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Laurie

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Everything posted by Laurie

  1. Laurie

    N 150 versus N 550

    You can wear barrels out pretty quickly with N150 too if pressures are high enough. Some of the hot loads for 185/200gn Bergers with N150 in Palma brass only give a 2,000-2,500 round barrel life in 308 Win. Steve D by comparison claims he gets around 3,500 with his N550 load, presumably running at lower pressures. However, these are all small samples and barrel steel / rifling type affects barrel life significantly too. I have a suspicion that if pressures are kept to moderate levels, most of the N500 series won't burn out barrels particualrly quickly. An exception may be N540 as it has a near 40% nitroglycerin content by weight - same as arsenal Cordite .303 British Mk.7. Powders with some nitroglycerin are almost becoming the norm now - the new IMR Endurons all have some and all Alliant powders whether from Nitrochemie, Bofors or General Dynamics St. Marks have this ingredient. All ball types are double-based, likewise Norma extruded powders. I bought a secondhand Musgrave TR 308 many years back with a nearly new Maddco stainless barrel on it and developed a mild 155gn SMK / Alliant Re15 load for it, shot the rifle for three or four seasons and sold it. I meet the buyer regularly who still owns this rifle maybe 15 years on, and he still uses that Re15 load. The barrel round count must be astronomic by now, but he says it still shoots as well as he can, if not better.
  2. Laurie

    N 150 versus N 550

    That's a good (and difficult) question Alan. Viht itself says the N550s are more temperature stable than N100s. Conventional wisdom says that it should be the other way round! Search on forums etc and you find what are in effect opinions, not facts - and they are contradictory from US users claiming everything from excellent to terrible. All I can say about N550 is that it appears to be a bit harder to ignite than N150 in cold weather conditions. (Lapua small primer 308 'Palma' which is ignition / temperature sensitive and N550 starts to lose MV / increase SDs at higher temperatures than N150 this being on or just above freezing.) Steve Donaldson, one of the UK's top F/TR shooters as was although he's now largely dropped out of League levels, has used Palma brass, Berger 210gn BT, and a stiff load of N550 for nearly 2,700 fps from a 34-inch barrel for many years with great results. Back in 2013, he dropped out out of the GB F/TR team and went to the FCWC in Raton, New Mexico as a privateer. Not being subject to team rules, he shot every competition and practice he could over the two weeks and put an enormous round count in - his rifle was borrowed by fellow Rutland team members too. With locally sourced primers and fresh N550, he used his UK load throughout without any charge weight reduction - and did very well in the US National F-Class Championships and then the World Championships. At ~7,500 ft ASL in a semi-desert climate and in a local heatwave temperatures went from cool first thing to very hot by our standards peaking in the mid to high 90s F in the shade by late afternoon on some days in week one, a little cooler (low 90s) in week two. Steve assured me his UK load worked fine throughout and he'd no pressure issues at any time. I believe many 'Match Rifle' competitors use N550 too with 200-230gn bullets in Palma brass and these lads and lasses go off to shoot MR in Australia in sometimes brutal temperatures as an NRA team. Vihtavuori has quietly added anti copper fouling additives to their powders recently and says it will be reformulating most (everything?) in its range to be temperature insensitive in the near future. I'm not surprised - it's becoming increasingly difficult to sell propellants into both sport and military markets these days if they have the reputation of being temperature affected. Hodgdon / ADI has been in the lead for years with the Extreme range of extruded powders, but now IMR (General Dynamics, Valleyfield, Ontario) is adding new 'Enduron' grades which although not quite as good as ADI is still very good indeed, and Alliant ATK's recent additions from Bofors, Karlshoga, Sweden such as Re16 have a new 'TZ' technology claimed to rival the Hodgdon/ADI 'Extreme'. Certainly American users are raving about them in every respect. (We don't get any here as yet - I hope that is going to change.)
  3. Laurie

    N 150 versus N 550

    Viht shows its N100 powders and their N500 equivalents with the same burning rates ........... but they're not. The high-energy versions are slower burning, sometimes significantly so. QuickLOAD lists N530 as slower than N140 never mind N130 through N135 and N560 as being slower burning than N165. Changes in quickness in themselves affect the charge weights that produce peak pressures.
  4. Laurie

