The 1911: The Importance Of Pin Sizes
May 10, 2013
When I was a 19-year-old Cold War tank driver lugging around a World War II-era 1911A1, trigger creep wasn't an issue in a killin' gun I would only use in dire circumstances. But times have changed. Now, I really appreciate a crisp trigger on the target range.
When we do a trigger job we attempt to remove excess movement from the fire control components to reduce creep. One thing to watch when tuning triggers is the relationship of the hammer and sear pins to the holes in the frame where they live. Loose pins will result in a mushy trigger rather than the crisp let off we desire.
Begin your inspection by measuring the pins with a micrometer. I'm working on an old Springfield Armory pistol from the 1980s that has been heavily used. Sear and hammer pin sizes are .109" and .156" respectively. The sear pin is within the original G.I. tolerance of .110"-.002". Checking the sear pin hole in the frame with gauge pins reveals a frame hole size of .111", also within the original G.I. spec (.110" dia. +.002"). The hammer pin hole will accept a .159" pin and almost take a .160" pin, so it's at the high end of the tolerance (.1575"+ .0015"). That's about .005" of movement by the original pins before we have touched the sear and hammer engagement surfaces with a stone.
Fortunately, oversized pins are available to solve our problem. Two sources are Marvel Custom Guns, Inc. in Jarrettsville, Md., and the Cylinder & Slide Shop in Nebraska. The C&S pins are .110" and .157" while Marvel offers .112" and .158" sizes. Use the pins that best fit your frame. Keep in mind that using oversized pins may require reaming the holes in the hammer and sear. Reamers in the appropriate sizes are available from industrial supply houses such as MSC. A good trigger job should start with custom fitted pins.
Measure the hammer and sear pins with a micrometer. The nominal sizes are .110Ã® and .156Ã®, respectively. There\'s a bit of tolerance, but not very much.
Checking pin hole
Checking the hammer pin hole with gauge pins shows this frame accepts a .159Ã® pin. That\'s at the high end of the tolerance range, and may be loose.
A set of gauge pins like this one by Meyer Gage Co. is a good investment for gunsmiths. Loose pins can degrade a pistol\'s trigger pull, Norcross says.
Oversized pins are available from Marvel Custom Guns and the Cylinder & Slide Shop. Installing them may require reaming the pin hole in the frame.