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For a few years now, I've been telling people not to worry about Ruger MK III's. I believed they were the same as the MK II but with a few extra pieces.

Yesterday, that opinion changed. Our range has two MK III's and a Mk III 22/45. These were bought about 2 years ago and see a lot of use. All three guns have a crack in the upper receiver in the same place.

The loaded chamber indicator has a pin that allows it to pivot. All three guns have cracks starting where the pin is and working up on the outside of the receiver. So far, two of them are all the way through.

All three guns will be going back to Ruger to see if they will replace the receivers.

Has anyone else seen this on MK III's??

Not I, but I would love to see some pictures of the cracks if that's possible.

R,
Bullseye

I was figuring that if anyone had come across this yet, it would be you Bullseye.

I took pics with my cell phone but they didn't come out. I'll bring a camera tomorrow to the range and see if I can get some clear shots.

All three cracks look identical. They all had about the same propogation. It appears like a stress riser crack that starts with the flat milled section of the indicator pivot pin.

I have no idea how long they have been this way since they were still on the rental line until last night when it was noticed. They were going to switch the upper from one to the other when it was noticed the second one was cracked. Then we grabbed the 22/45 from the case and saw the same thing.

I would guess these guns are have somewhere between 60K and 80K rounds through them.

The Mark III pistol has only been in production for a little over 5 years. I doubt that many folks have anywhere near that many rounds through their personal pistols yet. Do you know what year those pistols were manufactured?

Stress cracks would most likely have to come from high usage and Kruzr's description of 'rental guns' would definitely fit in that category. It also may be said that hyper velocity ammunition could also have been a casual factor, but since the type of ammunition used is an unknown variable, it cannot be directly blamed for this damage. People can bring in and shoot whatever they want and they usually do even if the facility's rules say otherwise.

I can envision this being a problem area since the receiver tube is fairly thin and the LCI pin is mounted directly behind the chamber. The forces of recoil would be flexing the receiver tube right behind the front lug pivot point from the gasses escaping out of the muzzle. The receiver tube's rigidity and flexibility would definitely be impacted by the drilled hole for the LCI pivot pin. I can also say that Ruger probably didn't anticipate this type of structural failure either, unless they did an extensive computer simulation modeling experiment on the Mark III model's usage/service life.

I cannot wait to see those pictures Kruzr. I wonder what Ruger's response is going to be? If it was only one pistol, I have an idea from my prior encounters with the original all metal LCI test results. But it's hard to deny there's a design flaw with multiple similar failures. They'll definitely want those pistols as examples of the failures and to do the appropriate engineering testing.

R,
Bullseye

When comparing the MK II to the III I had often pondered if something like this would be a possibility. This sure could set Ruger back.

It will be most interesting to see those pictures.

My experience with stress cracks is that most are caused my a mfg flaw. Most accour around sharp edges and corners. Like a sharp corner that was suppose to be radius. But most of my experience is with oil field equipment. You would be surprised on how a simple radius reduces stress.

What length barrels were on these guns?

The MKIII's are 6" tapered barrels with fixed sights. The 22/45 is a 5 1/2" slabside barrel. I think it was a Davidson's special. Ammo shot was all factory ammo and was high velocity but not hyper velocity. They have never seen a Stinger.

We won't know what Ruger has to say since all three are going back to Davidson's and will be replaced under their replacement warranty. The two MK III's were manufactured in 2005 and bought in 2006. The 22/45 was made and bought in 2006.

When I was taking the pics, I also saw that the plastic LCI has cracked on two of the guns.

MK III - 1


MK III - 2


22/45:

The cracks definitely originate at the LCI pin hole and travel the whole length of the hole's bore up to the LCI slot. They also appear to align right at the end of the front mounting lug hole.

Looking at the pictures carefully, it does appear like the crack is also showing on the inside of the pistol's receiver, especially in the shots of the Mark III without the frame installed.

One of the first things I noticed in the pictures was the broken LCIs. I can also see that the 22/45 has an empty magazine installed.

Davidson's has a good warranty policy. It's a shame that you won't get to talk to Ruger about the problem.

R,
Bullseye

I suggested to the range manager that he should send two to Davidson's and one to Ruger. He was more concerned about gettting 22's back on the "revenue" producing line than he was about why this happened. The last time he sent a gun to Ruger, it took about 6 weeks to get it back. The last time Davidson replaced a gun (S&W M&P .40 that cracked,) it took about a week.

As it is, he is borrowing a MK II and a MK III for the basic handgun class on Saturday morning.

....I told him he can't use my MK II slabside with the Doctor sight.

Ouch...... I hate to see that these were all stainless receivers. One would think that would be stronger. At least the 60K round count helps me feel a little better. I won't live to put that many through mine.

My LCI "plug" is stainless, follows the original shape, and is a tight fit. Especially, filling the notch next to the chamber. I expanded the curve to fill that completely, so the plug couldn't move. I can pretend that added some support.........

I'll stay tuned for further news, for sure.

One could hope this will cause Ruger to delete the idiot LCI ? Miracles do happen........

I'm sure that Davidson's will return the MK III's to Ruger. The sad thing is none of us will ever find out what Ruger's explanation will be.

ruger22 wrote:Ouch...... I hate to see that these were all stainless receivers. One would think that would be stronger. At least the 60K round count helps me feel a little better. I won't live to put that many through mine.

My LCI "plug" is stainless, follows the original shape, and is a tight fit. Especially, filling the notch next to the chamber. I expanded the curve to fill that completely, so the plug couldn't move. I can pretend that added some support.........

I'll stay tuned for further news, for sure.

They look like blue receivers to me...........

Could this be from work-hardening? Steel work hardens from repeated flexing by bending, blows, or vibration. Eventually it gets too hard, and brittle, and you get stress cracks.

I'm a former aircraft mechanic, and this is a big problem as airplanes age.

The punishment of 60-80K rounds would certainly work harden any steel. May be, these receivers just reached their limit. Nothing lasts forever.

Some SS do work harden but not all, carbon steel does not, some AL alloys can work harden too. You normally need nickle alloy in the steel to work harden. But in either case if the loads are near the material modulus/Yield point it will cause a fatigue failure which is what I think we have here. Most of my fracture mechanics research was on the Alaska Pipe line. I had equipment that I could do low load (below the yield spec) cycling to create the fatigue fracture. Normally it took me over 180k cycles to generate a fatigue fracture to our desired test length. Normally 2-3 days on my machine. In all cases if I stayed 20% below the yield point, you could not see the crack on the surface with out aids. The closer you get to or over the yield point produce the elongation on the surface. Which by looking at the photos the surface has a dipping appearance, which indicates that the yield of the material was exceeded on the surface.

I'm going to agree with Bullseye (keen eyes) that it started around the front locking lug. It does appear to go to (or from) the inside.

Do you by chance have a photo of the inside and bottom view.

In any case it would be nice to hear what Ruger has to say. Maybe if you were to press Davidson they will tell you what Ruger told them.

I don't see me putting 60-80k rounds through my MKIII 678 flutted SS gun, unless I live another 40 yrs.....

These guns are just fun to shoot.