The M14 Beta magazine, while obviously heavy, appears to make more sense than a Beta mag for a 5.56 weapons platform. For several reasons:
The 7.62x51/308 platform is ideally suited for putting a large volume of heavy metal on target at further ranges. When comparing the FPE of the 5.56 against the 7.62 @ 500yds- the 7.62 really shines. So here's some short points I've observed-
Why I don't own a 7.62 weapons platform- Too damn heavy.
Why I don't own a Beta C for my 5.56 weapons platform- For the cost, I can get a bunch of USGI 30s which I know will work, I can lose one or two & still have way more than 100rds on hand.
Further, it means adding weight to a weapon I prefer to remain light in weight.
Why I find the M14 Beta C intriguing- If I were to get what I already considered a heavy 7.62 rifle, why not bulk it up some more w/ a bipod and a 100rd magazine? It's a weapon I don't picture humping for prolonged distances, it's a suppressive response weapon. Go prone on the bipod and let the heavy metal rain.
Note, the above is purely IMHO.
It is worth mentioning that since the cost of 5, 20rd M14 mags will run +/- $150-180, the gap between those 5 against a single 100rd Beta could somewhat be shortened. That of course depends on the MSRP & actual cost of the M14 Beta (This takes into consideration a comparison to USGI AR mags. 22 USGI @ $11/ea vs. a single 100rd Beta. 660rds vs. 100 w/ the Beta)
Why I may consider getting a semi auto 308 weapons platform... The 100 rd Beta!
Sly