Load Data from different sources. Who is right?

[Laurie]

And in this very forum the photo below was posted and the OP stated he increased the load until he got ejector marks and then backed off 1 or 2 grains. Meaning he found the elastic limits of his brass and backed off, and this varies between the brands of cases and how long you want your primer pockets to last.

Years ago, I read an article by M. L. (Mic) Macpherson somewhere or other on cartridge design and wildcats. Mik noted that every manufacturer or handloading gunwriter like himself got enthusiasts turning up with marvelous claims for their modified 22-250 or whatever where the 31.3-deg double-radius shoulder and other relatively minor changes gave such an improvement in thermodynamic efficiency that the cartridge gained 200 fps MV.

In reality, if anybody bothered to test them, the 'improvements' gave little or nothing over the factory version but when the recipient asked for powder and charge details the cat was let out of the bag. These characters were invariably members of the increase-the-charge-until-the-primer-falls-out / prominent-ejector-marks-appear-then-reduce-charge-by-0.5gn school. As Mik pointed out these loads almost always exceeded proof pressures often by large margins and yes anybody can get a hefty MV increase through running crazy pressures.

I must say though that some company's data in some cartridges are puzzling - much of Vihtavuori's in 308 Win for instance. Tyro handloaders asking around on the range what people actually use are shocked to hear people are usually (and happily) using 45-46gn, sometimes even as high as 47gn N140 with 155s when Viht's maxima are 43.2-44.2 depending on bullet make/model. At one time, Viht's max N140 loads for the 155 Scenar were even lower, down in the 42s. The problem with this is that the word gets around that such and such a company always understates max loads to protect itself and people assume this applies to every cartridge and every powder which it almost certainly doesn't. ... and should never be assumed anyway.It's less common, but still occasionally applies that pressure signs and/or worryingly high velocities appear before reaching published max - that's what chronographs are for .... and bullet pullers.

Nowadays of course, many handloaders myself included, have another variable to add to the mix and increase the fun quotient - what QuickLOAD calculates. Having just reread my notes on testing some first go attempts in a long-throat 260 Rem late last year, of three powders used with the 142gn SMK, one (Viht N550) produced ~100 fps higher MVs than expected, and two (Viht N560 and Reload Swiss RS70) were the reverse under-producing by 100 fps. None showed pressure signs but the three rounds with the highest charge weight of N550 went home unfired and were pulled as almost certainly going to be over-pressure.

 

[Uncle Ed]

In actuality, the bullet will be fully engraved and sized down to groove diameter by the time of peak pressure so it wouldn’t really affect his 30-06 that much. PO Ackley chambered a 30 caliber barrel for 8mm Mauser then promptly fired a German WW2 Service round. The case ejected normally and had only “mild” evidence of any pressure.

Accuracy might suffer a lot with these mismatches, but unless diameters become extreme, peak pressures won’t change that much, if at all.

I hope Laurie will chimes in on this because I got it backwards the last time this came up. But the British NRA posted a warning about and I can't remember if it was tight bore barrels or oversized bullets in the .308 Winchester.

But the peak chamber pressures went over proof test pressure and was deemed a very unsafe practice, and the British NRA banned the practice. I read this over 12 years ago in a British Enfield rifle forum and the link below might be related. (help Laurie, this Colonial rebel can't remember the exact details)

AN INVESTIGATION INTO THE EFFECTS OF TIGHT THROAT AND BARREL DIMENSIONS ON MAXIMUM CHAMBER PRESSURES FOR THE 308 WINCHESTER CARTRIDGE

http://www.geoffrey-kolbe.com/articles/Pressure_Trials_Consortium.htm

 

[Laurie]

Yes, it goes back to the use of as-issued military 7.62mm ball ammunition in GB and British Commonwealth 'Target Rifle' shooting, our main prone sling shooting discipline. (Same kit as Fullbore / Palma and also regulated by ICFRA, but we shoot on different targets to US FB competitors.)

This 7.62mm ammo was really pretty poor stuff by today's standards, the usual UK version being the 146gn FMJBT 'Green Spot' UK forces' sniper round. In addition to various basic deficiencies, Royal Ordnance Radway Green Arsenal's output varied considerably by production lots too. To get it to shoot at all well at longer ranges the Target Rifle discipline's basic tool, the single-shot 30-inch barrel rifle with match iron sights saw the use of two features: 1) a very slow rifling pitch rate of 1:14"; 2) Much tighter bores than standard 30-calibre. IIRC today's TR rifles (and for reasons I've never understood their US FB and Palma equivalents) generally use barrels with 0.298/0.3075" land and groove dimensions instead of the standard SAAMI 0.300/0.3080" nowadays, but MUCH smaller dimensions were often used in the early 7.62mm days. Geoff Kolbe quotes them in that study.

