When I joined this forum a few years ago, one of my first inquiries related to suppressing the AR-10. I already had my YHM Phantom 338 suppressor and was aware of the Arma-Lite 338 Fed 22" upper. The pictures today show the result of what eventually was a 4 year project in the making and I have many people to thank for the end result (some of whom are on this site).
I wanted to utilize the YHM can and the uniqueness of the 338 FED round in the AR-10 format.
I initially placed calls to Arma-Lite and made an acquaintance with the lead tech, Tim Rooker. I told him about my project and he had some concerns about barrel length, gas system / gas port compatibility, etc. His initial recommendation was to shorten no less than 20" and proceed cautiously.
This spring, I bought an AR-10 in 338 Federal on Gunbroker.com. Around this time I got to know an excellent gunsmith in the greater Houston area named John Powers (Powers Metal Works). John worked on a couple of projects for me previously. I asked him if he would help me with this project. He agreed.
I wanted baseline performance data and took the stock rifle to the range and shot a few rounds through the chrony. Federal 185 SP's had an avg MV of 2764 fps. I also developed some subsonic loads using Nosler Accubonds 250grn and Trailboss powder.
At this time I called Arma-Lite and wanted to verify that the SASS hand guard would work on the 338 Federal Upper. Tim said yes it would. So I bought the SASS Adj Gas System.
Next, I took the upper, YHM Phantom suppressor and the Arma-Lite SASS hand guard to John's shop. We discussed barrel lengths. We decided upon 18" with the understanding that some gas port mods might be needed. First observation about John's work is the meticulous way in which he conducts this work. He explained how he sets up the equipment so that the threading is true to the bore. We were in fractions of thousandths at this point! That was cool to observe. He removed 4" from the barrel, re-crowned, and threaded to the 5/8 x 24 spec.
With the barrel cut and threaded, he measured the gas port at 0.087". At this time, there was some confusion as to what to do with the port size because the Tech Bulletins that come with the SASS hand guard are for the 308 WIN not a 338 FED. I placed a quick call to Tim and he advised me to try it first as-is and then increase as needed.
John assembled the upper.
I took the rifle to the range and shot the same Federal 185's WITHOUT the can through the chrony to see what effect trimming 4" off of the barrel had. Average MV was 2713 fps.
That is a difference of 50fps for 4" of barrel length (12.5 fps per inch). Not bad at all!
The rifle would not cycle properly in either configuration (suppressed or un-suppressed) with the full power loads. I took the rifle back to John a few weeks later. John began the process of drilling, re-assembling the SASS system and test firing through each of the following port sizes: 0.089, 0.093, 0.096, 0.098, 0.099, 0.101, and ended with 0.104". The cases would not fully extract until 0.099" but would not pick up the next case until 0.101.
Here's the finished project!
I wanted to thank Tim Rooker (Arma-Lite) for technical assistance, JasonFaz (here on the Hide) for the 338 Fed knowledge, Nortonious (here on the Hide) for the accessories! Lastly, thanks and kudos to John Powers for helping me get this project up and running safely!
TX COWDOC
I wanted to utilize the YHM can and the uniqueness of the 338 FED round in the AR-10 format.
I initially placed calls to Arma-Lite and made an acquaintance with the lead tech, Tim Rooker. I told him about my project and he had some concerns about barrel length, gas system / gas port compatibility, etc. His initial recommendation was to shorten no less than 20" and proceed cautiously.
This spring, I bought an AR-10 in 338 Federal on Gunbroker.com. Around this time I got to know an excellent gunsmith in the greater Houston area named John Powers (Powers Metal Works). John worked on a couple of projects for me previously. I asked him if he would help me with this project. He agreed.
I wanted baseline performance data and took the stock rifle to the range and shot a few rounds through the chrony. Federal 185 SP's had an avg MV of 2764 fps. I also developed some subsonic loads using Nosler Accubonds 250grn and Trailboss powder.
At this time I called Arma-Lite and wanted to verify that the SASS hand guard would work on the 338 Federal Upper. Tim said yes it would. So I bought the SASS Adj Gas System.
Next, I took the upper, YHM Phantom suppressor and the Arma-Lite SASS hand guard to John's shop. We discussed barrel lengths. We decided upon 18" with the understanding that some gas port mods might be needed. First observation about John's work is the meticulous way in which he conducts this work. He explained how he sets up the equipment so that the threading is true to the bore. We were in fractions of thousandths at this point! That was cool to observe. He removed 4" from the barrel, re-crowned, and threaded to the 5/8 x 24 spec.
With the barrel cut and threaded, he measured the gas port at 0.087". At this time, there was some confusion as to what to do with the port size because the Tech Bulletins that come with the SASS hand guard are for the 308 WIN not a 338 FED. I placed a quick call to Tim and he advised me to try it first as-is and then increase as needed.
John assembled the upper.
I took the rifle to the range and shot the same Federal 185's WITHOUT the can through the chrony to see what effect trimming 4" off of the barrel had. Average MV was 2713 fps.
That is a difference of 50fps for 4" of barrel length (12.5 fps per inch). Not bad at all!
The rifle would not cycle properly in either configuration (suppressed or un-suppressed) with the full power loads. I took the rifle back to John a few weeks later. John began the process of drilling, re-assembling the SASS system and test firing through each of the following port sizes: 0.089, 0.093, 0.096, 0.098, 0.099, 0.101, and ended with 0.104". The cases would not fully extract until 0.099" but would not pick up the next case until 0.101.
Here's the finished project!
I wanted to thank Tim Rooker (Arma-Lite) for technical assistance, JasonFaz (here on the Hide) for the 338 Fed knowledge, Nortonious (here on the Hide) for the accessories! Lastly, thanks and kudos to John Powers for helping me get this project up and running safely!
TX COWDOC
