Questions about head stamp markings 7.62 x 51 ammo

[cbrpete]

I have some 7.63 ammo with the following markings : 7.62 R1M1 B81 . It has staked primers with purple around the primer. I would like to know who made it and is it corrosive? Thanks, Pete

[MusgraveMan]

Pete,

When South Africa adopted the FN/FAL rifle in Nato 7.62x51 in about 1963 I remember that all our military ammo was head stamped R1M1 (can not recall the "B81" but that typically refers to year of manufacture).

It is a 147 gr bullet at 2700-2750 ft/sec.

It is a Berdan primer but I am unsure whether the modern Berdan products used mercury-fulminate.

In any case - I know of Musgrave target rifles that had digested 18 000 of those rounds and still winning Bisley shoots, this was in 10

[MusgraveMan]

Apologies...stupid laptop touch pad..

The one Musgrave target rifle I mentioned that had won the SA Bisley in 1974 had done more than 18,000 shots with the same barrel and for all I know had been going on for years after that. Even with corrosive primers if the barrel is cleaned the same day of even a 100 round shoot you will never have a problem with throat erosion.

As we speak my son in South Africa who hunts with a BRNO ZKK Model 601 .308W is sitting with a military round 7x51 in his hand with the R1M1 head stamp but of an earlier date. I'll get you more info shortly.

My own Musgrave Model Vrystaat .30W sporter, after 40 years (and off-the-shelf as it was) still consistently shoots sub MOA with R1M1 military ammunition.

[MusgraveMan]

Pete,

Your ammo is the South African manufactured military round. It is of very good quality. R1M1 is the head stamp for that manufacturer, and the purple primer sealant is unique to it. It was indeed made in 1981. The propellant would be from the SomChem factory in the Western Cape - a region that may be more known for its world quality wines than for its wide range of propellant manufacture! The cartridges would be made my Pretoria Metal Pressings (PMP) for the assembler.

That is a high pressure cartridge - typically 55,000 lbs/sq inch.

What rifle are you shooting? Let me know what groups you get.

I am getting you the proper info on the primer chemistry.

[MusgraveMan]

My best information is that since the change was made in South Africa from cordite propellant in the .303 British military round to nitro-cellulose in the 7.62x51 only "clean" primers were used. No mercury-fulminate in the compound.

You can shoot your R1M1 with confidence.

[cbrpete]

Thank you so much for the info. Pete

[gwp]

MusgraveMan, I have PMP M1A3 0 40D99 7.62x51mm with this headstamp; JJ at 12 o’clock and 7.62 at 6 o’clock. I would like to know what JJ indicated.

Thanks
gwp

[barkerwc4362]

It is not the mercury-fulminate that makes the primers corrosive, it is the potassium-chlorate. Mercury-fulminate has not been regularly used as a small arms priming compound for almost a 100 years. Mercury-fulminate primers when fired release mercury which combines with the zinc and copper in the brass cartridge case causing the case to become brittle. Not a good thing! Potassium-chlorate compound primers (what we normally consider as corrosive and a very stable compound, which is why militarys are reluctant to stop using them) when fired release various salt based compounds, which if not cleaned properly and often will quickly form rust in firearms. Also not a good thing!

Bill