In parts 1 and 2, I’ve got as far as listing the primers that are generally available in the UK and summarising their characteristics – in particular, cup thickness/strength. I’ve questioned the significance and role of the so-called ‘magnum’ type and worked up a 308 Win ‘Palma brass’ load to be used in the tests, also comparing it to a ‘control group’ loaded in standard large-primer Lapua cases – a side-by-side test shot on the same day in which the small primer ‘Palma’ loads emerged as markedly superior but saw much larger MV reductions (compared to LRP results) than expected.
Returning to the SR primer trials, I now had a rifle, a reliable chronograph unaffected by ambient changes (the MagnetoSpeed V3), a promising load combination that had put five shots into 0.2 inches at 100 yards in the load work-up and, some fifteen SR/SRM/SR BR primer models to try. 100 twice fired Lapua ‘Palma’ cases were sized and loaded in exactly the same way for every test round and were annealed before their first firing here and then again before each subsequent reloading.
They were kept in their MTM RS50 boxes as originally weight-batched and the contents of each box of 50 were loaded up with 45.5gn Viht N150 powder and good quality Lapua 167gn Scenar bullets with three primer models split 17, 17, and 16. As the barrel was fully cleaned and allowed to cool completely between each 16 or 17 round batch, the objective was to have readings for 14 or 15 shots in a freshly fouled barrel for each primer, assuming two rounds would be needed for MVs to settle down. As it turned out, velocities for nearly all batches settled into the ‘curve’ after the initial ‘fouler’, so the norm became 16 usable test rounds for each primer with a few having 15 (for those loaded as 16-round batches).
As with the Large Rifle primer tests carried out a couple of years ago for Target Shooter magazine, (http://www.targetshooter.co.uk/?p=1471) it was the chronograph readings that mainly interest us – how ‘mild’ or ‘hot’ primers are (as measured in average MV); how consistent (ES – extreme spread; SD – standard deviation). Groups were shot as carefully as possible to give representative results too and were interesting as is always the case but, don’t necessarily tell us much as it is usually necessary to fine-tune the charge-weight for each primer model to obtain maximum precision.
The MagnetoSpeed V3 and its readings were key
All tests were carried out in a four week period over the month of September. Early autumn tends to be either relatively settled in Northern England – or wild with Atlantic fronts bringing rain and wind. Fortunately, it was the former – test days remained mostly dry and, ambient temperatures stayed within a reasonably small range. My notes record 10 to15-deg C (50-59F), wind conditions ranged from near still to moderate winds of 10 mph or so. Within these variations, there would have been negligible temperature induced pressure and MV changes affecting results with the stable single-based N150 propellant.
The rifle was set up on the bench on the 100 yard range, MagnetoSpeed V3 attached and my usual 100-yard target (half-inch red dots on a one-inch grid background) employed for each batch of 16/17 rounds, with one/two ‘foulers’ fired then three, 5-round groups. The V3 was attached to the barrel in the same place for each test session, its straps hard up against a glued-on Velcro patch normally employed to affix a mirage band. This not only saw consistent placement across sessions but removes any slight possibility of the ‘bayo’ shifting mid-test – an occurrence which doesn’t affect its utility as a chronograph, but usually has dire effects on group size and shape.
Starting with a cold, newly cleaned barrel, I’d fire 10 shots which would take me part way into the second group, then pause for 15-20 minutes to let the barrel part-cool before shooting the last seven, finishing off group two and moving onto the third and final five-shot group. (The restart only rarely showed any tendency to produce a ‘flier’ with this superbly stable and consistent FTR rifle.) Although the chronograph was used to calculate average MV, ES and SD values, every shot value was also manually recorded in my range notebook over three lines – the ‘foulers’ on one; eight shots on the next; the final seven after the restart on line three.
