Recommend BCG and Bolt for 20" long range rifle

[va_connoisseur]

I am looking to build my first Grendel and need suggestions/help. The local precision shooting shop is trying to dissuade me from the 6.5 Grendel because he says bolts are the weakest link. That they are just shaved out 5.56 bolts and that makes the head and extractor weak and prone to breakage (and this is not a dig on them, they are good guys).

I would really like to build a 6.5 for long range 800+ yard shooting so my questions are:

a. Is the BCG/Bolt/Extractor really a weak spot?
b. If so, what is the solution?

Thanks.