    6.5 Creedmoor brass

    Good to know. The 'problem' with SRP brass and 40gn + charges is one of potential powder sensitivity. My experience is with the slightly larger case and charge weight 308 Win 'Palma', another two to six grains powder. In one case (Hodgdon CFE223 'spherical') I got 48 hangfires and two complete misfires at normal UK spring temperatures from 50 rounds; in others (Viht N140 particularly) performance began to be affected below around 3 or 4-deg C. Yet while N140 went to pieces and CFE apparently doesn't work at all in any temperature, N150 works right down to freezing (at least) and H414 'spherical' (made in the same factory as CFE) actually gave higher MVs and smaller ES than in Lapua LRP brass at just above freezing. One of the American 243 Win long-range shooters assured me on another forum that Peterson Cartridge Co. SRP 243 brass was hopeless with his favourite compressed load of coarse-grain / slow burning Hodgdon H1000 in US summer temperatures - 200 fps MV reduction and huge ES values. So, whilst the range user is pretty safe with most primer / powder combinations in the small primer / small flash-hole combination, there is a chance even in our climate that the sporting user could be caught out on particularly cold days and finding your rifle shoots several inches low at a couple of hundred yards range after a long Scottish Highland glen stalk on a red deer isn't fun for either stalker or deer I'd imagine. Just to complicate matters, it seems the small 1.5mm flash-hole is as much a cause of these behaviours as the primer size and brisance, maybe even more so, and it seems some of the new US made SRP versions have stuck to the large (2mm) flash-hole. Starline SRP brass is in this form inlcuding its Creedmoor it seems.
  5. Laurie

    6.5 Creedmoor brass

    As a deer rifle, you may be better using LRP brass. The SRP variety struggles with some powders, but more to the point, may see significant velocity drops in very cold conditions or even hang/misfires. The other potential downside with SRP in high-pressure cartridges is that the small primer is much more prone to severe extrusion back around the firing pin than the large variety. This can manifest itself as 'cratering' or in extreme cases 'blanking' where a disc of primer cup brass detaches and is blown back into the bolt. This is a firing pin tip diameter + pin tip fit in the bolt-face issue. Some rifles are prone to it. (Mik Mak of Dolphin Gun Co. tells me he has done the firing pin reduction / bolt bushing job on over 30 AI rifles - they were fine with 308 Win or 260 Rem etc, but struggled with a rebarrel to 6.5X47mm Lapua and its small primer. I have an FN SPR Winchester 70 based tactical rifle that is hopeless with SR brass, so I've kept as a 260 as I'd only switch to Creedmoor if I could use the SRP variants - entirely for range use in my case.) Note too, this will become a bit more of an issue over time. Peterson Cartridge is offering 243 Win, 260 Rem now in both varieties alongside Creedmoor and 308. We'll maybe see some confusion as these get here and are bought by those unaware of the differences and implications. 6.5 Grendel comes in various forms - at least three primer size / flash-hole diameter variations. I'm sure we're going to see more of these new versions of other cartridges too from Lapua, Peterson and some of the other young US case manafurers.
  6. Laurie

    Alternatives to QuickLoad

    Nor does QuickLOAD - there is no primer input so you cannot determine any effects of using SRP brass v LRP other than that calculated pressures / MVs will normally be overstated. IME with SRP brass, it is not possible to make sensible predictions anyway as it depends very much on the bullet + powder combination. In 308 Win 'Palma' brass, I've seen the SRP effect ranging from the equivalent of around half-grain to 1.4gn charge weight reduction compared to the same combination in Lapua LRP brass with the same capacity. QL is invaluable in other respects of course, such as where the combination contemplated cannot be found anywhere else in manufacturers' published or online datasets. Where possible though it is very important indeed to crosscheck QL results against published data.
  7. Laurie

    Sierra 155gr TMK for mid/long range?

