Could someone check their Apex replacement barrel for me?

[FredBart]

If you have an Apex M&P 1.0 full size replacement barrel, would you be be so kind to look at the bottom of the square area along the barrel's length and width to see if yours has small scratches or indentations from use? Apex says that this is a normal wear area, but it does not occur on the OEM factory barrel. The wear area looks similar to small center punch marks. Thank you for looking.

 

[bsoppet]

I noticed the same issue as you after only firing 50 rounds. I also contacted Apex with detailed photos and they also said it was normal 'burnishing' wear. I am a materials test engineer and questioned them about the barrel alloy and heat treatment hardness. The barrels by KKM and Storm Lake have published alloy and hardness in their specifications....Apex does not. I tested the barrel's hardness in our research lab and found the hardness of my SDI to be in the range of Rc-38 to 40. This is less than the KKM & Storm Lake specs...but then again their barrels are meant to be drop-in and with no fitting as the Apex SDI barrels do. You can prevent the Burnishing deformation (brinelling) by having the barrel hardened after test fitting AND before firing any rounds. The M&P OEM barrels are very very surface hardened by the melonite-carbonitriding process. I suspect the locking block is also hardened greater than the Apex barrel and that is where you are seeing the deformation on your Apex barrel and not on the OEM. I have checked on a few other forums and this Apex wear is noticed also. I took a lot of detailed measurements of the Apex barrel after initial fitting and before test firing. I noticed some wear on other areas such as the barrel hood-slide interface and barrel contact point to the breech face to name a few. This was not unexpected because the slide is also melonite hardened. So far I have about 1500 rounds through the Apex barrel and the wear has stabilized and not got any worse by checking with digital calipers. If I do another Apex barrel, I will send it out for carbo-nitriding treatment before beginning any test firing. That way I can maintain the integrity of the fitting tolerances and stabilized lock-up.

Hope this helps answer your concerns.
Bill

 

[FredBart]

Thank you, Bill. I understand the Brinell hardness testing system and ironically the marks are somewhat similar to the small dents found after a Rockwell "C" hardness test.

The black "melonite" OEM finish show no scratches or marks. You are correct that the softer Apex barrel has small surface scratches from wear. I suppose it would be difficult for the fitter to file the OEM material to fit properly. This may be why Apex leaves their barrel in a softer condition.

It must have been a coincidence that my slide release broke about 300 rounds after installing an Apex barrel.

Thanks again for your comprehensive answer.