7mm: The ideal military caliber?


#1

I’ve read elsewhere variations of the statement, “Tests have been done all the way back to before WWI and every time the 7mm has been shown to be the most effective caliber of bullet for a combat round.

Does anybody know of any such tests? Over the years, I’ve done a little reading on the subject and I don’t recall ever seeing anything to back up that claim. Understand, I’m not saying it’s wrong, just that I don’t know of any info that would corroborate it.

AFAIK, 7mm Mauser was the only 7mm cartridge ever to be blooded in warfare, anywhere. But, in both the Spanish-American War and the Boer War, 7mm Mauser fired round-nose bullets, which couldn’t have shown any better terminal performance than the .30-caliber bullets of the day. It probably saw use with spitzer bullets during WWI and WWII, but what tests from those time periods say it was more effective than the .30-06, .303 British or 8mm Mauser?

The Brits became enamored of 7mm caliber (.284" bullet diameter) as a result of the combat against the Boers in South Africa, and decided then that 7mm was the “ideal” caliber. I can’t help but think they were biased by that experience, which led to a later (post-WWII) study declaring that 7mm was the “ideal” caliber. Of course, their pre-WWI 7mm (.276 Enfield) round was equivalent to some of today’s 7mm Magnums, while the post-WWII 7mm (.280 British) cartridge was more of an intermediate-power round. Did the UK do any terminal effects testing?

In the 1920s, John Pedersen opted for 7mm caliber (.284" bullet diameter) for the .276 Pedersen cartridge, but I’ve never come across his rationale for choosing that caliber. As for testing, here’s a quote attributed to Hatcher’s Book of the Garand, in regard to the “Pig Board” test results summary:

I also remember reading in History of Modern U.S. Military Small Arms Ammunition, Vol. I, that .276 Pedersen was inferior to .30-06 in Army tests of armor penetration.

So, going by what I have read, I haven’t yet found any reference source that backs up the idea of “tests going back 100 years” showing 7mm to be better than either smaller or larger calibers. If anyone can cite reference works that support the claim, I’d greatly appreciate learning of them.


#2

stan

As you know, somebody saying something does not make it true. (Unless it’s repeated enough times. Then it becomes fact:)

Rather than ask here, I’d be inclined to first ask the guy who made the statement.

Ray


#3

Ray,

Actually, I did post the question on the two forums where I read this claim. Did not get an answer.

So, since many members of this forum have exceptional knowledge of military cartridge history, I thought perhaps this would be a good place to ask.

Stan


#4

The British did a lot of testing on 7mm varients but took too long over it and it was never adopted.Their research did indicate there was merit in the idea but they got hung up on issues like barrel life

I would say there is a good case to be made for something like the 7x57 to have been the best compromise between the big/small arguments that always polarised the discussion.

The 7x57 has an unecessarily large case for modern powders so that could have been reduced giving almost 7.62 performance but with a lighter round.


#5

Townsend Whelen once made a comment–which I cannot quote directly–to the effect that a 7 m/m bullet of good ballistic form was the largest that could be fired at a relatively high velocity in a rifle of moderate weight. He was likely speaking of a cartridge for big game hunting but many of the same criteria prevailed for military anti-personnel use in the period when service rifles were of full-power type and manually operated or semi-automatic. I understood Whelen to mean that if the bore size were increased beyond about 7m/m then a larger bullet of equal ballistic form would produce a more severe recoil and weight per round of ammunition would increase. My own experience in firing rifles running from 6.5 m/m through 8 m/m of the types I think he had in mind at paper targets convinces me the assertion was likely true in the period before the selective fire arms chambered for intermediate power cartridges became the norm. Jack


#6

The word “ideal” can mean different things to different people. The military uses a long list of critera and a drawn out process when developing and selecting rifles and ammunition for service use. Since the 7mm is not now, or has it been, a standardized US military cartridge, I’d have to say that it is not the ideal, in the USA.

