Frustrated with MicroGroove

[The Blade]

I cast and shoot lead bullets in all of my handguns, and for my 1895 45/70.  Those work pretty good.

A couple of months ago, I pulled out the old microgroove 30-30 and decided to work on the thing until I was able to get acceptable accuracy from cast bullets.  I shot several groups before I did anything to the rifle, and at 50 yards with 311041, was only able to get 2.5 inch groups.  The load was 26 grains of 3031.

I slugged the barrel, and found that it had a 0.02" constriction about midway down the barrel.  After a great deal of work firelapping the barrel to remove the constriction (which, for reasons that I won't go into here, I'll never do again) I set out to the range to shoot my newly reconditioned barrel.

The post-firelapping groups that I shot were loaded with the same bullet (311041), cast with WW, 2.5% tin added, and waterdropped.  The bullets were sized to 0.310" (the bore slugs around .309", but I've had trouble getting a consistant reading on this.)  The first 20 rounds were loaded with 10 gr Unique, and these bullets grouped around 1" at 50 yards, which is about all that I expected.  No leading.

Then, I started shooting groups loaded with 3031, beginning with 22 grains.  The following sets included 22.5, 23, and 23.5 grains 3031.   The 22 grain load should have had a similar velocity to the 10 grains of Unique.  I cleaned the bore after each 5 round group.

ALL of the 3031 loads leaded the bore severely.  Not only was there lead in the bore, but it came out in long thin pieces matching the geometry of the grooves.  Each time I cleaned the bore, the first patch had 12 pieces of lead on it, each about an inch long matching the groove.  It seems that the lead bullet was shearing off into the grooves.

These bullets loaded with 3031 were not loaded very hot.  I can't understand why this bullet won't shoot any faster than 1500 fps without leading severely.  Am I expecting too much from a cast bullet in a microgroove 30-30?

[Graycg]

The low load of your 3031 loads may not create enough pressure for your bullets to bump up to seal the bore and has gas running around the base of the bullet allowing the leading to occur as the the gases melt the sides of the bullets to  your bore.  You might get better accuracy with a softer bullet and the same loads or use a higher load to get the pressures up.  I shoot 2000 or so cast 30-30 bullets per year out of my 788 Remington and find the best  powders are 4227, 2400 for velocities up to around 1800 fps and reloader 7 for full velocity loads.  I like your bullet choice and have great results with the 311041 and the 311291.  I also have some custom moulds, but find the 311041 tought to beat.

my opinion only,
 regards  Graycg

[Nobade]

Wow, did you really mean to say you firelapped out twenty thousandths? If so, I'd throw that barrel away. Even two thousandths (.002) is a huge amount of constriction.
Either way, my secret for Marlin 30-30 performance is to first figure out just how big a bullet you can get away with. In my case it's .312 if I keep the chamber clean. I cast the bullets plenty hard, using range scrap and water quenching them. Gaschecks are a must. The best bullet I have found for it is the Lee C-312-155-2R. It is too long (and pointed) to feed through the magazine and won't eject unless it's been fired. But it groups like you wouldnt believe and has accounted for a heap of cowboy silhouette match wins. If I want a repeater I use the RCBS 150gr. flatnose, mould lapped out to .312. It shoots nearly as well and feeds fine. Powder choices seem to be cruicial as well. I never have gotten it to work with 3031, but it does well with the faster stuff. So far AA5744 is the best. 17.0gr. gives me right at 1800 fps with the Lee bullet. I haven't gotten terribly good accuracy at higher speeds, but it does't lead or do anything objectionable like yours did.
Oh, for a good lighter bullet try the Lee 115gr. flatnose. It shoots beautifully with Bullseye or Clays at around 1200 fps - great squirrel load.
But after all this, I'd for sure carefully slug that bore, and see what you find. If you lapped out a constriction that big, I'm betting you wiped out the throat and first part of the rifling. Remember Marlin will rebarrel their rifles for a very reasonable fee, and you can have whatever configuration you want from them. Good luck!

[The Blade]

I lapped out a constriction of 0.002".

I noticed before lapping that the 311041, when seated to the crimp groove, would obtain an imprint of the lands when cycled through the action.  After lapping, no impression was made by the lands even when the bullet was seated out so far that it would just barely cycle in the action.

I was able to do this job because the barrel was pretty well beat before I started.  I knew that I might ruin it, but it's no worse than it was before.

Even so, the groups tightened up from what they were before lapping.  My 3 shot groups, with 10 grains of Unique, now run in the 1" range (whereas before they were 2"+) at 50 yards.

I still think it should do better, and I'll take your advice and start looking for a way to throw larger bullets with this mould.  And I'll pick up a Lee Lee C-312-155-2R.

Do you size that Lee C-312 or shoot it as cast with tumble lube?

I'll let you know what happens...

Thanks again,

The Blade

[richp41]

Blade- The Microgroove barrels are noted for not being accurate with lead bullets. That is the prmary reason Marlin went back to Ballard type rifling for their Cowboy Action guns. The shallow rifling just doesn't have enough purchase on the soft lead bullets. However, I've heard of cases where reloaders have used heat treated  bullets with a fair degree of success and you mught want to try that approach.