    That G1 BC will only be one of a series of velocity-banded values, and by its looks the highest of the bunch. Litz (Ballistic Performance of Rifle Bullets 3rd edition) gives it an average G1 of 0.464. The far more useful G7 average is 0.238 (compared to the old 175's 0.243), good but in no way groundbreaking. By comparison, the 155 Berger Hybrid is 0.245 and the easy to tune 155.5gn Fullbore BT is 0.239. The antediluvian 155gn Berger VLD is in effect also so close as to identical for all practical purposes at 0.239 G7 average. The reason I mention this bullet is that the 155gn TMK is exactly that - a full-blown VLD form type with a very long (0.804") 13.39 calibres radius nose section and Rt/R nose juction form of 0.55 (0.50 = perfect / classic VLD). The old 175 has a shorter blunter front end with a longer shank in relation to the whole. Rt/R is 1.00 (perfect tangent ogive) and its nose radius is the classic SMK 7-calibres, these features making it one of the best behaved, easiest to tune designs that will accept worn throats, large jumps, etc, etc. Bearing in mind it was developed at the request of the US Army for use in the Remington manufactured M24 military adpatation of the Remington 700 and M118LR 7.62mm cartridge, it does everything it says on the tin - accepts Remy's long throats and works in a everything from a newly made or refurbished job to one with 5,000 rounds plus on the clock in all conditions and weathers. This is a classic trade-off: tolerance v form factor / BC, although some designs such as the 155.5gn Berger BT manage to combine good manners with low drag behaviours. The new TMKs in the various calibres are a heterogeneous collection - there is no 'theme' to them ranging from tangent to aggressive secant (VLD) forms, although there appear to be more of the latter. The 308s from 155 to 193gn are all VLD types with 13 to 14 calibre radius secant ogives and Rt/Rs from 0.46 to 0.55. By comparison, the 160gn 7mm TMK is like many modern high-performance bullets a half-way house job with a 10-cal radius nose and Rt/R of 0.84, nearer tangent than secant / ogive and I've found it an easy design to get to group well when jumped.
  8. Laurie

    FTR Newbie

    The price gap between the Dolphin FTR and Savage FTR is not as great as it once was as Savages are not the bargain they used to be and cost around £1,800 new these days. The 'basic' Dolphin with Nesika E action adds up to £2,650 if you avoid bling extras such as barrel fluting, or £2,550 for the same rifle with the Barnard 'S' action. If you do need to rebarrel the Savage after a year's experience, the cost will be the difference between new rifle prices, ie £750 (or more these days from many gunsmiths). When you go to an F match see if you can lie down with each type, ideally dry fire or take a shot to see how you like the very different stock configurations. (I'm a fan of the Dolphin but not everybody is.) Also as Brillo says, not everybody cares for the Savage AccuTrigger even in its match version. (I get on fine with it, but it is a real Marmite component, and it has a habit of unadjusting itself over time / recoil inevitably needing readjustment mid match and producing misfires.) The Savage 12 PTA rifles work well, sometimes excpetionally well, but it is a clunky action and trigger compared to many, and I say that as one who has used PTAs in various form and calibres for many years and still own two rifles using this action/trigger which I'm very fond of. A common derogatory nickname for the breed on the US Accurate Shooter forum is 'the Salvage' amongst its detractors. So far as Savage factory competition rifle barrels go, a fair percenhtage shoot brilliantly once the very lengthy running-in period is over, far better than any factory component should; most shoot adequately for a competition rifle, ie still good but not exceptionally; a small minority are 'dogs' and never perform well. See if you can find a good secondhand Sightron 8-32X56 Series III scope, an excellent starter model for FTR, and what you save on the Vortex will let you buy a more expensive base rifle. And ......... good luck and shooting. Any new FTR shooter is welcome, especially another lady to add to the growing field of female 'Effers'.
  9. Laurie

    7mm saum and 284 load n165

    You should be able to get higher MVs than 2,850 from the SAUM especially with RS70 which is one of Nitrochemie's 'high-energy' grades and has the advanced 'EI' infused deterrents technology. Nodes generally occur at around 100-150 fps MV intervals, sometimes smaller intervals though, so you need to work up in small steps and see when you hit the next one at higher velocities, checking that pressures remain acceptable for your barrel and in your highest local temperature conditions.
  10. Laurie

