Actually here’s something from Arf I just found....
“Originally Posted By firepyro515:
Your mileage may vary , but here is my experience with the Spikes/FN 11.5
We ordered a bunch for the shop back in 2011. They looked nice and we didn't notice any issue with them when installing. Shooting was a completely different story. When we took them out to zero, we ran out of windage. We pinned the rear sight all the way to the right and the gun was still shooting left at 25 yards. We thought it was a fluke and tried a different barrel. All 5 barrels we ordered had the same issue.
Fast forward to the end of 2014. I was looking for a new barrel for my SBR. I thought that maybe the last batch of Spikes/FN barrels were bad, so I decided to try them again. I picked up one from a distributor and installed it on my upper and took it out to the range. This time, I ended up pinning the rear sight all the way to the left and I was still hitting right at 25 yards. I ended up tossing the barrel and going with a Daniel Defense 11.5" barrel (1.28lbs)
I have used a 14.5" Spikes/FN barrel for over 4 years now and I haven't had any issues with it. But the Spikes/FN 11.5 barrels have been giving me problems.”
The reason why I post it is because one issue I had is that when zeroing my SBR with the Spikes 11.5 is that I had to make a bunch of clicks to the right to get it dialed in at 50yds, which put the aperture noticeably offset to the right (not quite all the way, but getting there). This happened with two different C7 style upper receivers from two different manufacturers (I had to change upper receivers because of a feed problem......which, is a long story but now that I’m remembering it, even though I changed uppers the barrel was the likely issue, switching uppers was just the easiest way to fix the problem) So anyway, I have OCD (literally) this offset rear sight annoyed me but my inclination was to suspect the guy who had pinned my FSB had canted it ever so slightly, it didn’t really occur to me that the issue could have been with the barrel itself. I got mine years after this guy’s experiences though.
So if the account from Arfcom is accurate, what causes this? The bore being asymmetric in the barrel?
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