Help with AR

[jjamna]

I bought a used AR. Vulcan Lower unknown upper(was told it was a complete Vulcan when I bought it) anyway.  When I shot it it wouldn't group. 6 inches at 100 yds. I thought, well the barrel is shot out so I bought a whole new upper. DPMS 223. Floated bull barrel and it is a tack driver. 1/2 inch groups or less. ( i can shoot) Now- I tried to get old upper shooting. Thought barrel was shot out so I ordered a new barrel Still no shoot. Hmmmm. I has a composit receiver so may be it is not strong enough for a floated barrel- New Aluminum receiver- still No shoot. I think well maybe it is the bolt- took bolt from DPMS- still no shoot. It also has a new gas block. The only thing that has not been replaced with brand new is the handguard. Is it possible that a FreeFloating hand guard would effect the way a gun shoots?
I have tried a Red Dot Scope
A 3x9x29 Tactical Scope
And a 3x9x32 Tasco
The Red Dot and the Tasco are prov-en shooters. The Red Dot had been on a 357 Pistol and the tasco was put on a 243 after removing from the AR. Less than one inch Groups

This is my first Ar but not my first gun. I have over 40. I am scratching my head on this one. I don't know what else it could be. The Handguard  just has a big nut that holds the barrel on then the handguard screws on it. That is all that is holding the barrel on. Is it missing something? The Schematics I see are all for a regular handguard and they show a Barrel snap ring, a Delta Ring and a Weld Spring which this one don't have. As I said this is my only AR so I have never took apart anything other than this one.
I thought about taking the new DPMS apart and looking at it but it shoots to good. I don't want to mess it up.
I have tried Rem, Hornady, Win and a couple generic brands of ammo along with several of my own handloads.
Any Ideas

[SharonAnne]

"composite" upper receiver? then a new barrel with a new aluminum upper receiver and still poor accuracy? all with the same free float hand guard? Then try a new free float hand guard with the new aluminum upper and barrel. Normally a free float upper INCREASES accuracy. Perhaps yours is a lemon.

[jmayton]

What bullet weights are you using and what is the twist rate on the three barrels you've used?

[jjamna]

32grain in a 1 and 12 twist- 204 Ruger
55, 65 and 69 grain in a 1 in 10 twist 223
the good upper shoots the Sierra 65 gr spirepoint the best, it is 1 in 9 223

What would be a good hand guard to try. This one is aluminum, Round Knurled with the one nut to hold barrel on then it screws on the nut. I don't know the brand name.
This is one problem i have had. There is no writing any where on the original barrel .hand guard or receiver any where telling the Brand, Rate of twist or Caliber. It is 20 inch Military contour (i think) with a muzzle brake.
Replacement Barrel is a DPMS 24 inch Stainless Bull in 204 Ruger headspaced and with gas block from Brownells
I have checked and double checked. The 204 Ruger takes the same bolt as the 223.
I have checked headspace on the Ruger. It is fine. I have not the original but I bought it as a complete unit from a gun store.  Anyone could have threw it together and traded it. This is probably why they traded it. I am just stubborn enough that I want to find out why it won't shoot.

The lower does say 5.56 x whatever for 223 so I am assuming that barrel is 5.56. I know they may not shoot very good with 223 ammo but I wouldn't think it would be 5 or six inches at 100 yds.
Besides that the 204 should shoot.
The new receiver is a Model 1 

[jmayton]

my guess is it's the handguard.  Bullet weights and twist rates match up good.  My 1:7 Colt shoots anything from 55-80grs but likes the heavies best.  The hanguard is the common thread on the bad upper with a new barrel and new upper receiver you shouldn't be having the same problem.  It sounds like the connection between the handguard/barrel/upper isn't real solid.  That would certainly affect accuracy no matter what barrel or upper is on it.  Since it's already a free-float I'd stay with that rather than going standard with barrel nut and delta ring.  Go to M4Carbine.net and ask the same question there.  You can also check out what handguards others are using.  Daniel Defense and YHM are a couple that seem to be on a lot of rifles so that may be a good way to go.  Sorry I can't be more help.

[jjamna]

J
I think you hit the nail on the head. I went and put it in a vice and really tightened the handguard-barrel nut and got improved results. I think I can tighten it more but it will be more than any 35 lbs. (your thoughts on this).

Left target is with experamental hand load (slow burning Powder)
Right Target is Win 32 gr Hollow point
Just want to add that this is a new barrel so it should get better after a couple hundred rounds. I may have 50 thru it now.

[jmayton]

Not knowing the make of the handguard I couldn't tell you about torque specs.  Most either use a propriety tool specific to their handguard or the standard barrel nut tool.  If it is propriety and you don't have the tool, I wouldn't mess with it.  If it were me, I'd get a new one that will come will all the necessary parts and tools.  It sounds like it wasn't installed correctly to begin with.  You have to remember that the barrel nut has to do several things well and every manufacturer has their method.  First it has to attach the barrel to the reciever.  Second it has to attach the handguard to the rifle (regardless of whether it is free-float or standard).  Third it must keep the handguard attachment from interfering with the barrel attachment.  Also, the gas tube has to pass through the nut in some way and this can cause problems.  With and unknown handguard, there's just too much to go wrong.  You said you have a Model 1 upper so check with them...I think they make a round handguard that is decent and not too expensive.  I think that is the type my friend installed on his DPMS and he has had good results.

[SharonAnne]

i would not torque the barrel nut any tighter. The military spec is 30 ft/lb. Are you using a proper barrel wrench with a torque wrench? If not, how are you reading torque?

[jjamna]

I don't know if it is "proper" or not but I made a spanner wrench to go on my torque wrench.
Isn't pretty but it works. Set it at 30 lbs and when it clicks line it up on the next hole. I am looking at handguards.

[jjamna]

Must have said something wrong.