archangel2003 Posted April 16, 2016 Report Share Posted April 16, 2016 I got the Mid length gas system but the mid length had guards do not fit. On my 16 inch AR-15 with a mid length gas system barrel, the had guard is just long enough so that the front had guard cover and gas block fits flush with the barrel step at the gas port. On my 18 inch AR-308 with a mid length gas system barrel, the hand guards are about 1/4 inch too long so the front cover is too far forward, and the gas block is is too far forward and the gas port does not line up. I though mid length was mid length no matter if it was AR-15 or AR-308. Everything on the AR-15 upper fits like it should. The barrel is a LOSOK Black Nitride 7.62 NATO (.308/7.62x51) 18 in. It's mounted on a DPMS 308 A3 upper receiver. It is held by a PSA PA10 .308 barrel nut and delta ring assembly. Any Ideas? I don't have the dimensions of the mid length barrel or gas system so am not sure what is off. Quote Link to comment Share on other sites More sharing options...
blue109 Posted April 16, 2016 Report Share Posted April 16, 2016 What handguard is it? I ran into a similar issue with my PRI delta handguard. It seems they have rifle length that is suppose to be used with a low pro gas block, and then a special rifle length that is 1/4" shorter for use with flip up gas block sights or FSBs. Quote Link to comment Share on other sites More sharing options...
NTXshooter Posted April 17, 2016 Report Share Posted April 17, 2016 I had the same problem with Magpul also. I tried to trim it but could not get it to fit. Had to go with a free float one instead. Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 17, 2016 Author Report Share Posted April 17, 2016 (edited) Here are some pictures. The had guards are from CDNN https://www.cdnnsports.com/handguard-midlength-single.html AR15 HANDGUARD MIDLENGTH SINGLE INSULATED ORIGINAL EQUIPMENT Manufacturer: ORIGINAL EQUIPMENT Model: AR15/M16 Color: BLACK Composition: SYNTHETIC SKU: DANML UPC: 783583556071 I have the same set on my AR-15 that is also a mid length barrel gas system and it fits. On the AR-15 the bottom is a PITA to get past the delta ring, but much easier to get past the delta ring on the 308 as the nut serrations are higher up, but if I put the top in first, the bottom would not even pass the Delta ring. Edited April 17, 2016 by archangel2003 Quote Link to comment Share on other sites More sharing options...
blue109 Posted April 17, 2016 Report Share Posted April 17, 2016 (edited) Generally speaking you can't expect an AR15 part to fit a 308. The delta ring isn't to the same spec, so it stand to reason it may push the handguard forward too much. Have you tried locking the front in first? I have a kac RAS and it won't go on if you try to slide it under the delta ring first. I slide it in the cap, then crank the delta ring back all the way and give the rail a good tap and it pops down onto the barrel nut. Edited April 17, 2016 by blue109 Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 17, 2016 Author Report Share Posted April 17, 2016 The had guards are supposed to fit both as long as they are mid length gas system. If you look at the pictures, the close up of the gas block, you will see that when the bottom is installed properly the hand guard is too long. If I had access to the proper dimensions of the mid length gas system barrel, I could verify where the mismatch is. I guess I'll be looking for the least expensive free float system I can find. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted April 17, 2016 Report Share Posted April 17, 2016 Who knows what spec's the Barrel maker made the gas system to , some don't make the barrels to be fitted with a std two piece hand guard . Most std two piece hand guards need some type of trimming to fit the larger 308AR. With Gas block mounted & gas Tube installed , where does the end of the gas Tube line top in the Upper Receiver ? Photo? Should sit in the middle of the Cam Pin recess in the Upper Receiver. Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 17, 2016 Author Report Share Posted April 17, 2016 (edited) Yep, looks like yours only cleaner as it has zero rounds through it. Edited April 17, 2016 by archangel2003 Quote Link to comment Share on other sites More sharing options...
survivalshop Posted April 17, 2016 Report Share Posted April 17, 2016 Thats good , is that with the Hand Guard cap between the Gas Block & the Barrels stop Flange ,for the Gas Block ? The reason I asked the first question was to make sure the Barrels Gas Block stop Flange was in the correct orientation . If you want to use those Hand Guards, you will need to find a way to fit them . Wait , are you saying my Rifle is dirty , well I take it as a Compliment , means I use them , thanks. Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 17, 2016 Author Report Share Posted April 17, 2016 Everything lengthwise seems to be correct except the barrel nut. It looks like the barrel nut serrations where the wrench grabs it, are spaced further forward, and that seems to be the reason the delta ring is so easy to get past. The barrel nut is from Palmetto State Armory so I'm going to take it off and measure it. Comparing those measurements to a known DPMS barrel nut should verify if that is the issue or not. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted April 18, 2016 Report Share Posted April 18, 2016 Your thinking is , it could be longer ? Makes sense . Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 18, 2016 Author Report Share Posted April 18, 2016 Well, I have 1.060 for the total length of the barrel nut, front to back, and the threads are .739 deep from the back to the barrel nut contact face. So the front of the barrel nut forward of the contact face is .321 from where the nut touches the barrel (nut contact face). The width of the serrations is .1180 so subtract 1/2 of that leaves the serrations centered at .262 in front of where the nut touches the barrel. Those serrations are where the groove that the hand guards locate on. If anyone had a DPMS 308 barrel nut and can take measurements we can verify if it is correct. I have to assume the gas block locating shoulder, and barrel mounting face are properly located as the gas tube is located where it should be in the upper. My bet is the serrations on the DPMS nut are further back from the end of the nut. If the serrations were even with the contact face, my hand guards would fit. Quote Link to comment Share on other sites More sharing options...