Individual readings were manually noted
I said my aim was to have a 15-20 minute break for a partial cooling down but being on a popular range on a day of the week that club members traditionally use for testing or a bit of plinking and a social day out, actual durations were variable dependant on whether the range was closed down for target changes or to let new arrivals set their gear up. The barrel cooling rate was inevitably variable too, depending on the direction and strength of the breezes, the prevailing SW wind in this part of the world blowing across the front of the benches and cooling barrels noticeably faster than during still days or those with winds from other directions.
Being scientific, adhesive temperature display strips could have been used and testing done in conditions where one could restart at the same point with each batch. You no doubt think I’m labouring over these minor details …. but please be patient, an unexpected phenomenon appeared when the results were later analysed.
The MagnetoSpeed is reputedly voltage sensitive, so a new battery was fitted after the load work-ups for the test sessions and a condition check carried out before each run with a new primer started. If and when the voltage dropped below 8.3V the battery would have been replaced but this wasn’t necessary. (When the voltage drops below a given level – which I’m unsure of myself – the chronograph apparently works OK but produces unreliable results, I’m told.)
As reported previously, the old Vihtavuori No. 22 SR primers proved hopelessly fragile and when a second example ‘blanked’ in only six shots, this number was dropped from the tests and the remaining unfired rounds pulled. So, then there were fourteen! No other primer saw any ‘blanked’ examples with the 167gn Scenar/N150 load but, the ‘soft’ (0.020” thick cups) CCI-400 and Remington 6½ standard models ‘cratered’ very badly, the latter so much so that failure/leakage looked a distinct possibility and that with a load that QuickLOAD suggests is running at less than 58,000 psi, some 4,000 psi below the SAAMI pressure ceiling.
Right, onto what the tests tell us. Table 1 lists average MVs as recorded during the sessions ranked low to high.
Immediately apparent is the relatively small spread in values across the 14 models – a modest 18 fps. This compares to a 35 fps spread for 16 LR primers from similar baseline MV levels when I did the exercise for this type, so changing to ‘Palma’ brass and SR primers almost halves the variability. This is significant, given the charge weight and pressure differences needed to change the MV of these load combinations by over 30 fps.
How about SR Magnum and Magnum/Match models in relation to standard types? Their ranking (keeping with the low to high MV order) is 2nd, 5th, 7th, 10th, and 13th equal. If I’d set out to spread their performance in this respect evenly throughout the ‘test population’, I couldn’t have improved on that! On these results, I don’t see SR ‘magnum’ primers as being much – if any – ‘hotter’ than standard varieties, their utility and value being thicker (0.025”) and stronger cups.
Table 2 lists their performance as taken straight off the MagnetoSpeed in Extreme Spread (ES) and Standard Deviation (SD) values, again ranked low to high. As with LR type primers, the best (smallest) values came from some unexpected models, the Brazilian CBC Magtech 7½ coming out as the ‘winner’. Note however, that excellent as an ES of 14 fps and SD of 4.6 are, they are higher than those I obtained a year or so earlier with the best of the LRP models, Sellier & Bellot’s LR model producing 12 fps spread and 3.1 fps SD as taken straight off the chronograph readings.
The ‘S.D. winner’ was the Brazilian CBC Magtech 7½ SRM
However, as with average MVs, the switch to the small primers has reduced the spread across the ‘statistical population’ substantially, SRP types covering 4.6 to 8.6 fps SD, a less than two to one ratio. (This compares to 3.1 to 14 fps for the equivalent values for LRP models, getting on for four to one). Taking the median values too from the two sets of results pits 23 fps ES and 6.8 fps SD (the values for the 7th and 8th ranking examples averaged) against 33 fps ES and 8.2 fps SD for the LRP equivalents (averaging the 8th and 9th models’ results out of a population of 16). So, those are significant reductions still bearing in mind that the two tests are not directly comparable given different test rifles and load combinations. The SR models’ median 6.8 represents a 17% reduction from the LRP equivalent, not the third we thought we might see, but significant.
