The answer is Yes and no. I have shot 500Jeferies and 460Wby mags without breaks and also 500 Nitro express rifles and they realy tell you they are going off. The 338 Allen mag would not be as stout as some of those loads. But i did not ever shoot them sitting at a bench or prone and i would not shoot the 338 Allen mag undreaked from the bench or prone. What you need is a standing rest where you stand up behind the adjustable rest for the forend to sit your forehand on the rest and firing it standing it is not to bad.
Just for chits and giggles i took the break off of a 13# 338 snipetac (300smk 3300fps) and fired 4 rounds down range from a sitting bench rest. I didnt want to do any more, but i think shooting at anything besides paper or steel you wouldnt notice. Off hand it was more like a 10ga shotgun, big push. (Everyone needs to do it at least once) This way you will know just how good the brake is working.
Yup, I'd have no qualms shooting it without a break. Afterall, I shoot my .416 Rigby CZ550 PRONE off of a Harris Bi-Pod with no brake......the load is a 350gr. Barnes TSX at 2750 fps. I had to go to a McMillian stock since the wood one started splitting.
As you can see, I removed the factory sights and re-contoured the rear sight "block", then sand-blasted the barrel and re-blued it. It wears a 4.5-14x50mm Vari-X III.