Primary sear engagement surface

[marshaul]

So, I've been working over the past few days on my EGW sear and Ed Brown hardcore hammer. The trigger pull was pretty good right off the bat, but I decided to clean it up some.

I bought an Ed Brown sear jig, and following the instructions that came with it, the trigger job page over at blindhogg (http://www.blindhogg.com/gunsmithing.html), and this page (http://www.thehighroad.org/showthread.php?s=&threadid=56376), I attempted to do some stoning.

Only problem is, after cutting a slight relief angle with my black stone, polishing everything with my white stone, very carefully (and minimally) stoning the hammer hooks (didn't change the height at all), and boosting the trigger, I have MORE CREEP than I started with!

Following the instructions that came with the Ed Brown jig, I continued to stone the relief angle, enlarging it and, in the process, reducing the primary sear engagement surface. So far I've removed just over 1/3 of the original sear engagement surface, and the creep remains.

http://www.brownells.com/UserDocs/Miscellaneous/wb308-untitled11.jpg

The thing is, I noticed that the sear engagement surface (D in the photo above) is fairly small, especially compared to the original part. Granted, it was over .040" on the RIA part, and it was much smaller than the sear engagement surface on the RIA piece to begin with, but now it's less than .020, maybe .018.

So I guess my questions are, what is the minimum size for the sear engagement surface (D in the photo above)? Am I doing something wrong? Should I continue to remove material from the escape (relief) angle, or should I buy another sear and just give it a quick polish then leave it be?

[John]

I can't help you with the minimum dimensions, I am sure Niemi will step in with those very soon, but I guess you have messed that sear. Get a new one, and just do the Poor Man's Trigger Job, as it is described in the "Technical Issues from M1911.ORG" forum. Guaranteed results.

[marshaul]

So I did a little experiment. Using the OEM sear and hammer, I tried every possible permutation of the parts I have and concluded the following:

*With the original sear and hammer, there is little creep.

*With the original hammer the new sear, there is no creep.

*With the new hammer and original sear, there is moderate creep.

*With the new hammer and original sear, there is moderate creep.

This would indicate that I must have messed up polishing the hammer hooks on my Ed Brown hammer. The sear is OK, (or it was) at least until I kept working at it unnecessarily. I will carefully go over the hammer hooks again and see if I can square/polish the creep away from them.

So I guess that leaves the most important question: what is the minimum width for the sear engagement surface (D in the photo above)? What is safe for a carry gun? How much would one expect to take away from the relief angle in an EGW sear?

My guess is I'll have to buy a new sear and cut a much smaller relief angle, but I'd like some input from those who may have a clue (1911Tuner?).

[Hawkmoon]

You keep removing material from the sear, but you haven't mentioned how deep the hammer hooks are.

[John]

The relief angle shouldn't be more than 25-30% of the sear nose. If you have polished your hammer hooks too, good luck with salvaging this set. I never touch the hammer hooks, except if they need to be made a little shallower. Usually, they are pretty good as they come from the factory.

[toolman]

Hawkmoon is probably on the right track. How deep ARE your hammer hooks?

[log man]

With hammer hooks that are square and polished and .018"-.020" in length the sear nose engagement should be .009"-.010". Creep is often the result of the engagement surfaces not being neutral.

LOG

[niemi24s]

Stock USGI hammer hooks and sear noses are both about 0.030" with the hook tips overhanging the forward edge of the sear nose a wee bit (about 0.002").
http://i129.photobucket.com/albums/p232/niemi24s/P8040002d.jpg
Cutting the relief angle on the sear without reducing the height of the hammer hooks allows the sear nose to get farther under the hammer hooks.

The relief angle is usually done in conjunction with reducing the hook height and changing the hook angle from the stock USGI 86° to 90º, as shown here:
http://i129.photobucket.com/albums/p232/niemi24s/P077190002e.jpg
Cutting the relief angle without reducing the hook height merely increases the distance the aft edge of the sear nose has to travel before getting to the tips (forward edges) of the hooks - and the hammer falls.

