Results of the early 1970s UK ammunition trials?


Hello all,
I am currently trying to find more information about the British Ammunition trials in the late 1960s to the early 1970s that experimented with a variety of cartridges including the earlier 7mm cartridge - the end cartridge was the 6.25mm. Does anyone have a source for the results of these experiments? Was the experiments conducted by the Armament Design Establishment at RSAF Enfield? For that matter, what was the name of the trial? I’m especially curious at the rational for switching from a 7mm caliber to a 6mm caliber - was recoil/weight an overriding factor? The trials seem to be most interesting!

What little I know about this cartridge is from Anthony William’s excellent book and website, so any additional information would be greatly appreciated! Thanks for reading!


They also switched again in the Mid 1970s to a 5.56 x 45 Necked down to take a 4.85mm bullet. The 4.85mm IW that was deigned to fire this round was designed to be easily converted to 5.56 if the 5.56 won the NATO trials, which it did. I am told that the 4.85 performed slightly better. Hope this information is helpful.


First, I think it would take a small book to answer your question comprehensively, and second, you are confusing two distinct sets of trials. I will do my best to provide a brief answer.

The British recognised that the rimmed .303 round would need replacing from an early stage but world events conspired against this both in 1914 and 1939. About mid WW2 the General Staff decreed that Britains future infantry cartridge would be the .30-06, but by 1944 this had changed and it was to be the 7.92 x 57. Quite a lot of work was done on future weapon systems including the design and manufacture of the 7.92 SLEM self loading rifle.
The advent of the 7.92 x 33 Kurz changed all that and immediately post war an investigation was held to determine from basics what the new round should be. This was called “The Small Arms Calibre Panel” and was chaired by Dr. Beeching (of later British Rail fame) and worked out of the Armament Design Department at Fort Halstead in Sevenoaks. They examined several calibres in a variety of bullet weights. These were 6.5mm (using KJ cases), .30-06, 7.92
and .33.

It reported in March 1947 with a recommendation that the calibre should be .27", but if tungsten cores were permitted the calibre could be reduced to .25". At the same time, the design teams at Cheshunt were working on the EM1, EM2 and other experimental rifles.

Two rounds were to be developed, the .270 and the .280, although both were actually .276 (7mm) calibre. The .270 did not last long and was only made in small quantities in late 1947 and possibly early 1948.

The 280 continued in the EM2 and other weapons and, being aware that this was a candidate for the new NATO cartridge, the extractor groove was modified to that of the .30-06 and the round became the .280/30.

I will not go into the details of the politics but the round was unacceptable to the US and so the .280/30 was developed futher. First was the .280 1st Optimum which was the same round with a Belgian bullet seated slightly less deep to allow a increase in charge weight. When it became apparent that this was not enough the case was extended to 49.5mm and became the 7mm 2nd Optimum. This was followed by a case redesign to produce the 7mmHigh Velocity with the same case length, This was tested against the T65 round in the US. Finally in an attempt to produce a round acceptable to the US the T65 case was necked to 7mm and became the 7mm Compromise.

As all this development work was done with the Belgians and Canadians the various 7mm rounds were tested in 1950 in Canada at the BBC Trials (Britain-Belgium-Canada) and Britain took the decision to re-arm with the .280/30 case with the belgian S11 bullet as the “Cartridge SA 7mm Mark I”.

This decision annoyed the US and when the Tories under Churchill won the next General Election he rescinded the decision and we adopted the 7.62 NATO round.

L. to R.
.280 aluminium case
7mm 1st Optimum
7mm 2nd Optimum
7mm H.V.
7mm Compromise
7.62 British made T65

I have a .270 but it was not in the picture.

Skip forward to 1969 and again the question of a new calibre was raised. This time a 6.25mm calibre was chosen and ammunition was made using .280/30 cases necked to 6.25mm. This was only a ballistic vehicle and bullet weight between 90 and 105grns were tested. The actual round was to be a longer thinner case, but only turned brass mock-ups were ever made. The round looked remarkably like the later US 6mm SAW amd some say this was a crib from the British work. This was done at the Development Lab at RSAF Enfield. but nothing ever came of it.

Left 7mm Mark I, right 6.25mm

In the late 1970s a trial was to be held for a new NATO round, eventually won by the modified 5.56mm. Britains entry was to be a 5mm round originally based on a necked down M193 case. It was found the bullet needed to be lengthened and this necessitated lengthening the case neck and it became the 4.85mm which was the round actually entered in the NATO trials at the Cold Meese development centre in the UK. A lot of work was done on the 4.85mm and it was made in ball, tracer, AP, blank, grenade and dummy loads.

Left to r.
5.56 British M193 type
4.85mm mock-up using 5mm case with additional brass collar

Various 4.85mm including grenade blank and short range.

Various 4.85mm traing blanks.

That is about it I think, but one day I intend to write the book!



Thank you both for the replies!

Tony, that is a most impressive story/saga with great pictures to illustrate it - I guess when the Brits do something, they do the most thorough job that they can! You answered my questions very well. As you can tell, I am quite fascinated at the development proccess! Equally fascinating to me is how the perception of an “ideal” caliber at changes over time. I suppose the desire to go to the 6.25 caliber was a result of the American experiences with the 5.56? Perhaps it was a missed opportunity - it is remarkable how it seems that we’ve gone full circle with the new 6mm cartidges that have been recently designed… I do hope to read your book someday!

