Marlin 336C Dimpling Primers on Load

[Airgead]

I was helping my dad do a detailed clean of his Marlin 336C in .35rem. Running a function test of running a round from the mag into the chamber and then ejecting it, I noted that the primer has a light dimple from the firing pin pushed into it. I did more testing and found that it happens as the level is squeezed "home" in preparation to fire but the depth of the dimple corresponds to the energy used to work the lever. Working the lever with what I would consider "firm" force but not slamming it home leaves a significant dimple. I didn't try slamming the lever as I don't currently have any dummy rounds made up (dies on order) and testing on fired brass is obviously not useful.

I'm a little concerned that this older gun (circa 1959) has something amiss in the bolt and is going to result in an unintended discharge if it gets smacked hard while hunting or the lever gets worked too hard -- especially as my dad wants to reload for it and I generally use Federal primers which are known to be soft.

Has anyone see this before? Is this some sort of cleaning issue (doubtful) or is this a job for a gunsmith?

Sorry for the nasty phone pictures. I have to find where my wife has the camera for a macro shot but she's asleep.

 

[rcmodel]

It shouldn't be doing that.

The bolt needs to come out and dissembled to find out what's going on.

It may be packed with dried oil & dirt?
It may be a broken FP?

The 336 has two firings pins.
One in the locking bolt, that can only align with the one in the bolt when it is fully in battery.

There is also a retractor spring that my be broke too.

If you are not comfortable tearing into it yourself?
Find a gunsmith.

http://www.brownells.com/schematics/Marlin-/336-sid774.aspx#s20977sid774

rc

 

[Jim K]

That is a pretty common occurrence, but Hornady may be using especially soft primers. Have you tried another brand of ammo? FWIW, I have never heard of the lever being pulled up fast or hard enough to fire a round.

Jim

 

[herrwalther]

Although unlikely, try cleaning out the bolt first. That is always my first step when my firearm starts doing something it shouldn't. I have the same rifle and caliber has your father's just a bit newer, mine won't do this no matter how hard I slam the lever. So something is amiss. I doubt it is soft primers in the ammo. Comparing primer depths of spent casings from CCI primed handloads, Hornady, and Remington on my 336CS, they look pretty uniform.

 

[Airgead]

I'll have to look closer into a bolt disassembly for a Marlin 336 - never done it before in my 30-30 either. I didn't think this was normal but wanted to check.

 

[rcmodel]

Check the schematic in post #2.

Take the lever screw out and the bolt falls out.

Drive out the two pins in the bolt and the FP falls out.

rc

 

[Milkmaster]

RC has it right. The bolt is not hard to get out of a 336. Just make sure you use a quality screwdriver and subsequent punch to drive the pins out when you are accessing the firing pin. Wish I was closer. I could show you in about 10 minutes. Youtube could also give you some help here. There are several disassembly videos on the Marlin 336. Have a glass of your favorite beverage while watching a gaggle of those videos. Some are better than others, but watching a few of them will give you a good idea on how to do it.

 

[Red Cent]

What RC and MM said. When you remove the bolt, the ejector may fall out of a slot on the left side of the receiver (#89 in schematic). Made that way. Replace the ejector in the slot before you replace the bolt. Slide back and forth to make it fall into proper slot/position. You will feel it. Spring goes into the slot.
This all seems complicated but it is not.
The dimpling of the primer is not right no matter what ammo you are using.

 

[Bart B.]

Semiauto, lever and pump action rifles with free floating firing pins have been dimpling chamberd rounds for decades. Very normal and harmless as they're typically .001" to .003" deep. I don't see any issues from the picture showing them. M1's and M14's always did that.

Rifle primers need about .020" deep dimples before they start firing. That's normally tested at factories making them.

 

[Airgead]

Very normal and harmless as they're typically .001" to .003" deep. I don't see any issues from the picture showing them.

The picture I took isn't that great but the dimple is definitely deeper than .001" to .002". That wouldn't be more than a round mark on the primer.

I'm going to try to disassemble the bolt tonight and clean it. Just haven't had the dedicate time to sit down and do it patiently and methodically.

 

[Airgead]

So that actually didn't take nearly as long as I thought it would. Was pretty simple and obvious after watching a few YouTube videos on the topic. There was some dirt and grime in there but nothing massive that would be hanging up the firing pin and preventing it from retracting. So I have a very clean bolt and firing pin that is still dimpling the primers. I took some pictures with the good camera on super-macro and have attached them here. Could it be something with the locking bolt?

 

[rcmodel]

Was the rear firing pin and spring in the back of the bolt intact and free?

PS: How hard & fast are you closing it to produce the dents??

rc

 

[Airgead]

Yes, they both appear to move freely. The firing pin spring pushes the rear pin down when it's out of the receiver but the rear firing pin is easily pushed into line with my finger. It also is rotating into place when the locking bolt is pushed up by the lever.

I am not slamming the lever shut. If anything, I'm cycling the lever a little slower and lighter than one might normally because I'm suspicious of this potential issue. If I close the lever very slowly and gently, the dimple isn't as deep.

It's almost as if something in the normal cycling is pushing the firing pin far enough forward that it's protruding beyond the bolt face. But I don't see anything amiss with the locking bolt and that would be the only part in play.