    RS powders for heavy .223/6.5CM/.308 bullets

    Maybe, but I've never had any issues with RS52 in this regard. When I was loading 308 Palma brass with a trial lot of Nitrochemie EI-N130 (nicknamed Elcho-15) some years back that I was given by Nigel Cole-Hawkins for review in its pre Reload Swiss days, I intended to use it in quite a 'warm' load at the Scottish LR Championship meeting at Blair Athol a couple of weeks later in what promised to be very warm conditions. So to test its temperature sensitivity, I left an MTM 50-round box open on the front seat of the car for three hours straddling midday in full sun on a hot day at Diggle to see if I could detect any difference. I couldn't and the chronograph only gave a modest increase in MV. (EI-N130 is the works code for what is now retailed as RS52.) No powder, even the much vaunted ADI / Hodgdon 'Extremes' is completely temperature insensitive, it's more about being manageable in one's own conditions, and managing ammunition exposure on the firing point. I cringe when I see F-Open competitors shooting a 40 minute or so relay on Stickledown with those big MTM R100 type ammo boxes sitting in full sun and the lid thrown back. By the end of that relay, those rounds will be noticeably hot to the touch. The same competitors will (rightly) take great care to keep their ammo out of the rain on a wet day knowing what water droplets can do to pressures and precision, but ignore full sunlight which even in the UK can be hot. The only powder I've had real issues with is Re15 in my old 223 90gn F/TR load that was pushing pressures. I could watch primer cratering get progressively worse as ammo heated over the course of a hot day. An insulated sandwich bag was bought and by scrupulously keeping it and the ammo in shade, opening the box as little as possible and not keeping rounds in a hot chamber got around this, but only barely. RS52 seems to be the answer to this issue in the cartridge and combination as VarGet solved the temperature problems but lost 60 vital fps and never performed as well as the Alliant grade.
  11. Laurie

    Lovex powders - opinions

    Interesting that (re S&B primers). Yes, they're excellent caps. More though, the more I play around with primers myself and the more that I read of other people's experiences, the more convinced I become that matching the primer to cartridge / powder / load can be very important, sometimes the difference between a mediocre performance and a really good result. Unfortunately, there is no easy way or set of ground rules as to what will or won't work best. Some makes / models seem to have a wider tolerance than others - Rem 7 1/2BR, Magtech 7 1/2, maybe Murom SR223 in SR models, and CCI-BR2, Fed 210M, S&B, and Murom KVB-7 (or 7M magnum) in LR. I include the KVB-7M as in my old (PMC branded) lot at any rate, it is almost as 'mild' as the standard KVB-7 and in some cartridges gives slightly smaller ES / SDs with no change in group size.
  12. Laurie

    RS powders for heavy .223/6.5CM/.308 bullets

    RS52 would just about do the lot, although I'd seriously recommend slower burning RS62 for the 6.5 where '4350 class' powders are optimal. 52 suits the 223 and 308 applications very well though. Nitrocellulose only RS50 probably will too but will give lower MVs, in mitigation produce a bit less barrel wear.
  13. Laurie

    Lovex powders - opinions

    SO62 is an excellent choice for 308 with 150-190gn bullets. It used to be branded Accurate-4064 as it closely matches the performance and loads of IMR-4064. (Use Explosia's data though, not IMR's.) It will also work in 223, but is really better suited to mid-weight bullets there. (You don't say what weight you intend to use and that has a very large impact on powder choice.) The three 'ball' type powders DO-73.4/5/6 from fast to slow burning are well suited to the 223, the choice of grade dependant again on bullet weight. They usually give high MVs and in the right combination excellent precision. IME, they are 'dirty' though and leave a very hard burned on fouling on case-necks and shoulders that unless cleaned off immediately, immediately as in within minutes, after shooting (spray WD40 or Ballistol onto paper tissue or towelling and wipe the fouling off) is the devil to remove. SO60 (extruded /tubular) is a good choice for 223 in all but very heavy bullets, and although I've never tried it, rather faster burning extruded SO53 should be an excellent choice with lighter (40-55gn) bullets in the cartridge. It was designed by Explosia as a single-based extruded type for the 7.62X39mm and is an alternative to DO63 ball type.
  14. Laurie

