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Discussion Starter · #1 ·
Had some fun today and wanted to share it with the rest of the class.

As a lot of you know we sell what we call a hard sear. It is 56 ish Rc. hardness.
Over the last 12 years we average less than One failure per year.
This includes a sear some nice rocket scientist stoned to a point and returned to brownells. and another that the half cock had beaten a dent in the sear. It takes quite a bit to dent 56 rockwell tool steel by the way.

So we went along with a failure rate of less than one sear in 1000 per year, That is alarming but considering we always ask for the broken ones back and half of the returned ones have strange things going on. The other thing we have to take into account is Many of our sears end up in competition guns that get shot a TON.

We went out looking into a new tool steel this year to improve from our 0.05% failure rate.

SO how do you break a sear?
first choice was take a demilled frame. install a 23# main spring
mill the hammer down and move the notch in .030
this leaves the hammer fall and smack into the half cock notch.
OUCH!
We than releived the half cock notch so it could get a longer running start.
Next we dry fire the hammer into a sear and stop on the half cock each and every time. (ok it was not a pretty sound.)
after 100 repeats we found the old sear had a shiny surface where it hit the hammer but no peaning.

Plan B
We wanted to get a sear to fail to test against another material.
Caspian sent us some blank bar stock we use around the shop for fixtures. a nice block of 4140 at 41 rc.
the block is 8" long .935 thick and 1.7" high
a Chunk of steel
next we drilled a pin hole in a plate and milled a slot to hold the sear. We drilled and tapped the steel bar to make a pivot point.
And we dropped this chunk on the sear. A much uglier sound :)
3 smashes later the sear tip broke off.

My first thought was wow, a sear is pretty darn tough!
100 times falling squarely on the half cock. and it didn't touch it.
KooL

So we pulled out another sear and 3 smashes and it cracked, on the fourth smack it parted with the point.

next we tried the new tool steel, unobtanium (you can only get it from us ;) )
it went 8 hits with the sledge. Again this was tested in the frame smack test also before the test fixture. On all these tests the sear pin bent long before the sear gave up the Ghost.


The other interesting thing that came up recently was about manufacturing. We close the shop one day a year for a field trip to our Yearly tool show. Speaking with one manufacture they mentioned they sold a machine to Kimber.

What struck me is they sell over 75k guns a year. Imaging making 60,000 bushings. (it was mim it failed and they went to bar stock fact) It was a turning center with a live tooling Z X C and Y axis and a live pick off spindle. The machine makes a bushing in about 110 seconds. They have to run one machine all year to make Bushings for a gun. One part for a 1911.

Think about WW1 or 2 making 45's at the rate they did. and all from forgings extrusions, and bar stock ONE at a Time on NON cnc machines. Now conside Today with our CNC mills and turning centers that Darn few manufactures do it the old fashon way. From bar stock or even from Castings.

Who wants to make 1500 firing pin stops, Sears, Hammers and thumb safetys a week. Mim is here to stay. It costs less.

geo
 

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George,

Are there any issues in using the new hard sear with a hammer that is not as hard?

Just curious.

Mike
 

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George Smith said:
This includes a sear some nice rocket scientist stoned to a point and returned to brownells.
Thanks for the kind words George, but I aren't no rocket scientist yet. But I is really close to gettin' my deeploma, and then I are one!

I filed and filed and I got my seer so sharp I reckons I could shave with it. I was a'feared that I was gonna cut me with it, so's I send it back and the nice lady at Brownell's gaves me all my money back cuz even she says that it was way too sharp and I was fixin' to hurt someone with something that dangerous.

Wait 'till youse guys see what I done did to your angle bored bushing that Brownell's just sended to me! I added a few more angles of my own, and now I thinks that I maybe needs to call the nice lady at Brownells again.

:biglaugh:
 

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George, when will you be making sears in the new steel? I almost don't want to know since then I'll want to replace all of my hard sears! I have to say that your sears and hammers make for great action jobs. Nice tidbit on Kimber and MIM, that was very interesting.
 

