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Discussion Starter · #1 · (Edited)
I chopped my 336 barrel and got around to carefully notching the relief slot in the barrel to allow space for the barrel band screw.

When it was all said and done, I had to cut into the barrel about .070".

I did some calculations to determine how much barrel wall I have left under the barrel band screw and here is what I get:

Barrel thickness at notch location = .675"
Bore size = .311" (well, that is what I size my cast bullets at)

So, I subtract the two numbers and get .364".

I then divide by 2 and get the wall thickness of the barrel wall at where the barrel band is and it is .182". Now, I subtract my .070" slot cut and get .112". So, I for sure have more that 1/10" (.100+) of barrel wall thickness underneath the barrel band screw.

I did the same calculation for the factory slot and get a measurement of about .075" wall thickness, so I am better than factory, but.......I am not sure, maybe my shorter barrel might run at higher pressure and is .112" ok?

So bottom line, am I still ok with a little less than 1/8" (.110"-.115" ish) of barrel thickness under there??

Thanks!
 

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If the notch is closer to the chamber than the factory notch pressure will be higher at that point. I recently read an article that dealt with drilling and tapping a barrel and it listed two ratings - one for over the chamber and another deeper allowance for the rest of the other barrel length. I do not have the link but I suspect you will be fine. I will try to find it and will post it, You may find it searching on the net for 'drilling and tapping barrels'. AC

here's a link of interest: http://www.practicalmachinist.com/vb/gunsmithing/scope-block-hole-depth-what-safe-260558/
 

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Gunscrewguy is correct in that pressures will be higher at the chamber area, but your .112" wall will be fine..............No need to worry with any load.

In fact, if you were to consider that the C/C distance between the Bore and the Mag tube is .750, and then look at the MagTube Clearance cut under the barrel of a 45-70, you'll see you have nothing to worry about..........I can't recall the actual wall thickness there, but its the weakest point in the 45-70 Bore, and it handles every SAAMI spec'd load fine.

Also, consider that your .112 dim is only correct (real) for a VERY small area at 6 O'clock on the bore...........

Pull the trigger.........NO worries.

Tom
 

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Discussion Starter · #4 · (Edited)
Thanks. My loads are usually moderate anyways. The location of the notch is about 3" from the muzzle. I read the link http://www.practicalmachinist.com/vb...t-safe-260558/ and even for a big #10 screw, they recommend about .100" thickness for non chamber area. A #10 screw has a diameter of .190". My .112" thickness is at one small spot that is most likely much smaller in area than a #10 screw. This is right at 6 o clock and as you go any direction, that thickness only grows.

I am pretty sure I can shoot all day with my moderate loads (28 gr of 3031) and not have a problem.

I found a guy who was doing something similar here Marlin 336 Marauder Conversion Project

He said he had to go 75% as deep as the original factory depth. My factory depth was about .095" and mine is .070" for about 75% depth of the original factory and in a thicker portion of the barrel. I am pretty sure I am OK. Looks like what others had to do when chopping the barrel. The factory notch is at 17.5" down the barrel and mine is at 13.75" down the barrel. I wonder how much more pressure the barrel sees at 4" less? It will be more, probably 125% of the 20"? Who knows.
 

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Actually, The depth of the tapped holes for the front sight ramp come within .020 /.030 of breaking thru to the bore, and the drill point is 140 degrees.........NO problems there, either...

I just thought you should know this to put your mind at ease.

Tom
 

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Then you can consider ported bbls don't hurt anything except your ears.
 

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Discussion Starter · #7 ·
I also just checked the fore arm barrel band screw location. The relief is .090", the barrel is .690" thick there and the wall thickness of the barrel is .100" thick. This is 4.5" TOWARD the chamber. So, I have been shooting all along with a similar notch in the barrel with no problems. The only difference is my notch widens by about .050" toward the top compared to the factory notches, but this is in the thick part of the barrel.

Pic of the rifle so far...need to drill and tap for the front site and mount the scope. (I don't really need the front site, but just want the option). I also need to shorten the forearm wood by about 3/4".

The barrel is threaded for mounting a suppressor and is currently wearing a thread protector.
View attachment 142808
 

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Discussion Starter · #8 · (Edited)
Ok,
Some pictures of my handy work. My slot is ugly, but functional. Once the barrel band is on, no one can see it anyways. Again, the thinnest part of the barrel at that slot point is .112", the slot for the forearm screw makes the barrel .100" thick at that point closer to the chamber. So my slot is not the weakest point, rather the factory forearm slot, which seems plenty strong enough. I am not worried anymore about this.

See my ugly slot!


Sideview of my ugly slot!


Picture of my slot compared to the factory one. My slot is .050" wider at the biggest width (in the thick barrel portion), but not as deep as factory slot. The factory slot left .076" barrel and mine leaves .112" barrel thickness, since I am in a thicker portion of the barrel and didn't go as deep. However I am a little wider. The screw was hitting the sides a lot, so I had to widen the slot accordingly.


Pic with thread protector on.


Pic with no thread protector

Cant wait until my paperwork for my suppressor is approved!
[URL=http://s3.photobucket.com/user/jmortens/media/b87a8887-d59b-4b3d-8d9e-426e3d204984_zpsddc9wdco.jpg.html][/URL]
 

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Discussion Starter · #9 ·
Had a guy run a pressure curve for 30-30. The location of my barrel band @14" will see about 10,000 PSI versus the factory band @18" seeing about 8000 PSI.
So, my barrel band location will see more pressure, but the barrel in this location is about 33% thicker to make up for the pressure difference. Should be good to go.

 

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Discussion Starter · #10 ·
Pulled the trigger....no problems.

Pulled the trigger. No problems. Here is a video of a suppressed Marlin 336. The supersonic 30-30 loads I fired sounded non suppressed .22, I put my ear plugs after shooting a few as the noise was getting annoying, but not something that would be a problem when hunting and shooting a few rounds. I was in a forest with trees so it really echoed back the sound. What surprised me the most was the recoil was reduced by almost half than usual.

The subsonic rounds I fired were like a small nail gun sound. No hearing protection needed. Fun versatile platform.
http://vid3.photobucket.com/albums/y94/jmortens/Marlin 336 Suppressed_zpsxy72nims.mp4

If the notch is closer to the chamber than the factory notch pressure will be higher at that point. I recently read an article that dealt with drilling and tapping a barrel and it listed two ratings - one for over the chamber and another deeper allowance for the rest of the other barrel length. I do not have the link but I suspect you will be fine. I will try to find it and will post it, You may find it searching on the net for 'drilling and tapping barrels'. AC

here's a link of interest: Scope Block Hole Depth...What Is "safe"?
 
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