I found that when I torqued my barrel at a minimum of 30 pounds, it needed a good bit more to line up with the hole in the reciever.  So, I set my torque wrench at 80 pounds and still couldn't get there.  then I took a chance and went to 100.  Still couldn't get it there.  So I backed it off and finally got the gas tube through at about 25 pounds of torque on the barrel.  It shoots fine.  Are there any problems I may experience in the future by being below the 30 pound recommended torque?

Thanks

I would make sure to use a good molly grease and try re-torque it, I would do this 3 times to see if it would line up. OR just keep an eye on it - should be ok.

thanks

I actually tighten/loosen/ tighten/loosen/tighten to 60-80 ft/lbs on the third torque. Usually in steps of 15 ft/lbs starting at 30. Tighten/ loosen steps may require more than 3 steps to align gas tube. You can't or shouldn't try to do it all in one shot. The steps will insure the grease is properly "spread" and prevent galling.  You should be able to get it to the next gas hole without too much stress.

OP,
Had the same problem once. I finally cleaned off all the grease and made sure the threads were immaculate. Greased again and it lined up somewhere past 30#. I think I must have gotten a bit of grit or something on it the first time and that messed things up.
FWIW
YMMV

People seem to take the torque spec thing a lot more seriously than they should.  The point is to get it snug, but tight enough to line up the gas tube.

If you get lucky enough to get the barrel nut snug and line up the gas tube, great.  If not, you have to work the wear into the upper threads until it lines up snug and you can align the gas tube.  That is it in a nutshell.

The problem is how to write that up into a tech manual without sounding like a hack, hence the 30-80 ft. lbs. and the 3x nonsense.

edit:  No problems to expect.  At 30 ft lbs it is snug and won't allow the barrel to wiggle around. The gas tube will prevent it from loosening much, anyways.  Hell, if it were a full turn too loose accuracy might suffer but I wouild expect good functioning all the same.

The three Ive built have all been this way, and yet, they all function fine. I think thirty is just a moderate number so that people dont just torque it until it breaks.

All of my builds are usually between 30 and 40 #s and the tube is lined up.  I put a dowel rod same size as the gas tube on the nut and push it in until it lines up.  I grease the upper bolt area lightly with my finger all the way around to ensure it gets an even amount of grease first.  I have never done the torque loosen torque loosen method.  To me you can over tighten and stretch the aluminum on the upper not something I want to deal with later down the road if stress fatigue cause an issue.  I tighten to 30 first if its not there I keep pushing and yes its a lot of pressure past that point but go up in small amounts.  I don't use a set torque wrench I have an arrow guide on mine so I just keep pushing one or two point more at a time...

Kind of the same way I do it..... I do not have a nice torque wrench but my arrow one does the job everytime all the time.

Wanna know why the manual says to do it 3 times.  I believe it is to overcome the threads binding on each other and the tightening and loosening smoothes off the threads.  Because just because your torque wrench clicks doesnt mean you are at that actual torque.  The bolt company ARP put out a video once where they used different types of oil on theads and then torqued them. They used a few special devices that showed the actual torque compared to what their torque wrench said,  it took multiple times with anti seize to get the torque wrench and their gauge to read the same thing.

25 ft/lbs is out of spec, if it were my weapon I would re-do it.
You do need to torque to 31-35 ft/lbs three times, and then turn until the gas tube fits (80 ft/lbs max).
Obviously proper lubrication is a necessity.
If you have to back off for any reason, back off till loose and re-torque.
A loose barrel is a deadline item. Checking for a loose barrel is part of a standard TI.
It has been a long time since I had a problem installing a barrel. I changed nuts and the new nut installed normally.

Torque to 30 ft-lbs, loosen.  Repeat three times.  If the next time you can't get something to line up at less than 80 ft-lbs, back off and repeat.  Over and over if needed. One effect of this practice is to work the grease (you DID use a good quality non-graphite, high moly lithium based grease, right? The torque spec is based on using a MIL-G 21164D compliant grease) into all the threads and to knock the roughness off of all the surfaces that need to mate.  It works.

Someone always comes up with a better idea, to screw up something so simple

Torquing is SUPPOSE to stretch the metal. That is what ANY metal does. There is a reason to torque to a certain amount. When you build an engine you first torque the rod bolts to spec (or they come pre-torqued/ stretched) then you loosen them and retorque to their specs. Race engine builders use a stretch gauge to determine or predict if a bolt is going to fail. They also use it instead of a torque value because it is more accurate. You do not torque to specs (min 30 ft/lbs), then go above specs (100 ft/lbs), then settle back to 25 ft/lbs. At this point you have STRETCHED the metal. You should not have that bolt lower than you initially torqued it.  
Is the barrel going to shoot off? No. Is the barrel nut going to wildly spin off? No. Is it detrimental to the weapon? Yes. Do I want to put thousands of rounds through it this way? No. Safe? Not for me to say.
Yes the gas tube will stop the barrel nut from rotating off. I believe that is one of the reasons why it was designed that way. But once the barrel nut becomes loose it will push on the gas tube causing it to push on the gas key. Etc etc...

[edit] I forgot to ask, Do you want to drive a car that whomever put it together just said "yeah, that feels tight"?