MK III broken sear pin

radio · Post by **radio** » Tue Nov 08, 2011 6:16 pm

blue68f100 wrote:I would like to see a picture of the fracture face if you have a macro capability with your camera. If it's a very fine surface on the face it's more than likely fatigue. Which brings up how a hammer rotating 90deg could fatigue a pin.

It's no way pounding on the receiver with a mallet would fail a pin. Something else is going on.

I don't know how to post a photo on this board.

The customer service lady said she could ship me one out, but would rather I speak with a technician because she had never heard of a sear pivot pin failing.

The technician called and asked a few questions--mainly if I had been shooting hyper-velocity stuff. I told him that I had never even owned hyper-ammo and mostly shoot Blazer or Federal bulk rounds. Anything else I shoot is subsonic or standard. He apologized for any inconvenience and took my address and stated that sear pin failure is almost unheard of.

Both representatives were very friendly and eager to help and simply trying to discern what may have happened.

radio · Post by **radio** » Tue Nov 08, 2011 6:20 pm

I could take a photo or 2 and email them to someone to post for me. I don't have anything like photobucket at this time.

thanks

blue68f100 · Post by **blue68f100** » Tue Nov 08, 2011 10:26 pm

You can send them to me or bullseye and I will post them for you.

Post by **Bullseye** » Tue Nov 08, 2011 11:51 pm

Strange, we've had two people over the last year with sear pin failures. Bigfatdave had a similar problem a while back and they sent him a new sear pin. I know of a few others too. Either way they're sending you out a new one so the problem will be resolved.

R,
Bullseye

blue68f100 · Post by **blue68f100** » Wed Nov 09, 2011 7:22 pm

I received the photos from Greg but they did not show the fracture face. Once he gets that to me I will post them. The fracture face will give me an indication if there was a flaw. If no flaw, we need to look at if the pin is hardened. With the scuff marks on the OD indicates that it may not. Which means that it's subjected to low stress fatigue due to lower yield properties. Which brings up another question of how a pin that is not rotating get loaded in the middle with < 1/16" movement. The hammer is subject it stress, but sear? If any has to be very low. The only stresses I can think of is the shock vibration from the hammer going forward/backwards. And the hammer following the bolt back down till the sear captures the hammer notch. Will hold out judgement till I can get a close up of the fracture. But it may be one of those that you need a microscope to find the actual cause. I no longer have access to a microscope.

Bullseye, Yes it's very odd that we have had 2 of these in a short period of time.

radio · Post by **radio** » Wed Nov 23, 2011 3:38 pm

Ruger sent out a sear pin free of charge. While reassembling the gun the other day, I noticed that the sear spring was bent (most likely when the pin broke) and I should have had Ruger send one out, but didn't notice initially. I bent the spring back as close as possible, reassembled and all seemed well UNTIL function check and, yes, it broke again.

There is little doubt in my mind that the pin simply "slid" left and out of the right side of the grip frame and sheared from spring pressure. It probably would not have broken with the grip panels installed as they hold all pins in place.

I called Ruger (and paid this time) for a sear pin and sear spring. I, once again, have them installed and DID NOT function check until I replaced the grip (I use a thumb rest Hogue) and it works just fine.

One thing I did notice, however, was the first (complimentary) sear pin was black and the other I paid for was metallic, silver-gray. The original was black, the second pin was black and they both broke. Again, most likely due to me not installing the grips before function testing. I'm sure there is no "conspiracy" or anything--just found it a little odd that they would be different. Seems like they would have came from the same bin.

Thanks, again, for the help.

Baldy · Post by **Baldy** » Wed Nov 23, 2011 7:18 pm

Some times companies do use color coding on small parts so things don't get mixed up on the assembly lines.

blue68f100 · Post by **blue68f100** » Thu Nov 24, 2011 6:08 pm

The silver pin was for the SS model. Though it makes no difference since it's hidden behind the grips.

Post by **Bullseye** » Fri Nov 25, 2011 10:55 am

When the hammer hooks reset on the sear the full force of the mainspring is applied to the sear pin, this is likely how the unsupported pin fractured.

R,
Bullseye

radio · Post by **radio** » Sat Nov 26, 2011 11:01 am

Bullseye wrote:When the hammer hooks reset on the sear the full force of the mainspring is applied to the sear pin, this is likely how the unsupported pin fractured.

R,
Bullseye

I agree and would deem this case "solved".

charlesb · Post by **charlesb** » Mon Nov 28, 2011 9:26 pm

Sometimes if I need a pin and can mike the old one for the exact diameter, I will make a new one out of the shank of a drill bit of the same size.

I cut it off a bit long with a Dremel cutoff wheel, then grind the end flat or rounded as needed by hand to get the length right.

A machine shop or gunsmiths supply can fix you up with a drill of just about any diameter up to 1/2" or so. Besides the regular fractional drills, there are letter drills A thru Z, and number drills 1-60. All of these are different sizes under 1/2", so one or another of them will be just right.

They are often better finished, and of better material than the original pin.

If the original pin is a sloppy fit, allowing unwanted movement, you can make one out of a drill that is a few thousandths fatter for a better fit.

If you don't get too carried away, you'll probably have enough shank left so that you can still use the drill.

Just a thot!

radio · Post by **radio** » Mon Nov 28, 2011 10:04 pm

charlesb,

This last pin they sent me is a little looser than the original. I really have to watch to make sure it is still in the correct place before installing the grips.