Need more details on the rifle, especially the butt stock assembly.
In 223, most of the felt recoil is the buffer moving in the receiver extension, and could just be a weaker hammer spring, weaker carbine recoil spring, and even too light of a buffer for the upper receivers function. By this, the barrel may have a slightly larger gas port with is causing the bolt to unlock too soon, and with the lighter items pointed out above, will cause the buffer to slam off the back of the tube harder than normal on the back of stroke instead. Also, if the above items are lighter/weaker than needed, it in itself will cause the bolt to unlock too soon as well.
So a couple quick checks is to put a tape measure down the inside of the receiver extension, and make sure that you are coming up with a 7" tube void to the lip of the tube. On the recoil spring, should be around 10.5" and the buffer should come in about 2.9oz (note when you shake the carbine buffer, should sound like discs moving, and not a hand full of BB's isntead).
Note, if you bought a cheap butt stock assembly, suspect that they may be air soft parts, and out of spec isntead!!!!
Next, pull all the way back on the charging handle with the rifle back together, and make sure that the face of the bolt stops 1/4" to 1/8" in front of the back edge of the ejection port. I bring this up, since if you are using a carbine spring and buffer in a full length receiver extension, then the felt recoil you may be feeling is the back of the carrier key crashing into the lower receiver, and trying to crack the lower receiver instead.
Now if all the above is good, and the bolt is locking back on the catch after the last round fired, then what is needed is to slow the bolt unlock isntead. Here, two ways to attack the problem for cheap, being either change the carbine recoil spring out to a extra tension carbine spring, or pick up a H3 buffer instead.
If you have a standard carbine buffer (2.9 oz) and a H-3 buffer, then you can swap the internal weight in the two buffer to come up with a buffer in the middle of the two isntead. Hence the differences between the buffer is the type of material that is used for the weights, and which can be swapped around between the two isntead.
So you first start off with the rifle cleaned and lubed, with the H3 buffer, and see if the bolt will lock back (single loaded round in a mag). If the bolt will not lock back, then the mass of the buffer is too great (bolt unlocking too slow), so you pull the two buffers apart, and make a H1 out of the standard buffer (one carbide disc, 2 steel discs) and make a H2 out of the H3 buffer (1 steel disc and two carbide discs). Now with these two buffer, you can try out the H2 to see if the bolt will lock back, then the H1 if the bolt will not lock back on the H2 instead.
Hence what we are trying to do is slow the bolt down from unlocking too fast, and whacking off the back of the tube with too much force to cause the felt recoil isntead.
Note, if the H-3 locks the bolt back and still feels like too much felt recoil, then you can add a extra tension carbine spring to slow the bolt unlock down every more. Just make sure that the bolt still has enough energy on unlock to make it all the way back so the bolt catch and lock the bolt back on the last round fired.