Two Very Basic Barrel Attachment Questions

[DocLarsen]

I am almost embarrassed to ask these questions, but I have searched until I'm about to pull my hair out, so here goes:

Weld Spring and C Clip are shown on AR-15 drawings, but I have seen them only in a DPMS parts kit on 308s.  The DPMS schematics don't show them for the SASS, which is the barrel I'm using. Are these used only on standard, barrel supported handguards?  On several FF installs, I have seen no mention of them.  The reason I am asking is that my FFHG is turning about 120º past the rail lining up and thought that these might make the difference if needed.

What is the barrel nut thread size for DPMS?  for Armalite?  I know that I read this somewhere on the forum, but for the life of me, I can't find it no matter how cleverly I try to word my searches.  If I get shims for the above problem, I want to make sure I get the proper size.

Hopefully this will help someone else who is new to ARs find this information.

DocLarsen

[imschur]

Hey Doc, I lose track of what hardware folks are using. Please post pictures and links etc. Also I am not familiar with weld spring and c clip you are referring too. Please post the schematics you are using as well. The more info the better.  <thumbsup>

[DocLarsen]

Parts 7, 101 and 32 above come together in the Delta pack (DPMS part no. 308-BL-09D): Delta Pack includes, delta ring (32), weld spring(101) and weld spring snap ring(7) for the 308.

[imschur]

Those parts are for the Delta ring and should not be needed with a FFHG. They basically allow the delta ring to be spring loaded.

[imschur]

The size proportion in that picture makes thing deceiving.

This is slightly better

[DocLarsen]

Thanks!  That is what I suspected, but could not verify it.  So, if comes down to it, then I'll shim if necessary.  Hopefully, when everything is torqued down properly, it won't be an issue or I'll have to go the other way and can lap parts as survivalshop described in Matt's thread on installing a VTAC here .

DocLarsen

[imschur]

Can you post pictures of your FFHG and barrel nut so we can see how they interact?

[DocLarsen]

I don't have a digital camera at the moment.  My FFHG has a jamb nut, of sorts.  It is very thin and have very little contact with the handguard. I would like very much to have more contact on the handguard so as to have it be more monolithic in the same way as survivalshop was going for in the previously mentioned thread and to have the rails line up in the same way his did as well.

DocLarsen

[imschur]

How about a link to the part?

[SWshooter]

Doc, there are two basic float type handguards. The two piece type, you install the barrel with a threaded barrel nut and then just screw on the float tube until it's tight. The three piece type uses a threaded barrel nut, a jam nut, and the tube itself. You install the barrel with the barrel nut, thread the jam nut on, then screw on the tube itself. When the tube is all the way on then back it off until the rail lines up. I find it easier to use something like a scope mount to span the two rail sections and hold them into alignment. Then tighten the jam nut against the tube to lock it in place. These are basic instructions and I'm sure there are variations, read the instructions is your best bet. Remember that the barrel nut is locked in place by the gas tube passing through it, the jam nut is just for securing the tube in place.

[DocLarsen]

10-4 SWshooter, the handguard in question is the new DPMS SASS handguard seen below. While I am waiting for my barrel wrench, I bought a couple of strap wrenches that came in a single pack at Sears for $13, so that I could mock things up a little closer to final than hand tight.  What I am trying to achieve (and what I believe survialshop was talking about in the previously mentioned post) is having everything tightened to the rear of the gun AND have the rails lined up at the same time.  When using a jamb nut to lock the tube with the rails lined up, there are two degrees of freedom (3 if you include the barrel nut itself) which can serve to loosen the assembly. With everything tightly stacked from the receiver forward, only the tube loosening can loosen the assembly as only the barrel falling off  ::) or the upper receiver fracturing would allow forward movement of any of the parts. 

I know this is kind of picking the fly poop out of the pepper and judicious use of loctite would greatly reduce the chances of loosening. But as survivalshop said, the goal is a more monolithic final product. 

Does anyone know the thread size of the two types of barrel nuts?  I still can't find them; rough measurement makes me think that they are 1¼"-?

Thank you all,

DocLarsen

Edit to comment on pictures:  The top picture is not quite right. I don't know what the round thing on the lower right end of the HG is, but it is not on mine.  Mine look exactly like the bottom pic.

[SWshooter]

What you really want is the one piece receiver and handguard made by someone out there in AR land. It also allows quick barrel changing.

[DocLarsen]

SWshooter,

Mega makes some very nice monolithic parts; a wee bit pricey though. Also Adams Arms, LMT and Noveske all offer various forms of monolithic parts. See Rainier Arms - monolithic key word for some of them.

DocLarsen