Before playing further with averages, ES and SD values, let’s look at the groups the various primers produced (Table 3).
This is the least significant result of the tests in that loads are normally tuned to suit the total combination of components used – which obviously couldn’t be done here. The use of the MagnetoSpeed ‘bayo’ on the barrel acts as an abnormal influence too with unknown effects, albeit every combination had to cope with them to an equal degree. Finally, the CCI-BR4 was used in the work-up loads and a tight grouping charge-weight chosen, so it has an ‘unfair advantage’ over other models. Predictably therefore, the BR4 shared first equal spot with an average under 0.4” but two others did so too – European contenders from Italy (Fiocchi) and the Czech Republic (S&B). With this pair having done well in the S.D. listings, 2nd and 4th places respectively, that’s a very good overall showing from them. Over half of the types produced group averages of a half-inch or smaller, better than the LR primers’ performance but, as the other components and the test rifle were different, no conclusions can be drawn from that.
Fiocchi (left target) and S&B primers did well with low SDs and good groups
The biggest surprise and disappointment, was the poor showing from the PMC SR Magnum (KVB-5,56M) which also came last in the ES/SD listings. This is quite contrary to my findings in 223 Rem from when I shot 90gn JLKs and Bergers in high-level FTR competition out to 1000 yards where this primer was a ‘star performer’. So it may well be that my findings would be turned on their head if the tests were repeated for the small 20 and 224 calibre cartridges, maybe too for the PPC, Grendel, 6BR and similar with their 30gn charges and shorter powder columns. I suspect that the larger capacity numbers from 6.5x47mm Lapua up will see similar behaviours though.
With relatively small sample numbers (15 or 16 per primer), mean MVs are reliable but spreads and standard deviations much less so. A single MV out of the distribution curve has a major effect. The results are still far more meaningful than the figures bandied around in range house discussions and boasts based on five shots, sometimes only three! Nevertheless, when I looked at LRP models I redid the three values using a ‘Best 13’ approach (out of 14 shots fired with each primer in that series). Removing a single way-out-on-its-own value made dramatic differences to some models’ performance and ranking in that series.
Therefore, I went and had a look for those hard to explain odd results. With a major exception, I’ll come to presently, only two out of the 14 had any such ‘outliers’, far less than was the case with LRP models – again pointing to excellent consistency from the SRP/small flash-hole model, not to forget the quality brass, dies, and components used in making up the cartridges. The ‘funnies’ affected the Remington 7½BR match primer where shot #5 produced an unaccountably low velocity of 2812 fps against a mean of 2827 and 8 fps lower than the next slowest shot; the Federal 205 where shot #4 was unaccountably high, 2847 fps against a mean of 2827 and 12 fps above the next highest value.
Redoing this pair minus the outliers produced:
Rem 7½BR …………. 2828 fps average MV; 18 ES; 4.8 SD
Fed 205 …………….. 2826 fps average MV; 14 ES; 5.2 SD
They had been equal highest MVs in the original ranking and remained there with Remington fastest of the bunch and the Federal second highest. On SD position, the Remington 7½BR’s change from 6.0 to 4.8 moved it up from 5th to 2nd place overall; the F205’s improvement from 8.4 to 5.2 moved it a long way up the chart from 13th to 5th.
Federal 205 and 205M (match) primers
However, a still more significant feature became apparent on analysing the numbers – the effect of the mid string pause to let the barrel cool, or more precisely the restart – always on shot #10 (16-round batches) or #11 (for the 17s). In a bit of serendipity, I had recorded the last seven shots post restart on a new line in my notebook and, when I was looking for the highest and lowest values in each string, soon noticed how often the lowest overall reading turned up as the first entry on line 3. That applied to no fewer than nine out of thirteen strings.
