Manurhin MR73's forcing cone.

H

HenryT

Inactive
Upon examining a friend's old Manurhin MR73 (real old combat model), not sure what vintage year, I was surprised to see a lot of flash burns on the forcing cone. This was verified when I observed on the sideline while he was firing the gun. Yes, a lot of blow-by flashes came out on the side. I further examined the gun and noted that the forcing cone has a flat cutout right at the 6'0 clock position, just like the SW K-frame which is known for the forcing cone to crack. SW corrected this with their newer K-frame beefing up the forcing cone by eliminating the flattened area. I am surprised that the MR73 which is touted as the toughest revolver has the same design as the vintage SW K-frame with the flatten forcing cone on the 6'0 clock position.

My question is whether Manurhin changed the design for the new MR73. Can someone who owns a newer model MR73 verify whether they made an improvement in this area ? The attached picture will show the flat cutout at 6'0 clock on the forcing cone.
 

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I think the Manurhin earned its reputation for long life because the French used French-style .357 magnums. :D
 
You mean like GTV at 50000 psi of which the manufacturer says "But it is of only the briefest fraction of a second, monsieur."
 
French provided 90% of firearms/powder for the American revolution...Lafayette square directly in front of the White House, etc. :) Their democratic revolution was a bit more horrible than ours. Nothing wrong with the French.

Manurhin says it proofs with Norma which is equal to Federal American Eagle 357. Mild.

I too look forward to seeing the forcing cone from the MR73 experts on here...
 
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France is a member of CIP and must follow its specifications and proof requirements.
They may get their proof ammo from Norma but it is not over the counter blasting ammo.
Maximum average CIP chamber pressure for .357 Magnum is 3000 bar = 43500 psi.
Proof pressure is 30% over, 3900 bar = 56500 psi.
SAAMI test methods differ so we can't say we load .357 lighter at 35000 psi, 45000 CUP. But European .357 doesn't seem "mild."

I was not kidding above, a French ammo maker really did tell a US reporter that 50000 psi was ok because it did not last long.
 
OK, here is a picture of the forcing cone on my example. I am not a great photographer. I am also not an expert on much of anything. Please forgive the lint.

This Forum does seem to have more than it share of self acclaimed experts. Hope it helps others affirm or dispute their thoughts on a fine revolver. I am blessed and do own more than my share of S&W revolvers.

It is your choice, as it is mine, to own one or not. I am fine with it being French. I also have a Chinese Norinco SKS just to add to my lack of credibility.
 

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Self-acclaimed experts on this forum ? I thought this is a forum for gun enthusiasts exchanging ideas. Your picture also illustrate the flat cutout on the 6'0 clock position to make room for the cylinder hinge. It is a fact that the older SW K-frame has a tendency of the forcing cone cracking due to the weakened design. They did rectified this on their recent K-frame to alleviate this problem. Not a self-acclaimed expert in this field, but I was merely pointing out what I observed which seems to contradict Manuhrin's touting their MR73 as the toughest revolver ever made that can endure firing a million rounds with no noticeable damage.
 
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I'm here to learn.

I'll post up a box in my hand of Norma 357 CIP Hungarian made 357mag later. Not sure your point. Norma surely isn't providing Manurhin with a specific non commercial load that is 1,500fps in 158gr? It can be CIP and still be light. You can't have higher pressure and same FPS as American Eagle? I'm confused by this?
 
As I said in the other thread, CIP proof requires a 30% overload above maximum standard pressure. They may well function test guns with plain vanilla Norma ammunition, but the actual proof test is indeed done with a "specific non commercial load."

I should clarify, the proof test is not done by Manurhin like Colt does for a VP, CIP proof testing is done for everybody in France at the St Etienne proof house which was established by royal appointment in 1782. There is a video on the CIP site of a worker loading a revolver, putting it in a machine rest, pulling down a steel hood just in case it doesn't pass proof, and pulling the firing lever.
 
Thanks for posting the pic of your MR73. Apparently, the flat cutout on the forcing cone is also there on the newer ones. I'm no expert in this area and will refrain from commenting on this issue.
 
Flat or not, the proportions look like the MR73 barrel tenon is larger than Smith.
I'll compare mine.

ETA: Optical illusion, my MR73 SN 125062 tenon is a bit smaller than Smith M19-0, ca 0.485" vs .495". But the protrusion back through the frame is less, .075" in MR73, .140" for Smith.

My M67 has the most tenon flat, the M19 not as much, the MR73 none visible. Perhaps they changed the gas ring to need clearance, I have had mine some years.
 
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Just as an educated guess, I'd say it's probably either differences in American vs European ammo, different quality/composition of steel, or a combination of both.

The issues with K-Frame forcing cones wasn't so much one of pressure but rather of bullet weight. The majority of K-Frames that cracked forcing cones did so after extensive use of full-power Magnum ammo with 110-125 gr bullets. Using them with magnum ammo loaded with 158-180 gr bullets usually doesn't cause forcing cones problems. Most of the European .357 Magnum ammo I've seen uses heavier bullets with 158 gr being most common. I would venture to guess that the MR-73's reputation was probably gained with 158 gr bullets.

The other possibility is that Manurhin is using better, more durable steel that is simply more resistant to erosion and cracking. Given their reputation, I'd think this fairly likely. Considering that the MR-73 seems more resistant to other revolver wear and tear like timing and endshake problems without necessitating a radically different design, I can only conclude that their toughness is a result of superior material.
 
An MR73 is not a K frame Smith. So there is really no comparison.
Flash coming out of the barrel cylinder gap is normal for all revolvers.
Its a matter of the ammo power and lighting that makes the flash more or less visible.
 
The flat is not the problem. The K-frame took too much material off that area leaving it too thin for the high pressure rounds. The Manurhin can have the flat there as long as it still has enough thickness at that point to withstand the force.
 
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