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Discussion Starter · #1 ·
I am hoping some one who knows the 336 will be able to guide me here a little bit. After my last two range sessions I noticed my primers had 'backed out ' just a bit. The first range session I had used some brass that I had not cleaned the primer pockets out, I know no good for consistent ammo but I did it. I thought that possibly that was causing my symptom. Last trip showed the same thing my primers are moving out about .010 with fully prepped brass. The rifle in question is an older A model 24" barrel and in 30-30. This very well could have happened to the factory ammo I had fired in it earlier I did not check it and have since reloaded that brass. Also right now I don't have any factory stuff to test with.

Now at someone's suggestion I lightly oiled a cartridge and fired it and this backing did not happen. I can see what would be circular rings or tooling marks from the chamber on the fired cases. What I need help with is this do I have a problem with headspace? Or do I have a rough chamber that is gripping the case walls? both are possible my nearest gunsmith that can check this is almost 50 miles away and I would like to avoid a 100 mile round trip if there is a way to determine this at home.

The up side is I have another 336 I plan on using this season as well. I had intended to swap them out but until I find out whats going on here I will just use the other one.
 

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Doesn't sound like headspace to me. What load are you using in these cases? Are the primers holding their shape, or are they overly flat? I would think that oiling the case would only exaggerate the problem, by allowing it to move even more. Did you still get the marks on the case when it was lightly oiled?
 

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A lot of .30-30's have this problem, I experienced the same thing in 94WIN once. Contrary to Marlinman93, I believe it to be a headspace problem. How great a problem depends on how much excessive it is. If you can measure the difference between the back of the case and the protruding primer you can get an idea of the problem's magnitude. If it is greater than .004", then it should be corrected. The rule of thumb on headspace is that .004" is OK, .006" is definately excessive. As the headspace on the rimmed case is determined by the distance from the face of the closed bolt to the face of the barrel, the difference between that and the thickness of the case rim determines whether or not there is excessive headspace. When the cartridge is fired in a rifle with excessive headspace, the firing pin drives the cartridge forward into the chamber and, at the point of ignition, the case tends to grip the chamber at it's thinnest point (the neck) and the expanding gas drives the thickest portion of the case (the solid head at the rear) back to meet the bolt face. If your loads are not particularly warm, the case won't make it back to the bolt but, the primer will back out. This thins the case out forward of the rim about 1/4" and shows it self in a lengthened case. You can check this by bending the end of a papaer clip 90 degrees and sharpening it to a point. Running this point down the inside of the case wall will often reveal the beginnings of a case separation not visible from the outside. This is an indication of excessive headspace. You stated that the primers are backing out about .010", I wouldn't shoot the rifle until I checked it with a "NO GO" and/or a "FIeld" headspace gauge. If it will close on a "FIELD" gauge it is horribly excessive and if it closes on a "NO GO" it's just excessive. In either situation, it should be corrected by a gunsmith or returned to Marlin for repair. I would opt for Marlin as they have given me great service in the past.
 

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Bman if you don't have headspace gauges you can take a 30-30 case no bullet, primer or powder. Now get a peice of tin, brass anything .006" and cut it just smaller than the head of the 30-30. Now stick this on the back of the head ( supper glue, greese anything just to hold it). Now put this in your rifle and see if it will close? If it does, don't shoot it. Get it to a gunsmith or better send it back to Marlin. Good Luck >Tombstone
 

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Discussion Starter · #5 ·
Well I guess for Christmas I will send her off to Marlin. I tried the shim thing and quit when the action closed easily on a .010 shim.

Reckon with proper head space it will shoot any better? Turns is very good groups now...

Thanks for the help!

Brian
 

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Bman, it may not be a headspace problem. Primers back out a little in my '76 model 336A. However, the bolt will not close on a no go gauge so I know excessive headspace is not the cause. Do yourself a favor and get a no go gauge or have a gunsmith check your gun before you send it off. This is a fairly common happening with lever action .30-30s. If your rifle won't close on the no go gauge, forget about it and enjoy shooting.
 

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There's another way to check the headspace.
Take a primed case with no powder or bullet, sized full length, and chamber it. Then with the hammer cocked, manually push the back of the firing pin firmly forward. Then put a cleaning rod down the barrel, and push the case back. You should be able to see the firing pin move back, or feel it, if there is a headspace problem.
If this method shows perceivable movement, then get it to a gunsmith for a checkup.
 

