I had a friend that had a 300 RUM in his Encore - It shot great until his father loaded some "special" cartridges for it. He lost his right eye when the locking lugs failed due to the pressure spike and exploded. The company that made the barrel for him went out of business. It was a sad story.
I've had an Encore in a 7 MAG and a 6mm Cheatah (6mm-7mag), I continued to shoot both barrels, but at lower velocity loads. I would definitely advise against a 338 Edge in an Encore - plus, you'd have a hard time finding any one willing to build the barrel. that's my 2 cents.....
I was going to chamber the barrel myself I am a tool and die maker. I believe it was Virgin Valley who chambered the warbird however they are now out of business I believe. Possibly the one who chambered the ultra.
If you download these cartridges that with a large case head, you can do a lot of things in the Encore.
Truth be known, even the Rem/Win Mag cases will cause problems if you run the pressure up to what many do in a bolt rig-Benn there and done that
Been wildcatting on the break open concept since the mid 70's not long after the contender came out. 30 Herrett and 357 Herrett along with the 6&7 TCU's. When the Encore came out I started wildcatting this one as well.
Note: someday we will be leaving these toys for someone else to play with. In my case I had at one time so many wildcats that if loaded within the cartridge/action safety limit were just fine. SInce my children have no concept what is a safe limit for a particuler cartridge I sold every wildcat that of loaded to max could destroy a barrel.
Having built and tested more than 40 barrels from scratch I personally would not put a case larger than the 375 Ruger case diameter in an encore barrel. As the chamber walls thin from larger calibers one reaches excess chamber pressures sooner, the thinner the chamber walls. Some break open barrel makers in the beginning were chambering the short mags in their barrels. They no longer do this. One might give these people a call and ask them why!
I have a number of wildcats based on the 7X65R RWS case that will duplicate anything the short mag cases can produce. They are safe and do not push the envelope in chamber wall thickness. The afore mentioned case is smaller in diameter then the standard 06 case. Take the Rocky Gibbs concept from the 50's and put a 30-35 degree shoulder on the drastically improved case.
From a 16" stainless none Nitrided barrel I am running a 200grain Accubond at 2750 without issue. I have been shooting these loads since the 180 and 200 grain Accubonds first came. out. I have yet to loose any cases and some are now at 15+ reloads. With a RWS 280 case and a 19" barrel on my Savage Striker rear grip I am running those same Accubonds in excess of 150 fps faster than the 16" Encore barrel. NOTE: This is a Nitrided barrel!
Check the Barnes Reloading book under 338 Scoville (Dave Scoville) for similer cartridge preformance. My case capacity has the neck at .250 allowing more powder than the Scoville.