Ray


#7

Yes Ray but the switch from 7.62 to 5.56 was an over correction in a lot of people’s minds. Had they stopped somewhere in the middle they might have been able to square both sides of the debate.
With a military spitzer FMJ bullet terminal energy is not terribly important because the bullet is going to go straight through no matter what, so little of the energy is expended. The holy grail was velocity and shocking power which may have had merit against the VC in the jungles but in theatres since it has its critics.

Its a “what if” debate because it never happened


#8

“What ifs” are fun. What if we had never gotten involved in Viet Nam? The 5.56x45 would be a cartridge used by USAAF gate guards and the “over correction” would not have happened and today’s troops in the Stans would be fighting with the 7.62mm NATO or maybe the 7mm NATO.

What if the old guard US Army brass had all retired after WWII? Maybe there would not even have been a 7.62mm NATO.

Ray


#9

What most people forget is that the switch from 7.62 to 5.56 was forced upon the US Army by the SecDef. Left to itself, the Army would have continued to field the 7.62x51 and M14 rifles. Support for the small caliber, high velocity concept was a very small minority; the majority wanted to stick with .30 caliber.

Here’s my “what if”: The Army had a historical record of incremental changes in small arms ammo – .50-70 to .45-70 to .30-40 to .30-03/06 to 7.62x51 – and often copied foreign designs (but usually with some changes/improvements). I think that after several years of combat in Vietnam, facing the AK47 and 7.62x39, the Army would’ve instituted development of a true assault rifle and an intermediate cartridge probably based on the .30 Remington. Something like today’s .30 HRT.


#10

Somewhat like the endless arguments as to whether the .30-'06 is better than a .270, or vice-versa. There are so many variables regarding performance at various ranges, accuracy, bullet weight and construction, terminal performance of the bullet, what’s the target, etc. that it’s just not possible to make any flat statements about a 7mm being the ideal caliber.

Note that the 5.56mm in both the M193 and M855 performs well at closer ranges because of yaw and bullet breakup, not so much as a result of its caliber. It’s not so hot at extended ranges.


#11

[quote=“RayMeketa”]
What if the old guard US Army brass had all retired after WWII? Maybe there would not even have been a 7.62mm NATO.

Ray[/quote]
The 7.62 is really only a shortened 30-06 made possible/necessary by the better powders available. Harldy more than an evolutionary step rather than an entirely new calibre. All the old military and civilian calibres of a similar age could have benefitted from a similar adjustment for the same reason. The point is nobody in the military was prepared to go further and that is the significant feature of this debate.
All sorts of possibilities spring to mind along the lines of a 7X51NATO or even a 7x39NATO but they never happened. A shame for us as cartridge geeks. Was it really an opportunity missed or just unnecessary tinkering? A good subject for a winters night though. We ought to revive this one around early January.


#12

I can’t say whether they did any terminal testing but I would imagine they did. The significant indicator about the whole 7mm thing with the British was that it spanned decades. Now you have to read something into that, a search on a purely higher academic level perhaps or plagued by indecision. I tend towards the first possiblity.

After WW1 they had the design of the P14/17 rifle and it was a winner. It could have been a bit lighter as an infantry rifle but never mind. They also had the 7x57 cartridge as an unofficial calibre because they had bought in thousands of rolling block rifles in that calibre to arm secondary personnel. They knew it was a good calibre because they had first hand experience of being on the receiving end of it. It was their admiration of the calibre that inspired their interest in the first place.

How hard would it have been to chamber the P14/17 for 7x57, lighten the woodwork a bit and produce what could easily have been the best combat rifle possible? Why spend decades trying to re-invent what they already had in front of them?


#13

Any military rifle/MG cartridge is a compromise between range and terminal effectiveness on the one hand, and weight and recoil on the other. Which calibre comes out the best in comparisons does of course depend on the weighting given to the different criteria.