‘Restart shots’ (left hand of line 3 ringed in red ink) turned out to be abnormally low in two thirds of the strings
In some cases it wasn’t by much, just one or two fps compared to the next lowest but, for others, it was very significant indeed – 15 fps for the PMC SR Magnum; 7 for the Rem 6½ standard SR; 9 for the CCI-BR4; 6 for the S&B SR; 11 for F205; and 16 for the Winchester WSR – this one shot doubling that primer’s extreme spread. Even in the four strings where the ‘restart’ didn’t produce the lowest overall value, it was always in the lower half or quarter of the range, the actual values being 2, 8, 9, and 12 fps below the arithmetical mean. Thirteen results – where’s number 14 you’re asking? Red face time here – I forgot to switch the MagnetoSpeed back on for the first shot after the break with the Prvi Partizan SR string, so it was an unrecorded shot for that model.
Of the two primers with non-restart outliers, the Remington 7½BR and Federal 205, the former wasn’t affected by the phenomenon but the F205 had taken one of the major hits, shot #11 at 2810 fps being 11 fps lower than the last shot before the pause which was also the next lowest at 2821 fps. So this particular primer’s results got a second adjustment.
The revised results are shown in Table 4
Some models which had taken a major ‘hit’ on the first shot after the barrel cooling break have seen their results and positions much improved, the Russian PMC SR Magnum and Winchester WSR in particular. The Brazilian CBC Magtech retained its first place despite only seeing a single fps knocked off the revised spread and the Czech Sellier & Bellot retained an excellent third place. As with the LR test, the ‘winners’ proved to be unexpected, moreover handily in that if you can find Magtech, Murom, and S&B primers they are much cheaper than US products.
I mentioned that there was a 15th primer (or 16th if you include the unhappily dropped Vihtavuori example) that came along later. This was another Russian – the Murom ‘Small Rifle 223 Rem’, or SR223 as it’s also known. The cardboard ‘outer’ marked with the useful factory product code had been ditched by the retailer unfortunately but I’m pretty sure this is the Murom KVB-223M, a thick cup, tough ‘magnum’ model that is slightly ‘hotter’ than the older KVB-5,56M ‘magnum’.
Latecomer Murom ‘Small Rifle 223 Rem’ was an excellent performer
What with one thing and another, it wasn’t until the following summer that I was able to load some ammunition up using twice fired prepped cases, also annealed. A day was chosen when the weather was forecast to be cool and my records duly record 15-deg C (59F), still within the original temperature range. Unfortunately, there was one change that couldn’t be avoided – I had used up the last of the N150 lot from the main tests before this model appeared on the scene, so a different powder lot was involved.
That’s almost certainly why I got an average MV a step higher than the other 14 models’ range so I haven’t included it in the tables for this reason. I believe the ES and SD values should still be valid even though it’s impossible to say whether the new powder would or wouldn’t have had an effect here. Anyway, for what it’s worth, here is the straight off the chronograph result:
Murom KVB-223M 2838 fps average MV; 15 fps E.S.; 3.8 fps SD.
An excellent result that betters that of the previous test ‘winner’, the CBC Magtech model. The three groups averaged just over the half-inch, so a good result here too. The test was run exactly as for the others, so the mid-string restart shot was examined and, yet again, (the 10th occurrence) it fell below the rest of the spread – by 4 fps this time. Knocking that reading off and redoing the calculations gives a revised:
2838 fps average MV; 11 fps E.S.; 3.3 fps S.D
So let’s maybe rush out and buy these primers? As I mentioned in Part 2, there is a fly in this particular pot of ointment – trade sanctions against Russia mean that they cannot be imported into any EU country (or the USA now after the row over alleged Russian interference in last year’s presidential election saw Congress also pass a sanctions bill).
