This morning while at the range my buffer retaining pin managed to come half way out and snag the bolt while on it's way back to battery. This cracked the lower on the fwd edge of the hole machined for the retaining pin (pin was canted to about 80deg to the line of fire instead of perpindicular.

After the fact I see how it happened and (gulp) it was caused but operator oversight (read: stupidity).

I am now tring to come up with a repair.

What do yall think of the idea of overboring the hole and fitting a stainless steel sleeve that would restore the correct bore diameter and vertical axis.

Would it be feasible to weld it?  

This is on a PWA preban rifle so just getting a replacment lower in not a simple(read: cost effective) solution.

Thanks for any and all suggestions.

It's preban so it has some intrinsic value.

The manufacturer CAN legally exchange the pre-ban lower for a new one (which will be assigned the same serial number) and it will retain its pre-ban legal status.   This may indeed be your best option.

The damage is done, but it's not necessarily irreparable.  You will need the services of both a machinist/gunsmith AND a skilled welder who can weld aluminum.  It'll need Heliarc welding.

It SHOULD be possible for them to repair it without leaving any external signs of the repair, though it will likely show signs of the repair when you look inside.

CJ

Unfortunatly, like I said it is a PWA, which is now long dead and reassimilated as RRA (if the stories are true). I havn't contacted them, but I think I know what the ansure would be.



I am skilled welder and currently hold AWS certs in GTAW for alum and SS, as well a a 6G for SMAW. I am also competent on a Bridgeport mill.

Seeing as I do not know what alloy and it is and it is a forged and heat treated part I would prefer not put heat to it.



I am realy not concerned about signs of repair, only function and longevity of the repair.

It would be my opinion that sleeving it would probably be the strongest type of repair and have done it to equipment, just not on a rifle.

Has anyone seen or had this done?
How has it held up

CJ, I do appriciate the reply, it was just not the answers I am looking for.
Thanks

It should be a 7075T6 Forging.

Note: That detent is a convenience, not a requirement. It is there so the buffer & spring will stay in place when opening / separating the upper and lower. I know a few people who have removed it so that there is never a gap between bolt carrier and buffer. In some badly mismatched guns this does make the gun function smoother.

Personally I make sure my assemblies match, or they are rebuilt till they do match.

I don't know about the crack but...

According to my drawing the hole for the buffer detent is supposed to be at 84 degrees.  It's tilted toward the front of the receiver.

oldguy
I do not have that info, so it would appear that I misspoke. At this time I would like to ammend my statement: the buffer pin was 10-15 degrees canted fwd from it's normal line of travel.

ProfGAB101,
Very interesting info! I will have to look into this as I will still be able to shoot until I come up with a satisfactory repair.

Thanks all

Swamp Rat;
The lower is probably 3056(T6), as previously stated. Personally, I like the idea of the sleeve, but I'd also weld the crack so that it doesn't get any worse. Since you are competant with a Bridgeport and certified in AL welding, I don't see this as a big problem for you to accomplish.

Now you've heard two different alloy specs.

Let me clear up THAT confusion.

The standard spec alloy used on M16/AR forgings is 7075, heat treated to the T6 condition.

As all of the AR manufacturers use raw forgings that come from a limited number of manufacturers, and all of them supply to military contractors from time to time,  you can be fairly sure that any forged receiver (upper or lower) will be 7075.

Use a 4000 series rod when welding it, if you don't have a piece of 7075 lying around.  It works fine.   (This, I know.  I milled out two lowers from raw Alcoa forgings and had to have some corrective welding done to repair my goofs. The receiver (the one I didn't scrap) fits and functions as well as my Bushmaster.  

The idea of boring out the damaged area and inserting a sleeve actually sounds pretty good, too, if you're really concerned about the heat treatment.    

You may be able to use the opportunity to fine-tune the location of the detent hole so that the buffer makes light but solid contact with the back of the bolt carrier yet doesn't interfere with closing the weapon, too.  

The detent should be angled six degrees off vertical, toward the front.

If you have to clean up the buffer threads, Brownell's sells the tap. It won't do much damage to the anodizing on the buffer threads, I think.

CJ

I have the lower receiver machining drawing in ACAD and Adobe PD Format (PDF).

The ACAD dwg is very clean but you need AutoCAD r14 or newer to open it.

The PDF is crude but readable and the software to read it is free from [url]www.adobe.com[/url].

IM or e-mail with your return address if you can use them.

For what it's worth, the stainless sleeve idea is bad juju... Putting stainless and aluminum in contact like that is just begging for electrolysis.

[b]cmjohnson[/b] is dead on. adding to his statement and mine above, Forged is 7075T6. Most CAST receivers are made using 356 alloy which ends up at a T3 temper as cast. Further heat treating can be done, but there is a danger of warpage.

re: [b]SciFiNut[/b] stainless and Al. - Sure thats why the Mil spec REQUIRES stainless Heli-coils in most Al Chassis applications... Right?

I appriciate all the input!

After a trip to the range this morning to conferm what ProfGAB said about running without the pin I believe I am going follow CJ's thought of repair/fine tune as there was a gap between the buffer and the rear of the BC.

Thanks again for the replies!