My take on it is that the upper power limit is set by recoil, which should be low enough to permit controllability in a light rifle, in terms of rapid semi-auto firing and burst fire in emergencies. Obviously people vary in their recoil sensitivity, but the 7.62x51 NATO is clearly too powerful for this. The 6.8mm Rem calibre seems around the upper limit (having fired 5.56mm and 6.8mm versions of the HK 416 in quick succession, I was surprised by the small difference in perceived recoil - the HK 417 thumped a lot harder, despite its extra weight).

In fact, if you just want a 5.56mm replacement which is a lot more reliably effective against people and barriers, the 6.8mm Rem is probably around the ideal. The only problem is that, although it has a longer effective range than 5.56mm M855, it does not have the long-range performance of the 7.62mm. So if you want a small-arms cartridge similar in recoil and weight to the 6.8mm Rem but good enough to engage the enemy at 800-1,000 metres (as occasionally happens in Afghanistan) you need something closer to the 6.5mm Grendel.

Putting this together with the British work post-WW2 (which resulted in two options: .270 and .280, or 6.8mm and 7mm) I would say that the ideal compromise military calibre lies in the 6.5mm to 7mm range. Recent ARDEC trials (which reportedly didn’t test 6.5mm and 7mm, but 6.35mm and 6.8mm along with 5.56mm, 6mm and 7.62mm) apparently concluded that the 6.8mm was the best compromise with military style bullets. I understand that they only analysed the performance up to 600 metres though.

If you’re happy to retain a two-calibre solution with one good for 400m, say, and the other for the 400+m bracket, then the calculations differ. You might as well keep 7.62x51 for the MG/DMR - it isn’t ideal but is good enough. For the rifle, something like the .30 HRT or even the 7.62x40 Wilson Tactical or .300 BLK then comes into play. Which is of course exactly what the Germans had at the end of WW2 (with the 7.92x57 + 7.92x33) and the Russians from 1949 into the 1970s (7.62x54R + 7.62x39).

I should perhaps add that a motivator for adopting a long-range cartridge smaller than the 7.62x51 is the burden of the weight of the ammunition belts humped by dismounted infantry, which is a major issue for all Western armies.


#14

Where to start on this one? It would really take a book to answer your points but the talk I gave at SLICS a couple of years ago covered the history of the 7m from a British perspective. I also had an article on the journal covering the same (Cannot remember which issue)

However, here are a few comments.

You say that the British were biased by their experiences of the Boer war. Certainly it made them very aware of the deficiencies of the .303 Mark II ball round compared to the flatness of the trajectory of the Boer 7x57mm, but they were not biased. You are obviously unaware of the amount of testing that went on in the 1909-1814 period by the British military.

The requirement of the new calibre was that it should have an apogee of no more that 4 feet when sights were set at 800 yards and that the calibre should be either .256" or .276". There was no pre-ordained decision that it should be .276" (7mm). Some forty different cartridge case designs were tried with probably the same numevr of different bullets, the final design selected being the one you mention, RL18000C in .276" calibre. There is plenty of documentation describing thesee very thorough trials and I have copies of much of it. Just as examples I have attached pictures not just of several types of the selected round, but also two steel dummies of designs that were not selected.

We will gloss over the British involvement with the .276" Pederson as this was largly driven by expectations that the U.S. were about to adopt it.

By the late 1930s another program was under way, using calibres of .256", .276", .303" and 7.92mm, again with a large number od different case designs and extensive actual firing trials. Strange to say, the .276" again proved an excellent choice but WW2 put paid to any furtehr work as had WW!.

Post WW2 when the subject of a new calibre arose again, very extensive trials were held, again with no pre-conceived ideas about the result. To obtain ballistic data over a range of calibres three vehicles were chosen. The 6.5x55 case for the lower option, the .30-06 for the median and the .330 for the upper calibre option. A wide range of bullets was designed for each calibre and these were fired for both trajectory data and terminal effect against the usual targets, helmets, vehicles, earth, concrete etc. The control round was the 7.92x57mm and this was also used to investigate extreme forms of bullet form.

In addition a wide ranging theorectical study was undertaken and the whole, theoretical and practical documented in the 1947 report that recommended that the calibre should be .276", or if tungsten cores were allowed, .256".

