test sessions and actual competitions involving large quantities of handloads using the same components. This has been replicated many times since and is why nearly all national and international FTR competitors also use this brass now in 308. So, it's proven, and it's a given.

Also, the brass is very hard and strong in the case-head and web and there may be, emphasise may, be a beneficial change to the powder burn that sees pressures flattened a bit. In either event, FTR shooters now routinely use loadings that would not be 'on' in standard brass, and produce MVs that even now cause a degree of incredulity and questions about safety amongst many experienced 308 competitive shooters in other disciplines.

The other main changes are that the Palma case usually needs a slightly heavier charge than the LRP type to get the same MV, around a half grain in charges around the 45-47gn level, and that cold weather performance / reliability can be degraded the exact temperature at which undesirable effects kick in being related to the powder type and how easily it ignites. I found that some otherwise untemperamental grades started to see increased ES, groups and reduced MVs at anything below 5-deg C / 40F. Recently I got a load of hangfires and two complete misfires out of a box of 50 trial loads with Hodgdon CFE 223 in around 13-deg C ambient temperatures, on or a bit above 50F. So, certain ball powders are apparently a bad idea in this version of 308 in at least cool conditions.

 

[M-61]

Again I see the word 'anecdotal' come into use. And again (possibly) with a negative connotation. I think every proven fact has its start as being anecdotal. This is not a bad or wrong thing, merely something that has been observed or thought of and not carried through to a proven or scientific fact. So here is another anecdotal occurrence.
Colt Sauer in 22-250. Nice shooting varmint rifle that in my earlier years wound up on a bench as I experimented with 5 shot groups. ( long time ago) Not what it was meant for at all. I found that PMC made small rifle primer brass for a 22-250. The rifle loved it. The group size shrank appreciably. I was not becoming a better shooter that brass was making the groups shrink. I don't recall by how much the group shrank but suffice to say from that point on it was the PMC brass (SRP) that I used exclusively.
So I have NO facts for you, just some more anecdotal info observed in MY rifle, with MY reloads, a long time ago. I still have the brass and rifle.

Make no mistake that ALL of these small rifle primer brass (the BR's for example) seem to be unusually accurate to me. But that is just my observation.

 

[JohnKielly]

If German Salazar's web page was still active, I suspect that you would find the answer there. The one thing I recall that he reiterated often was to use the least aggressive primer that would light the powder charge.

 

[mikecr]

David Tubb: "A detailed study of large and small rifle primers showed that large rifle primers worked best when the propellant charge exceeds 35 grains as is the case with the 6XC".
You might email David and obtain the study he's talking about(maybe the palma team stuff).

Myself, I don't know. But I'm sure there is potential for higher pressure loads with small primers.

 

[JohnKielly]

Then again, the Palma team uses/used the small primer Lapua brass with 45+ grains of powder.

 

[savagedasher]

If German Salazar's web page was still active, I suspect that you would find the answer there. The one thing I recall that he reiterated often was to use the least aggressive primer that would light the powder charge.

The way I see it small primer were made for smaller cases the primers had displatement enough for small amounts of powder . And from their size didn't weaken the case head .
They also use faster burning powder.
That is why primers at critical it tune of a load Larry

 

[Laurie]

If German Salazar's web page was still active, I suspect that you would find the answer there. The one thing I recall that he reiterated often was to use the least aggressive primer that would light the powder charge.

Unfortunately, the Shooter's Journal Blogspot is all gone. Some articles turn up archived in other online locations occasionally.

 

[JohnKielly]

The way I see it small primer were made for smaller cases the primers had displatement enough for small amounts of powder . And from their size didn't weaken the case head .
They also use faster burning powder.
That is why primers at critical it tune of a load Larry

6x47 Lapua, .308 Palma aren't small cases, don't have small powder capacities. Both seem to be working particularly well.

 

[savagedasher]

6x47 Lapua, .308 Palma aren't small cases, don't have small powder capacities. Both seem to be working particularly well.

