Signs of high pressure test?

**constructor** · 06-03-23, 12:09

Originally Posted by prepare

Interesting...

So as a manufacturer you can basically order 100% TDP BCG's from Microbest?

From what the VP told me in 2008 yes, they have been the same BCGs except for the last extractor spring change when they went to the piano wire spring.
Yeah I know Colt owns the TDP and no one should know the true details right? If that is true no one is making BCGs to the TDP. Colt changed to piano wire springs and MB did about the same time.
BTW I don't know anything about SOLGW.

**lysander** · 06-03-23, 20:49

Originally Posted by constructor

. . . except for the last extractor spring change when they went to the piano wire spring.

. . . Colt changed to piano wire springs and MB did about the same time.

When did this happen?

According to the information I have from Rock Island, the extractor spring has been music wire spring, ASTM A228 since at least 1964.

The diameter and/or number of coils has changed a time or two, and even the number of springs has changed*, but the material has always been ASTM A228, music wire.

___________
* The first extractor spring was a single 5 coil spring, the second design of the extractor spring assembly was two nested springs. The third design was the one with the white, then blue insert. The forth design was the same spring as the third, but with a stiffer black insert, we are currently on the fifth design with the new copper washed spring and the same insert as the forth.

**constructor** · 06-03-23, 21:32

Originally Posted by lysander

When did this happen?

According to the information I have from Rock Island, the extractor spring has been music wire spring, ASTM A228 since at least 1964.

The diameter and/or number of coils has changed a time or two, and even the number of springs has changed*, but the material has always been ASTM A228, music wire.

___________
* The first extractor spring was a single 5 coil spring, the second design of the extractor spring assembly was two nested springs. The third design was the one with the white, then blue insert. The forth design was the same spring as the third, but with a stiffer black insert, we are currently on the fifth design with the new copper washed spring and the same insert as the forth.

It's the same stuff, it looks like copper instead of the black springs( Chrome Silicon wirestock). The current springs look like this
Attachment 70396

**T2C** · 06-03-23, 21:39

Does anyone know the testing standards used by L.W. Schneider? For those who do not know, they are a parts source for multiple firearm manufacturers.

**lysander** · 06-03-23, 22:20

Originally Posted by constructor

It's the same stuff, it looks like copper instead of the black springs( Chrome Silicon wirestock). The current springs look like this
Attachment 70396

Chrome silicon was never in the Colt TDP . . . Always music wire ASTM A228.

**constructor** · 06-03-23, 22:52

Originally Posted by lysander

Chrome silicon was never in the Colt TDP . . . Always music wire ASTM A228.

IIRC I noticed the spring change in Microbest bolts around 2009-2010, my shop was still in Colorado at that time. I thought they were music wire/piano wire or whatever you wish to call it in the beginning(m16) but were changed to Cs to try to fix the extraction issues with carbine gas barrels. They still say CS springs will outlast a piano wire spring by 4 times and provides 80% more force. BCM, Brownells, Tubbs and many others still sell them(CS) as an upgrade.
Do you have a copy or copies of the Colt TDP of the years involved from 1966 to present?

**lysander** · 06-04-23, 09:02

As stated above, there have been five (5) iterations of the extractor spring assembly

P/N 61568 - Spring. A single 5 coil spring, referenced in Air Force Manual 50-12, dated 30 Aug 1963, and "The Black Rifle"

P/N ??? - two nested springs, the outer of which might be 61568. There are a number of references to "extractor springs" in PS Magazines from the late 1960s, and "Report of the M16 Rifle Review Panel, Appendix 11, M16 Product Improvement Modifications" (available on line)

P/N 8448755 - Spring Assembly, Extractor, consisting of P/N 8448754 - Insert, and P/N 8448753 - Spring, Extractor. This is the blue rubber insert and silver or black spring (no color is specified)

P/N 12972692 - Spring Assembly, Extractor, consisting of P/N 1297293 - Buffer, Extractor, and 8448753 - Spring, Extractor. This was released in December 1995 as the initial extractor spring assembly for the M4 carbine, this is the black rubber insert and black (or silver) spring.

P/N 13004786 - Spring Assembly, Extractor, consisting of P/N 12972693 - Buffer, Extractor, and P/N 12999901 - Spring Extractor. This was released in January 2003, and is the latest assembly with the black rubber insert and copper colored spring.

I have access to all but the first two drawings, but I am not at liberty to give them out, even though you can find your own copies online with a little digging. Trust me, the extractor spring has always been music wire.

As to this:

They still say Chrome Silicon (CS) springs will outlast a piano wire spring by 4 times and provides 80% more force.

IT IS ONLY TRUE AT TEMPERATURES ABOVE 300° F, and since the extractor spring is not maintained at that kind of temperature, this is a non-issue. Also, many people compare CS to carbon steel and say that it is better than music wire. "Carbon steel" springs are not the same as "music wire" springs.

But wait, there's more.

Music wire springs generally have better fatigue life at room temperature (below 250° F) due to the fact that music wire can maintain a better surface finish than CS or plain carbon steel wire. Also, the belief that CS springs are stronger is not necessarily true. It is only true at wire diameters larger than 0.08" (the thickest spring in the AR is the Action Spring, and that's only 0.078" in diameter).

Generally speaking, music wire is the best choice for springs unless you require:

- the spring is going to live in an environment with a temperature above 300° F or below 0° F.
- the spring is going to be subjected to a corrosive environment.
- the spring wire is going to be larger than 0.080".

Further, CS is no better at resisting corrosion than music wire, there is no reason it would be used over music wire or stainless steel in any rifle. And, never replace stainless steel spring with CS springs, you won't like it.

**constructor** · 06-04-23, 09:26

The only complete TDP ever released was in 1996 when they wanted bids for the M4 SOPMOD project.
Are you saying all springs were music wire but could be black or copper colored? I didn't remove the springs and send them to a lab for analysis, just noted the extractor springs in the Microbest bolts changed to a copper color.
Thanks for the history of springs.
I don't seem to have issues with extractor springs, I have a big bag that probably had 10,000 in it to start. I installed them in the bolts we machined and shot, can't ever recall one failing or having a customer call and say one failed.