I recently fitted my Alpex 4k LRF to the S20 in preparation for a DMQ NSC - didn't use it in the end as I was getting variable shot placement. However, the rounds I was using then were the first reloads of my 130gr TTSX load in US NAS stainless steel cases rather than my usual reloaded Lapua cases (courtesty of
@Mountain Bug). What really ****ed me off on that range shoot was that both 5-round and the 10-round mags wouldn't reliably feed. I put this down to the NAS cases but on going to the range again with this combo after lowering the mounts yesterday, I got the same result with Lapua reloaded cases, having to single feed all cartridges!
My mags are very old and probably from the first batches made which anecdotally do seem to be problematic. In a rash opening of the wallet last night, I splashed out on a new mag from a high volume mag outlet which should ensure it is recent stock. Waiting with interest to see if its an improvement. Over Christmas, I'll disassemble the original mags and will have a play. One of the 5-rounds has an aftermarket 3D-printed filler piece in it which was an early fix for misfeeding.