12 Groove Micro-Groove Technology

[scottmcwms]

One of my buddies told me that I shouldn't buy a 336 that didn't have the 12 groove micro-groove technology. He said that there isn't anything wrong with the older 6 rifling grooves, but the 12 Micro-Grooves are much better. What are your opinions on this? Also, when did Marlin introduce the Micro-Groove technology. Thanks.

[6pt-sika]

If the micr-groove is so great why is Marlin rifling the large bores with ballerd type rifling :?: I own guns with both types and with out a doubt , I have had great success with ballerd rifling. And out of the more then two dozen Marlin's I own the only two I have accuracy issues with are micro-groove's (out of more then 24 only 5 are micros, 60% success with micro and 100% with ballerd). Now that is just my own personal experience not to say that I am right and any one that says different is wrong. But thats my experience :!:

[Custom Rodsmith]

This taken from the Marlin site FAQ section.

14. Q) Why has Marlin changed its rifling on Models 1894S, 1894CS and 1895SS from Micro-Groove® to Ballard-type cut rifling?

A) To accommodate the use of cast lead bullets.(Jacketed bullets will still function reliably.)

[Bman]

6pt, You shoot mostly cast bullets right?
I have a little embarrassing story about that. I have not read Veral's book and was asking how to fit a cast bullet to a micro groove barrel. One poster told me to match the bullet to the throat. Well I thought he was an idiot since revolver cylinders have throats. Later I found out who the idiot was.

Folks with a bunch more experience than I have explained it this way to me. Most MG barrels will shoot cast without a hiccup. Others need a little bigger slug to fill what is at times a nominally larger bore diameter. In general a little tweaking will find an accurate combination.

[6pt-sika]

No I have about 16 rifles that are cast guns with some jacketed,and the rest are jacketed. As of yet I have not shot a cast bullet in a bolt gun, and I have 6 bolt actions that are shot regularly. I wouldn't consider shooting cast in either my 260 or my 300RSUM. I do have an old 30-06 BDL that might end up digesting some lead . The only two rifles that have given me greif are a new 1894Fg and the 375. And these two don't seem to happy with jacketed bullets either. I'll keep the 375 regardless because they are semi hard to come by , but the FG if it and I can't work out our diffrences by the end of February ...down the road it will go But it might not be the 41's fault, heck the gaschecks for the slugs are even an issue . We shall see what happens :!: It will probably take awhile, every time it pisses me off I put it away for a while. So it might get put away 6 or 8 more times before it's fixed :?

[30wcf]

scottmcwms,

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.

Another myth I've seen is that is that soft cast bullets won't work in a micro-grooved barrel because they will strip the rifling. Hmmmm. A 12 grooved barrel has 2X the purchase on a bullet that a 6 grooved barrel has. .308-.301 x 6 = .042 .308-.301= 12 = .084
I once did a test with a 20/1 lead tin bullet in my 336A Marlin Rifle. I pushed it to 2,300 f.p.s. and it was still shooting accurately. In a 6 grooved barrel, accuracy went out the window at around 2,000 f.p.s.

I will say that I have had nothing but excellent results shooting cast bullets in my 336A .30-30 at velocities as high as 2,500 f.p.s.

w30wcf