The Polonium 30 can handle your list, the K is a 556 can? Have you contacted them about your 6 Arc?
" Description for Polonium and Polonium-K 5.56
The Polonium is made to be a quiet, duty rated, hard use 5.56 suppressor and is offered in
both standard and K length options. If you’re looking for the best size, weight and price to sound performance ratio on the market that you can beat the absolute crap out of then look no further than the Polonium series. We don’t need to make up fake, fancy marketing language or give you padded/deflated dB numbers taken on subpar equipment – the reputation, performance and track record of the Polonium and Polonium-K speak for themselves.
The Polonium uses a 6mm bore that is also compatible with any 6mm/.243 cartridges and has a highly effective built in internal and external flash hider that offers superior flash reduction over the competition when using night vision or when shooting in low light conditions. The unique look comes from external weight reduction, removing all unnecessary material to keep the weight down but still as strong as possible. This results in a suppressor that has 10% more surface area depending on the length that will shed heat and cool down quicker.
The Polonium and Polonium-K features industry standard universal 1.375×24 rear threads so you can pick what mounting system best fits your needs."
The above cut and paste was from OCL, I didn't include the description for the Polonium -30 which you can review the whole series here:
The polonium is made to be a quiet, duty rated, hard use, 5.56 suppressor.
ottercreeklabs.com
That being said I would use alignment rods with the Polonium series for a 6mm projectile. The above actually caused me to go with that series ( I went with the longer Polonium to handle the 6mm Ackley, so yeah the ARC should be fine) .... NO Regrets.. Solid can across the board for my usage YMMV.
The Polonium -30 is the 30 caliber can, I only state this as many usually quote that it's only the K is 5.56, which in fact the standard Polonium is the same as the K for bore ,just longer in length. (yes there is three offerings in the series which is what causes confusion, many think the longer Polonium and Polonium-30 are the same can, simply because the specs are pretty much the same)
But to
@Spurchaser man code quote I fully concur get a 30 caliber can as well.
@Plant.One comments yeah I went down the Yankee Hill Wraith 45 SMG can (caught it on closeout years ago) route truly impressive with the SBR 9mm AR with a 1.5" barrel length. Yes it's the Man code thing LMAO