If you haven't made the relief angle cut too big, you may be able to salvage the job by reducing the height of the hammer hooks.

[marshaul]

My hammer hooks are .021" deep, on both the Ed Brown hammer and the OEM hammer.

The EGW sear came with a square sear engagement surface of about .026, and with my relief angle cut it's now about .015" (to the best of my measuring ability, it's kind of hard to isolate the primary angle from the relief angle in my calipers).

[Lazarus]

Marshaul,
If I understand correctly, you are following instructions in order to make a secondary cut on the sear face. Here are a few pointers that might help in a general way. Doing trigger work on any firearm requires more than a few jigs and some instructions. Knowing what you're trying to do is vital for safety reasons as well as to achieve the results you desire. Read everything you can find before filing!

Having the proper tools are also important. But being able to actually see your finished engagement is 100 percent necessary. Most people use Brownells frame pins to mount the hammer and sear on the outside of the frame, and inspect their work with a good quality loupe. You can see your basic engagement angles that way, but you also need some felt marker or layout fluid to adjust the parts so they bear evenly accross the engagement. These last steps can't be done on a jig, they have to be done by hand.

Here is one thing that has helped me do better triggers: whenever you file or stone something, you are creating a burr at the edges. This fact holds even for the finest of stones. The burr may not be visible, but it is there and it must be removed by light beveling or rounding. One common place to create interference is by lowering the hammer hook height. That is what your hammer "jig" actually does. Many modern hammers have already been lowered plenty far enough, but opinions vary on what is safe. Anyway, a burr is created at the top of the hooks, that interferes with the sear movement.

Another common place to get a burr is the filing of the secondary angle on the sear face. That secondary surface may shine like a mirror, but it never has to touch anything so it is wasted effort. You have created a sharp, burred edge in the middle of the sear face that will scrape the hammer hooks as the trigger is pulled. That is the situation you have just described, assuming that the engagement angles were workable to begin with (not known).

So, I encourage you to use those frame pins and good magnifier as a first step, look at Niemi's drawings as a guide, and use some felt marker to see where the metal is in contact. Finally, remove the sharp edges that are created by polishing or stoning.

Lazarus

[niemi24s]

My hammer hooks are .021" deep, on both the Ed Brown hammer and the OEM hammer.
Oops! I guess your hooks were already trimmed at the factory - do not shorten them! Your 0.021" is perilously close to the prudent limit of about 0.018".

Have you read "Poor Man's Trigger Job" in our Technical Issues section?

As a suggestion, you might do well to find the thread "Roll Trigger" and browse through it. It's pretty long, but there's a lot of good info in it.

[toolman]

I'm sure no expert with this, but if your hammer hooks are .021", looking at the photo of the sear, dimension "D" may be OK but the secondary angle on the sear is cut at to sharp of an angle allowing the sear to sit to far back into the hammer hooks creating the creep you are experiencing.

You probably need to start over again with a new sear. The secondary angle on the sear isn't supposed to be cut at a 90 degree angle to the primary angle on the sear, if that's what I'm actually seeing in the photo.

I have no idea whatsoever why the new sear doesn't have any creep with the old hammer.

[marshaul]

Don't worry, I haven't lowered my hammer hooks. First thing I did was measure them, and determine that I was satisfied with the original height of .021". Too bad I think where I messed up was trying to polish them, so I'll have to buy a new hammer anyway. :(

BTW, that sear isn't mine. I just used that photo so I would be clear with my terminology. :)

Most people use Brownells frame pins to mount the hammer and sear on the outside of the frame, and inspect their work with a good quality loupe.

Any idea what brownells calls these? I've been trying to find them for a while and only ever located their $125 sear/hammer block kit.

[John]

Great advice Lazarus!

[DuckRyder]

Any idea what brownells calls these? I've been trying to find them for a while and only ever located their $125 sear/hammer block kit.

080-622-001 Trigger Adj. Pins fit Colt Govt., Commander & Gold Cup

http://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=677&title=TRIGGER%20ADJUSTMENT%20PINS

HTH

[marshaul]

Thanks so much! I dunno why I never found those before.