That takes me onto the follow-up test series that took one of my two ‘standard’ FTR loads and substituted five other makes of primer for my usual CCI-BR4. The MagnetoSpeed was left off this time as I was looking for two non-MV related results – primer substitution effects on group size/shape and whether a couple of weaker models would stand up to a ‘hot’ FTR load’s pressures. These latter were the standard PMCs (copper colour Murom KVB-223) and Winchester WSR. The other trio comprised the Remington 7½BR, Magtech 7½ SRM, and Fiocchi SR. Thirteen rounds were loaded with each of the five, ten shot as two 5-round groups, three as ‘foulers’. My standard CCI-BR4 based load was used to re-sight and I also intended to shoot a couple of ‘control’ groups with it. These particular (BR4) rounds had been loaded over a year earlier, so their likely performance was open to question depending on one’s views on ‘fresh’ v ‘stale’ ammunition.
Let’s look at this ‘hot’ load before moving onto results. When the rifle was newly built in early summer 2013 and the load developed, MVs were right on 3050 fps average in 15-20° C ambient temperatures according to my MagnetoSpeed V3. In August of that year in Raton, USA the load was checked out prior to the F-Class World Championship matches and it was assumed would need ‘fine-tuning’ to cope with shade temperatures running in the 90s F (34/35-deg C) and hotter still in direct sunlight. Despite IMR-8208 XBR (an ADI manufactured ‘Extreme’ grade) being claimed to be even less temperature affected than Hodgdon VarGet, my UK load now produced an average MV of exactly 3100 fps over a 5-round string as measured on a borrowed V3.
Members of the GB F-Class team test/fine-tune their loads in searing Raton heat, August 2013
That may have been all temperature related, or all down to using pre-ordered locally supplied lots of powder and primers, or a mixture of the two factors. To my surprise, despite the MV/pressure changes, my UK load of 46.4gn under the Berger 155.5gn BT Fullbore bullet still gave smaller groups than those from reduced charges by a considerable margin – and with easy extraction and no pressure signs. Moving on a couple of years to the primer tests, some 2000 or more rounds had now gone down the barrel and average MV had dropped to 3027 fps – no doubt due to barrel-throat wear. So, let’s look at loads and possible pressures.
Hodgdon gives a starting load of 41.0gn 8208 XBR for the 155gn Sierra HPBT MatchKing (model not specified, but likely the older #2155) and a maximum of 45.3gn for 2854 fps and 60,900 psi pressure in a 24-inch barrel.
That however is in a Winchester (LRP) case with the Federal 210M match primer. The thin-walled Winchester 308 case has around a grain more water-capacity than either Lapua version, so my rule of thumb is to reduce maximum loads by around 1gn for the LRP variant of the latter to compensate for the higher pressures resulting from its smaller capacity, so we’re talking 44.3-44.5gn for standard LRP Lapua brass based loads, whereas I was running 46.4gn with the Berger 155.5gn BT Fullbore projectile in the ‘Palma’ case.
Playing around in QuickLOAD and matching actual MVs to possible pressures for the three Lapua ‘Palma’ load MVs recorded we get:
Original UK temp. MV (3050 fps) ……… 64,468 psi
Raton USA high temp. MV (3100 fps) … 68,585 psi
Autumn 2015 UK test MV (3027 fps) … 62,722 psi
All are above the SAAMI 62,000 psi MAP. (Actually as the ‘A’ in MAP is for Average, the 3027 fps load might just squeak under). The ‘Raton brass’ was loaded and fired twice during the event and gave no problems at all either in results (dropped points down to my wind-reading not elevations or fliers) or in any physical pressure-related issue arising, the brass is still in use four years on, with half a dozen or more firings at these pressures. My warning in Part 2 about transferring ‘Palma brass loads’ to standard LRP case handloads still applies and is, if anything, reinforced.
So, even with some barrel wear and consequently reduced MVs/pressures the load is ‘hot’ enough to test primer-cup strength. The BR4 has never shown any sign of stress, even in the high US temperatures.
So, back to the 100 yard benchrest range for a final session (actually penultimate given the subsequent appearance and testing of the Murom Small Rifle 223 Rem primer), temperatures still in the same range but unfortunately with more typical Diggle ‘A’ Range wind conditions. The plan was to use 13 rounds of my BR4 load out of old stock as the ‘control’ then 13 fresh rounds for each of the other models.
