maxgusmc Posted April 23, 2011 Report Share Posted April 23, 2011 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? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted April 23, 2011 Report Share Posted April 23, 2011 Use the search feature on this site - before you order those parts, find out what's going on with that SASS barrel. I'm not so sure that those parts will work together - I've never built one, but I've watched others try. <dontknow> Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted April 23, 2011 Author Report Share Posted April 23, 2011 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! Quote Link to comment Share on other sites More sharing options...
imschur Posted April 23, 2011 Report Share Posted April 23, 2011 He meant search this site, SASS barrel requires a proprietary gas block. Theres only two options and both are DPMS and pricey Quote Link to comment Share on other sites More sharing options...
imschur Posted April 23, 2011 Report Share Posted April 23, 2011 I also explain it here about half way down Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted April 23, 2011 Author Report Share Posted April 23, 2011 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. Quote Link to comment Share on other sites More sharing options...
imschur Posted April 23, 2011 Report Share Posted April 23, 2011 I ended up with the $90 gas block Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted April 23, 2011 Author Report Share Posted April 23, 2011 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. Quote Link to comment Share on other sites More sharing options...
imschur Posted April 23, 2011 Report Share Posted April 23, 2011 Sorry man It cant fit without modifying the barrel diameter. The JP is based on Milspec AR-15 dimensions. The SASS is a different beast. I believe DPMS recently introduced a low cost SASS GB. None of them are as slick as the JP though Quote Link to comment Share on other sites More sharing options...
6132expert Posted April 24, 2011 Report Share Posted April 24, 2011 Is this problematic only to the DPMS SASS barrel, or is this an issue with all SASS barrels? Quote Link to comment Share on other sites More sharing options...
imschur Posted April 24, 2011 Report Share Posted April 24, 2011 DPMS SASS The major barrel diameter is substantially larger then a typical barrel. When the milspec block is installed the barrel blocks a portion of the gas tube hole in the gas block. Quote Link to comment Share on other sites More sharing options...
6132expert Posted April 24, 2011 Report Share Posted April 24, 2011 So something like the SI SASS barrel would not have the same issues. I feel like DPMS is is really move there products to fit there products like RR has done. I guess we should be thankful that there are other great manufacturers to turn to. Quote Link to comment Share on other sites More sharing options...
imschur Posted April 24, 2011 Report Share Posted April 24, 2011 I have no idea on the SI but I would be surprised if it exhibited the same issue as the DPMS. While most here agree DPMS is headed in a proprietary direction I actually like the concept of the heavier, larger OD DPMS SASS barrel Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted May 7, 2011 Author Report Share Posted May 7, 2011 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. Quote Link to comment Share on other sites More sharing options...
imschur Posted May 7, 2011 Report Share Posted May 7, 2011 DPMS responds best to the phone and Jon on their forum. CMMG used to be great at replying to emails. Sorry to hear they didnt get back to you Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted May 7, 2011 Author Report Share Posted May 7, 2011 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! Quote Link to comment Share on other sites More sharing options...
JMoto Posted May 13, 2011 Report Share Posted May 13, 2011 Just to clarify, you were able to get the JP ADJUSTABLE gas block to fit with the JP hand guard? I am looking at doing this with my DPMS SASS but after looking at the measurements I thought it would not fit. On JPs site, it lists the handguard inside dimensions for the 308 to be 1.75in which is the same as the AR-15 rail. Quote Link to comment Share on other sites More sharing options...
washguy Posted May 27, 2011 Report Share Posted May 27, 2011 Hi Guys! I just ordered a dpms 18" sass barrel and got the new dpms sass gas block ....cost is twenty bucks from jse surplus...and its low profile too:) Wash Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted June 1, 2011 Author Report Share Posted June 1, 2011 It all came together this weekend! Scope is a U.S. Optics SN-12R. Quote Link to comment Share on other sites More sharing options...
JMoto Posted June 2, 2011 Report Share Posted June 2, 2011 I have optic envy! Is there any way you can measure the height of jp tube from the centerline? I have heard the tube is offset, but nobody has been able to tell me how much clearance there is top side. If you want you could even measure from the top of the barrel and give me that dimension as i have the same barrel. Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted June 2, 2011 Author Report Share Posted June 2, 2011 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. Quote Link to comment Share on other sites More sharing options...
imschur Posted June 2, 2011 Report Share Posted June 2, 2011 Thats a fine looking rifle. Can I use the image on the site? Quote Link to comment Share on other sites More sharing options...
maxgusmc Posted June 2, 2011 Author Report Share Posted June 2, 2011 Absolutely; use either or both photos if you like. It will be an honor. Quote Link to comment Share on other sites More sharing options...
imschur Posted June 2, 2011 Report Share Posted June 2, 2011 Thanks. Can I get them uncropped so I can crop them at 575x350. If you dont mind pm me for my email. I want to use them on the rotating image thingy on the home page.Much appreciated. Quote Link to comment Share on other sites More sharing options...
JMoto Posted June 4, 2011 Report Share Posted June 4, 2011 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.Max, thank you so much. It has been very hard to get data on this kind of stuff. It looks like that tube will leave me a couple of hairs of room for what I need to do. Quote Link to comment Share on other sites More sharing options...
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