More on Micro Groove rifling

[mdi]

I didn't want to hijack Mr LaRoche's thread so I started this one. I don't own a gun with micro groove rifling (but a Marlin in 45/70 has been tugging at my heart for a while), so this is mainly for my own curiosity. There have been many threads about shooting lead in micro groove bbls and I have an idea about the process, but have other questions. (I really don't like castboolits' search feature). I have been casting for my "standard" rifling guns (9 handguns and rifles) for roughly 22 years but never for a micro groove barreled gun.

What is the percentage of the groove depth of micro groove vs. Ballard? I have a good grasp of the bullet to gun fit necessity, but do the "standards" for Ballard rifling fit micro groove? The same as Ballard rifling? I've read quite a bit of "stuff" about micro groove rifling like "micro groove fill up with lead much sooner than regular rifling", and "micro groove barrels are inherently inaccurate with lead".

So fellers, share your thoughts and experiences with shooting lead in micro groove rifled guns...

Thnx
Mike

I'd welcome any input from Mr. Gibson...

[Harry O]

I have a number of microgroove barrels that I load for in different Marlins. Slug the barrel to find the ACTUAL groove diameter. One or two thousandths over that is fine. I also found that a slightly harder bullet works best, too. Bhn 10-13 works great for me. Do it right, and microgroove will shoot just as well (maybe even better) than conventional rifling.

The microgroove rifling will lead quicker and easier than other types of rifling if the bullet is too soft or too small. When it does start leading, it the grooves fill up quickly. Don't get too small or too soft and you won't have a problem.

[popper]

Interesting about the various types of rifling. Note - Military cannon use 'micro groove' barrels. They work. Don't think the 45/70 is MG. I have a MG 30/30, seems to do OK with soft alloy, for the limited testing I've done. Groups are larger though.
Attachment 229840 M30/30 ~40 yds 175gr RD GC hard 311 with veggy oil lube. Full load of LeverE, from sitting position. 3x9 scope as I can't see worth a darn.
Yes, those 308MX are dandy even with cast -VERY accurate. about 3x the $ of my 30/30.

[MyFlatline]

Harry is right, slug the barrel. All of my Marlin rifles are micro groove. I cast between 10 and 13 BHN and powder coat. Have never leaded a barrel.
I cast for 30-30/308 mx.,35 rem.,444/44,375 and 357 in Marlin

Best of luck.

[Gohon]

The microgroove rifling will lead quicker and easier than other types of rifling if the bullet is too soft

This is only true if one attempts to shoot soft lead at higher pressure than normal. Black Powder shooters are at 20,000 psi and rimfire shooters are at 24,000 psi, both using very soft lead. These shooters are not experiencing barrel leading problems. As long as the casts are .002-.003 over groove diameter, whether hard or soft, your good to go with microgroove barrels. Actually the over groove diameter is a good rule to follow even with Ballard rifling.

[17nut]

Marlin MG barrels are no diffferent than any other rifled barrel.
+.002" bullet and shoot away.

What "killed" the wibe was that Marlin made them slightly bigger thus gas cutting and leading with commercial ammo/bullets.

Here is a pic of my Marlin 94 in 44MAG that is close to 5k (full house lead) shots since last cleaning.

[rwadley]

The new 45/70s are not microgroove. I don't know what year they changed (1998?), but they were microgroove in the 70s, 80s and most of the 90s. They are "Ballard" rifled now.

[gundownunder]

I've never owned a micro groove rifle, other than my .22 39A. Which will shoot sub-moa groups with most standard velocity ammo, and even does it with a couple of high velocity brands.

Apart from the recommendation to go 2 thou over size, the other wisdom I have heard is not to use quick powders, such as Unique. Apparently they accelerate too quickly and don't allow the bullet to engage the rifling, which causes skidding on the shallow rifling, which causes leading.

I've also heard that the tapered bore rider design of bullet is not a good idea because the bore rider portion of the bullet is a smaller diameter than the microgroove bore. This causes the bullet to flex in the bore under pressure resulting in a loss of accuracy.

[JonB_in_Glencoe]

my guess is that some of the problem (people complaining about microgroove barrels) comes from the 44 mag, since SAAMI specs pistol and Rifle different (.002 different).

So when some reloaders (myself included when I first started loading for a Marlin with commercial cast bullets that measured .429, about 15 years ago) load up some 44 mag for their pistols and their Marlin leverguns with the same .429 or .430 projectiles, not knowing that Marlin (and most other manufacturers) makes them with a .431 groove diameter (typically).

[GregLaROCHE]

I love my Marlin .45-70. We’ve been thtough a lot together and if you ever saw it you would understand why. It made my heart sink when I heard about how they were taken over by Remington. Then later the poor quality control issues they have had. I hope they get them worked out. I thought all recent Marlins were micro groove until they were taken over by Remington.

I have been shooting almost only powder coating with mine since I started casting and am now moving into paper patching. I be never had a leading problem even shooting gas check type boolits only powder coated. I’m getting ready to drill out the mold to turn it into a flat base. I’m shooting with pretty rough iron sights and it does fine for what I want it for.

I noticed they are offering them in all different versions now. What I don’t like is the .45-70 version with the six shot tube. I’ve never shot one,even though my so has one. We just don’t seem to be in the same place at the same time with our guns. This long tube loaded with all those cartridges, has got to have that gun way off balance and front heavy. The four shot tube just feels right.

I know that wasn’t much about the micro groove barrel, but you said you were interested in one.

Last word, if you are going to use it as a brush gun, change the rear sight to a solid peep sight. The standard flat sight is way too fragile and will get ripped off in the least little amount of brush.

