I’ve got a lifetime supply (crates stacked deep) of 7.62 NATO surplus which I shoot primary through M14 types. Now that I’ve sold off my G3 and FAL variants, I’m down to 3 centerfire rifles. I intended to modernize to KAC SR-25 and FN SCAR rifles as they are honestly leaps and bounds better than what I bought during the parts kit era.
It strikes me that I could go all the way and divest the ammo as well, converting to 5.56 or .300 Blackout. I will not stock multiple centerfire rifle cartridges.
I shoot steel primarily in the 200 to 600 meter zone with the option to shoot up to 1000. I don’t hunt and I rarely shoot matches. Hell, I barely make it to the range once a month. In my position, would you stick with 7.62 or dump it and go 5.56?
Honestly, in your position, I don’t think it’s worthwhile to convert the calibers if you have a significant supply of 7.62. That is if you are firmly set on one caliber only. It just sounds like too much hassle - you have to sell your existing ammo and rifles, buy a new one, what if you don’t like it, and etc.
On the other hand I don’t think it would be a bad idea to keep some 5.56 as well just to diversify a bit - probably just for fun more than anything else. 10-25% of the total main caliber maybe.
300 Blackout - I wouldn’t choose as an exclusive primary caliber. Basically, if you have a specific purpose/intended use for it (it doesn’t sound like you are from your post) - by all means use it as a secondary round.
Well the big reason most people don’t shoot 7.62x51 is ammo cost, and you have that covered. From a recoil and ammo capacity standpoint the 5.56 is easier to manage but it sounds like this is a non issue for you.
I would stick with what ya got and pick up another one of those more advanced 7.62 rifles. There are so many good options today - LMT MWS, SCAR, SR-25, BT APC 308, etc.
The 300 BLK is a niche cartridge for those who want a combo that is works good with a suppressor and want to maintain commonality with 5.56 AR parts. I have one, and like it, but I don’t think it is for you.