30-06 with FA 'dot' 51 'dot' headstamp


#1

While these cartridges are not too uncommon, I had never seen a full box before I picked up pictured here in a mixed lot of boxes. I would have expected the label to give at least a hint as to the reason for this special headstamp. Has any additional information come to light since the publication of Chris Punnett’s 30-06 book that might indicate what the dots are supposed to tell us?


#2

Guy

Since there are also FA 50 “dot” cartridges in the Light Rifle experimental series (T1E3), it would seem that it was something that FA was experimenting with Arsenal wide. Hackley thought that it signifies cases “. . . made with a special pocket sized for the P4 primer.”, whatever that is.

Ray


#3

Ray,
The silver colored primers on these are unusual; they have a dull finish, and may be zinc plated. As this is quite apparent, there would be no need for the dots, unless there is something else about them that was not standard. Chris mentions a plastic disc in the bottom of the primer pocket that was experimented with in the late 40s and early 50s to prevent a reaction between the red phosphorus in the primers and the powder. I’m getting the urge to section one of these.


#4

Guy

The primer in the FA .50. T1E3 cartridge that I have looks exactly like all the others. But if there’s a plastic disc in the bottom of the pocket wouldn’t the pocket have to be deeper to accomodate it? Or the primer made thinner? If I had a bunch of them I’d section one. Unless Chris or Paul has already done it???

Ray


#5

I couldn’t resist the urge to section one of the cartridges. It does have a thin disc in the bottom of the primer pocket - it is reddish-brown plastic or paper. I have been having a time getting it to show up in a picture. My camera has no close-up capability, so I tried shooting through a magnifying glass. The results aren’t great but the disc can be seen in this picture.


#6

I can see a project on the horizon for the Alberta cutter . . . this would be a neat variation to have in the drawer!

Thank you, Guy!

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#7

So now we need some measurements. If the pocket is deeper it would seem to indicate that the primer is the P4 as mentioned by Hackley. But that’s just one SWAG on my part.

Anybody got a bunch of the FA .50. T1E3 cartridges?

It appears that decapping an unfired case would ruin the prmer disc.

Guy, if you took that photo thru a magnifying glass you’re a better photographer than most of us here.

Ray


#8

Ray,
It was actually quite easy to take the picture, once I rigged up the jig to hold the cartridge and the magnifier, which was the lens from an old video recorder, in place.

Here’s the setup:

and the image in the lens:

and the resulting picture after I had cropped and enlarged it, and then fiddled with the balance (brightness, contrast and gamma) to the point that the disc would show up:


#9

Ray,
I took some measurements:

The base is .200" thick; the primer picket is .131" deep. I didn’t remove the primer to measure it, but it appears to be standard diameter.


#10

Guy

.131" primer pocket depth is very close to the .30 Service Cartridge standard of .125 + .004 tolerance. To make an accurate determination would probably require disassembly and exact measurements.

Ray


#11

My measurements could hardly be called exact; perhaps more like ‘looks about right’. I’d be happy to send one of these to someone who would like to take a more scientific approach to dissecting and measuring it.

I will say that the disc is thin enough that the seated primer could possibly fall within the tolerences allowed with a standard primer pocket.