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Discussion Starter · #7 ·
eerw

Yes we stood aound and put on our safety glasses and it was fun. There is something really unsetteling about letting the hammer fall knowing it is going to smack the sear. I was surprised that it went 100 hits and did not even show a peen.
Man the one Brownells sent back that had the center half cock peened on a sear that hard. How many times would that have to fall to move steel like that.

Mike
No, the hardness is the same old and new. just more shock resistant. You have to choose. We make the koenig hammer at 52-53 rc and the sear at 56 57 rc. I would rather have the sear hold shape, ie flat stoned surface, and have the hammer notch form to the sear. than the sear dent. The hammer contact on a sear is typ. a point contact.


Thanks 10 ring

shane, Nasa called, they wanted your number so I had a talk with them. don't expect a call. :)

What will you call your bushing the facet bushing? ;)

Slowhand we have them in stock. That is why we had to crush some. make sure the theory translated into the finished part.

geo
 

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Why not S-7

Mr. Smith, why not use shock resisting S-7 tool steel hardend to 52-54 rc. It is used in forging dies. It can take repeated blows into the 10,000's before failure. I do not know what steel you use presently, and I am NOT a metalurgist, but just a tool and die maker. Anyway it is some pretty tuff stuff!
Just my $ .02:D
 

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This is why my stuff goes to EGW.....I did stray but found out the northwest ain't the place........nice to be back home........:)
 

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Discussion Starter · #10 ·
Doug

Excellent Question.
Sorry, Just a tool and die maker? I would have to differ with you, Probably the highest rating of a machinest.

We looked at several factors.
S7 is a good choice.
it is shock resistant as you mentioned.
We also looked at the wear factor numbers.
You have a hammer with a point contact that is around .090 per side and under spring pressure for every cycle.

The wearability number on O1 tool steel is 30 but the shock # is also 30.
S7 moves way up on the shock# 75 if I remember correctly.
but the wear number drops from 30 to 22. not a compromise we were willing to make. and as you mention the hardness numbers are close on many of the tool steels. Max hardness in the 65 to 68 range and anealed down to 56 range is down 10 points off of max.

We always look at sears out of guns that we and others build.
some have a small dent after 30,000 rounds. Some of the softer ones, often other process ones (cast, mim etc.), get quite a dent. And one in particular is prone to doubling after a couple thousand rounds. (para).

One question that I had lingering is how much of a work out does a sear get? after dropping it to half cock over 100 times and the fact that the pivot point is in the center. Naturally all failures ever observed (many brands many years) were from the pin up. usually at the top where the sear is thinest at the end of the slot. Good design dictates radiused corners. One sear I have not seen for years was EDM ed out in the middle. Several of these failed. As have EDM cut Sights and EDM comps. the process causes a micro crack structure in the steel. and Like Glass if you have a scratch or crack that is a stress riser you can predict where it will fail.

The finish comes into play in other parts also. One time cutting a larger radius into a ramp barrel to alter the ramp cut out in the frame I used a chain saw file. The lug cracked off in pretty short order. The radius was fine. The fact that the chain saw file left score markes all across the shear plane was all the barrel needed to break off. Now we polish any radius cut to remove machine marks. Inside square corners in the hostle environment inside a gun don't last long. We have in our collection of parts that failed Mag catches that cracked right across where the cut out is for the key. Firing pin stops cracked all the way across. Hammers the top broke clean off the body, Struts that cracked where a machine mark was left, Guide rods where a sharp thread left a stress riser, Barrel feet often, Slides where the dust cover meets the rails, Bushings where there was no corner radius for the lug, Slides over the top of the ejection port, Dust covers where they meet the rails on the frame (very common) Safeties where the pin meets the body. Extractor Hooks..... etc. many gun parts failures are inside square corners. Radiused corners, cleaner machineing would help in most cases.

The combination of Design and Material is what holds up.

geo
 

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You know George, FWIW I've been using your sears for some time in my customs and decided to do some scientific research on my own.

Took one of your sears and put it on a railroad track. It derailed a freight train. I gave the authorities your name and address.

:rofl:

Seriously, you make the BEST sear out there.

Cheers, Tim
 
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