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Bman if you can close your rifle with an extra .010" on top of a case you have a problem !!! I have worked as a gunsmith and built rifles and handguns in the past. Safety is all that concerns me. Have that rifle checked. It's better to be safe than sorry. >Tombstone
 

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Discussion Starter · #9 ·
Tombstone, I agree I am not a gunsmith and have almost enough knowledge to be dangerous. I understand that one of the things the bolt action crowd say about leverguns is that leverguns have poor gas handleing properties in the event of a case rupture, pirced primer etc. Well I for one do not want to find out I have already boxed the gun up and it will be going back to Marlin soon.

Is there any reason to expect it to shoot differently when it gets back?? Right now this is about my most accurate rifle and I'd hate for that to change for the worse.

Thanks all for the help.
 

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bman,

Maximum headspace is .015".

Best thing next to a go/no go gage is to take a case and measure the over all length. Then insert a fired primer into the case so at least .020" is exposed. Put it in the rifle, close the action and then measure the overall length over the primer. The difference between the two overall lengths is the headspace.

If your rifle does have maximum headspace and you are nervous about
it, you could take the cases you will be using and lightly oil them as you did. I would fire moderate loads in fireforming these oiled cases to reduce bolt thrust. This will allow your cases to fit your rifle's chamber, thus almost eliminating all headspace (with those cases).

Remove all traces of oil and then either neck size only (the Lee collet die is great for this) or set your sizing die so that it does not set the shoulder back.

I have done this with one of my older .30-30's whose headspace is at the maximum limit and it has worked very well over the years.

Good luck,
w30wcf
 

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Hay Bman I was in a gun shop today and on a table they had all kinds of stuff for sale. One of the things was a new 30-30 field headspace guage. Five bucks, I had to buy it after talking to you. It's marked field .070". My info gives a 30-30 .063" as standard, so thats .007 over. I tryed it in all my 30-30s. None would close. That was with Marlins, Winchesters, Petersoli ( rolling block) and a C-Sharps.
I just thought I should let you know. Now I gess I will check a used rifle before I buy it, just because I can. It's also good for 32 spl. 32-40, 38/55 Good five bucks spent. Thanks >>Tombstone
 

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Discussion Starter · #13 ·
Tombstone I would have to say that was 5 very well spent dollars. A very good barganing tool as well since a gun that fails will need work to be shootable.

I will do the primer thing soon. I took an old feeler gauge and cut two case head sized disks from the .011 gauge. My 30-30 closed right up. Used the same set up on my .35 Rem and it would not close. So I feel like it obviously needs some attention.

Thanks for all the Help.

B.
 

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Backed out primers can be normal in low pressure rounds like .30-30's. When the firing pin hits the primer, the case is pushed forward until the rim or the case shoulder stops the movement. As the pressue builds the neck expands first and grips the chamber wall. The pressure also will back the primer out. In the higher pressure rounds like the .30-06 the higher pressure will then push the case head backwards toward the breechface. This is what cuts case life in those cases. The stretching to fill the space behind the case is done by the metal just above the case head. A round like the .30-30 doesn't have the extra pressure to stretch the case and so the primer doesn't get pushed back into the case.
 

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Backed out primers can be normal in low pressure rounds like .30-30's. When the firing pin hits the primer, the case is pushed forward until the rim or the case shoulder stops the movement. As the pressue builds the neck expands first and grips the chamber wall. The pressure also will back the primer out. In the higher pressure rounds like the .30-06 the higher pressure will then push the case head backwards toward the breechface. This is what cuts case life in those cases. The stretching to fill the space behind the case is done by the metal just above the case head. A round like the .30-30 doesn't have the extra pressure to stretch the case and so the primer doesn't get pushed back into the case.
 

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Backed out primers can be normal in low pressure rounds like .30-30's. When the firing pin hits the primer, the case is pushed forward until the rim or the case shoulder stops the movement. As the pressue builds the neck expands first and grips the chamber wall. The pressure also will back the primer out. In the higher pressure rounds like the .30-06 the higher pressure will then push the case head backwards toward the breechface. This is what cuts case life in those cases. The stretching to fill the space behind the case is done by the metal just above the case head. A round like the .30-30 doesn't have the extra pressure to stretch the case and so the primer doesn't get pushed back into the case.
 
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