View Full Version : Broken Sear Nose - what caused it?
25th March 2009, 13:12
What a way to go for a first post, lol. Long time lurker though. I recently purchased a fairly expensive, nice 1911 from a well known, highly respected manufacturer (name omitted until I get my pistol back after repairs). I did the initial field strip, lubricated all the components and ran 300 rounds of PMC ammo through it, cleaning it after every 100 rounds.
Now here's where the problem happens after a couple weeks of ownership. I went to lower the hammer on it and it would not drop. Squeezing the trigger was having no effect on it. So after a few slide racks and a little hammer manipulation it finally goes down but now will not stay cocked in any of the positions. I immediately detail stripped the pistol and found the culprit: a broken sear nose. I want to blame the breakage on myself but I have barely dry fired it and never abused it so I can't seem to find any other reason than a material flaw. The hammer didn't have any burrs on it that could have caught it, either.
What in the world could have caused this kind of catastrophic failure? I carried it on a daily basis and if I'd needed this pistol in a life threatening situation it would have been a life ending situation and now my confidence is entirely shaken. I sent the pistol back to them for the repair and was told it could possibly take 4-6 weeks :( It's going to be heck waiting for it to come back home but I'd rather have it completely sorted out by the people who built it.
25th March 2009, 13:41
Hi FMF: :wc: to the Forum!
Bummer, huh? Other than the material flaw you mentioned the only cause I can think of is a misadjusted trigger overtravel screw.
Insufficient overtravel can allow the sear nose to get hit by the hammer's half-cock notch as the hammer falls. However, I'm not sure if this all by itself would break a healthy sear. If this had been happening there might be some evidence of contact on the forward part of the half-cock notch.
Maybe someone else will chime in with a more likely cause.
25th March 2009, 13:58
I wish I still had the parts in front of me or else I'd look for signs of what you describe. Good info. I'll look for it when I get it back.
25th March 2009, 14:34
The sear is broken, Ahhhh, you knew that. A couple things come to mind that shouldn't cause it, but........pulling the trigger hard when it's in the half cock notch, de-cocking and letting the hammer slam on the half cock, hard bumping of the hammer when it's in half cock or full cock, as mentioned an over adjusted overtravel screw..... but don't know. Rockwell off the chart. Never store a gun in the half cock position. Well at least it didn't break while cocked and fire, so far so good. :)
25th March 2009, 17:53
Besides the reasons already listed, some sears noses will wedge into the half-cock notch and this pressure can break the nose (or break the half-cock notch)
25th March 2009, 18:29
all great info. I'm going to give it a good hard look before I ever put another round down the pipe after I get it back.
Dave! I still have one of the small tubs of grease I ordered a few months ago, have cleaned and lubed my AR, shotgun and pistols at least 10 times and STILL have more than 90% of it left. Your grease is awesome. Thanks again!
25th March 2009, 20:29
I don't know about this one. My Colt MKIV is 37 years old and I done just about every thing you guys can mention: except the trigger. My guns have the 1911 trigger in them no overtravel screw. The sear and disconnector and hammer are original.
If someone squeezed the trigger on half cock, hard enough it would probably break the sear. And this has already been mentioned.
Is this a real 1911, or a well its supposed to be a 1911.
Parts do fail, they make hundreds and thousands of them somebody is going to get a bum part.
26th March 2009, 06:05
If you look at the first photo of the sear with the nose next to it you can see a different color in the fractured metal surface. This is usually an indication of a flaw that grew as the part was in use and the oil from maintenance crept into the crack. This part IMHO was installed during the build with the crack started and it failed in use, probably with out undue stress. I don't believe any owner/user stress other than normal cycling caused the failure.
26th March 2009, 07:23
That is an unusual break. What we have seen is where the two legs meet the top of the sear is where a sear failure usually occures.
Good observation on the dirty area, crack was there for a wile before it finished. The external finish of the sear looks good so not a lot of stress risers. Perhaps too hard or could also be a bar end part. (end of a bar can have inclusons so a part machined at the edge can have a stringer into the bar that gives a pre existing problem
26th March 2009, 10:15
. . .could also be a bar end part. (end of a bar can have inclusons so a part machined at the edge can have a stringer into the bar that gives a pre existing problemThere is always very useful information in your posts.
Thanks for sharing that gem with us.
P.S.: Within a week someone will probably ask where they can get a sear machined from the middle of the bar! :D
26th March 2009, 11:17
Kind of reminds me of when I used to work for a railroad we'd occasionally have a coupling knuckle break on a car. You could easily see the pre-existing break before the final failure after it failed. Usually it was rusted, or greasy grimy. 30% pre-existing break was deemed nobody's fault, stuff happens. Less than 30% and they were on your butt for not stretching them out slow enough.
26th March 2009, 11:22
Good observation on the dirty area, crack was there for a wile before it finished.
Credit goes to the photographer. ;)
It was like the part was on my bench...
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