The reason for the slow twist was that the bullets in many ammunition lots had so many examples with inconsistent jacket thickness, too much run-out or other faults, that there was a genuine improvement in scores through spinning them as slowly as the absolute minimum needed for stabilisation.

The reason for the tight bores was twofold - 7.62mm bullets were undersized against the nominal 0.308" never mind the slightly larger dimensions of 0.3082-0.3083" found in most commercial match bullets. IIRC NATO STANAGs specified 0.3073-0.3077". Fired in a SAAMI dimensioned barrel even of 30-inch length MVs were inadequate for 900 and 1,000 yard matches. So, the tight bores literally squeezed the essential extra fps MV out of the issue ammo. At one stage, bores really were tight, and the long since closed Royal Smallarms Factory at Enfield Lock in north London produced hammer forged heavy barrels for No.4 Rifle conversions from 0.303 to 7.62mm - push a standard 1.75 sq-in patch down one of these barrels and then a modern F/TR rifle barrel and the difference in effort required is staggering.

These tight barrels increased pressures of course, but that wasn't an issue with the NATO ammo - even the old (Lee-Enfield) No.4 rifle coped happily (as long as you kept the chamber and ammo dry - get them wet and it was almost unsafe!) And ... the British forces were still shooting Lee-Enfields in this guise as the L39 target rifle and L42A1 sniper rifle until the late 1980s. Firing a commercial 308 Win cartridge in these rifles, especially the No.4 conversions could see dangerous pressures though.

The 1982 Falklands War saw the start of changes. In the postwar reviews, the L42A1 sniper rifle and 146gn Green Spot round got a lot of stick for performing poorly. Shortly after the war's end, the British MoD started the process of specifying and procuring an up to date replacement and stage 1 of that was collecting as many other nations' equivalents of both rifle and ammo as they could lay hands on and comparing them to the existing British combination. The (unofficial) word was that officials and senior soldiers were shocked and embarrassed by how poorly the L42A1 / Green Spot performed against equivalents in service elsewhere in NATO. The Accuracy International manufactured rifle was soon procured to replace the L42A1 and Radway Green produced an improved 155gn FMJBT sniper round equivalent, not as undersize as older 7.62 bullets and the 0.298/0.3075/6 bore became the norm as it could also handle commercial bullets like the 155gn SMK without going mad on pressures.

Radway Green continued to supply this new cartridge to the GB NRA for several years until around 10 (?) maybe 15 (?) years ago when two different pressures changed everything. One came from the shooters who despite the improvements were still VERY unhappy with its consistency and lot to lot variations and this became the evergreen source of discussion and dissension in the NRA Journal and in Bisley clubhouses. (The GB NRA didn't allow use of handloaded cartridges in any major NRA sponsored match then, nor does it now in 2019 - everybody uses match organiser issued stuff.) The other was that the now privatised Radway Green outfit (part of British Aerospace PLC at that time) found annual NRA 7.62mm sniper ammo orders increasingly difficult and expensive to fulfil - 5.56 had become the stanadard smallarms round and the British Army had discovered the 338 Lapua Magnum and increasingly used AI rifles in this calibre for its sniper work instead of 7.62mm. So, RORG wrote to its civilian customers one day that as from 01.01.199X they would no longer do any commercial ammunition supply and would only accept government orders.

This put the GB NRA in a fix to put it mildly and saw a move to procuring commercial match 308 Win ammo that meets the ICFRA 'less than 156gn bullet' rule. Much commercial 155gn ammo was too high pressure in the tight bores, so it was in effect a mild download to suit the barrels in use. A decision had to be taken on the bullet and the NRA settled on using only the early 155gn SMK (#2155). After a lot of range trial work and ammo lot testing, RUAG Ammotech in Germany got the first contract made by its RWS division and kept it for a few years. It has now moved to the Lithuanian company GGG still with the 2155 SMK. Generally, competitors are now happy with the ammo and despite grumbles about price rises, it's a steal compared to what we Brits would pay for say Federal GMM or equivalent over the gunshop counter.

