I've certainly not seen every 39A manufactured but it seems some have a hole, abotu 1/8" diameter, through the left side of the receiver at just about the bolt head location, some don't. What's the hole for? When did they start or stop putting in or leaving it out?

I am not 100% either, but my guess would be a gas pressure relief. I have a CZ .22 in my safe and it has the same hole. I have many others that do not. I am curoius too as to why now and not before? Why some ant not all?

The hole shows when you have a round in the chamber. I'm not sure when Marlin started using the loaded chamber indicators; it might have been when they went with the cross bolt safety.

The hole shows when you have a round in the chamber. I'm not sure when Marlin started using the loaded chamber indicators; it might have been when they went with the cross bolt safety.

I'VE SEEN NON-CROSS-BOLT SAFETY 39'S WITH THE HOLE.

The hole shows when you have a round in the chamber. I'm not sure when Marlin started using the loaded chamber indicators; it might have been when they went with the cross bolt safety.

That does make more sense than a vent hole for a .22. I just never thought much about it before.

Take it from me leon it's a gas release in case of a rare gas build up. I have a 39A without the hole but it was made in 1958. Maybe too old for the hole. I also have .22 magnum made in 1983 but with the hole and a couple of gunsmiths have assured me it's a gas release. Best I can do john

I finally got around to digging out the owner's manual for my 1897T, which should be the same as for any other 39/39A, and should shed some light on this mysterious hole. On page four, under Unloading Instructions, it has an illustration labeled "Figure J, Magazine Inspection Port".

The text of the paragraph reads as follows: "... inspect the chamber, carrier and magazine carefully to be sure there are no cartridges left. Then check the magazine inspection port on the left side of the receiver (See J). If the magazine is empty, the red follower will be visible through this hole. ..." I hope this helps.

I finally got around to digging out the owner's manual for my 1897T, which should be the same as for any other 39/39A, and should shed some light on this mysterious hole. On page four, under Unloading Instructions, it has an illustration labeled "Figure J, Magazine Inspection Port".

The text of the paragraph reads as follows: "... inspect the chamber, carrier and magazine carefully to be sure there are no cartridges left. Then check the magazine inspection port on the left side of the receiver (See J). If the magazine is empty, the red follower will be visible through this hole. ..." I hope this helps.

That is down by the Mag. tube, not the barrel/chamber area. You cannot see the red follower from that hole. I do also believe like my first statement that it is a gas release. I have a 700 remington with the same hole. No way to check the mag. from that hole.

I havent looked at the 39 lately, like for about 12 years.
It wouldnt be one of the drilled and tapped holes for the peep sights would it. Those holes normally have a blank screwed into them when not in use and they where standard on marlins for many years up until a couple years ago.
If not, sorry, i cant help

Bob