    Reloading 7SAUM, with RS70

    I am frequently, but not this time!
  15. Laurie

    S070 vs RS62

    You could try both SO65 and SO70 in Creedmoor with 139/140gn bullets. QuickLOAD suggests that maximum usable loads are about 1-1.5gn apart; both give a near full case and MVs in the 2,700-2,750 fps range from a 24-inch barrel.
  16. Laurie

    S070 vs RS62

    Lovex's SO-series single-based extruded grades are excellent powders and can give very consistent results. Up to around 10 years ago, SO70 was better known as Accurate Arms-4350, but of the three 4350s on the market was the slowest by quite a margin. (Accurate 4350 is still around, but not here. It is made for Western Powders by General Dynamics in Canada the plant which manufactures most IMR grades.) Explosia's burning rate chart isn't very accurate unfortunately. It shows SO65 on the same line as Hodgdon VarGet which got people rather excited about it during the first great VarGet shortage. Excitement gave way to frustration as a VarGet substitute, it is not. It is slower burning, bulkier, and has less energy - well suited to 7mm-08, 7X57mm, 7X64mm and similar, but gave heavily compressed loads and low MVs in 308 Win. Even when accurately listed, as has been said many times before, burning rate is only one of several metrics that affect suitability and performance. IME, SO70 works well in applications that suit '4350-class' powders, so should be an alternative choice to RS62. However, it usually gives lower MVs than IMR or Hodgdon H4350, and as RS62 usually outperforms this pair, I'd expect a yet larger gap between it and the Lovex grade. With smaller cartridges like the Creedmoor, it'll also likely be limited by case capacity reaching compressed levels at modest pressures / MVs. (Nothing wrong with that if you don't need or want every last fps MV, of course.) In larger, roomier numbers such as 7X57mm, .30-06, and 6.5X55mm, it's well suited to them.
  17. Laurie

    Alpha munitions / Peterson brass

    Peterson is very good, .............. but how it compares to Lapua and Norma? We'll have to see on that one when people have got 10-20 firings in.. Their 6XC cases (in either primer form) and small primer brass for 243 and 260 are very new lines, so new that most Americans have yet to see any, so I doubt if it has come anywhere near reaching us yet. Bernie Montana of Extreme Performance in Lincs was importing / distributing Peterson brass and I assume he still is. 1967 Spud of UKV fame and Dauntsey Gun Company both retail Peterson cases that I know of, so talking to Mark (Spud) would be a sensible starting point. I've not heard of any Alpha brass here yet or anybody importing their products.
  18. Laurie

    .260Rem Load.