blue109 Posted April 18, 2016 Report Share Posted April 18, 2016 How does it measure against the AR15 barrel nut? Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 18, 2016 Author Report Share Posted April 18, 2016 I don't have an ARA-15 barrel nut available without tearing down a rifle. I have been looking on line and the DPMS-308 look just like mine with the serrations at the front, and with the delta ring installed, the serrations seem to be closer to the front like mine look. Just to make sure I'm not pulling a bonehead, but, the slip in hand guards ARE the same lengths (Carbine, Mid length, and Rifle length) for the AR-15 and the AR-308. When looking for them, they all indicated they were the same lengths, so mid length AR-15 grips and gas system was the same as a mid length AR-308. The mid length gas system on both of my rifles used the same gas tube and gas block (the AR-15 and the AR-308). Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 18, 2016 Author Report Share Posted April 18, 2016 1 hour ago, blue109 said: How does it measure against the AR15 barrel nut? I did notice the AR-15 is near impossible to get the delta ring back far enough by hand to get the guards off, and the AR-308 is real easy as they are not as deep in the delta ring. Quote Link to comment Share on other sites More sharing options...
DNP Posted April 18, 2016 Report Share Posted April 18, 2016 I had to buy one of those girly tools for pulling back the ring on my 15. Hope you get it figured out. Would hate to see you spend more money Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 18, 2016 Author Report Share Posted April 18, 2016 (edited) I already have 2 sets of (thankfully cheap) hand guards that are too long. I wish I knew someone near me who builds AR's Edited April 18, 2016 by archangel2003 Quote Link to comment Share on other sites More sharing options...
survivalshop Posted April 18, 2016 Report Share Posted April 18, 2016 I have never measured a DPMS 308LR Barrel nut or a AR 15 to tell the difference , but the Barrel & Barrel Extension on a 308AR has to be larger , so there will probably be differences in the two . I have a couple of AR 15 barrel nuts around here & will take some measurements , so you can compare . Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 18, 2016 Author Report Share Posted April 18, 2016 4 hours ago, survivalshop said: I have never measured a DPMS 308LR Barrel nut or a AR 15 to tell the difference , but the Barrel & Barrel Extension on a 308AR has to be larger , so there will probably be differences in the two . I have a couple of AR 15 barrel nuts around here & will take some measurements , so you can compare . Thank you. I await your dimensions. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted April 18, 2016 Report Share Posted April 18, 2016 18 hours ago, archangel2003 said: Well, I have 1.060 for the total length of the barrel nut, front to back, and the threads are .739 deep from the back to the barrel nut contact face. AR 15 Barrel Nut -0.861" length. Thread Depth from face of Nut ( Receiver side )to Barrel Extension Flange inside Nut - 0.5255" , Face of Barrel Nut ( facing Muzzle ) to Extension Flange ( outside edge ) 0.203" , makes that Flange 0.133" thick . So the front of the barrel nut forward of the contact face is .321 from where the nut touches the barrel (nut contact face). Not sure what you mean by this measurement The width of the serrations is .1180 so subtract 1/2 of that leaves the serrations centered at .262 in front of where the nut touches the barrel. Width or thickness of Wrench Notch 's 0.134" , Nut Body Dia . -1.364" & 1.570" in Dia. at the Wrench notches . Those serrations are where the groove that the hand guards locate on. If anyone had a DPMS 308 barrel nut and can take measurements we can verify if it is correct. I have to assume the gas block locating shoulder, and barrel mounting face are properly located as the gas tube is located where it should be in the upper. My bet is the serrations on the DPMS nut are further back from the end of the nut. If the serrations were even with the contact face, my hand guards would fit. Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 20, 2016 Author Report Share Posted April 20, 2016 Here are my measurements. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted April 21, 2016 Report Share Posted April 21, 2016 Is that a drawing of your Barrel Nut ? Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 21, 2016 Author Report Share Posted April 21, 2016 1 hour ago, survivalshop said: Is that a drawing of your Barrel Nut ? Yeah, it's a cross section of the barrel nut with the .733 measurement being the inner threads. I refer to the left side as the front. The .121 measurement width is the serrations that the hand guard mounts to and if it were so that the front of the .121 measurement were at the back of the .125 measurement (.250 back from the face) it would align for the hand guard. Quote Link to comment Share on other sites More sharing options...
DNP Posted April 21, 2016 Report Share Posted April 21, 2016 (edited) By my rough calculations....your handguard doesn't fit by about 0.2" ....but i I know nothing about this and probably should just be quiet and watch. Edited April 21, 2016 by DNP Quote Link to comment Share on other sites More sharing options...
archangel2003 Posted April 21, 2016 Author Report Share Posted April 21, 2016 Yep, it looked to be somewhere in the 1/4 area. The question is why? I looked at the local gun stores and non had a DPMS 308 barrel nut, or any barrel nus of any kind. They had stripped lowers and the parts for them, stripped uppers, and all kind of other parts, but no barrel nuts. Quote Link to comment Share on other sites More sharing options...
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