Melonited barrel with 4358 logged rounds. The barrel extension turned off before the AAC 51T Miter mount so I got to see something unexpected. The bolt, a Colt has nearly 12,000 rounds and looks new by comparison. Apparently the relative hardness of the extension may have suffered in the heat treatment of the melonite bath.
I remember Grant mentioning that barrel extensions are prone to loosening after a barrel assembly is melonited.
^^ Yes. Constructor mentioned meloniting barrels with the extension off for that very reason. I dont know about the wear though… AFAIK, the process should increase the surface hardness of the extension. One issue I have read, IIRC, is the possibility or instances of the extension becoming brittle. I dont know if this had to do with the length of time the process took to do a barrel correctly and thus affecting the relatively smaller barrel extension or the process itself, regardless of duration, due to the minimal surface area of the extension.
Great pic of how an extension wears and headspace can become problematic. Not sure about the fruit finish nonsense piece of the equation… but this pic illustrates why the proper heat treat/hardness on an extension is critical for longevity.
I wish the picture I took of the bore was as clear, the 4358 rounds haven’t begun to wear the bore.
Yes, I think this is a rarely seen item of interest.
I had to go back and look at that :eek: I don’t know how I missed it before.
Who’s barrel is that?
Can someone tell me what I’m looking at? I know its a barrel extension but what’s the issue?
- The barrel is gone.
- The bolt seems to have worn the shit out of it for a hair over 4k rds.
Wow. Im Not sure how I missed either of those, thanks.
It is a custom one off from a major cut-rifled barrel maker. It was turned in a custom AR shop in TN, and QPQ’d by Joel Kendrick’s firm. No blame here on my part, only speculation as to what I am looking at. Measurable headspace is in line with other rifles, function has been fine has had precision.
Who thought it was a good idea to case harden a critical component that had already been heat treated?
Daniel Defense does…?
Source?
If DD is heat treating and case hardening, I have to believe they are managing the processes to achieve a properly manufactured part. Joel Kendrick and MMi have something to sell and apparently the OP got sold…
Well, they do qpq barrel extensions in place, and then re torque them.
Always use a barrel vise with barrel clamped in front of gas block to remove muzzle devices instead of a receiver clamp for that reason.
I think a bunch of companies just starting to use Melonite are going to find out the extensions must be removed, cleaned and torqued after the Melonite process.
One company says to just drill the alignment pin deeper. That may keep the extension from turning much but if it isn’t torqued tight to begin with all it will do is hold it loose.
A loose extension isn’t good for accuracy.
Take a stainless extension and a melonite extension and check both with a hardness testing file. http://www.mscdirect.com/product/00692533
I think the results will surprise you.
It’s scary… the shit that goes on at some of these companies.
What’s the company name?
Thanks for your post.
I’m not sure that Joel is still involved with the same firm that did this work.