Lets break this down to either service rifle, or match DCM rig instead.

In the former service rifle, never loctite the barrel into the barrel socket,  nor the barrel nut, since it will be a PITA to remove the barrel at a later date.

On a DCM rig, not only will I loctite the barrel into the upper receiver socket to minimize harmonic changes, but will also loctite the float tube system barrel  to the upper receiver, so it does not twist under sling tension as well.
Hence on such a rig and running a Broach cut barrel, know that the barrel will be only good for about 2K rounds before the barrel stops printing tight groups ( good for one season only). And when it comes time to pull is all apart between each season for a new barrel, heat will needed to be used to get everything back apart, including the FSB since it get wicking loctite once the side tension screws are correctly adjusted for Zeroed out rear windage as well.

As for loctite on DCM rig, on the barrel extension, prefer 294 since its wicking and will fill all the voids, while float tube system, just depend on which part, and if it needs to wicking or not.  
And again, will need to use heat to get the high strength loctite's to break down before anything can be un-threaded and pulled, so don't screw around with med strength locktite instead.

Note, if you are using a production barrel (leade for ball ammo), never going to get a 20 shot string to stay sub-MOA anyways, so pissing in the wind using loctite between the barrel extension and barrel socket to begin with.

First off, the bearing surface of the barrel extension flanged lip to the upper barrel socket face, with the barrel nut holding it in place at 35FTlbs, but not to exceed 80ftlbs to get the spine void to index with the upper tube channel is more than enough for any SBR rig.

On longer barrels like say a 20" or longer such as a 26" long bow in 308, here the loctite between the barrel extenson sides to barrel socket to fill the void  will help to minimize the differances in barrel harmonics instead (using more of the upper barrel socket as reinforcement.

So back to locktite, and since you are trying to fill the entire void area of the barrel socket side walls to side walls of barrel extension surface to face of receiver extension on the lug side, barrel socket and it lip are left dry (cleaned with acetone), only the outer lip flange and front of the barrel receiver is moly greased to get the correct torque, and barrel nut is installed with receiver lugs correctly indexed.  


Now muzzle down after barrel is installed, here is where the wicking loctite comes into play, to fill the void completely between the two (air will bubble up and out) and allowed to set up, verse going in wet on the two surface with loctite,  installing the barrel in the upper level, and ending up with air voids in the loctite between the two isntead.

As for barrel nut to upper, and even tube to barrel nut on DCM float system, the  upper receiver and barrel nut threads need to be mated to each other with moly to start with (barrel nut to receiver), then moly removed, and you can go with a loctite to Glue the three together in the end.  Again, on a DCM float tube, you have the barrel nut that is tighted to the upper receiver barrel socket, then tube section that is tighten to it, since the outward appearance of the rig has to look like a service rifle in the end.  Also, with the amount of torque you will on the front end via sling, so it will end up with the float tube thread twisting over the season.


Bluntly, if you wanted to loctite your rig now (for grins, since it not going to make a difference on your SBR barrel if the barrel nut is correctly tighten to begin with), could just use brake cleaner to hose out the void area now between the two, and them using wicking loctite to fill the void with the muzzle straight down.  
Just keep in mind that you will be filling the receiver socket channel for the barrel extension pin with loctite, and going to take a lot of heat to break the locktite down, including around the  receiver pin to  receiver socket pin channel, before you will be able to pull the barrel.

As for loctite, the quick break down is blue is med strength that you can wrench it apart if needed, while Red loctite, have to break the loctite bond down via heat since it pretty much glues the parts together, before the its going to wrench free.
Green is wicking, and it goes from wrenchable, to gluing action where you have to use heat before trying to wrench instead.

Simply, when it comes to the amount of threads in play, going to need heat to pull the parts apart  anyways, so go for the strongest bond you can get to hold the two together (that heat will break the bond down in the end), and the correct fluid for the Job at hand (wicking or not).

Never going to hit that round count with a Broach cut rifle barrel, since just before that point, group are going to go from tight groups, to just spray pattern in just the span of one shooting session.

Button cut barrel on the other hand, can go up to around 8K, with a gradual degeneration is accuricy around the same 4K count, that you just have to make the call when it not grouping tight enough instead.

As for Broach cut, or button produces rifleing in a match barrel, just depends if you are trying to stay sub MOA, or happy with MOA for your shot strings instead.   Don't get me wrong since Douglas does make a good match barrel, but not going to hold its own against a Krieger match barrel.