Small vs Large primers: Gospel or Koolaid?

[wolley]

My own experience in a 308 pushing both the 155 and 168 Berger Hybrid on top of H4895 was that weak flame SR primers were not gonna cut it. ES' of 60+. Trying a few hotter primers and settling on the CCI450 I now have loads with single digit ES'. None of my LR primered loads ever got below 13 for an extreme spread.
I took some time to get here but it appears to be worth it.
Being a sling shooter only, I hate spending hours at the range testing!

 

[Larryh128]

We hunt coyotes in temp down to -20+ with wind chill involved, mostly AR platformed 223's and they sling bullets out without fail. The only powder that I use for my AR loads is Benchmark so apparently it lights easily with CCI primers.

 

[jhord]

What primers? I had the same thing happen with my .223 service rifle cartridges, CFE and Wolf primers. Click-bang. Switched to Rem 7 1/2, end of problem.

Testing Hodgdon CFE223 a few weeks ago with temperatures in the 40s, two different sets of loads (two different bullets / weights) gave poor groups, large ES values and a number of slight 'hangfires' with the Palma case, while there had been no problems a week earlier with standard brass and LR primers in slightly colder temperatures.

 

[Laurie]

We hunt coyotes in temp down to -20+ with wind chill involved, mostly AR platformed 223's and they sling bullets out without fail. The only powder that I use for my AR loads is Benchmark so apparently it lights easily with CCI primers.

That's not too surprising. The 223 is a civilian adaptation of the military 5.56 which is product tested to perform in true Arctic conditions, and most military loadings use harder to ignite ball type propellants. The SR primer is well matched to the 223's typical 24-28gn charges, and - this is a crucial factor - the design uses the standard 2mm (0.079-inch) diameter flash-hole. The PPCs, BRs, 6.5X47mm Lapua and 308 Win 'Palma' case not only use the small primer, but also employ a smaller flash-hole size of 1.5mm / 0.059-inch. This is not a minor matter as flash-hole diameter plays a major role in the speed of transition of the primer flame into the powder granules and the rate they heat up to the point where they ignite. The small flash-hole is used in these few cartridges alongside the small primer to deliberately slow this process down and give 'gentler' ignition to improve the consistency of the cartridge's performance.

It's interesting that the former Soviet designers of the M43 7.62X39mm battle cartridge and competitor to the 5.56 opted for large primers for this small cartridge presumably as they envisaged its use in really cold conditions and the old USSR and its satellites mostly used pretty crude ball powders in this cartridge. This (LR primers) is the norm for the 7.62X39 even in civilian use although Remington made some SR primer versions under its Peters name at one time. Another 'on the boundary' design with both military and civilian uses also sees both used - the 6.8mm Rem SPC. The Remington / SAAMI / military specification sees LR primers. Hornady opted for SR in its brass presumably to improve case-head strength with a smaller primer pocket and reasoning that an LR primer was overkill for this small cartridge's likely civilian use. (Having extensively tested the 6.8 with both types of brass I couldn't see any differences between their performance or even MVs in normal conditions with extruded powders.)

It's been proven many times that drilling the BR cases' 0.059" out to 0.079" improves ignition reliability in adverse ignition conditions, but increases group sizes and velocity spreads in normal useage where ignition reliablility isn't an issue. When the US Palma Teams' captains announced the team would move from standard Lapua 308 Win brass fired up with the F210 primer some years back to the pre-production SR type, this caused no end of controversy on its in-house forum, The Long Range Target Shooting Forums. Many 'old hands' prophesied disaster based on their experience of the old Remington 308 Win UBBR 'basic' case, a thin-walled small primer / flash-hole number which wasn't intended for use in 308 but as the base model for forming BR brass in the days before anybody made production stuff. Used as a 308, these guys told dire tales of poor ignition and big ES values, unreliability in anything except warm conditions and even then not guaranteed. A number said the only way they could get reliable performance was to increase the flash-hole diameter. It seems things have moved on over the last 30 years since the Lapua Palma brass gives very good results provided a magnum or BR primer is used and the weather isn't too cold.

 

[Laurie]

What primers? I had the same thing happen with my .223 service rifle cartridges, CFE and Wolf primers. Click-bang. Switched to Rem 7 1/2, end of problem.

CFE tests were done in both types of brass with Italian Fiocchi primers. The Winchester case + LR Fiocchi combination produced no issues, the 'Palma' brass + SR version did. Earlier in the year, in comparative testing of SR primers in the 308 'Palma' case using a 168gn bullet and Viht N150, the Fiocchi SR had performed OK and produced MVs close to the 'warmer' primers with the 11th highest average MV (out of 14). It was nearly identical in this respect to the CCI-BR4, WSR, Rem 7 1/2BR, and F205. This doesn't suggest it's a 'mild' primer.

 

[BoydAllen]

I think that these posts show that the large vs. small issue is a lot more complicated than one might expect. There is also the matter of how well the loads were tuned and shot for in the writer/shooter's test. Some differences are so subtle that they would not show up unless equipment, tune and shooting were at the highest level. This is the reason that I often do not comment on posted groups. We cannot really know enough of the relevant details to make an accurate judgment. On a related matter, the typical primer accuracy test is done by changing only the primer, and leaving the rest of the load constant even though there is good evidence that tune is velocity specific, and different primers produce different pressures and velocities if charge weight is not adjusted. These sorts of errors are common.

 

[Laurie]

Boyd, I'm very aware of your point here and agree fully. In the primer tests I've done in 308, I always tell people that group isn't important .... it's about MVs and consistency and groups are about (re)tuning the load. And even here, a result that shows that primer A gives say lower MVs and a smaller or bigger ES than primers B, C, and D cannot be extrapolated across all cartridges, or even a range of powders in a particular cartridge. Frustrating isn't it?

FWIW, my SR primer comparative test results in Lapua Palma brass (waiting for one more primer to be tested when the weather improves and then to go into print) suggests that SR / SRM / SR-BR primers vary much less in terms of the MVs they produce and their ES/SD values than the results from a similar test series I did a year earlier using LR primers. The other factor with SR primers is of course their cup thickness and cup brass alloy hardness. One primer had to be abandoned after a few rounds and the remainder pulled after blanking two out of five test shots; some others cratered very badly and came near blanking. (Stolle Atlas FTR action.) One model which did very well in the comparative test proved too weak when transferred to my old FTR L-R load of 155.5gn Berger / IMR-8208 at 3,050 fps which CCI-BR4s cope with very happily (even in Raton August '13 FC US Nationals and FCWC week one temperatures in the mid 90s which saw MVs rise to 3,100 fps).

 

[BoydAllen]

Excellent info. Thanks. One thing that has come up for those that do not have the option of a small primer case is to opt for the coolest primer available, which I believe are the Russian Wolf and Tulas.

 

[Larryh128]

Thanks Laurie for your posts, always interesting.