The FTX 30-30 bullet is the better bullet for your use since is has a shorter ogive and is meant to be loaded where action length is a concern.
I'm not sure where you heard that the OSSW is having accuracy issues since I've heard the opposite exclusively. While the OSSW is a proprietary design, so is yours. The biggest difference is that theirs is tested and proven by a firearms company and has pressure tested load data to go along with it. It also isn't that expensive. Especially not compared to a one-off custom job. They use an upper with a larger ejection point to accomodate the larger case diameter as well as a larger diameter. The bolt, barrel extension and barrel shank are larger than normal to accomodate the fat little round. They developed the oversized parts for their .223, .245 and .25 WSSM rifles a few years ago so the parts are tested. The bolt isn't the strongest possible bolt out there, but it has proven more than capable of standing up to use with a 65K psi cartridge. That is the max that SAAMI permits. How much stronger does it need to be?
The problem with getting a powerful round in the AR-15 platform is the limited cartridge length dictated by the dimensions of the mag well. Mess with the magazine itself and you run into interchangelability problems as well as reliability issues. You can't make a longer case so that leaves the only option of going with a fatter case if you want an increased powder capacity. The 6.8 SPC was the first commercial endeavour in that direction since it was generally determined that going with a bigger rim diameter that that of the .30 Rem (parent case of the 6.8 SPC) would excessively weaken the AR-15 bolt. There have been strength problems with the 7.62x39, PPC series and 6.5 Grendel (all based at least somewhat on the .220 Russian) bolts. Running a case head larger than the 6.8 has led to several different bolt sizes and barrel extensions being developed by several different companies. Olympic and D-tech worked out the WSSM case size. Remington (or more correctly Bushmaster) worked with making the .473 case head work for the .30 RAR and the result was an oversized bolt based on the AR-10 bolt and a barrel extension to match it. The ballistics of the .30RAR are VERY close to the .250 Savage and the OSSM has demonstrated ballistics on the order of the .30-06.
Me, personally, I have no particular fascination or obsession with the .30 cal bore size and think that it isn't very well suited to much of anything and is especially poorly suited to any cartridge with a limited length or powder capacity. You can punch a bigger hole with the likes of the .458 SOCOM, .450 Bushmaster and the .50 Beowulf and can get better long range performance from a smaller diameter bullet that can be pushed faster and has a higher BC. From my perspective a 6.5 or 7mm OSSM would be the ideal cartridge for the AR-15 platform. It would take a non-standard upper and bolt but would stomp the crap out of nearly everything else possible across the course with its advantage only increasing as the range increased.
Your time, effort and money. Do what you want but realize that you're unlikely to exceed the performance anything already available and you're firmly in wildcat territory.