John
I worked 6 months with a 6-47 never could get the Es down or the vertical out of it . With any primer . The last day I tested it I drilled the primer hole .004 larger it shot great. But I had lost confidence in it and made it a dasher . Sometimes it my not be the primer but the hole size . Larry

 

[LHSmith]

The way I see it small primer were made for smaller cases the primers had displatement enough for small amounts of powder . And from their size didn't weaken the case head .
They also use faster burning powder.
That is why primers at critical it tune of a load Larry

Roy Weatherby had no qualms in using a LR primer for the .224 Weatherby. What is displatement? Do it also tune it at a load?

 

[XBBR Shooter]

Roy Weatherby had no qualms in using a LR primer for the .224 Weatherby. What is displatement? Do it also tune it at a load?

38 grains of water - half way in between the 222 Magnum and the 22-250.

 

[Laurie]

Some years back when prototype 308 Lapua brass was being trialled, the issue was extensively reported on and discussed in the Palma teams long range forum:

http://www.usrifleteams.com/lrforum/

Many of the 'old BR and fullbore hands' came out of the woodwork saying they didn't care what the team captains said, but they knew that small primer / small flash-hole brass simply doesn't work consistently and reliably in the 308 Win through their own past experiences.

This was with the old very thin-wall / high capacity Remington UBBR (Unformed Basic BR) cases. For those who've never heard of this, it goes back to the dawn of the 6mm and other calibre BR cartridges, the genre starting out as a reformed 308 case, the Barnes .308X1.5" prototype short assault rifle military number. Remington developed the BR, produced chamber and reamer specs, but didn't sell ammunition or cases for 20 plus years, instead making some lots of the thin-walled UBBR brass for would-be BR shooters to reform to whichever version they desired.

As well as becoming the raw material for goodness knows how many other wildcats, many American rifle competitors thought to themselves - hey let's leave it as 308 Win, it's high quality, got a high capacity = scope for increased charges and MVs within acceptable pressures, and it's small primer which = improved precision / smaller spreads.

Now these guys almost without exception said it didn't work, or at any rate not consistently enough, basically because the small primer is inadequate for 45+ gn charges of medium burning speed powders. Some reported that drilling out the flash-holes as per savagedasher above effected a partial or complete cure. All said the resulting rounds became overly temperature sensitive, in this case low temperatures the issue.

So, that was the observed experience of a lot of experienced and knowledgeable guys 30, maybe 40 years ago, call it 'anecdotal' or 'experimental' according to views and taste, and these survivors of that era were adamant that Lapua and their national Palma team were on a hiding to nothing. Experience has show the complete reverse with Palma brass a great success story with only marginal downsides that can be lived with. So, either this was inaccurate / plain wrong anecdotal stuff, or (in my view more likely) evidence that something has changed between the 1970s/80s and the 20-oughties. Maybe powder technology, most likely in the deterrent coatings, has moved on making propellants easier to ignite and with more consistent burning behaviours and/or small rifle primers have improved their effectiveness greatly.

 

[spclark]

David Tubb: "A detailed study of large and small rifle primers showed that large rifle primers worked best when the propellant charge exceeds 35 grains as is the case with the 6XC".
You might email David and obtain the study he's talking about(maybe the palma team stuff).

Myself, I don't know. But I'm sure there is potential for higher pressure loads with small primers.

I believe what you quoted above from Mr. Tubb was his referring back to his own testing of primer sizes undertaken while he was developing his 6XC cartridge. That may have been concurrent with availability of Remington's 308BR brass, one of the only cases with capacity sufficient for what he was aiming towards that also had a small rifle primer pocket, which he very well may have used during development.

After being dissatisfied with every large rifle primer case that could be used for 6XC I tried making some from Lapua's Palma brass around 2010. It's all I use now as it just keeps on going (with proper attention to sizing and annealing) well beyond what was the best I could do with LR cases. Curiously the results of using some of that Remington 308BR brass was disappointing.

