Frame Material and Rockwell?

[Kendog]

Hello all. This is my first post to this forum. I have a Colt Series 70 Gov't. Model from around 1980. It has developed a crack at the left side dust cover/frame rail junction as mentioned many times in this forum. Can anyone identify the steel analysis used on these frames and the rockwell hardness? My weldor is requesting this information before we fix the crack.
Thanks
Kendog

[niemi24s]

Hi Kendog:

Welcome to the forum. Most anything you need to know about the 1911 is available here.

The Army Ordnance Dept frame blueprints in our Technical Issues section has the steel composition data, but not the hardness - at least I can't find it. But, whether or not your frame is the same is the unknown.

You might be able to get that data from Colt - if it's not a closely guarded trade secret.

Maybe someone who's welded one will post some useful info for you. Or try a search of this site using "frame weld".

Regards

[1911Tuner]

That crack is very likely self-limiting, and welding it will do funky things to the steel...either overhardening it or annealing it...probably anneal...and that ain't good.
Choose your welder wisely. The honor pipefitting student down at the local community college ain't where you want to take it. Contact George Smith at Evolution Gun Works. He knows the ropes.

The cause of the crack is insufficient clearance between the top front edge of the spring tunnel and the bottom of the slide rail when the slide is at full rearward travel.
The thin steel flexes on impact, and bounces up...striking the slide and starting a crack in the most likely of places...in a sharp corner.

I've got an early Colt 1991A1 beater that cracked there 10-12 years ago. Afer check-drilling the crack at its terminus with a tiny drill bit, I filed a little more clearance on the front corner of the side that it occurred...starting about a half-inch from the end, and on a very slight angle...and have shot the gun at least a hundred thousand rounds since. The crack hasn't traveled. If you don't plan on beating the gun as hard as I have mine, you probably don't even need to check drill it.

[RickB]

I think Kuhnhausen's manual has the USGI hardness specs. I believe the frame is low-mid 20s on the C scale. Don't know if Colt has stayed with those specs, though.

[1911Tuner]

The Rc scale reading isn't all there is to consider. The welder needs to know exactly what grade of steel that he's working with...and that is the fly in the ointment.

[niemi24s]

Would there be any merit in stop-drilling this crack (assuming the end of it could be located)?

[John]

That crack is very likely self-limiting, and welding it will do funky things to the steel...either overhardening it or annealing it...probably anneal...and that ain't good.
Choose your welder wisely. The honor pipefitting student down at the local community college ain't where you want to take it. Contact George Smith at Evolution Gun Works. He knows the ropes.

The cause of the crack is insufficient clearance between the top front edge of the spring tunnel and the bottom of the slide rail when the slide is at full rearward travel.
The thin steel flexes on impact, and bounces up...striking the slide and starting a crack in the most likely of places...in a sharp corner.

I've got an early Colt 1991A1 beater that cracked there 10-12 years ago. Afer check-drilling the crack at its terminus with a tiny drill bit, I filed a little more clearance on the front corner of the side that it occurred...starting about a half-inch from the end, and on a very slight angle...and have shot the gun at least a hundred thousand rounds since. The crack hasn't traveled. If you don't plan on beating the gun as hard as I have mine, you probably don't even need to check drill it.
Tuner, a picture of the area that should be checked for clearance would be worth 1000 words. Could you please show us what we need to check to keep our frames from cracking?

[1911Tuner]

You asked:

Could you please show us what we need to check to keep our frames from cracking?

I said:

I filed a little more clearance on the front corner of the side

My bad. Shoulda been a little less vague. Haste...again. :rolleyes:

With the recoil spring free, pull the slide to the impact abutment and slip feeler gauges between the bottom of the slide rail and the top of the spring tunnel as far forward on the tunnel as you can get a clean measurement. Push down on the slide to take up any vertical clearance. You want a minimum of .007 inch, and I like to see .010 inch, or a little more.

If it's too tight, don't file the whole length of the tunnel. You'll create too much gap and the pistol will look all funky.


Look at Dana's illustration of the frame...the crack at the junction of the rail and spring tunnel. Go to the end of the tunnel. That corner. Start about a half-inch back of the corner and use a smooth mill file to cut a very slight downward angle until you've removed enough to compensate for the lack of clearance. Then, lightly break the sharp corner with a stone.

[John]

With the recoil spring free, pull the slide to the impact abutment ...

Which impact abutment? You mean to align the slide so that the front of the frame's dust cover is aligned with the rear face of the slide's spring tunnel?

[1911Tuner]

Which imact abutment?

The one that the guide rod flange lays against and gets smacked by the slide.

You mean to align the slide so that the front of the frame's dust cover is aligned with the rear face of the slide's spring tunnel?

No. Just check the clearance with the pistol assembled. If it's not wide enough...cut an angle on the front of the frame's spring tunnel...or dust cover if that helps...starting a half-inch from the end.

[John]

It must be a problem due to the lack of nicotine. OK, if I pull the slide all the way back, how can I measure the clearance between it and the dust cover? The only case I can measure that, is when the slide is in its full forward position. That "impact abutment" surface gets me confused, I know which one you are talking about, but if the slide is pulled back to meet it, then I can't measure the clearance between it and the top edges of the dust cover!!

CONFUSED!!!

[niemi24s]

Maybe the measurement's taken between the x's:

http://i129.photobucket.com/albums/p232/niemi24s/P085210001ctxt.jpg

Line on slide is aft end of recoil spring plug tunnel. Line on frame is impact abutment. Slide is fully aft with recoil spring guide in place.

[John]

Niemi, I do not think so. From what Johnny said, if your tolerances are tight, you have to file the top edges of the dust cover (or spring tunnel) creating a slight angle. That measurement you show doesn't mean much for this problem. Then again, as I said by brain is ... sick due to not smoking.

[niemi24s]

Hi John: Maybe the measurement is someplace else, but that was all I could figure out. Then again, maybe my brain is . . . sick from smoking! ;)

Maybe Tuner will set us (me) straight.

Cheers

[1911Tuner]

Niemi got it. SLip the feeler gauge in at the middle X position. Forgot to add to check it again with the slide full forward, as close to the end of the frame as you can get a clean pull on the thickest gauge that'll enter. Sorry...Haste will be my undoing, I fear.

If the clearance is at or below the minimum behind the end of the tunnel...under the right conditions...the tunnel can flex...or bounce when the slide hits the impact abutment and contact the slide. Even a light bump at the very end of the tunnel can bring on a crack because that's the point of greatest leverage imposed on the rear...in the corners...and it's cumulative. Using a new spring may prevent the contact until the spring starts to weaken, allowing the slide to hit the frame a little harder...so it could tale a long time to show up...or it could happen pretty quickly...depending on the clearances.

And, yes. A shock buff will forestall the cracks.