    I had very good results with 123 and 130gn bullets with N150. There is a downside though with this powder - pressures seem to peak rather quickly when you get to maximum. N160 is likely a bit (lot?) more tolerant. By coincidence, when I get back to shooting (convalescing after surgery right now) 260 is back on my 'play list' having had my old FN SPR rebarreled in it yet again, but this time in 'long throat' form for shooting 140s at around 2.95" COALs. I'll also use it to see how well Berger's impressive looking new 130gn 'Tactical AR-Hybrid' manages at magazine length and around 160- thou' jump. I'd more likely go 6.5 Creedmoor in SRP Brass form these days all other things being equal, but with the SPR being a b*gg*r for blanking SR primers and the cost of a firing pin turning / bolt bushing job being another £300 on top of the rebarrel, it was simply too expensive. There's nothing wrong with the old 260 anyway and plenty of good brass available for it.
  19. I was confusing the Rifleshooter test with a video piece from Johnny's Reloading Bench or some such that appeared some months back and claimed mis/hangfires with SRP Creedmoor brass with Viht N550 loads. It was almost certainly a temperature issue as this was during the winter. The methodology was crap because the tests involved different ambient temperatures for the differing case types as well as very small sample sizes. He thoroughly confused me too by apparently doing a flash-hole reaming job on the SRP brass using what was obviously a large diameter uniformer tool for the 2mm size hole. This left me wondering what size US made SRP Creeedmoor brass actually was. My memory may be letting me down again, but I think this was Peterson SRP Creedmoor - and this company assures customers its SRP cases have the correct 1.5mm flash-holes. This one is OK as far as it goes, but with large flash-hole SRP brass it's pretty pointless IMO. I like the Rifleshooter.com stuff - good down to earth nice builds without frills and they're genuinely pleased to get results under 1-MOA, and ecstatic to get half-MOA compared to the 'shoot quarter-MOA all day long if I do my stuff' pieces that have become the norm online it seems. A shame though about the images of the targets in this report - I tried making sense of them but to be honest gave up after a couple of minutes as I found them so hard to see. So far as actual MVs are concerned in the cartridge, nothing surprises me too much these days. Years back I had a Dr Geoff Kolbe designed and made chamber pressure measuring device for review - it used an accelerometer to measure recoil speeds and software that converted it into pressure. All you had to do apart from attaching the sensor was to input rifle all up weight, bullet and charge weight, and finally the bullet diameter, shoot a round or two and see what the machine said was being generated internally. Out of scientific interest I tried a standard Small Pistol primer in a pretty well mainstream 223 Rem loading alongside the SR magnum I normally used. The SP model gave higher MVs and according to the Dr Kolbe device. around 5,000 psi higher pressure. When it comes to cartridge ignition, nothing is as it seems ..... seemingly ☺️
  20. It needs a long action for repeater / magazine use with the 6.5-284 and you'd have to be happy the shorter / thinner body 308 rounds would still feed reliably. In a short-action, the 6.5-284 has to be a single-shot only option and depending on the action and size of its top-opening / port, you might have to remove the bolt from the action to unload a live round.
  21. To gain the benefits of SR priming, you also need the small (1.5mm / 0.059" dia.) flash-hole instead of the standard size (2mm /0.079" dia.). The Starline brass used in the tests has the large flash-hole in both versions. This alone almost certainly accounts for any odd findings on average MVs - the small flash-hole is reckoned to reduce MVs as much as, more likely more, than the primer size. I looked at this test a long time ago and although don't remember much about it now, do remember being distinctly unimpressed by its methodology and the numbers of cartridges fired. However, since IMHO there are no internal ballistics / accuracy benefits in using SRP Brass with a large size flash-hole compared to the standard LRP variety, I'd never buy any cases like this. The only potential benefit is that with a smaller pocket, the SRP version might last longer before pockets become slack and the cases have to be scrapped. There are a few cartridges around where you can get either primer size allied to the 2mm flash-hole - 7.62X39mm and 6.8mm Rem SPC being the two most common. When I had a 6.8 SPC AR-15 straight-pull, I did a side by side test between Remington (LRP) and Hornady (SRP) cases which fortuitously had very similar case capacities as measured using the water overflow method. With this small capacity case and powder charge - a great deal less than those of the Creedmoor, I expected to see the Remington variety produce significantly higher MVs, but there was nothing at all between them, likewise in ES and group sizes. It seems that if the powder is cleanly ignited, it's cleanly ignited when the only difference is the primer alone.(In the case of the 6.8, it seems Remington made a poor move in going for LRP with this smaller diameter case-head. The best, strongest, and longest lasting brass for the cartridge was Silver State Armory's SRP version when it was produced.)
  22. Laurie

    6,5mm Creedmore or 6,5x47L for F Open?