I fired Palma loads using Palma brass early this year under 23-30°F conditions (Benchmark propellant, KVB-223REM or NCSRM primers) with no loss of performance compared to identical cartridges fired at 80°F.

I also believe a great deal depends on which small rifle primer one chooses to use with what kind of propellant (stick vs ball) as member Laurie mentions above.

 

[M-61]

John
I worked 6 months with a 6-47 never could get the Es down or the vertical out of it . With any primer . The last day I tested it I drilled the primer hole .004 larger it shot great. But I had lost confidence in it and made it a dasher . Sometimes it my not be the primer but the hole size . Larry

Your last sentence I can work with Larry. I am pretty sure that the people at Lapua did not wake up one morning and just decide to drill smaller than standard size flash holes. My guess is there is a reason.....beyond me....but none the less a reason.

 

[Laurie]

After being dissatisfied with every large rifle primer case that could be used for 6XC I tried making some from Lapua's Palma brass around 2010. It's all I use now as it just keeps on going (with proper attention to sizing and annealing) well beyond what was the best I could do with LR cases. Curiously the results of using some of that Remington 308BR brass was disappointing.

My good friend and very knowledgeable shooting companion Vince Bottomley who is a long-time 6mm fan for BR and F-Class has been a fan of the 6mm SM (Swiss Match) and the 6 SMACK (Ackley-Improved) version of the same. The SM spec says LR primer and that's what Vince used for some years with super expensive, hard to get RWS brass until the small-primer 6.5X47L appeared - and he's used that as a 'basic case' for the SM/SMACK ever since with considerably improved results just as you found in the very similar 6XC.

Interestingly, after I ran a 6XC for a season in F and mid/long-range BR, but never quite got it working as well as I had expected, Vince took my barrel, Norma brass and dies off me and was a fan for a while, but then went back to the non-standard small primer 6 SMACK as it gave better brass life and over several firings of the cases, more consistent results.

Our posts obviously crossed and I was interested / amused to see your efforts with the UBBR cases didn't work out either, so there seems to be something 'special' (but not in a good way) about this particular variation of small primer 308 Win case!

 

[5spd]

I have run my own testing on the 6.8spc brass I use for my 6x6.8.
I have both LRP & SRP 6.8 brass in 3 different brands & in my own range time over the chrony, accuracy, group size, speed was the same (within variations of ES)
Now of course this was not a scientific test by any means, weighing brass etc, just load & shoot to see if I could find any thing that would stand out & make me say just buy SRP brass over the LP brass. The R-P brass is my go to and the SRP will be backup stuff.
I don't shoot comps so my thoughts are it makes no real world difference for what I do.

 

[LHSmith]

Your last sentence I can work with Larry. I am pretty sure that the people at Lapua did not wake up one morning and just decide to drill smaller than standard size flash holes. My guess is there is a reason.....beyond me....but none the less a reason.

If one does a search, it will show Lapua went through exhaustive testing with primer size on this case....IIRC one of the reasons it took so long to get the 6.5 x 47 into production. IMHO, Lapua has their act together when it comes to case design.

 

[Stumpy1]

I am not sure I have 'facts', but I have data .

I have 200 pieces of Lapua 308 Palma brass that are on their 24th firing at Palma velocities/pressures (155 class bullets at ~3040 fps). I have annealed the neck/shoulder several times over those 24 firings. I chronographed a load in that brass last week, and got an average velocity of 3041, Hi velocity of 3046, low velocity of 3039 an Extreme spread of 7 fps, and a standard deviation of 2.4. The load is Tula primers under a healthy dose of H4895 with Berger 155.5 Fullbores.

I have not lost one piece of this brass to loose primer pockets, but am starting to get case head separations now. Note that this brass has seen two different barrels, with slightly different headspace in each barrel.

Your mileage may vary, but I am impressed with the life of the brass, the consistency of the velocity I can readily attain, and the low cost of 'doing business' using this brass.

Accuracy differences? Probably none that I can take advantage of, and given a load that is in 'tune' with the rifle for each type of brass, probably non-existent.

Just another data point.

Frank