[Nobade]

I just run 'em through a .312 sizer to crimp on the gascheck, and tumble lube. A dusting of motor mica after the lube dries keeps 'em from being too sticky.

[Graycg]

I think that the idea that Microgroove barrels won't shoot lead bullets is just because folks try to treat them the same as a 4 groove barrel, I have a 357 Marlin that is extremely accurate with cast bullets when prepared in the proper manner.  I won't say they are ideal, just that they can work well if you fit the bullet to the bore, and most marlin barrels are on the quite large side.  I size .360 for my .357 because anything smaller will not group and will cause leading.  If you think about it, all marlin's 22 barrels are microgrooved and they shoot lead bullets very well don't they?  

I think that the ballard style rifling probably is better, but you can make the microgrooves work if you approach the issue with logic and common sense.

again, only my opinion,
 regards  Graycg

[Nobade]

I still maintain the microgroove design would be the best thing going for cast bullets if the quality was there - i.e. the bores were the right size, didn't change size in the middle, and were smooth. I'd love to see a custom barrel maker do some high grade microgroove barrels, it'd settle this debate finally and we could see what really happens. As it is the best we can do is buy old Marlin barrels and lap them as well as possible. I wonder if they ever let any unchambered ones out of the factory? Lap that, chamber it properly, and have a "cheater" cowboy rifle!

[The Blade]

Interestingly enough, I weighed a bullet from the 311041 mould.  The weight was 180 grains; the mould is supposed to throw a 173 grain bullet with Lyman #2 alloy.

It seems that the ingots that I was given (supposedly of WW metal) is actually pure lead.  Although I water dropped them and they did harden up, I believe that the leading problem may be a result of soft bullets.  Maybe I over-firelapped the barrel, maybe I didn't.  

I'll cast up some WW metal and see if the leading is reduced.

More to come...

The Blade

[Joe Kool]

I once loaded cast bullets for my nephew's 336 Marlin 30/30, with the Mirco Groove barrel. I used Lyman #311466 cast of wheel weights +2% and water dropped. I used a fairly heavy charge of IMR 3031, don't remember the exact amount without looking through my records. The groups were an 1.5" at a 100 yds.. But the gun had a strange quirk. The first shot would be 2.5" high, then the following shots would group an 1.5", but 2.5" below the first shot. If the gun cooled for about a half hour, the first shot would again be 2.5" above the main group. I got good groups with little effort, just the first shot from a cold barrel was always high. I never solved the problem, I did work with the gun very much.  

[The Blade]

Success!

Using bullets cast of WW and 2% tin, sized to .310", and loaded over 22.5 grains of 3031, I acheived 0.5" groups at 50 yards today.  I estimate that the velocity is in the neighborhood of 1600 fps.

It's all in the alloy and the diameter of the bullet.

Microgroove ain't so bad after all.

Next, to improve on that...

The Blade

[Joe Kool]

The Blade, with cast bullets, velocity is very important. I've read a few articles that said for accuracy, to keep the velocity at 1700-1750 fps. This is an old standard that has been used by cast bullet, target shooters for a long time, as I understand. I my experence this seems to be true. In general it don't matter what bullet or powder is used, if the velocity is held at 1700-1750 fps., most of the time at least good accuracy will be achieved. By playing with different powder and bullets, in plain, sporter, hunting rifles, getting groups near an inch or even under an inch, at 100 yds. is not uncommon. It sounds like your 30/30 is shooting pretty good. If you shoot it at 100 yds. let us know what kind of groups you get.  

[w30wcf]

The Blade,

Sorry I came in late, but was happy to see that you worked out th e problem.

With regards to micro-groove rifling,  it actually has more (100%!) of a purchase on the bullet!  Since 1968  .30-30 micro-groove barrels have the same bore and groove dimensions as a ballard cut barrels (.300/.308).
(Prior to 1968 the grooves were shallower.)

I have a 336A .30-30 w/ a micro-groove barrel and I can push 150 gr. cast bullets w/ gas checks to 2,400 f.p.s. with good accuracy and no problems whatsoever.

w30wcf

[Darrell Davis]

See that this topic started back a bit, but may as well throw my nickle into the hat.

I personally would guess that most of the bad press about Micro Groove is just that, bads press.

My experience is limited with that barrel, but if the .44mag I had (wish I still did) is any example, they shoot great with cast.

Shot the same 310gr LBT, load and all, that I shoot in my RH. Water quenched WW, sized .430 and lubed with my very secret (ha) home brew lube.

The only problem if you wanted to call it that, was the fact that the 310gr LBT is a bit long and care was needed when working the action. It was a good thumper and shot great. :wink:

[The Blade]

Darrell,

My microgroove 30-30 now shoots four out of five in a five shot group under 1" at 100 yards.  Sometimes the 4 will be in a half inch or less at this range.  

My original frustration with microgroove has now changed significantly.  Now that I have the alloy, bullet diameter, and powder charge right, it's a GREAT cast bullet shooter.  It just takes time to figure it out.

I didn't even have to use a secret lube...just plain old Lee tumble lube!

The Blade