The one problem / issue was that of surviving early TR rifles with very tight barrels, especially the No.4 conversions with the relatively weak WW2 Lee-Enfield action. The RWS/GGG ammo is over-pressure in these rifles and the GB NRA has had to warn about its use in them. Whether that's 'advice' or an actual ban, I'm unsure, but no doubt about it, this ammunition is really marginal in these rifles unless rebarreled with a modern 0.298/0.3075 or 300/3080 tube - but you'd have to have great affection for your old No.4 TR rifle to ever pay the £900-1,000 cost of doing that on one of these old soldiers.

 

[cem]

Comparing data from 2 sources. Can someone explain the variation between the 2 sources? …..

Adding my two cents only to emphasize a point that I think matters more, much more, than has been addressed here.

The variation between these two sources can be more than adequately explained as the difference between apples and oranges rears its ugly head once again.

When I read the Hornady manual I find load data for Hornady bullets. When I read the Hodgdon website I find data for a variety of bullets. When I look at the .30-06 I find the data quoted is for Nosler bullets including a Nosler E-tip.

Time was bullets were almost all plain base traditional cup and core with much in common. Time was it was less dangerous to mix and match data. Not guaranteed safe but less dangerous with cup and core bullets and nitrocellulose (IMR) powders.

These days of trick bullets and even lead free as the E-tip is data for one bullet may never be taken as applicable to a different bullet.

At a bare minimum pick a load and follow it exactly including bullets and primers and let it go at that.

To address other questions in the original post I'd say start by reading more, much more, from your local library with interlibrary loan if necessary. I suggest starting with Earl Naramore and Phil Sharpe for a complete grounding in book length, not magazine article and internet snippets. Then Waters and Hagel and Wooters and Nonte and so up to today's writers.

If that's too much trouble then perhaps the two or three books by John Barsness directly addressing handloading for rifles and Mic McPherson's (mentioned above) book to start.

There is no way short of a ballistics lab for the home loader to know actual pressures. Using identical components in a similar rifle to get roughly equal external ballistics implies that internal ballistics are also roughly equal for whatever that might be. So yes if there an interest in doing more than following a book load slavishly then a chronograph is mighty useful.

 

[riflewoman]

The culprits, as Laurie identifies, were the bores and very tight throats. Combine them p, and pressures can spike...the report indicated that tight throats were a bigger issue than tight bores. Which is what Ackley found as well.

I first got started in Highpower shooting in Canada when I lived there. My first CF target rifle was a Parker Hale 1200TX. I still have it. It shot the issued C1A1 ammo OK. But it shot 168s with 42 N203 MUCH better. The issue ball was even less consistent than RG GreenSpot. The “hot setup” was to put a Schulz & Larsen Barrel on your rifle and then pray that your shiny new barrel shot well. The best shooters built 2 or 3 rifles and chose the better as their “big match” rifle... Then someone found out that a No4 Lee-Enfield in L42 configuration shot better at 800 and 900 because of “compensation”...and that became another equipment race. By this time the was fed up with the limits, found US Highpower and haven’t looked back.

 

[Laurie]

The issue ball was even less consistent than RG GreenSpot.

Wasn't the Canadian TR shooter's on-range joke about the standard military 7.62mm ball ammo made by IVI and supplied via the government and DCRA that its manufacturer's initials (IVI) was an abbreviation of Impact Varies Indeterminately?

 

[riflewoman]

Wasn't the Canadian TR shooter's on-range joke about the standard military 7.62mm ball ammo made by IVI and supplied via the government and DCRA that its manufacturer's initials (IVI) was an abbreviation of Impact Varies Indeterminately?

Prior to about 1971 or so, the DCRA was using up the stock of DA ammo. That shot somewhat better. Groups were big but if you held well and had it centered, all bullseyes were possible. When the government privatized the arsenal, the QC suffered badly.

 

[Flouncer]

Back to the original question and early replies ... . all are by very experienced and qualified shooters and reloaders. Just for consideration. The Hornady 10th edition, the new one shows no less than 10 different 150g bullets, from Hornady alone, with the same charge weights. Including the GMX, an all alloy monolithic bullet. Differing OAl as well they should. Page 513. My general perception without investing considerable time is that the online powder Mfgs are less conservative than the bullet manufacturers like Burger, Hornady and Sierra. i.e. the online powder mfg loads are higher than the books. The referenced IMR 4064 and the 150g seem to me to be an anomaly. To the new loader, always start low and work up. Every single person here will agree on that advice for one new to the persuasion.