This resulted in the .270" and .280 and then the various 7mm designs tested from 1947 to 1953.

That is only the British side. I am sure Ray or others can give details of the U.S. experience.

Regards
TonyE


#15

In developing a new rifle and cartridge combination, the single most important factor of all is - politics. A veto by PM Chruchill or Gen. MacArthur, trumps all. And, maybe, that’s is the way it should be? Without the strong hand of such men we could well find ouselves like the Japanese prior to and during WWII.

And Vince, Frankford Arsenal did collectors a favor by sticking with 30 caliber. I have a lifetime job in trying to identify and find just one each of all the various Cal .30 LR cartridges. Throw in one minor variation, such as caliber, and I’d turn to collecting post-cards. ;) ;)

Ray


#16

It’s well to remember that there was also considerable interest in the 7m/m caliber on the other side of La Manche, which is to say the French did a good bit of work in this bore size, particularly in the first decade of the twentieth century. Could someone add a word of two on this activity? Jack


#17

[quote=“VinceGreen”]The significant indicator about the whole 7mm thing with the British was that it spanned decades. Now you have to read something into that, a search on a purely higher academic level perhaps or plagued by indecision. I tend towards the first possiblity.

After WW1 they had the design of the P14/17 rifle and it was a winner. It could have been a bit lighter as an infantry rifle but never mind. They also had the 7x57 cartridge as an unofficial calibre because they had bought in thousands of rolling block rifles in that calibre to arm secondary personnel.[/quote]
That is something I didn’t know. I had read (on Tony Williams’ site, I think) that 6.5x50 rifles and ammo had been brought in, but this is the first mention of 7x57 I’ve seen.

[quote]They knew it was a good calibre because they had first hand experience of being on the receiving end of it. It was their admiration of the calibre that inspired their interest in the first place.

How hard would it have been to chamber the P14/17 for 7x57, lighten the woodwork a bit and produce what could easily have been the best combat rifle possible? Why spend decades trying to re-invent what they already had in front of them?[/quote]
I don’t know if it’s true, but I once read that Teddy Roosevelt – due to his battlefield experience – had urged the US Army to replace the .30 Krag rifle with the 7mm Mauser.

In both cases, adopting 7x57 would’ve been the logical, rational decision. But, since humans are more emotional than rational, I think the answer to your last question is that a combination of “not invented here” and national pride* was the reason why.

*Admit that the enemy you just defeated had technology superior to what you could devise? Unthinkable! Another example is the German MG42 GPMG. Rather than adopt that superb machine gun in 7.62x51, the US Army just had to create their own “original” design (with features copied from German weapons, of course).


#18

I agree, if the desire is to convert existing 5.56mm weapons. However, for a next generation rifle and LMG, 6.8mm Rem appears as if it may be quite capable of those long range engagements…providing it’s loaded with long, streamlined bullets, and not limited by the M16 magazine dimensions.

I didn’t mean to imply that .30 HRT should be adopted now. I was only citing it as an example of what I think the US Army would’ve adopted in the late-1960s or early-1970s, if 5.56x45 hadn’t been forced down their collective throat. There are currently better options available.

Concur. Which is one reason I wrote g2mil.com/6mm_optimum_cartridge.htm

Your proposed 6.5-7mm cartridges are probably better, but both concepts use the same basic case. If I still had access to loading equipment and necessary dies, I’d assemble some 6.5-7mm dummy rounds. I have a few 6mm SAW links, which would be a perfect fit for a photograph.


#19

“Biased” was not the right word, but it was the only one that came to mind. Perhaps “fixated” is more accurate? A century ago they decided that 7mm was the best caliber, and they stuck with that idea over the following 50 years.

Quite true.

[quote]The requirement of the new calibre was that it should have an apogee of no more that 4 feet when sights were set at 800 yards and that the calibre should be either .256" or .276". There was no pre-ordained decision that it should be .276" (7mm). Some forty different cartridge case designs were tried with probably the same numevr of different bullets, the final design selected being the one you mention, RL18000C in .276" calibre. There is plenty of documentation describing thesee very thorough trials and I have copies of much of it.

