These are images of the first layups in carbon fiber (only used it as I had some handy and it layups up real stiff - I never get the ratio right, but carbon fiber has either 1/10th the weight of a comparable piece of 4130 chrome moly steel and 5 times the strength or vice versa, 1/5th the weight and 10 times the strength - I believe its the first ratio but CRS is serious factor here at the ranch.

Anyway, after laying up the carbon fiber against the receiver (idea is to make a mirror image of the receiver side so the clamping surface has full contact from top to bottom - when you wet out your fiberglass or carbon fiber, after first waxing the receiver 2 - 3 times, then applying 2 coats of an alcohol based mold release agent, then wrap with saran wrap - this is only to make sure no epoxy makes it's way into contact with the receiver's surface.

Then, after laying the wet carbon fiber onto the receiver, cover that with a layer of saran wrap and then lay a 1" thick piece of foam over that and then clamp with moderate pressure two pcs of flat material over the foam so as to sandwich the receiver between the flats pcs of wood, metal, or whatever, pressing the foam to cause it to press the carbon fiber to following the contours of the receiver sides.

(for general info, if I could get a person to stay perfectly still for 6 - 8 hours, I could take a mirror impression of their face including every folicale of hair, dimple, whatever -- did a layup one time making a female mold of a polished 1 & 1/2" polished rod 
after making the mold, went to make my first casting - when I pulled it out, it had a fingerprint on the casting - thought my finger must have had some oil on it when I handled the casting - nope, the fingerprint was on the original pc I had copied and had transferred to the female mold)

The little wooden block in the 3rd image is so that when the carbon fiber has cured, I can cut it along the top with a dremel and not worry about cutting into the surface of the receiver top - that wooden block will be used in the same place it was in the layup stage when I have the finished product and am clamping the receiver.  I could cut the clamping shells down to the level of the receiver top, but it gives a little more clamping force or a little more complete clamping force to the top of the receiver.  I would have laid the carbon fiber up directly to the receiver top but do not like the idea of slipping with the dremel and scarring the finish.

Next step will be to position the two carbon fiber clamping halves back on the receiver, and then bond those 3" square steel plates you see in the back ground to back or outside of the carbon fiber clamping shells. While the epoxy is still wet, clamp the whole affair in the vise and the vise jaws will align the steel plates so they are parrallel. 

Those drilled "dimples" in the steel plates are so the epoxy slurry mixture gets a better "bite" to the surface of the plates - you can't tell it well from the images but those surfaces are also roughened by a angle grinder with a coarse wheel on it 

Then, when that's cured, fill in between the steel plates and the backside of the clamping shells with a thickened epoxy mix (looks like dry caulk).

When that's cured, lay up carbon fiber over the outside of the steel plates onto the backside of the clamping shells so all the load from the vise gets transferred to the clamping shells, ie to make the clamping shells as integral with the steel plates as possible 

Another note to folks that are going to change out their own bbls, a lot of the sig recievers corrode where the bbl threads into them 
and some have loctite on the threads, so one suggestion - soak the receiver in WD40 for a day or so, being sure the front end of the receiver is immersed in the wd40.  Then, before removing bbl, apply some heat (maybe 250 degrees F) to the bbl where it enters the receiver - the loctite SIG used (they didn't use it on all) is not a very high temp loctite but you need to get that threaded area on the bbl up to 235 - 250 F for the thread locktite to release