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.45-70 conversion

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    Posted: December 13 2009 at 12:35am
So, I have the .45-70 barrel and a No.1Mk3* receiver, and .45-70 brass... it would seem the .45-70 conversion requires just a little more work than some people have made out.

The receiver has a .585" hole from one end to the other. That includes the web behind the barrel threads. The .303 rim is .540", so there's .045" of rattle room in there. No problemo.

The .45-70 rim diameter, on the other hand, is .608".

The right side of the receiver barely shows the drilled (probably broached) .585" up by the receiver ring. The sidewall is .380" thick there, cut back to .330" by the charger bridge, likely for rim clearance so a .303 is guided into the breech.

The bolt is guided almost entirely by the left receiver wall. This works okay, since thrust from the bolt handle pushes it that direction when the bolt is closed.

It looks like the way to do this is to cut .025" or so from the front of the right receiver wall. Then the web in the receiver ring would have to be opened up to .610 or so... but it'd have to be opened up well back into the left receiver rail so the cartridge would go in straight and centered.

I'd give a lot to see how Gibbs or Navy Arms did their .45-70s conversions. Looks like I'll just have to grind a little bit at a time until it works.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldbikewrench Quote  Post ReplyReply Direct Link To This Post Posted: December 13 2009 at 4:30am
I can send you pictures and some dimensions of a Gibbs Frontier I have access to if it would help.
Love your neighbor as yourself.'...Mark12:31
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Smokey Quote  Post ReplyReply Direct Link To This Post Posted: December 13 2009 at 7:18am
I wonder if .444 Marlin might be a better conversion in terms of not having to grind the reciever?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: December 13 2009 at 7:45pm
bikewrench: I'd love to see some photos.

smokey: I already have a threaded and chambered .45-70 barrel and a big full of .45-70 brass, so I'd like to continue in that direction.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldbikewrench Quote  Post ReplyReply Direct Link To This Post Posted: December 13 2009 at 11:00pm
All righty then. Let me know what areas you want pictures of and at what angles. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: December 14 2009 at 6:55am
Okay. If you'll arrange a lamp or flashlight to light up the area where the flash can't get...


(what we're looking for)

On an ordinary SMLE, there's a 5/8 inch hole all the way through from the back to front, going through a bulkhead or web right behind the barrel. The right side of the bulkhead has a notch for the extractor. If you look, you'll see the shiny area on the left side where the bolt rides; that's the remains of the 5/8" hole when they get done with all the cuts. The shiny area should be almost nonexistent on the right side between the charger bridge and the ring. There's basically a straight shot from one end to the other, except where it's cut away for weight reduction or magazine clearance.

The .45-70 rim is bigger than the bolt hole of a stock SMLE, so Gibbs had to cut away part of the inside of the receiver so the rim could come up and let the case slide into the breech. If you slide the bolt up into battery, it should be fairly snug along both sides until it gets somewhere maybe halfway along the magazine, where you should see more clearance ground to clear the rim.

Theoretically, anyway.


(what I would like to see)

pictures of:

from underneath, through the magwell with the bolt open, looking forward into the ring

from the top with the bolt open, looking forward into the breech

from the top, with the bolt closed

from the top right, at maybe two o'clock, with the bolt closed


That ought to give me a pretty good idea of how much grinding they did, and where.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: December 14 2009 at 8:02am
Y'know, it just occurred to me that the left side rail might be cut back all the way to the ejector screw... the bolt might feel a bit loose if they did, though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: January 28 2010 at 9:07pm
Okay, a list member was kind enough to let me borrow his Gibbs Frontier for a while. It was a Lithgow Mk1 virtually identical to mine, which made the comparison much easier than it might otherwise have been.

Basically, the magic is in the magazine.

The Gibbs magazine has very short lips on the top. It's also single stack. The magazine presents the rim of the cartridge to the "thumbnail" cutouts on the underside of the receiver. These grab the rim and force the whole cartridge up into line with the breech as it moves forward for the first half inch or so.

It sounds complex, but if you look at an SMLE from the magazine well opening you can see how it works.

Where I was getting fixated was, all of the rifles and pistols I've dealt with before stripped their cartridges straight out of the magazine, which was sometimes notched for bolt clearance, or the cartridges slipped off the magazine at an angle, with the nose entering the breech and the base being levered up as the cartridge went in. I thought the Enfield did that, too. Of course I have a receiver, barrel, and bolt so far, with no magazine yet...

The .45-70 still won't fit into the .45-70 barrel screwed into the Enfield receiver; the rim wedges into the rails about 3/4 inch from the breech ring. It looks like the Gibbs people used a Dremel with a 1/2" sanding drum and reached in and took off .010 to .015" of the sharp corners at the bottom, not much more than just rounding the corners off. That's all it takes for the cartridge to slide forward.

There's a bulkhead in the receiver ring; the rim must pass through, and it's too big. Gibbs probably used a lathe to open it up. I thought the rifle's owner might not appreciate wrench marks, so I didn't pull the barrel for a look. Opening up the ring would be simple enough with a grinder if you didn't have a lathe; it's just clearance for the rim.

That's it for the receiver mods!

Like I said earlier, the magic is in the magazine. The magic consists of the short feed lips, which are 1-1/16" long, with the front edges cut back about 45 degrees.

The lips are so short that if you hold the magazine upside down, a cartridge will hang down at a 45 degree angle. The lips just hold the rim for long enough to get it started into the "fingernail mark" guide cuts in the receiver.

