303 British Brass Options?

You are getting your information from second hand information that you have read about regarding N540 from LR shooters.  The same shooters that need to keep the velocities up to get the bullet down range post haste.

 Every written testimonial about a burned out barrel came from a LR or F-Class "Bob Lee Swagger Shooter" that is firing more rounds down range on a weekend than your average shooter does in a year.  Your comment "experimented on and well proven" is taken with a grain of salt. 

I predominantly use the N540 for my .243W loads which are kept to a bare minimum in charge weight and have been tested between temperatures of 17°F and 117°F with no noticeable change in accuracy or pressure variances.

AR small bore calibers range anywhere from .204 Ruger to 6.8 SPC with the .223 Rem. being the most common and reloaders have a tendency to keep the bullet weights @ 55grns which even using a "mild" charge weight, the averaged FPS is still above 3000+ regardless if you use a single base or double based propellant. You will still burn the barrel out using a single based propellant, it just takes a little longer. 

I use the minimum charge weight of 37.7grns when using N540 in my .308W chambered rifles and my chronographed FPS has been averaged out to 2246. 

I use the minimum charge weight of 39.7grns for the .303B rifles and the chronographed FPS has been averaged out to 2377. 

Very respectable numbers for both calibers. Definitely not worried about throat erosion with those low FPS readings.

 Even with the .243W, the FPS has been shown to stay consistently around 2799 with a plus or minus fluctuation of no more than 10-12 FPS. 

Unless you have done your own research and verifications using N540 in a .243Win, .308W,  and .303B chambered rifle such as I have, taking your word for it seems a little foolhardy.

All rifle barrels will eventually become useless if you keep firing enough rounds down range regardless of smokeless powder used...

Post Script: I took notice that you continuously shoot at distances between 500 and 1000 yards as often as possible and you NEED to keep the velocities up to trigger the electronic sensor on the target. You would therefore need to keep the charge weight closer to or right at the maximum charge weight to achieve the velocity to trigger those sensors. I can see where using a double based smokeless propellant will eventually burn a barrel out at those higher velocities but, I can see a single based smokeless propellant doing the same thing...

 By no means at all am I trying to convince you to use the VihtaVuori N540 and I understand that nitroglycerin burns hot.

What I am merely suggesting is that if you do not use it on a regular basis and only have the testimonies of others and none of your own regarding its capabilities of burning down a rifle barrel in 1500 rounds or less, you would be wise to do less badmouthing the product and more actual research by using it for yourself. 

The one comment I focused on from a F-Class shooter was quoted as saying, "I was at a 3 Day shoot and my barrel was trashed before I had got past 1300 rounds out of it! It has to be because I used the 500 series VihtaVuori instead of sticking to the 100 series."

3 days and 1300 rounds? I know of a person that has owned their respective rifle for 50 plus years and have yet to put 150 rounds through it.  It is not the powder, rather the shooter who is to blame for the short barrel life. Single or double based propellant will erode a barrel down to becoming useless if you are firing that rifle repeatedly and often, especially if you are trying to be as competitive with it as possible. Remember this Geoff.  There are people that do not have the time or money to invest in weekend "Sport Shooting" and that includes being able to replace a junked barrel whenever. Those people shoot when time and money allows them to do so and with that, they take the necessary time to research  their chosen bullet weight and propellant and then they sparingly use it to keep both theirself and equipment in check. Your comment, "I've got much better choices at my disposal." is great, for you. Not so much for the shooter that can only afford 1 brand, such as VihtaVuori, which is currently a bargain brand propellant. I have said this before and it bears repeating.  You do you and let others do them...