[IamScotticus]

Here we are with my new replacement RDB piston Bolt Carrier Weldment (BCW) assembly. Thank you KT for the excellent shipping and packaging!

As some are aware of, and I became very aware of before my first 100 rounds, the RDB piston bushing can eject from out the font of the BCW tube.

This is the brass (?) bushing that retains the spring and centers the BCW on the OP rod. There is a picture of it below (not actual size).

There is a fillet weld on the top of the tube that is supposed to reinforce the method for securing this bushing in place which I have to assume is a stamp or stake. The caliper is showing the depth at which the bushing is inserted.

A view inside of the BCW tube that my bushing came out of does not show any obvious sign of a method to retain the bushing. Also looking at the bushing, I can't find any evidence of any stake or indention.
The view you see is directly under where the weldment is just in front of the shoulder that serves as the bushing stop.
Looking at these parts, I cannot see any effective means that would have kept my bushing from walking out.

Inspecting my new BCW, I do not see any obvious difference in construction or any updated method for retaining the bushing.

Therefore, based on my experience, I need to monitor my bushing for creep after every shooting session as part of my maintenance. I will do this with a caliper probe and measure the bushing depth in the tube from the tube face to bushing face.

I measure about 12mm or .585". I have crude cheap instruments now.
I will buy a digital caliper with depth probe soon.

The point I am trying to make here is all RDB users should be watching this for themselves and why. I did speak with a gentleman at KT about this who could take the issue to the engineers meeting. I suggested changing the direction of the bushing splines so the stamp would have better purchase.

I would be very happy to see anyone check and chime in with their piston depth!

 

[BlakeHanson]

You never show this part here of your original part.

It obviously does something.
Perhaps it was misplaced or malformed and the reason that the bushing came out

.

 

[IamScotticus]

Here ya go. I suspect its a weld fill in a hole. Which I wouldn't expect to weld to brass.
I don't see any defect.

 

[BlakeHanson]

Now if you had done that about oh, 42 posts ago, someone would have said:
"Well, no wonder it came apart, it never got tigged and punched".
Basically, it skipped a manufacturing step. Easy to do. Just drop a part in the wrong bin.
One that was 'un-done' got dropped into the 'done' pile.
The divot in yours is basically the "target" for the welder guy to know where to drop the torch in.

 

[mikego_34]

I suppose we wouldnt know if this is occuring in other people's RDBs if they arent members of this forum, but it does seem like its not occuring often enough to call it a design flaw based on the lack of occurrences reported here. Ive seen a few post on here that speak to RDBs with pretty high round counts and have not had to deal with this issue. It also sounds like this issue occured very early on in your round count, correct me if I am wrong iamscottasus. That to me says your particular RDB had a manufacturing defect to a particular component of the bolt/piston assembly, which would mean a less likely chance of there being a systemic design flaw in the RDB. Keep us posted on how the new part works out for you!

 

[BlakeHanson]

That to me says your particular RDB had a manufacturing defect to a particular component of the bolt/piston assembly, which would mean a less likely chance of there being a systemic design flaw in the RDB.

The bushing only holds the spring in the tube long enough for the guy to put the punch-dent in the tube; which holds the spring.

One guy, made a mistake, on one part, and dropped it into the wrong bin.
Humans

No reason to redesign the gun or recall all the RDB's.

 

[IamScotticus]

Yes, my bush walked out at about 80 rounds. So Blake, you say that the weld fill is stamped and mine was not stamped?
Mikego, I dunno if the issue is a systemic flaw, I just stand on the philosophy of "if something can go wrong, it will".
Unless something is put in front of or through the bushing to keep it from moving, it can get moved.

 

[BlakeHanson]

Yes, my bush walked out at about 80 rounds. So Blake, you say that the weld fill is stamped and mine was not stamped?

It's not a weld. It's not a stamp.
It's heated and punched.
The guy puts the tip of his TIG torch into the divot hole and the arc flies around to all of the sides of the dent heating it bright-red hot in a couple of seconds.
Since the metal is almost molten, it is very soft. When he pulls the torch out, he puts a punch on the soft metal and strikes it bulging the soft metal on the inside of the tube down onto the metal spring in the tube locking it in place forever.
Your original part skipped this step.
It's a "before" picture.

If you look close at the new part you can see the circular heat-signature of the torch where the metal was turned blue by the torch before it was coated.

 

[IamScotticus]

Hbereta commented early on tht my puch looked neater than his. I didn't know what that meant.
Perhaps some folks will put up some pics of their piston punches??

Regardless, new BCW, 75 rounds down the pipe, clean brass, RDB back on line.

Pile of brass

 

[BlakeHanson]

Regardless, new BCW, 75 rounds down the pipe, clean brass, RDB back on line.

Orrrrrr, maybe we could just mark it, "Case Closed"?