Buffer Tube material

[BoilerUp]

Is there an easy and reliable way to tell if a receiver extension is made from 7075 or 6061? I got one as part of a stock deal (used) but suspect it is not from the manufacturer as claimed. It is mil-spec dimensions.

Edit: anyone know if they weigh the same?

[SINNER]

If you know anyone with a hardness tester 6061 should be 40 on the Rockwell A scale. 7075 should be 53-54. Visually no way to tell.

[RiverRat]

Not that I've found. There are semi destructive tests (e.g., hydrochloric acid on bare alloy, 7075 will turn black) - but I doubt you want to go that way.

There is a small density difference between the alloys (7075 is more dense) but it doesn't seem possible to reliably differentiate finished tubes on weight.

If it's got rolled threads or a grey dry lube film on the inside, chances that it's 7075 go WAY up (like almost 100%). Not having these things doesn't mean it's 6061 though: there are plenty of uncoated, cut 7075 extensions out there.

[DutyUse]

Take a photo for us. Be a lot easier to judge

[BoilerUp]

Thanks for the input. The extension came with a used BCM gunfighter stock which the seller said came as a complete assy from BCM. But it had a PSA buffer so he knew he lost track of which parts were on which rifles. Looking at the pics on the BCM website, the buffer does look to be the same (it has the ridge extending forward under the spine, which is unique to any extensions in my inventory and is clearly seen in the stock photos on BCMs website). I was a little skeptical at first because it is a darker black finish and my LMT has the grey-looking anodizing.

I'm not particularly concerned, but was a bit curious

https://photos.smugmug.com/photos/i-LxFDLHC/0/XL/i-LxFDLHC-XL.jpg