That is simply a different caliber AR. I don't know where "SAW" comes into this scenario. The 6.5 Grendel is a larger diameter round for the M-16/AR-15 platform. The M-249 SAW could theoretically be set up for this caliber as well. It would require new metal links and considerable reworking of the action. I believe the Grendel uses a bolt for the 7.62X39 round.
The comparison on the pepper poppers is not quite fair as the M-4 hits were lower that the other two calibers. Low hits equal less leverage to knock down the popper.
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