Fitting an Ambi Safety
by Bob Londrigan, published in Front Sight Magazine, January 2006
Installing an ambidextrous safety is one of the most often requested aftermarket modifications I get. Thatís because there are several situations that require fitting of a safety: you may want to install one on your new gun, you may need to replace one thatís broken, or you may be doing a trigger job that also requires fitting a safety. With a little knowledge about how the safety works and with only a minimum number of tools, this is a modification the average shooter can successfully perform.
The thumb safety is the primary safety on 1911-style guns. It works by physically blocking the sear when the safety is in the up position. When properly installed and adjusted, the thumb safety prevents the sear from moving even if you pull the trigger. As such, any work performed on the safety must be checked thoroughly to make sure that when the job is completed the safety still works as intended in this design. Do not undertake any safety work unless you are willing to take the time to complete the safety checks mentioned towards the end of this article. If you are doing a trigger job or whenever you change any of the trigger components, the last step of that process needs to be checking the operation of the safety. It may need to be adjusted as a result of your trigger modifications. Therefore, do any planned trigger work before you begin installing a new safety.
The first step to fitting an ambi safety is to completely disassemble the gun. We covered this in an earlier article but if you need a refresher course you can check this link for more info: http://www.brazoscustom.com/magart/0501.htm . You do not need to disassemble the grips on a 2011 pistol, but if you have a 1911 you will need to take off the grips.
Once you have the gun torn down, check your new safety to see if it installs in the frame without binding. First look at the left-hand side (as viewed from the rear). It will insert into the frame only if you have it in the correct position Ė about halfway between on and off. The safety should rotate back and forth between safe and off without binding. In the off position it should go down enough so that the top of the safety allows the slide to pass. It is very common for the safety to not go down far enough. If this is the case, check the width of the key slot in the sear stop stud.
This slot needs to be wide enough so that it can slide down over the engagement surface in the frame. If it is not, then widen it a little. Look through the back of the frame and you will be able to see where it needs to be adjusted. Sometimes the stud may need to be filed where it hits the frame. Check and relieve that area until the safety drops down far enough so that the safety lock plunger fully engages the detent in the safety. At this point make sure that the top of the safety does not extend up to where it drags on the bottom of the slide. If it does, take a little material off the top of the safety until you have at least 0.025 inch clearance with the bottom rail of the slide.
Now that you have the left side sliding well, fit the right side. If you are installing the safety in a 2011 you will have to shorten the bottom leg so that it will move into the slot in the frame.
Go slowly Ė you need only to be able to clear the top of the slot. Take off too much and you wonít have anything to hold the safety in the frame. On a 1911 you can leave the leg long but you will need to clearance the underside of the grip panel so that there is no interference. You should also check for interference when moving the safety up and down. You may need to take a little off the inside of the paddle to clear the frame. Now blend the safety into the frame removing any sharp edges and any material that might bite into your hand.
Once you have the safety moving smoothly with no other parts in the gun and itís nicely blended in, it is time to do the actual fitting. Reinstall the disconnector, sear, hammer, sear spring, and mainspring housing. Now cock the hammer leaving the grip safety off so you can see both the sear and safety. Notice that the stud on the left side of the safety has excess material for fitting. This must be adjusted so that the safety can be inserted in the gun yet still block the sear from any motion when the safety is engaged. If you place the left side of the safety partially in the gun, you will see where the material needs to be removed. You want to remove enough material so that the safety can be inserted but so that it still makes full contact with the sear when in the up position. Check the photos for the angle and approximate amount of material to be removed. It is important to try to match the angle of engagement with the leg of the sear. This will give you a solid lockup with the sear and prevent it from moving. Go slowly and keep trying the fit in the gun. Once you can just barely get the safety to go in move it up and down. This movement will likely be stiff as the safety will be rubbing the sear. It should leave a mark on the safety lock stud. Remove a little material where the safety is marked and try again. You should eventually get to the point where the safety engages with just a little resistance Ė this is good.
Now check the safety for engagement. Put the slide back on the frame and move the safety into the notch in the slide to the fully engaged position. Pull the trigger and watch the sear. The sear should not move at all. Move the safety to the off position while again watching the sear. There should be no movement. Next pull the hammer back a little. You should not hear a click. If you do then the sear moved when you pulled the hammer back. If the pistol fails any of these safety checks it is unsafe to shoot because the gun could fire when the safety is released. If the safety needs just a small adjustment, you can fix it by peening a little material on the safety stud to get some more engagement.
Place a shim in the stud key slot, place the safety on a flat surface, and hit it with a hammer so that you move a little material to replace the excess that you filed off. It should not take much. Re-install the safety in the frame and check for engagement. If there is still movement, you will need to have the stud welded up or fit a new safety.
Now reassemble the entire gun and, again, check the safety operation. If everything checks out you are ready to take your gun out and test fire it.