I assembled a 1911 using parts from a Colt 1911 and a KTO frame. For some reason, the sear doesn't appear to work all of the time. I'm afraid to fire it, because if the sear doesn't catch the hammer, I think it could possibly fire completely automatically. Have any of you had similar problems? Any ideas as to how I can correct the problem?
Check the sear spring. Also make sure that the frame has no rough areas that the sear may be rubbing on. check over all your parts for burrs, etc. Polish the "square" hole in the disconnector, and the contact point where the sear spring rubs on the disconnector. PERHAPS the thumb safety could be doing something, but I'm still learning about thumb safety work myself :)
I would try adding a little more tension to the sear spring, also check and make sure that your sear's face and the hammer hooks are in good shape.
There are several thing that can be causing the problems,
First off you say the sear doesnt catch the hammer all the time? How are you checking this, if you are dropping the slide from hold open on an empty mag/chamber, BAD BOY that is the fastest way to stuff a hammer/sear and frame.
If you are manually cycling the slide by hand the trigger bow and disconnector must be almost drag free to allow them to reset by slow hand cycling that is common when checking function.
First thing I would do is remove the mag and top end, thumb cock the hammer and see if it catches, dont drop the hammer onto the frame without the slide in place as you will batter the frame, Brownells sell a little tool that clamps on the rails and lets you drop the hammer until the cows come home without frame dammage.
If the hammer won't catch, remove the MSH, hammer, sear, disconector and check for bind with the trigger bow in the frame, it should be snug but have no resistance at all, check also with mags in place as they can rub in the inside of the trigger bow and cause it not to return.
Next is refit the sear, disconector, sear spring and hammer but not the MSH, (well, you will have to fit the MHS but dont put the hammer strut into it) now see if the sear will catch the hammer and release when the trigger is pulled, does the trigger reset ? now do the same but depress the disconnector when the hammer is in the cocked position, did it drop to half cock?
I would add a little bit of wieght to the sear spring center leg first, not the LHS as veiwed from the rear, the center leg returns the trigger bow and the disconector, if they dont reset you will never get the hammer to catch. re-assemble and try again.
If it still doesn't work then add more (not a lot) weight to the LH leg of the sear spring, make sure you have everything coated in either Wilsons Ultimate lube or if you are in a COLD area CLP, I use McCormick trigger slick on all sear, hammer and disconnector surfaces, Wilsons on the trigger bow and pins, this alone will allow you to have more spring pressure but it will fell like a lighter "trigger job".
At the very least you will be good at disassembling and reassembling your 1911.
For your test fire, start with only 2 or 3 round in a mag and if it does run away it wont go far, saying that, I shoot IPSC and between me and friend fire over 30,000 per year in 1911 ptatform guns and I have only seen on gun go auto and that was caused by a worn out hammer and sear, no half cock, and HOT HOT HOT ammo. 23 round mag of 195 PF .38 Super emptied in about 1.6 secs made us all look. About .07sec splits or about 850 rpm.
Pull apart, clean check and lube, over and over until you are happy. Then shoot it tell your hand are bleeding from hammer bite and mag lips, then go home load more ammo and do it all again, don't stop smiling.
Check to see if the disconnect is getting out from under the sear when the slide pushes it down.
Once in a while, a tolerance stack issue lets the top of the disconnector drag on the bottom of the sear legs and prevents the sear from resetting completely.
Assemble the gun without the grip safety and observe the function under a strong light. Slide on... pull the trigger and hold it. Hand-cycle the slide slowly and watch the disconnect as the slide pushes it down. If it doesn't completely clear the sear legs, it causes the sear to drag, and partially reset or fail to reset. Releasing the recoil spring will let you cycle the slide easier.
Stone the bottoms of the sear legs a little, following the radius with a swiping motion. Use a square hammer hook file to remove a tiny bit of material from the top of the sear paddle to get a little more clearance... better to get a little from two places than all from one.
The Full-Auto experience isn't as bad as one might suspect, especially if you're expecting it. A friend's pistol went full auto on us last month, and the pistol didn't move more than 3-4 inches off target... slightly up and left. It didn't climb to the sky or get out of control.
It was over too quickly, even firing it one-handed. We played with it for a while and brought it here and fixed it.
The problem was as noted above. Sear and disconnect contact, along with an over-tweaked middle leaf on the sear spring. 10-minute fix.
You may need to scrape the disconnect's timing slot a little deeper in the slide to let the disconnect reset high enough for positive engagement with the sear and allow the hammer to fall when you pull the trigger. Not highly likely... but a possibility, especially when things are a little out of spec anyway.
I disassembled the gun, tried to clean the parts up, oil them and refit them. When I reassembled the gun, the hammer and sear were working perfectly. I don't exactly know what the problem was, but it is no longer an issue.