Micro-Groove rifling and cast bullets?

[jlwilliams]

  I heard that micro groove rofled barrels don't like cast bullets?  True, false, or somewhere in between?

[sidewinder319]

They will shoot cast bullets. Problem is it takes a very over sized bullet. The Browning 92 .44 Mag has a Micro-Groove barrel. The one I have takes a .432 cast hard with a Gas check. Problem is these are not interchangeable with my Mdl 29. There is a fellow on the web who sells custom Lee Molds for Micro-Barrels only. I would not buy another Micro-Groove barrel of any kind. I cast my own bullets and even though MG will work they are not a good choice for cast.

[jlchucker]

I have shot cast bullets from Marlin Microgroove barrels in the following calibers:  30-30, 35 Remington, and 45-70.  I've loaded cast bullets for these rifles since I started casting in 1974.  I've only got one 45-70 Marlin, but have had several different rifles in the other two calibers.  All have been Microgroove, and I've never had any accuracy problems with my cast bullet loads.  In my 35 Remington, I find the RCBS 200 grain flatnose cast bullet to be slightly more accurate than jacketed bullets.  If you handload, and are careful with your loading procedures, you should have no problem at all.  Before you begin loading though, slug your bore to find the proper diameter cast bullet you'll need.  I'm not much of a handgun shooter, and my pistol caliber leverguns have Ballard rifling, so I haven't encountered the situation that Sidewinder has.  That having been said, though--every gun is different. What is an optimal cast bullet for your rifle may not be optimal for your handgun of the same caliber, microgroove or not.  I cast my own bullets, and do not rely on storebought cast bullets in any of my rifles.  I certainly wouldn't pass up a bargain if I found a Microgroove Marlin in a caliber that I wanted, in good shape.

[mauser98us]

I got a smoking deal on a 1949 Marlin 336 in 32 Special that was all beat up and had a sewer pipe tube. I located a new barrel for $35.00 and restored the rifle. All I shoot are cast slugs thru it. It does just fine.

[quickdtoo]

http://www.leverguns.com/articles/fryxell/microgrove-barrels.htm 

There has been a great deal of concern over the years about whether or not Microgroove rifling would shoot cast bullets well. One group of folks says that Microgroove rifles can't hit a barn from the inside with cast bullets, one group says that Microgroove barrels shoot cast just fine just so long as velocities are kept below 1600 fps, and one groups says that Microgroove barrels shoot cast just fine at full throttle. The key to success with cast bullets in a Marlin with Microgroove rifling is to keep in mind that these barrels tend to have oversized groove diameters, and that the grooves/lands are shallow. Therefore, in order to get proper engraving (and minimize "slippage" of the cast bullet as it enters the shallow rifling), it is necessary that the bullet completely fill up the groove diameter of the barrel, and engage the maximum amount of the driving surface of the lands. Since Microgroove barrels are commonly oversized, this means that the cast bullet must also be oversized to effectively "fill up" the grooves. Other factors that also contribute to good accuracy with cast bullet in Microgroove barrels are the use of a GC bullet (which helps to provide a better grip and seal), and making sure that bullet are cast hard enough for the application (generally a BHN of 12 or more). It is also worth remembering that throats in modern rifles are almost always cut larger than groove diameter of the barrel (to insure that ammunition can chamber easily), and that best cast bullet accuracy is obtained by fitting the bullet to the throat, hence reinforcing the need for oversized cast bullets in Microgroove barrels (for example, the throats on my .30-30s run almost .311", so I size cast bullets to .310" for these guns).

Examples of Microgroove barrels shooting cast bullets accurately are easy to find. For example, I have a Marlin 1894 in .41 Magnum that was made in the first production run about 20 years ago. I don't know the throat diameter on this gun, but it shoots it's best with .412" bullets. Bullets sized .410" don't shoot well at all, and while .411" bullets group so-so, they have a really annoying habit of throwing flyers wide of the group by a notable margin. In this levergun the NEI .410-260-GC (#215F) is the key to success. I cast these bullets to a BHN of 13, size them .412" and lube them with homemade moly lube. Loaded over 19.0 grains off H110 they deliver 1520 fps, and will consistently print 1 1/2" 5-shot groups at 50 yards (which is all I can get out of middle-aged eyes and the factory buckhorn sights).

Another example is found in the .35 Remington shooting the Lyman 358315 GC-HP (which weighs 206 grains as it drops from the blocks, when cast to a BHN of 13). Sized .359", checked with a Hornady crimp-on GC, and lubed with moly lube, a very accurate load is obtained by seating these bullets over 36.0 grains of H4895. This combination generates right at 2000 fps, and will routinely group 5 shots into an inch at 50 yards from a Microgroove Marlin 336. The cast HP expands violently at 2000 fps.

Other examples can be found in the .30-30, .32 Special, .444 Marlin, etc., but you get the point. Microgroove rifles can shoot cast bullets just fine -- just keep them oversized, GC-ed and hard enough.

Back in the late 1990s, with the rising popularity of cowboy action shooting and its emphasis on historical accuracy, a whole new group of shooters started picking up Marlin leverguns. Because of their desire to load cast bullets in them, and because of the on-going, nagging (and inaccurate) rumors of poor accuracy from Microgroove barrels, Marlin eventually caved in and dropped Microgroove rifling for a number of their leverguns in the late 1990s. Sales of the cowboy guns have been brisk (especially those chambered for period correct cartridges, like the .45 Colt and .45-70). Marlin helps to feed this nostalgia by referring to these guns as "Ballard rifled".

[jlwilliams]

  Thanks for all the response, guys.  I'm new to casting so I'm starting to look at my various cartridges with a different eye.  My only 30-30 being a Glenfield, I had my doubts about being able to cast for it.  Now I'm feeling better about it.
 
  It would be a shame to not cast for 30-30.

[jlchucker]

  Thanks for all the response, guys.  I'm new to casting so I'm starting to look at my various cartridges with a different eye.  My only 30-30 being a Glenfield, I had my doubts about being able to cast for it.  Now I'm feeling better about it.
 
  It would be a shame to not cast for 30-30.

A shame indeed.  I've got four 30-30's-- two Marlins and two Winchesters.  They all work pretty well with the Lyman 311041 bullets and a Hornady gascheck, lubed with Javalina Alox.  If you can find a mold for it, the discontinued Lyman 311316, originally intended for the 32-20 but sized for your 30-30, with a Hornady gascheck makes a nice, accurate plinker/small game round.  Nothing wrong with a Glenfield.  They are a 336 Marlin with hardwood instead of Walnut. 

[jlwilliams]

  Thanks.  I picked up that Glenfield a while back because I recognised it as a regular Marlin (pre safety) in a lower cost, un-checkered stock.  No problem with that for a hunting rifle. 

[Greg B.]

I cast for a Model 95 Marlin 45-70 with Ballard rifleing. The current buzz for this type of rifling is that you need oversize bullets to better approximate throat size. The jury is still out for me as bullets sized .457 are working better than .459's with the same powder. If I was you I would follow what people are saying about micro-groves and using appropriate cast bullet load data see what results you get. Lee molds are cheap so I could experiment a little without breaking the bank.
 
One thing about Marlin levers is that you have to re-load to the specified overall length otherwise they will jam. Good luck.
 
Greg B.