maxgusmc

You shouldn't have any fit-up issues unless you are intending the free float tube to pass over the JP railed adjustable gas block. In that case, I'd elect to go with the JP Low Profile adjustable gas block.

I used Duracoat Magpul OD Green.

I have had several questions about the JP gas block fit up, so here is a couple of pictures:

Absolutely; use either or both photos if you like. It will be an honor.

As close as I can measure, it appears to be 1.00" from centerline to the inner diameter of the JP free float tube on the top side and 0.75" on the bottom side.

It all came together this weekend! Scope is a U.S. Optics SN-12R.

There wasn't any problem communicating with CMMG, only with DPMS. I didn't need to contact CMMG. I may try to call DPMS before exchanging the upper with MidwayUSA since you say they respond best to a phone call. Thanks!

Well, I thought it was time for an update on the build. The JP gas block arrived and I put a micrometer on it to measure the height of the gas tube above the top of the barrel opening. Found it to be precisely the same height of the larger part of the barrel above the smaller part. Decided to try a loose fit up to see how everything came together. It's a go!!! I put the loose fit upper on my completed lower to get a glimpse of what it will look like. Looked great but ran into a small problem… The DPMS upper receiver fit nicely into the CMMG lower. There was a little difficulty with the pivot pin, but I expect a snub fit. Then I experienced something I wasn't expecting. The upper receiver would rotate forward only about 15 degrees. The pivot stud contacts the lower receiver and prevents further rotation. The rotation is limited enough to prevent removing the bolt carrier group while the upper is attached to the lower. It appears that the pivot pin hole may have been drilled slightly closer to the upper receiver body than it should be, causing there to exist excess metal below the hole. When rotated, the pivot stud comes into contact with the lower receiver. I took the upper off and tried to put it on the DPMS action block that I bought to help with barrel installation. The pin won't go through the hole in the pivot stud. On examination of the fit up with the action block, my suspicion that the hole was misdrilled was confirmed. So I emailed DPMS customer service to explain the situation. No reply. After 3 days, I wrote MidwayUSA where I bought the upper. Had a reply within a couple of hours. They wrote to DPMS on my behalf. Three more days passed. There was still no contact from DPMS. I wrote MidwayUSA again and they said to return it to them for an exchange. BRAVO MidwayUSA!!! I can't believe that DPMS, a company I had great respect for, won't stand behind their products. Disappointing. I am boxing the upper up this weekend to send out to MidwayUSA on Monday. Hopefully within a couple of weeks, I will have a new upper and be able to complete the build. In the mean time I will duracoat the hand guard to match the stock and pistol grip.

Great looking rifle! You did a great job! It is very similar to what I have in mind (See my concept drawing below). Everything is together except the gas block & tube and the flash hider. I'll post a photo of the completed rifle once it's all together. I'm holding out hope I can put the JP adjustable gas block on mine. Otherwise, I will be following your lead with the DPMS gas block.

imschur - Thanks for sending the link. Good info. Looks like there may be an issue with the height of the gas tube opening above the barrel for a non DPMS SASS gas block in that the gas tube port may be obstructed. I'll take some measurements before attempting the install and adjust my plan if the gas tube port on the JP gas block doesn't have sufficient height for the gas tube to clear. Since the JP doesn't require set screws, I don't think that is going to be an issue. I'll let y'all know if the will JP work or not once I have had a chance to look at it. Thanks again for the help. Now I know where to look and what may present a challenge.

Thanks, 98Z5V! I had searched here and elsewhere with no luck on this particular configuration. That's why I posed my question. I don't know what I may not have thought of to get everything to come together. The barrel step down in diameter to 0.936" is 9.3125" from the base. The overall length of the VTAC 308 mid length hand guard is 9.125". This leaves a 0.1875" clearance from the closest point the gas block can be installed. So I don't see an interference problem. The gas block has a .936″ bore. This matches the barrel diameter at the gas port. So I don't see an issue with this. If I have any issues or if it goes smoothly, I'll pass it on in this string to include photos. Parts to arrive this coming week!

I'm building an LR-308 using the DPMS 18" SASS barrel. Have ordered the JP VTAC 308 mid length hand guard and the JP .936 railed adjustable gas block. Has anybody had any experience with this configuration? Any problems / insight you can share?