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One thing I noticed about my zero with the MP15: With PMC Bronze and Prvi 69 gr OTMs the zero at one hundred yards is almost at the same place. Maybe about an inch difference. Using this zero, then switching the ammo to Remington UMC green box, the POI is over 4 inches to the right.
I repeated this test with my DDM4 and I didn't have such a large variation. The POI was maybe an inch to the right. Just something I noticed with the different ammo on the different gun.
Yea if you have ever heard the term "confounding variable" the story of this particular gun fits the definition to the tee. you can buy what you want, but anyone that uses this one story as justification against a company is being rash and reactionary.
Buy what you want I don't care.
Last edited by ThirdWatcher; 09-10-09 at 03:36. Reason: grammer
The ammo might be part of the zero thing. I used a steel rule and aligned on the edge of top rail and extended to the edge of gas block. The gas block appeared to be out of alignment by about 1/32" or so. S&W has it now in their shipping room. I've been trying to get them to throw it on a truck since middle last week. They are busy.
Hi ThirdWatcher - When I took my gun to the range, I always made sure the bolt and bolt carrier group was very lubed (dripping with lube), and the chamber clean and free of carbon and debris. Unfortunately, I still had problems manually extracting live 5.56 cartridges. Hopefully S&W will be able to diagnose and correct the issue.
It should still be able to easily extract any round regardless of how nasty looking and filthy the chamber is. My chamber on one of my carbines has got all sorts of crud in it and it's good to go.
The only thing I might have tried before shipping it off to S&W is adding the BCM extractor upgrade kit (minus the black rubber o-ring, as it doesn't likely need it) and see if that fixed the problem. I wouldn't have put any more effort into it than that though, since it's a new rifle and everything. You were right to ship it off to S&W though, hopefully they will resolve the issue for good.
BTW I would go ahead and buy the BCM extractor upgrade kit anyways after you get your M&P15 back from S&W, as it's always great to have that added reliability.
Thanks for the tip RetreatHell. I will look into the BCM upgrade kit.
Do you think I should test my S&W M&P15a without the black rubber O-ring in place on the extractor? My Colt 6920 does not have the rubber O-ring and it extracts fine (manually and when firing).
Well, I was only referring to the BCM extractor upgrade when I said not to include the black rubber o-ring around the extractor spring, because it probably wouldn't need it. But if it was having a difficulty extracting, or you felt that the extraction was a little "weak," after installing the BCM upgrade kit, then I'd go ahead and use the black rubber o-ring.
However, if the bolt that came with your S&W M&P15 has an o-ring around the extractor spring, I would just leave it there since it came that way from S&W.
My reasoning for that is simply because when I asked a similar question to a much more experienced shooter on this forum about an internal part of my KAC rifle, he told me to just leave it the way it came because Knight's Armament included it, so that probably means I should just not mess with it.
So I'm basically just passing that same info on to you now. But I don't think it would be that big a deal if you just wanted to see how it performed without the o-ring in place, as you can always put it back on there easily.
Thanks RetreatHell. If I get a chance to go to the range this week, I'll try it without the O-ring.
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