Still learning!! Marlin lever guns

Eagleye

Eagleye

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So, I am still finding out things I did not know before.

I have 2 - Marlin 336 Lever actions in 30-30. One is the regular carbine, the other is a 336-A, with a 24"
barrel and half magazine.

These rifles are amazingly accurate with loads they like [different bullets preferred, mind you]

However, when cleaning them up after a shooting session, I discovered something interesting.
Both these rifles have micro-groove rifling, but the rifling in one is different from the other.

The 336 A has 12 grooves and has a bore of about .302" The Carbine has more grooves [looks like about 16]
and they are shallower, with a bore of about .304"

It showed up on cleaning patches....I noticed the finer lines from the one rifle, so took out the bore scope and had a look.
Has anyone else seen this variation? Obviously there was a production change somewhere along the line.

Regards, Dave
 
Found this on marlinowners.

"Micro-groove rifling first appeared in the mid 1950's. The first type in.30 caliber barrels had 16 lands and grooves grooves. In the late 1950's - early 1960's they switched to 22 lands and grooves.

These early types had bore dimensions of around .305" and a groove dimension of around .308" which worked fine with jacketed and Loverin type cast bullets where most of the bullet was full groove diameter. It did not do well with cast bullets that had a bore riding section which typically measured .300-.301" because they did not fill the bore.

These bores were too large to provide the proper cast bullet support and less than desireable accuracy was the result and is probably the main reason that micro-groove got a bad rap with cast bullets. The other is using too soft an alloy and trying to push it too fast, which would also give problems in a 6 groove barrel. Obviously, shooters in the know could have their mold modified to match their rifle's bore dimensions and accurate shooting would return.

In 1968, the 12 groove rifling was adopted, the bore dimension was reduced to .300-.301 which, in my experience works very well with cast bullets since it will provide the proper support to bore riding bullets.

Interesting that Marlin would say that it changed to Ballard type rifling to accomidate the use with cast bullets, WHILE THEY STILL USE MICRO-GROOVED RIFLING IN THEIR 22's! It's a case where legend has overshadowed reality.
 
That time given for the 12 groove models worked out for the big bores I have. The 45-70 is a 1974, the second year they came out with the modern 45-70.
The 444 is a 1982 and the 44 mag is probably early '80s, plus the 22 Golden Mountie is in the '70s.
They all work very well with cast bullets.
 
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