Years back when PPCs and 6BR were the only semi-common small FH types around, people played around with this and wrote the tests up in
Precision Shooter magazine and suchlike. The consensus is that they shouldn't be reamed out (in the PPC and BR / Dasher etc at any rate) other than a small amount. I've seen the figure of 0.070" mentioned. Get near that, and certainly if you exceed it, and precision drops while MV ES and SD increase.
An early production small FH case was Remington's 1960s era 308 Win UBBR (unformed basic BR) brass. It was very thin-walled and had the small primer / flash-hole set-up we now associate with the BRs, 6.5X47L etc. It was sold with the intention of being reformed by the user into the appropriate calibre BR with sets of forming dies made by Fred Huntington's RCBS and others. (Remington didn't manufacture any BR cases for many years, the 7mm version being AFAIK the only one to be made in any quantity / for period of time, and that was some years after the BR cartridges' introduction.) However, back in 1960s or 70s whenever, various Palma and other shooters thought they'd try this special brass in its out of the box 308 Win form, logical in that 308 was the competition cartridge of the era. They ran into all sorts of problems, primarily ignition even in apparently good and not too cold conditions. In the end, some users reamed the flash-holes out to the standard 0.079" as they said this was the only way they could make the things perform reliably.
As a result, a generation of very experienced and knowledgeable US shooters wrote the SRP / small FH form off as impractical in anything bigger than 'improved' 6BRs or similar. When Dan Simpson of the US Palma Teams' announced back in 2010 (I think) on the Palma Teams' long-Range Forum that team members and officials had done a year's testing in conjunction with Lapua and that the US Palma Team would use the brass in its ammo the following year in international competition, those with such experience turned up on the forum and predicted disaster. However, it seems something had changed between say 1970 and 2010 in the primers or powders as on the whole the 308 form works fine with single-based extruded propellants in charges up to 50/51gn even.
BUT ... in the UK where we shoot competitions through the (usually) mild winters, there is a hint that some powders see degraded performance in Palma brass when you get down to around the freezing mark or a degree or two above. Use of some slow burning powders would make any such problems worse, likewise some ball types which are usually harder to ignite. The only time I've ever had a really noticeable problem was trying Hodgdon CFE223 in 308 Palma - in 50 rounds, two failed to ignite completely and the other 48 suffered very slight hangfires - slight but more than enough to give very poor results and large ES values. (... and yet, the elderly Hodgdon H414 grade had performed brilliantly for me in winter tests at 3-deg C previously, another ball type and from the same manufacturer - General Dynamics Corp., St. Marks Powder Co., FLA.)
The 6.5X47L is an all year round all-weather all-role cartridge for many UK users, although when I say all-weather we wouldn't expect to get
anywhere near the temperature lows of many parts of North America in cold winter spells. That's with 38-42gn charges and the Creedmoor isn't greatly above those. So, I wouldn't expect any problems in reasonable temperatures and with most powders with SRP Creedmoor ammunition, likewise 260 Rem and 243 Win. I'd still hesitate to recommend their use to a Scottish Highlands deerstalker though for winter conditions.
FWIW, there are a few non-precision cartridges where you can find both SR and LRP brass, but they all use the larger 0.079" FH size irrespective of primer type. 7.62X39mm (some Remington was SRP) and 6.8mm Rem SPC (where Remington is LRP and Hornady is SRP as is some long gone SSA stuff). I tried mighty hard to find any difference between results in Hornady and Remington SPC brass and there just wasn't any with any powder I tried. I had expected higher MVs from LRP with a bit of additional primer energy even if it didn't change the powder burn characteristics, but they were really close. Same with ES values. Go figure! What is a definite issue with the small-dia. case-head SPC design though is that SRP form improves case-life. In this narrow case, the LR pocket must seriously weaken the case-head and Remington had to row back on its early specifications and loads with a big MV reduction after a year in production IIRC, albeit there were other factors involved with this particular design in its early days that increased pressures too much.
The one conclusion seems to be that the small 0.059" FH is an essential part of the mix that puts some cartridges into a league of their own for precision. Now that Peterson Cartridge Co. is making 243 Win and 260 Rem in both varieties, I'm waiting with bated breath (alright, waiting !!
) for reports that show how much of a difference, if any, it makes to a more 'normal' common or garden variety.
I have a little relevant experience here. I run prepped Winchester LRP, necked-down prepped LRP 308 Norma, and necked-down 308 Lapua Palma SRP brass in my mid-range 7mm-08 F-Class rifle. I can't say I see any improvement from the SRP loads although it's not a straightforward like for like comparison using different bullet and powder combinations with the two primer types, but I expect the reformed SRP 308 cases to last for nearly forever with regular annealing in what will be a 59,000-60,000 psi load. All three lots perform very well, I'm glad to say.
. He had a 44 Magnum revolver in his youth and invariably used H110 plus a standard large pistol primer because they were always available locally and cheap despite a magnum type being strongly recommended by Hodgdon with this powder. This worked great until one one very cold day when in his job on a ranch he'd been out on horseback all day in way below freezing temperatures with the gun in a belt holster. When he got back to the ranch there was a near starving coyote in the yard stalking some sheep in a pen. So he draws the revolver, steadies it on a fence post and takes a shot he'd be confident of an easy hit with - and you guess it - misses! So after the animal has lit out for the next county, he tests his loads and finds the velocities are so low the bullets are hitting the ground 40 or 50 yards ahead of the muzzle. When the weather gets warmer, or he takes the revolver straight out of a warm house, performance is restored.
