Corrosive, Berdan, or both?

[XRING]

I'm sure there are those on this forum who will know. I have several boxes marked .303 inch Mk 7 I.S.A.A. (under an arrow).
The headstamp is:
R(arrow)L
51
and an upside-down 7.

I pulled a round but the powder is locked in with a tight-fitting wad. So I could not determine if it was berdan. Is this corrosive? Who made it?
Thanx

Regards
XRING

Information

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[Alan de Enfield]

The R /|\ L is "Royal Laboratories" manufacture.
The 51 is 1951 for year of manufacture.
The 7 could be Mk7 ammunition but it is normally coded "MkVII"

Is almost definately corrosive.
Berdan - probably but dont know for sure.

[smellione]

Yes definitely corrosive. Would be amazed if it was not berdan primed as well. Do what i do collect the military stuff and reload your own regards Al.

[Peter Laidler]

Best advice I was ever taught is this. Treat ALL ammo as corrosive AND errosive

[cary m2a]

I would also treat it as corrosive and if you use it clean good then ck. in a day or two and clean again .I'm with smellione, reload the stuff you want to shoot so you know what your feeding your rifle.

Cary

[Bruce_in_Oz]

If (as I suspect) the primer is copper coloured and 1/4" diameter, it is a mercuric/chlorate based primer.

Thus it is wildly corrosive, because of the chlorate, and the brass will be contaminated by the mercury upon firing and rapidly become brittle.

The thing about those primers is that they were designed to go off first time, every time, regardless of the weather outside. We scrooge-like reloaders were not in the calculation.

The Germans were messing about with lead-based priming compounds well before WW1, but the early stuff was not 100% reliable. Nobody in military circles got too excited about the corrosive angle until gas operated weapons appeared in large quantities: the troops just had to clean things properly and regularly, usually under NCO supervision. And, if something got a bit too scruffy, you could always get the armourer to fix it or the Quartermaster to replace it, and hit the slack digger with a charge for good measure.

[Mk VII]

Yes, it will be corrosive. They remained so until about 1960. This appears to be the last year RG loaded Mk.7 - next year they were loading Mk.7z with a noticeably different primer residue; not nearly so tenacious (Eleyprime, I seem to recall).
The Woolwich Arsenal seem to have got out of the smallarms ammunition business by this time. Kynoch seem to have loaded Mk.7 as late as 1965, presumably for commercial sales.