45-70 BC rifling type?

[tomme boy]

What do these have for rifling? Is it ballard or MG? I want to order one, but am unsure of the MG barrels. I have had 2 30-30's LA Marlins that would not shoot cast. I want to shoot cast in the 45-70 as I have a couple of tons of lead at the house that needs something to do. It has gotten pretty lazy latley and it has to go. Down range that is.

[gcrank1]

FWIW, there are guys in The Cast Bullet Assoc. who have been shooting cast in MicroGroove barrels successfully for some years.

[quickdtoo]

All of my H&R 45-70 barrels(6 of em) have microgroove rifling, as gcrank said, they'll shoot cast bullets just fine if you know how to do it, specifically, load bullets of the right diameter(oversize, as big as you can chamber)to shoot well.  The group below was shot at 200yds with a Williams FP-TK out of my 45-120, 525gr BTB Piledriver at ~1800fps, I adjusted the sight after the first high shot.

Tim

http://www.lasc.us/fryxellmarlin-microgroove.htm

[tomme boy]

Quick, what size have these been running on the bore? I am just starting to look at molds and sizers. What seems to be the common size to get for a mold? I know nothing about this calibre.

[quickdtoo]

.459"/.460" or just as cast. If the bullet will just fit in an unsized once fired case, you'll know how big they can be and still chamber. 

Tim

[gcrank1]

+1 that.
The biggest mistake most make early on in cast bullet shooting is to buy bullets, or size what they cast, at the same typical dia. as jacketed bullets for the caliber.

[knight0334]

My both of my BC's and my Handi have 8 groove rifling that appear to be more like shallow Ballard rifling.  Going by Marlin's patent for specs of "micro groove" I'd hardly call it a micro-groove barrel even though they are/were advertized as such. 

From the patent - "as having 5 grooves for every 1/10th of an inch bore diameter, and that the driving side of each land would be "tangentially disposed" to prevent accumulating fouling in use."

My Marlin 60 has a true micro-groove barrel with about 16 grooves.  If we were to apply that same ratio to the 45-70 it'd have 33 grooves or so.

[Smokin Joe]

It's a misnomer for "very shallow grooves"

Here's a real microgroove barrel:

[quickdtoo]

Not all microgroove bores have the appearance of the rimfire bores, the groove and land specs vary a lot. Here's a previous discussion on MG barreled H&Rs, I was in error when I said all of my 45-70 barrels are MG, CRS!! My 4 older H&Rs are 6-groove, but both my 45-70 SS Ultra Hunter and my extractor 45-70 BC barrels appear to be an 8-groove MG as well as some other chamberings I have, 44mag, 308 Win and 30-30 to name a few I recollect checking. 

Tim

http://www.gboreloaded.com/forums/index.php/topic,206287.msg1099083017.html#msg1099083017

This is the email I got from the H&R/Marlin brand manager in Oct 2008 when I asked about MG H&R barrels.

I can't find any info that says that Marlin made any blanks for H&R using the microgrrove pattern. This past year, H&R was making some of their own rifle blanks in the larger calibers with tooling borrowed from Marlin. There is the possibility that some could have been produced during that period. No one left in Gardner to confirm.

Here's info on Marlin MG barrel history by Glenn Fryxell with some specs.

http://www.lasc.us/FryxellMarlin-MicroGroove.htm

For the common centerfire calibers, the initial specifications (circa 1956) for Microgroove barrels were as follows:

    * .22 centerfire -- 16 grooves, .015" wide, .001" deep
    * .30 caliber -- 16 grooves, .030" wide and .002" deep (this would be changed in 1958 to 22 grooves .024" wide, and .002" deep; and then again in 1968 to 12 grooves, .040" wide, .0028" deep)
    * .32 caliber -- 16 grooves, .035" wide, and .0015" deep
    * .35 caliber -- 16 grooves, .040" wide, and .002" deep (this would be changed in 1968 to 12 grooves, .055" wide, .0028" deep)

In 1972, Marlin introduced the Model 1895 chambered in .45-70. Initially, these rifles were made with 8-groove Microgroove barrels, with grooves that were .060" wide and .003" deep. The next year this was changed to a 12-groove barrel, with the other specs remaining the same. Again, groove diameter is spec-ed out at .4587", so oversized cast bullets are called for in these guns. All of these .45-70 Microgroove barrels had a 1 in 20-" twist.

As of fall of 2007, Marlin still makes a number of guns that have Microgroove barrels on them (according to the 2007 Marlin catalog posted on their website; Marlin Firearms). All of their .22 LR and .22 Magnum rifles still have Microgroove barrels. The 336s in .30-30 and .35 Remington are still made with Microgroove barrels, however the stainless 336XLR in .30-30 and .35 Remington have Ballard rifled barrels. All of the big-bore Marlin leverguns (e.g. 444, 1895, etc.) are now fitted with Ballard rifled barrels (both blued and stainless guns), as are the 1894 and 1895 Cowboy models. Interestingly, in the 1894 series, the.44 Magnum and .357 Magnum guns are Ballard rifled, but the .32-20 1894CL and .41 Magnum 1894 FG are both fitted with Microgroove barrels.

There seems to be some confusion on my part as well as others what MG barrels actually are and there are obviously more MG H&R barrels out there than previously thought,  8-groove barreled 45-70s which is what my 2008 Stainless barrel has, I've never slugged it, but it definitely has 8 grooves compared to the 6 grooves of the other four 45-70 barrels I have are. I checked the slugs that I've made in the past, one is from Pete's older overbore 44mag that I rechambered to 445Supermag and converted to an extractor for him, it has 12-grooves which agrees with Fryxell's statement....

Also in the 1960s, Marlin introduced the .44 Magnum to the Model 336. This rifle was fitted with Microgroove barrels, containing 12 grooves that were .062" wide and .0043" deep. Factory specs for the .44 Magnum barrels also called for a 1 in 38" twist, but that this time nominal groove diameter was to be held to .4315", and a bore diameter of .4230", so oversized cast bullets are once again called for. It is interesting to note that given the difference in groove width, groove diameter and bore diameter, suggesting that the .44 Magnum barrels were produced using a separate process and tooling than were the .444 Marlin barrels.

Tim

[gcrank1]

I know your question is specific to the BC, but we may as well muddy the waters a bit since we have morphed already.
My CBA code SS UH has 6 shallow, but true lands and grooves.