Keyholing - likely cause

robc · February 18, 2007, 12:36 AM

Hi guys. I have a Mauser Modelo Argentino 1891, Manufactura Loewe Berlin that keyholes SUPER bad (vertical holes @ 50 yds.). The rounds that came with the gun are head-stamped "SF 7.5-7.65x54. They seem to chamber appropriately and fire fine (although I did get a SERIOUS blowback on one round out of thirty).

Rifling looks good. Crown does not. It's cut flat, not rounded off, and the chamfer does not look perfectly symetrical (close, but not perfect).

What is the likely culprit? Will re-crowning this possibly help? I'm looking at doing it myself just for the experience, but if the crown isn't the culprit I won't bother. TIA.

bswiv · February 18, 2007, 07:49 AM

I'm no smith but you might try this........

A few years ago I purchased a old .35 Remington lever action. Barrel was long so I decided to have it shortened. The cost was going to be $40 and I'd have to drive about 20 miles and wait a week or so.

My brother in law suggested that we do it ourselves and see what happend. We cut it off square and dressed the outside but did not know what to do to crown it. He suggested that we take a large drill bit, not in a drill but in a hand vice, and just bevel the inner edges and see what happened.

We figured that if it didn't work I could still take it to the shop and it'd still be $40 to do it right. Took us about 30 minutes.

When i took it to the range it shot fine. Bullet holes round and square at 100yds.

The point of the story is that you might try messing with the crown yourself and see if that makes it better. If it does then you know you need a smith to fix it right. Or you might be satisfied with it the way it is.

That said I'd be worried by the other issues, especially the blowout!

BHP9 · February 18, 2007, 04:25 PM

Slug the barrel, the bullets may be undersize.

ocharry · February 18, 2007, 06:51 PM

i would go with BHP9,,, that's what it sounds like to me,,, bullets to small of diameter for the bore. just my .02

ocharry

James K · February 18, 2007, 08:24 PM

Unless the rifle has been reworked, that is the correct ammo. (The "75" is the year of manufacture, not the caliber, which is 7.65x54. The "SF" stands for Fábrica Militar de Cartuchos San Francisco, San Francisco, Argentina (San Francisco Military Cartridge Factory, San Francisco, Argentina.)

The Argentine 91 has a normal round crown just like most rifles, so yours was cut off at some point, probably not evenly, resulting in the inaccuracy. Many suggestions have been made on how to crown a barrel using everything from drill bits to ball bearings. Sometimes, they work. If you don't have a lathe and know how to use it, I suggest you take the gun to a gunsmith and have the job done right.

Jim

Harry Bonar · February 18, 2007, 08:35 PM

Sirs:
Long time ago an old gunsmith taught me how to start a large dill in a small hole without chatter - cut several thickneces of denin and put that in between the drill (better a countersink) and flat bore and it removes the chatter - you still need to grind with some valve grinding compound.
If you get the right thickness it looks almost like a reamed hole!
Harry B.

A gunsmith named Frazier also told how to make a spring out of "spring steel" - Heat it to a cherry red and quench - beat a dip in an old oil can (metal

) - put spring in dip, cover with used motor oil and set on fire - let it all burn off and Hooray! you've got a spring - works for me on my muzzle-loader locks.

James K · February 18, 2007, 08:45 PM

We used a crowning tool that I have never seen in Brownells or elsewhere. We made them out of tool steel and cut the face to a half round internal curve. With the barrel through the headstock, you set the tool to go straight, in a line with the barrel bore, with one side of the "U" in the barrel bore and the other side outside the barrel. Set up right, the result was a perfect crown every time. Nothing went into the bore to mess up the rifling. We had several different sizes for different thicknesses of barrel.