Three with the BR4 were fired to foul the barrel/re-zero and a 5-round group followed. Looking down the ‘scope at the small single hole on the paper, I ‘chickened out’ over a follow-up! No way was I going to shoot a second group and risk spoiling that, so it was straight onto another primer, the Remington 7½BR in freshly loaded ammunition. That produced 0.5” and 0.6” groups with a lot more ‘elevation’ in them, illustrating why primer substitution without reworking the load combination is a poor idea.
The CCI-BR4 ‘Chicken group’ (right side) and Remington 7½BR groups on the left show the difference that primer substitution can make if the load isn’t retuned.
Of the others, the Magtech 7½ and PMC Standard SR (KVB-223) averaged a creditable 0.4” despite suffering lateral ‘fliers’ that may have been at least partly wind-induced. The WSR and Fiocchi models averaged 0.5”. So, if you change primer, retest and if necessary retune.
Magtech and PMC SR (KVB-223) Groups
As to cup strengths, every model looks different (see photographs) illustrating yet again how potentially misleading fired primer appearance is in trying to judge chamber pressures. (That’s short of getting primer leaks or blown primers from expanded case-heads – very different situations.) One soft PMC (KVB-223) ‘blanked’ so, fine performer that it is, obviously has marginal strength for a maximum SAAMI pressure loading even with the Stolle bolt. The Fiocchi and even more so the Rem 7½BR ‘cratered’, neither by enough to cause real concern; the thin-cup Winchester WSR flattened considerably but neither ‘cratered’ nor ‘blanked’.
Fired primers with the ‘hot’ 8208 XBR load. Top to Bottom Winchester WSR, Fiocchi, PMC/Murom SR, Magtech 7½, Remington 7½BR ………
…….. and again from an angle to show primer cup radii.
In my callow youth, the commonly used phrase ‘it’s cold enough to freeze the balls off a brass monkey’ caused much hilarity, although as always, the likely derivations have nothing saucy about them – it may have referred to stacked cannonballs and it seems that in the original version it was the proverbial metal beast’s tail that fell off anyway. The question here is whether the ‘wheels will fall off’ your Palma brass ammunition trolley should you attempt to shoot it on a chilly winter’s morning with the frost or snow lying crisp and even over Stickledown or any other venue. Lapua says this case is not recommended ‘for hunting’, a blanket admonition but surely only applying to the cold weather varieties.
Will your 308 ‘Palma’ loads perform well in these conditions? Possibly not
The issue is that with small primer ignition – only just sufficient to light up a 308 Win case-load of powder consistently – the primer flame may be on the feeble side (and further restricted thanks to the small diameter flash-hole) when the powder kernels and case-walls are very cold. Put simply, if too much primer energy is sucked up by these cold components, there may be insufficient remaining heat to raise powder kernels’ temperatures to that needed for reliable ignition. Possible problems are complete failure to fire (misfire); partial failure (hangfire); or apparently satisfactory operation but where velocity spreads stretch and/or average velocity is significantly reduced.
I looked at this aspect of the ‘Palma’ case when we first received them over the winter of 2011/12 and tried them on a cold Diggle morning with the ambient temperature just above freezing, also placing cartridges in the path of a bitingly cold wind. Standard LRP brass loads were used as controls. Everything ignited OK but there was some evidence that one powder performed poorly while two or three others tried seemed unaffected. (The affected sample was retried later in the year in higher temperatures and its performance was restored). There doesn’t seem to be an issue with the Hodgdon/ADI powders such as H4895 and VarGet – the US Palma team testers even put Varget charged SRP cartridges in fridges and freezers overnight and they still worked fine.
My sample was small and one doesn’t hear many complaints from GB shooters – but we’re rarely out in temperatures below 3 or 4-deg C given recent mild winters. So, it’s more something to be aware of especially if changing powders and if a load is worked up in the winter, a retest and chronograph check may well be a good idea in summer conditions.