We will gloss over the British involvement with the .276" Pederson as this was largly driven by expectations that the U.S. were about to adopt it.

By the late 1930s another program was under way, using calibres of .256", .276", .303" and 7.92mm, again with a large number od different case designs and extensive actual firing trials. Strange to say, the .276" again proved an excellent choice but WW2 put paid to any furtehr work as had WW!.

Post WW2 when the subject of a new calibre arose again, very extensive trials were held, again with no pre-conceived ideas about the result. To obtain ballistic data over a range of calibres three vehicles were chosen. The 6.5x55 case for the lower option, the .30-06 for the median and the .330 for the upper calibre option. A wide range of bullets was designed for each calibre and these were fired for both trajectory data and terminal effect against the usual targets, helmets, vehicles, earth, concrete etc. The control round was the 7.92x57mm and this was also used to investigate extreme forms of bullet form.[/quote]
Thanks! I knew this was the best forum to ask the question. No other has so many highly knowledgeable members. Much appreciate the info.

I was aware of this. I wonder what caliber they’d recommend today, what with the requirement for “eco-friendly” ball projectiles (with no lead or tungsten)?


#20

[quote=“stanc”][quote=“VinceGreen”]The significant indicator about the whole 7mm thing with the British was that it spanned decades. Now you have to read something into that, a search on a purely higher academic level perhaps or plagued by indecision. I tend towards the first possiblity.

After WW1 they had the design of the P14/17 rifle and it was a winner. It could have been a bit lighter as an infantry rifle but never mind. They also had the 7x57 cartridge as an unofficial calibre because they had bought in thousands of rolling block rifles in that calibre to arm secondary personnel.[/quote]
That is something I didn’t know. I had read (on Tony Williams’ site, I think) that 6.5x50 rifles and ammo had been brought in, but this is the first mention of 7x57 I’ve seen.

[quote]They knew it was a good calibre because they had first hand experience of being on the receiving end of it. It was their admiration of the calibre that inspired their interest in the first place.

How hard would it have been to chamber the P14/17 for 7x57, lighten the woodwork a bit and produce what could easily have been the best combat rifle possible? Why spend decades trying to re-invent what they already had in front of them?[/quote]
I don’t know if it’s true, but I once read that Teddy Roosevelt – due to his battlefield experience – had urged the US Army to replace the .30 Krag rifle with the 7mm Mauser.

In both cases, adopting 7x57 would’ve been the logical, rational decision. But, since humans are more emotional than rational, I think the answer to your last question is that a combination of “not invented here” and national pride* was the reason why.

*Admit that the enemy you just defeated had technology superior to what you could devise? Unthinkable! Another example is the German MG42 GPMG. Rather than adopt that superb machine gun in 7.62x51, the US Army just had to create their own “original” design (with features copied from German weapons, of course).[/quote]

Just had another example of a long reply which has disappeared into the ether when i pressed “submit”!

Here goes again.

The 7x57 Rolling Blocks were purchased for the Royal Navy by Sir Trevor Dawson, the Vice Chairman of Vickers when he visited the United States on behalf of the Admiralty in late 1914/early 1915 to buy whatever he could as they were so short of rifles. When delivered they were in poor condition and relegated to DP status. He also bought the M1892 and M1894 Winchesters at the same time. The full story of these and all the other odd weapons is covered in my Secondary Weapon series.

The 6.5x50SR Arisakas came to Britain via France and again are fully covered in Part 1 of the secondary weapon series.

I don’t think many people appreciate the tremendous amount of research that went into the investigation of a new calibre infantry rifle both before WWI and after WW2.

Vince - The effort in 1935-38 to find an new rifle concentrated on updating the Pattern 14. See the Ainsley rifle. In fact a number of prototypes were manufactured and a provisional contract placed for troop trial rifles, but as previously stated WW2 got in the way!.

Regards
TonyE