Jim

February 18, 2007, 12:36 AM	#1
robc Senior Member Join Date: January 7, 2007 Location: Minnesota Posts: 422	Keyholing - likely cause Hi guys. I have a Mauser Modelo Argentino 1891, Manufactura Loewe Berlin that keyholes SUPER bad (vertical holes @ 50 yds.). The rounds that came with the gun are head-stamped "SF 7.5-7.65x54. They seem to chamber appropriately and fire fine (although I did get a SERIOUS blowback on one round out of thirty). Rifling looks good. Crown does not. It's cut flat, not rounded off, and the chamfer does not look perfectly symetrical (close, but not perfect). What is the likely culprit? Will re-crowning this possibly help? I'm looking at doing it myself just for the experience, but if the crown isn't the culprit I won't bother. TIA. __________________ "If it bleeds, we can kill it."

February 18, 2007, 08:35 PM	#6
Harry Bonar Senior Member Join Date: December 5, 2004 Location: In the Vincent, Ohio general area. Posts: 1,804	crowning Sirs: Long time ago an old gunsmith taught me how to start a large dill in a small hole without chatter - cut several thickneces of denin and put that in between the drill (better a countersink) and flat bore and it removes the chatter - you still need to grind with some valve grinding compound. If you get the right thickness it looks almost like a reamed hole! Harry B. A gunsmith named Frazier also told how to make a spring out of "spring steel" - Heat it to a cherry red and quench - beat a dip in an old oil can (metal ) - put spring in dip, cover with used motor oil and set on fire - let it all burn off and Hooray! you've got a spring - works for me on my muzzle-loader locks.

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February 18, 2007, 07:49 AM	#2
bswiv Senior Member Join Date: June 4, 2006 Location: NE FL....... Posts: 1,081	I'm no smith but you might try this........ A few years ago I purchased a old .35 Remington lever action. Barrel was long so I decided to have it shortened. The cost was going to be $40 and I'd have to drive about 20 miles and wait a week or so. My brother in law suggested that we do it ourselves and see what happend. We cut it off square and dressed the outside but did not know what to do to crown it. He suggested that we take a large drill bit, not in a drill but in a hand vice, and just bevel the inner edges and see what happened. We figured that if it didn't work I could still take it to the shop and it'd still be $40 to do it right. Took us about 30 minutes. When i took it to the range it shot fine. Bullet holes round and square at 100yds. The point of the story is that you might try messing with the crown yourself and see if that makes it better. If it does then you know you need a smith to fix it right. Or you might be satisfied with it the way it is. That said I'd be worried by the other issues, especially the blowout!

February 18, 2007, 04:25 PM	#3
BHP9 Member Join Date: May 19, 2004 Posts: 76	Slug the barrel, the bullets may be undersize.

February 18, 2007, 06:51 PM	#4
ocharry Senior Member Join Date: October 20, 2006 Posts: 685	i would go with BHP9,,, that's what it sounds like to me,,, bullets to small of diameter for the bore. just my .02 ocharry

February 18, 2007, 08:24 PM	#5
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Unless the rifle has been reworked, that is the correct ammo. (The "75" is the year of manufacture, not the caliber, which is 7.65x54. The "SF" stands for Fábrica Militar de Cartuchos San Francisco, San Francisco, Argentina (San Francisco Military Cartridge Factory, San Francisco, Argentina.) The Argentine 91 has a normal round crown just like most rifles, so yours was cut off at some point, probably not evenly, resulting in the inaccuracy. Many suggestions have been made on how to crown a barrel using everything from drill bits to ball bearings. Sometimes, they work. If you don't have a lathe and know how to use it, I suggest you take the gun to a gunsmith and have the job done right. Jim

February 18, 2007, 08:45 PM	#7
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	We used a crowning tool that I have never seen in Brownells or elsewhere. We made them out of tool steel and cut the face to a half round internal curve. With the barrel through the headstock, you set the tool to go straight, in a line with the barrel bore, with one side of the "U" in the barrel bore and the other side outside the barrel. Set up right, the result was a perfect crown every time. Nothing went into the bore to mess up the rifling. We had several different sizes for different thicknesses of barrel. Jim