Micro-groove rifling

[middy]

What year did Marlin start using their micro-groove rifling?

I have a 1974 Glenfield 36A and I'm not smart enough to tell the difference by looking, so I'm just wondering... I hear jacketed bullets work better with micro-groove and lead work better with standard rifling.

Lovely rifle for $150 BTW, except for the birchwood and the pressed checkering

Correction: It's a 1972 Glenfield 30A

 

[kaferhaus]

I have one made in 72 and it's mirco-grooved.... lead bullets are a no-no.

I paid $100 for mine along about 2002.... the old fart I bought it from gave me the receipt ....he paid $129 for it new.

 

[Steve F]

Does that mean that copper jacketed rounds are OK,just not cast lead rounds?

 

[kaferhaus]

jacketed work great.... mine will honestly shoot 3 under an inch (100M)almost religiously with factory federal 170gr flat points..

 

[Vern Humphrey]

Ask the gun. Many Marlins with microgruv rifling will shoot cast bullets very well.

 

[Jim Watson]

Marlin went to Microgroove rifling in the mid-1950s, I have a 1957 Shooter's Bible describing the transition.

It is ok on .22s and low pressure jacketed bullet cartridges like .30-30. Marlin once chambered and threaded an unturned .30-30 blank and put it on a 336 action without the tube magazine and just a rough cut foreend, and it shot MOA with factory loads.

The Microgroove .222s Marlin built on Sako actions were noted for short barrel life. I don't know of anybody who shot one of their .30-06 FN Mauser action rifles to find out how long it lasted.

Some people can get a Microgroove barrel to shoot cast bullets, some can't. Three of us tried everything we could think of or read or hear about but never did get a .44 more than barely adequate for large close Cowboy targets.

 

[P95Carry]

With a good bore light - the difference should be fairly apparent. I forget the lands/grooves density with micro-grooves but it is more than std. Maybe twelve sets or more. Engraving possibly in region of 0.5 thou? Not sure offhand.

Std button rifling probably 5 to 6 - too lazy to check my Win 94!! Engraving probably in order of 1 to 1.5 thou' - up to 2 maybe.

The critical factor with lead in micro - is IMO the lead sizing and hardness. fact is - the engaving is so shallow with micro - too soft a lead will just charge on thru stripping off lead!

If - and I have yet to try - I could lubrisize for my 44 mag Marlin - so as to have a genuine .430, and - hardcast, with gas check - I think it might be workable. But a too-soft .429 is probably not gonna do. I stick to MagTec .44's for now in that gun - probably won't change!

 

[ClarkEMyers]

Microgroove bore and groove diameters are DIFFERENT

Microgroove bore and groove diameter is DIFFERENT. The bore diameter is a little above expectations, the grooves are a little shallow as compared to more conventional or commonly encountered rifling patterns. The claim was the bore cross sectional area made a better match with the bullet cross sectional area.

Given a perfect rifle cast bullet with a .308 engraving band and a .300 bore riding pilot the bore riding pilot will be undersize and the engraving band oversize. Gas checks may not be that good a fit either.

Lots of other things to argue about - 2 groove Springfield vs. 5 groove P17 for cast bullets - I like the 5 groove P17 - my point is there are differences all around us.

Hardly shocking that size matters in cast bullets. Many people report good results with cast bullets in Marlins but in my experience not the same cast bullets so.....

 

[JohnKSa]

From everything I've heard, the microgroove barrels do just fine with lead bullets as long as the bullets aren't too soft, and as long as they're matched to the bore.

The guys who always seemed to get good results slugged their bores to determine ACTUAL bore diameter and then went a thousandth or two larger for their bullets.