04-10-2019, 05:19 PM
WickedInexperienced Wrote:Is there any way for me to determine definitively that the upper reciever is out of spec? I'd hate to have to send the upper back and have Sanders Armory tell me everything is fine
You already did that when you tryed the grendel mag with the 556 upper.
You could probably pull the bolt and try it in the bcg that is in your 556 upper and repeat the first test you did and see if it happens the same.
The surefire way would be to strip both uppers and rebuild the grendel on the upper that has the 556 barrel in it now. And install the 556 stuff in the upper that had the grendel barrel and then repeat the test you already did.
This is just me talking but if it was mine I would just order a stripped upper from a online dealer and rebuild the grendel upper with the new stripped upper.
I hate sending stuff back if there is a problem, I tend to just fix it myself, most times it's cheaper and quicker.
But to recap.
Grendel mag into grendel upper, mag very hard to seat and bad feeding and rifle jams up and you have to get physical with it to remove round.
Grendel mag into 556 upper, mag inserts easliy.
If it was mine that would be enough for me to pull a cheap matrix stripped upper out the safe and rebuild it.
Try swapping the bcg's and rerun the test you did with the mag and both uppers and see if the problem repeats itself.