Choosing to have a 338 Allen Magnum is not a decision to be made lightly. My goal is to have my customers that order one of my rifles actually USE my rifles. Many want to order a 338 Allen Magnum simply because its the biggest and baddest practical 338 magnum around, or at least on the top of the performance ladder with a few others in the same class. That's not a bad thing but these rifles are big, long, heavy and expensive. For what they are designed for, they are amazing weapon systems but often times, guys want them for other reasons then what they are designed for and in the end, they get into a rifle that is not REALLY what they want or need.
As such, when a potential customer comes to me wanting me to build them a custom rifle
, I talk things over with them first to determine what exactly they plan to do with the rifle. In the end, if someone just WANTS one of these weapon systems to have, no problem with that, but if we find out that their hunting goals really do not require a weapon system as specialized as a 338 Allen Magnum, I often recommend one of my lesser wildcats.
Many are much better suited to a more all around weapon system such as one of my Raptor Stalker rifles in 300 Allen Xpress or 338 Allen Xpress for hunting from 0 to 1000 yards. Some are better suited with the same chamberings but in a more dedicated long range rifle such as my Raptor LRSS which is designed for use from 500 to 2000 yards.
As mentioned, in talking with potential customers and together finding out what system will meet their goals best we pass on the 338 Allen Magnum 90% of the time in favor of on of the Allen Xpress chamberings.
There are certain situations that the 338 Allen Magnum is the perfect choice but many more where it is out classed for a specific use by lesser chamberings.
I do not know much about the 40 Hart. If it is based on the 375 RUM necked up to 40 cal, it would have a DRAMATIC barrel life advantage but then its also limited significantly by the bullet selection in 40 cal. Solid bullets can be a bit finicky depending on bore diameter. Building a rifle for use with a very limited selection of bullets is a serious gamble unless that one bullet is a proven bullet that works well over a wide range of bore diameters, for example, the 350 gr 375 cal SMK for my 375 Allen Magnum. Its not the best game bullet in the world but it generally shoots extremely well in most barrels I have shot them in.
Ballistically, I personally do not think the RUM case has enough capacity to get velocity up where it should be for a 40 cal projo used for long range hunting. For target shooting or rock bustin, no problems but for big game we do need a certain level of retained velocity for proper terminal performance.
Anyway, not saying the 338 Allen Magnum is not a good choice for your application. Just that there may be better options out there for what your looking to do with a new rifle.