Marlin 336 keyhole-ing - Cleaning suggestions?

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Paul_TO

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Hey all,

Looking for some advice. About to take my late father's Marlin 336 30-30 from 1957 out to do some trouble shooting.

The last time he fired it (about 12 years ago) it was keyhole-ing and he assumed it needed a new barrel. He had it from the late 50's or early 60's (originally it was barrelled in .22, and he had it changed to 30-30 in the same timeframe) and shot deer extensively with it up until 12 years ago. From my research, the keyhole-ing is most likely the result of fouling. Although all his guns are in great condition, his cleaning supplies are all from the same era, and I'm thinking they didn't actually do anything for copper fouling, despite his best efforts.

Crown Pictures

Album with shots of the crown. I believe that is copper fouling.

I've tried Outers Nitro Solvent with a brush, and it doesn't seem to budge. I'm planning on getting a new brush (the old one is pretty worn and dirty) and a foaming bore cleaner. I don't see any crown damage, and although I don't have a bore scope, pulling the bolt and peering down doesn't show any obvious damage.

I've also read that ammunition choice can be a huge factor as well.

Any other suggestions?
 
Believe it or not, yes .22

336 Zipper

Essentially a 30-30 case with a .22 pellet loaded in it. My father made incredibly outlandish claims at the distance and accuracy he obtained with it vs groundhogs.

Is brass the best brush to use? I hear people saying nylon is superior.
 
Bowyer said:
Rate of twist and/or bore diameter might be causing it. What type of barrel was installed?
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Marlin RC cal 30 - 30 Micro Groove.

The gun is probably just pissed that its no longer the rare zipper anymore.

Do you still have the barrel ?
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Nope. It was swapped out only a few years after he got it, so early 1960s. It had a much more powerful scope on it, and my Dad traded a gun smith the scope for a new barrel and installation, new scope, and 2 boxes of 30-30 shells.

It was still in production at the time, so no one knew how rare it was going to be. With the new barrel it's a pretty common gun now. I sighed deeply when I learned about the rarity of the zippers.
 
My books list the Marlin 336 /Rem 788 as a 1-10 twist as opposed to everything else Win 94/64 at 1-12" No reason it won't stabilize 150-170 gr factory as that's what it was made for? I've loaded 180RN in a Win 94 and an H+R 158 and had great accuracy. Are you sure they didn't put a .32 Special barrel on it? Micro-groove rifling came in 1955......Harold
 
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Slugging the barrel was my first thought as well.

Don't even want to imagine how much fouling it would take to cause this problem! Copper fouling, or lead because someone was casting his own bullets? I've read that microgroove barrels don't mix well with cast bullets.

Most common cause is an over size bore, from what I've read, and not by much, either. One article was about a 30 caliber with a bore dimension that was .311 instead of .308. Same problem with bullets tumbling. Apparently this isn't uncommon in earlier made big bore Winchester levers.
 
I have 2 - Marlin 30-30 rifles, a 336 and a 336A [24" barrel] Both are Micro-groove units, and both are like new.
The Carbine keyholes the 160 FTX bullet, about 1 out of 8 shots. However, with the Speer or Hornady 170 grain
bullets designed for the 30-30, It shoots amazing groups, without any keyholes.
The Rifle with the longer barrel, does not keyhole any bullet, including that 160 FTX, and shoots about as well as
the carbine does.
One observation I have made, is the Micro-groove rifling is different in these rifles....one has more lands and grooves
than the other. In researching that, I found that Marlin has marketed about 3 different styles of Micro-groove.
Whether this has anything to do with your issues or not, I cannot say, but I would try a different bullet before getting
too excited about the keyholing issues. D.
 
If the bore looks really gungy start with a few passes of nitro solvent but if that's not doing much get something specifically for copper and a new brush. Brass will be affected by the solvent stainless won't.

You want it clean before moving on to slugging the bore anyway. Measuring the twist will let you know if that can be eliminated from the list of possibilities too.
 
Cleaning with Barnes CR-10 solved a key-holing .22-250 Remington 788 for me. I won't argue with anyone saying some other product is better, that's just what I tried and it worked.
 
As stated, these guns were made overbore.with micro groove rifling, these guns wear out a lot quicker than conventional rifled guns. I'd try and re-crown first. If that doesn't fix the problem, you need a new barrel.
sir_springer said:
Slugging the barrel was my first thought as well.

Don't even want to imagine how much fouling it would take to cause this problem! Copper fouling, or lead because someone was casting his own bullets? I've read that microgroove barrels don't mix well with cast bullets.

Most common cause is an over size bore, from what I've read, and not by much, either. One article was about a 30 caliber with a bore dimension that was .311 instead of .308. Same problem with bullets tumbling. Apparently this isn't uncommon in earlier made big bore Winchester levers.
Click to expand...
 
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