[wv109323]

The rifling in standard barrels is usually .004" deep with 2,4,5 or 6 lands. Micro groove has 12 to 16 lands and are about .001 or.002" deep. It is common that Marlin's actual bore size is larger than nominal bore size. Given the larger bore size many times a mold will not cast large enough to be used in a MG barrel. A .357 barrel on a Marlin may be .3585 actual and needs a .360 or .361 boolit. The mold may only cast .359 with your alloy. You will need to beagle your mold or powder coat your boolit to get it to shoot.
Lead hardness can enter into the equation when boolit diameter is less than optimal. Of course smaller boolits will lead the barrel much easier.
I have a Marlin in .44 mag. It will shoot a hard commercial cast bullet at .429 but my softer cast boolit needs to be .431.
Marlin MG barrels will shoot cast as well as Ballard but they do need a little tlc to do so.

[GregLaROCHE]

The rifling in standard barrels is usually .004" deep with 2,4,5 or 6 lands. Micro groove has 12 to 16 lands and are about .001 or.002" deep. It is common that Marlin's actual bore size is larger than nominal bore size. Given the larger bore size many times a mold will not cast large enough to be used in a MG barrel. A .357 barrel on a Marlin may be .3585 actual and needs a .360 or .361 boolit. The mold may only cast .359 with your alloy. You will need to beagle your mold or powder coat your boolit to get it to shoot.
Lead hardness can enter into the equation when boolit diameter is less than optimal. Of course smaller boolits will lead the barrel much easier.
I have a Marlin in .44 mag. It will shoot a hard commercial cast bullet at .429 but my softer cast boolit needs to be .431.
Marlin MG barrels will shoot cast as well as Ballard but they do need a little tlc to do so.

Thanks for sharing this knowledge it’s very interesting and informative.

[Walks]

MARLIN changed to Ballard rifling with the introduction of the 1894CB Rifle in .45 COLT.
At the End of Trail 1996.
Followed by .357MAG, .44MAG, .44WCF. All with 24" bbl's.

I have 3 pre-safety rifles; 1894 - .44Mag, 1894C - .357Mag and an 1895.
All 3 micro-groove guns shoot great with bullets cast of LINOTYPE and sized .001 over groove diameter.

[243winxb]

Marlin 44 mag micro groove = Poor accuracy. Plain base bullet. A GC may help.

[mdi]

Thanks fellers. I cast for 5, 44 Magnums (along with 9mm, 45 ACP, 45 Colt, and 3 rifle calibers) and have loads/bullets that nearly eliminate all leading. I have a Puma in 44. Magnum and yes, SAAMI dimensions for 44 Magnum rifle barrels is .431", but my rifle slugs at a hair over .432", which gave me a bit of trouble at first but now leading is almost nonexistent. Thanks for the facts like .001"-.002" vs .004" I slug the barrels of all my guns just to have the info on hand whether I'll cast for them or not and size bullets appropriately. I've even customized some 44 cal Lee sizer dies to .430". .432" and .434". I'm still thinkin' if I found a Marlin on the used rifle rack, 44 Mag., 45/70, .444 Marlin (?). I'd be sorely tempted, regardless of the riling...

Thanks fellers, keep 'em comin'...

[odfairfaxsub]

My 35 rem is a micro groove. I shoot .360 dia bullets in it and super pleased no issues. My marlin 375 Winchester is also micro grooved I shoot .380 dia bullets and it’s awesome to say the least

The 35 is gas checked and of 50-50 lead variety ww/range scrap The 375 is plain based of the same lead.

[blackthorn]

Has Marlin always used MG rifling? If not, when did Marlin begin to use MG in their firearms?

[Nobade]

Marlin 44 mag micro groove = Poor accuracy. Plain base bullet. A GC may help.

Mine works great as long as the bullet is 433". Any smaller and it's terrible. And it does best with paper patched.

[Chihuahua Floyd]

Only clover leaf group I have ever gotten out of my 44 Mag Micro-groove barrel was with cast. 100 yards, three shots, one hole. Do not know what the bullet was as they where commercial reloads, I had requested 240g JHP, but got LSWC instead. shot great, but I started reloading again right after.
Don't push my cast bullets quite so fast.
CF

[Char-Gar]

I was shooting cast bullets through various Marlin MG barrels for many years before Marlin decided to reintroduce the "Ballard" rifling in some models.

Most of negative stuff written about Marlin MG barrels is based on a lack of understanding of these barrels. The groove diamter is over a few thou over normal and/or the land diamter is a few thou over normal. This means that bullets designed for traditonal rifling often do very poorly in the MG barrels. Either the bullet is too small for the grooves or too small for the lands or both. Cast bullets to do well requires both to be right. Find a bullet that fits and the Marlin MG bullets will deliver accuracy as good at any barrel.

I spent couple of years, looking for a 30 cal cast bullet for my 30-30 Marlins made from 1960 -72, all MG of course. The bullets that did well in my Winchesters rolled eye in the Marlins. I knew the problem but the bore specs, but what to do.

It was about the year 2,000 that I looked at the SAECO moulds and discovered that their #305 which they sold as a 31 cal mould, was nothing more than a fat #307 which was their 30-30 mold. This proved to be my salvation, and with the #305 my Marlins would outshoot the Winchesters with cast bullet of similiar design and weight. Life was good.

Since that time Ranch Dog came along with a line of moulds in all Marlin calibers designed to deal with the special nature of the Marlin rifle. Another issue was the lack of a throat, I might add. Chose a mould designed for the MG barrel and they will perform like a show pony in you rifles. Bottom line is we should not shy away from Micro-Groove barrels, but be aware they have special needs when it comes to bullet fit.