    Lapua alone loads factory 6.5X47L - four Scenar match loads and one Naturalis deer load. http://www.lapua.com/en/ammunition/calibers/65x47-lapua Unusually the small to mid-size US ammunition companies which produce boutique versions of 260 Rem and 6.5-284 largely or entirely ignore the cartridge too. The near complete absence of adoption by mainstream rifle and ammunition manufacturers contrasts with the Creedmoor situation where there is a Gadarene rush onto a near runaway bandwagon and suggests that the 6.5X47L is and will remain a specialist number mostly used by shooters who handloader
  23. Laurie

    New .243 load help

    I'd be a little wary with QuickLOAD. Having run several combinations and then compared them to published data in reloading manuals, some QL results are close, but in some combinations an apparently suitable QL result producing an estimated 57 or 58,000 psi PMax may be as much as three grains higher than the loading manuals' maximum figure - a lot in this cartridge to put it mildly. One possible reason for this is that there is apparently a great deal of variance in 243 brass capacity. The Speer manual uses Winchester cases and states in a general warning on the cartridge that its staff found unusually large variances between case makes and stresses that its loads apply to this one make of brass only and should not be transferred to any other. In the loads that I will work up in due course, I'm using several makes of case, but so far have no fireformed examples so have been using QuickLOAD's default capacity. Where there is a significant discrepancy with loads from manuals, I've used the latter and will see in due course which is closer to reality based on Labradar MV results.
  24. Laurie

    .308 Target rounds

    I'm not saying it's unsuitable, rather sub-optimal as it was designed for a lower bullet weight. But it's still a free country (just) and you're welcome to use any powder you fancy in the cartridge as long as it's safe, and N135 is safe enough as long as the manufacturer's loadings are adhered to. You won't find any serious long-range 308 shooting competitors using it though.
  25. Laurie

    243 powder

    Not that I've seen. Sierra Bullets (which has for years collaborated closely with the US Army) mentioned it in a loading manual many years back. The US Army did its research in the aftermath of introducing the 7.62X51 round / M14 rifle and deciding on a policy of ball powders only for non-specialist 7.62 types, so I'd assume it dates from the late 50s or maybe early 60s. Almost everything that the US Government and its agencies researches is available somewhere online unless it is 'classified', .... but finding it. With so many developments in propellants in recent years, it's dubious how much one would learn now anyway from 50 + year old research. People shouldn't get too worked up over 'double-base'. Most recent introductions have nitroglycerin in the mix somewhere - all of the new IMR 'Endurons' for instance; every Alliant 'Reloder' grade; all ball types. Viht N100 series, RS 30/50/62, and Lovex SO extruded grades are the only true single-based types left to us now. However, Viht N500 series aside and some of the older grades, the norm is 3-10% nitroglycerin content by weight and if loads are sensible, barrel life appears as good with these grades as with anything else. I bought a secondhand low round count Musgrave 7.62 TR rifle with a Maddco stainless barrel maybe 25 years ago, shot it regularly in TR matches all season for some five years and sold it to a fellow club member who still has it. The load was (and is) the old Sierra 155 MK and Alliant Re15. I passed the load on and the new owner still uses it. That barrel is still going well today, and the round count must be really something. As we never shot beyond 600 yards and more often than not at 300 only, the loading was mild. Some Viht N500s have very high nitroglycerin levels - N540 was reported as 45% on its introduction many moons ago and I assume it's still very high. What does kill barrels fast is the combination of a high-energy mix allied to advanced deterrents early burn modifying technology, in particular RS's 'EI' grades (RS 40/52/60/70/80 and some Alliant powders supplied by Nitrochemie). They will give a step increase in performance but the extension of the peak burning pressure and heat period increases the stress on the chamber throat rear end of the barrel. Don't load them up to peak pressures and performance and they should be fine. (I have an FTR rifle with a Broughton 5-groove that has had a lot of RS52 down it and its performance is holding up very well.) With the 243 being a known barrel burner, there is a good case though for the high round-count user to choose powders carefully. Viht N160 and N165 are obvious candidates for the heavier bullets. (John Whidden keeps winning US national championships with the 'straight 243' 105 Hybrids and N160 too - ~1,300 rounds barrel accuracy life he says and remember American prone competitors string-shoot, so rounds will go downrange as fast as the target is marked and a lot faster than our TR or F-Class.) For ball powder lovers, I imagine the Ramshots will give acceptable if not in fact very good life if pressures are sensible.
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