What about ball or spherical powders given their reputation for being harder to ignite than extruded varieties due to their heavier, thicker deterrent coatings? When I did my little cold weather test, I included Hodgdon H414 with heavy bullets and it performed brilliantly. In fact it performed so well it ‘beat’ the same LRP combination and some charge weights even produced slightly higher velocities in SRP form.
So, when Hodgdon’s latest mid burning rate ‘spherical’ grade, CFE223 appeared with the promise of exceptionally high MVs in both 223 and 308, I soon tried it in both cartridges, using both standard LRP and ‘Palma’ cases in the latter. Two Hornady bullets were loaded, the old 155gn Amax and newer 178gn HPBT Match. Fiocchi primers in the appropriate size provided ignition. Standard LRP brass loads performed very well and met all expectations. The Palma case ammunition produced lower MVs, very variable spreads ranging from OK to terrible, a worryingly large velocity (hence pressure) jump with a small charge-weight increment as I approached maximum and groups that it would be a kindness to describe as ‘mediocre’.
These two Hodgdon / St. Marks Powder Co. ‘spherical’ propellants gave very different results in ‘Palma’ brass
There was also a very strange rifle behaviour that kept stopping me shooting to check it out – a sound on firing I could best describe as a rattle but everything on the rifle was good and tight. When I got the first of two misfires, the penny dropped – I was hearing hangfires. The gap between firing-pin fall and ignition was tiny and probably wouldn’t have been noticed without electronic earmuffs, these amplifying the ‘click’ of the striker fall, so I was hearing an almost instantaneous click-bang in 48 out of 50 test rounds with so little gap between the sounds they partially merged.
The two rounds that misfired were pulled and the primers were found to have ignited, so the problem wasn’t primer failure, rather the translation to charge ignition. The CFE223 granules were closely examined but no trace of damage, scorching, or partial ignition was found. Temperature at the time was around 15-deg C, so these problems cannot be blamed on a cold winter’s day. It could be that a ‘hotter’ SR primer might have been hang/misfire free but, even so, ignition would likely have been so marginal that results could have been affected, perhaps on a random basis.
On a happier note, I’ve reformed a couple of hundred 308 Palma cases to 7mm-08 for short/mid-range F-Class whose loads have been refined down to a single bullet-powder combination – 49 and a bit grains of Viht N160 under 160gn Sierra TMKs. I also experimented with 175/180gn bullets and N165 extruded magnum rifle powder working up to massively compressed charges of over 51gn weight in this long freebore chambered rifle (3-inch COALs) and never had any hint of ignition issues with any combination tried in any temperature above freezing using Remington 7½BRs. Spreads have been small and performance consistently good at out to 1000 yards with the TMK/N160 combination.
In conclusion, it seems that the SR primer will cope with most propellants and up to 50gn charges, in 7mm and 30 calibre cartridges. Although it exhibits less performance variability than the LRP type in 308, it will reward, even require, experimentation in matching primer model to powder and loading. Unlike with Large Rifle primers, there is the thin/weak cup issue to be aware of which constrains use of some models. As in my older LRP tests, it was gratifying to find that less popular (and expensive) models performed every bit as well as and sometimes better than most people’s first choices. Given that a recently revised price list from a major UK handloading supplies retailer shows CCI-BR2 (LRP) and BR4 (SRP) match primers at £92.50/1000 that is no bad thing!
Warning – Both load combinations quoted in the test exceeded the propellant manufacturers’ maximum charges. They proved safe in the author’s rifle when loaded in Lapua ‘Palma’ small-primer cases. They may not do so in other rifles, and almost will not do so in standard Large Rifle primed brass. Do not copy these loads for use in any other make / type of case, moreover drop charges by three to four grains weight and work up in small increments whilst looking for pressure signs.