Thank you again!


WOW Tony!!! Great Reply!!! Thanks. Lew


As good as it gets and should serve as the high standard for those seeking the merit of the IAA Forum and its invaluable access to scholarly experts. That is an impressive answer and surely would be a welcomed IAA SLICS seminar presentation should Tony ever be in a position to deliver it. WOW


Thank you gentlemen, I am flattered.



Tony, are you certain that the .270 had the same .276 calibre as the .280? My understanding is that it was actually a .270 calibre. Certainly the bullets for it were much lighter.

Those interested in the development of the assault rifle cartridge might be interested in this overview:


The diameter of the .270 bullets is .279", whilst the .280 bullets are normally .285", although the weight is generally around 100 grns compared to the 130 or 140 grns of the .280. Labbett reports that the .270 tracer bullet had a diameter of .278 ". I cannot confirm this as I only have a ball round.

By saying that they were both .276" I meant they were both nominally 7mm calibre. Perhaps I should have been clearer or more precise.




As I expect you know, the bullet diameter of commercial .270 hunting rounds is .277", and of commercial 7mm (aka .275/.276/.280/.284) rounds is .284", so the designations “.270” and “.280” for these cartridges were appropriate, I think.


Very interesting! Is there a particular reason why the .270 and .280 have a difference of diameter of .005" - .006"? It seems like a such small difference that it makes me wonder if it was worth the effort to develop two seperate sizes?


Tony E

I agree with the others. A very impressive collection and well presented documentation.

Believe me, this is not intended to criticize your work in any way but I have a question regarding your comments and photographs in reference to the T65 cartridge. The U.S. T65 was 47mm in length and had a shoulder angle of 30 degrees. The one pictured appears to be a 51mm case with a 20 degree shoulder which would make it equivilent of the T1E3. (I realize that your cartridge is not one of the FA specimens.) The T1E3 first appeared in 1949 which would put it more in synch with your time frame.

If you can easily measure your cartridge for length and shoulder angle I would really like to hear what you find.




Again I am guilty of a lack of precision. The round I have is a 51mm case length and is described in British records as a Berdan capped copy of the US T65E3 case. This I believe was the 51mm case with a 40 degree shoulder.

The BBC trials had included the new US .30 ammunition and the rounds used were T104E2 ball, T101E1 API, T102E1 tracer and T93E1and T93E2 AP.

I am not sufficiently well versed in the US ammo to know if these designations are correct, but they are as reported in the trials.



Tony E

Thanks for taking the time to measure the cartridge. The case is, indeed, a T1E3 with a 20 degree (40 degree included) shoulder angle.

There is still some confusion, at least on my part, regarding the proper designations for the US experimental series. It’s my understanding that the cartridge case itsef had it’s own unique designation but that loaded cartridges, using that same case, were designated differently. This makes perfect sense. Except when it comes to those instances where there is an apparent mixing of designations such as the T65E3. I’m sure that designation was not one made up by the British labaratories but originated somewhere in the U.S.

But, I suppose it’s best to not try and figure out anything the Government does.

Once again, an impressive collection.



A longer cartridge case was required for the 4.85mm round than could be obtained by necking down standard 5.56x45mm cases. The British team used cases intended for the 5.56x45mm extended neck blank for some early trials.



All cases I have seen were either the short case necked down 5.56 which is generally termed the 5mm or specially made long cases. The early examples were unheadsamped but I know of no use of extended case 5.56 blanks to make cases. Even the unheadstamped cases are distinctly British with the 69T cap.

I would be very interseted to see any documentary evidence of this.Whose cases did they use as there were no British mnufacture 5.56mm blanks at that time (1976)?

Also, blank cases tend to be of much lighter construction than those intended for ball rounds.



I am not certain whether you are actually querying the existence of the 7.62mm T65E3 but if you are then I can confirm that there most definitely is such a round and I have one in my collection along with a scan of it’s label. I bought this round for a bargain price of



No, I’m not questioning the existance of T65E3 cartridges. I know they do exist and I have seen photos of box labels identifying them as such. What I wondered about was why they chose to mix the 2 distinct case designations, T65 and T1E3, into one? I have one of the WCC 54 specimins in my collection also. As I understand it, the WCC rounds were pre-production rounds provided to weapons contractors.

There’s no doubt that Winchester made out like a bandit on that contract since they already had tooling in place to make the commercial 308 Winchester ammo. Now they could dump the start-up expense onto the US Govt.

Is it possible for you to somehow send me a copy of the box label scan?



Scan of label is on it’s way.


[quote=“TonyE”]All cases I have seen were either the short case necked down 5.56 which is generally termed the 5mm or specially made long cases. The early examples were unheadsamped but I know of no use of extended case 5.56 blanks to make cases. Even the unheadstamped cases are distinctly British with the 69T cap.

I would be very interseted to see any documentary evidence of this.Whose cases did they use as there were no British mnufacture 5.56mm blanks at that time (1976)?

Also, blank cases tend to be of much lighter construction than those intended for ball rounds.


Now you’ve got me there. I have read this somewhere but will have to search through my bookshelves to try to turn up the evidence, starting with Peter Labbetts’ TAG. If I find it I shall get back to you.