It's a single-stack magazine. There's a rib stamped into the front that guides the front of the cartridge. In back, they spot welded some L-shaped pieces of sheet metal. These are way back and close to the cartridge, and keep the rims lined up neatly. The rims can't pass forward and let the cartridges slam back and forth in the magazine, and they hold them in position to present to the fingernail marks. If the cartridge slid forward in the magazine when the bolt picked up the rim, it'd jam in the receiver rails.

I don't see any particular reason you couldn't modify a standard SMLE magazine to work the same way.

The magazine holds three rounds. As advertised, you can put four in there, but you get a big wedgie when you try to work the bolt. Five cartridges will fit, same problem.

I played with this for a couple of hours. My best guess is that A) the magazine spring is too weak and B) the follower gets tilted as the cartridges feed, letting things wedge up. I think it should be possible to tweak the magazine to feed four or five cartridges reliably, and I don't see any big reason they can't be double-stacked like the standard Enfield layout.

What it looks like is, Gibbs allocated a certain amount of time or money to the magazine work, then ran out of time (or money) and said, "to heck with it, just tell them not to put more than three in there."


Working the bolt took a bit of authority. The blunt front of the .45-70 bumps against inside bits the pointy .303 slides right past. After an evening's experimentation, I had a bunch of .45-70s with noticeably battered noses. You don't have to be abusive, but if you try to flick the bolt back and forth like you can with a .303, it's likely the cartridge will get a wedgie and you'll have to either force it or open the bolt and straighten it out.

It looks like you could safely grind clearances into the receiver to fix this. I'm guessing Gibbs didn't do it due to expense - it worked, and it was in inexpensive hunting rifle on a war-surplus action, what do you want for $299?

That would also explain the ejection problem. The Gibbs flings empty brass just fine. Trying to clear a loaded round will usually give you another wedgie.

If you look at an Enfield receiver ring, you'll see a notch up at the right side front just about the side to hold a pencil. The notch is to clear the point of a .303 bullet. The ,45-70 bullet is much bigger, and the notch needs to be bigger too. Again, opening it up should be safe and simple.

You might wonder why the cartridge wouldn't eject properly when it's short enough to slide entirely back from the breech. The cutout shouldn't be necessary. The reason is the rim gets caught on some of the edges near the back, and it gets stuck. A tiny amount of grinding or polishing might well fix the problem; it might be preferable to clearancing the ring.

I wound up clearing loaded rounds by dropping the magazine, opening the bolt, and letting the chambered round drop out.

Now, we're talking about very small amounts of interference here; with normal production tolerances, it's likely that not all the Gibbs guns do this. It's a bit quirky, but again, how much custom gunsmithing do you expect for the price?

Frankly, I don't see how they could justify the blueing job, which (in my opinion) was freakin' gorgeous. They'd done some polishing on the surplus bits, and the barrel was slick. I'm used to phosphated military stuff, and I felt like a vandal every time I put a greasy fingerprint on the Gibbs.

The bolt is a matte silver color; various articles say it's chromed, and it does indeed look like industrial matte chrome. The fit is snug and the movement is smooth. I'll probably send mine off somewhere to have it done; the couple of thousandths of plating really snugs up the fit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote yumastepside Quote  Post ReplyReply Direct Link To This Post Posted: February 15 2010 at 5:07am
Any chance of some pics of the mag ??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: February 15 2010 at 9:55am
I'll post some in a few days.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cookie Monster Quote  Post ReplyReply Direct Link To This Post Posted: February 15 2010 at 12:01pm
I was recently given a Navy Arms 45-70 conversation from a early No1 MkIII and looking for a magazine any pictures would be helpful.

Thanks from The "Cookie Monster"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote yumastepside Quote  Post ReplyReply Direct Link To This Post Posted: March 03 2010 at 7:28am
......don't mean to be pushy, but any progress on the mag pics ??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote yumastepside Quote  Post ReplyReply Direct Link To This Post Posted: March 04 2010 at 7:40am
....found this on one of the auction sites........

              

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: March 27 2010 at 11:52pm
Okay, the round tuits finally got aligned with the cosmos, or something... I trimmed the pictures and here they are.

This first set is the Gibbs magazine. It's made from scratch. It's a single stack configuration, with the short lips at the back being the only thing that holds the cartridges in. Note how they hang loose when the magazine is inverted.

Though the magazine will hold four or five cartridges, only three will feed. This is because the follower gets tilted out of position because the cartridges are only held at the rim, so the fronts lift too high and stovepipe when the bolt is operated.

http://www.bacomatic.org/~dw/gun/Gibbs/Gibbs-mag-1-sm.jpg
http://www.bacomatic.org/~dw/gun/Gibbs/Gibbs-mag-2-sm.jpg
http://www.bacomatic.org/~dw/gun/Gibbs/Gibbs-mag-3-sm.jpg
http://www.bacomatic.org/~dw/gun/Gibbs/GibbsMag-rightside-up-1-sm.jpg
http://www.bacomatic.org/~dw/gun/Gibbs/GibbsMag-upside-down-1-sm.jpg
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRX Quote  Post ReplyReply Direct Link To This Post Posted: March 27 2010 at 11:58pm
Okay, I can't find any option on the reply form to attach a picture, so I uploaded the images to my web site and posted links, but they're just showing up as ordinary text. How do I put images into a message?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote yumastepside Quote  Post ReplyReply Direct Link To This Post Posted: March 28 2010 at 4:29am
The pics come out fine, all I did was ,click and drag each line to the google box, and they come up.Then the return button to go back and get the next one.
Just a thought, but what about a 308 mag? With the follower made for a straighter case, it might work better ??
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