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Discussion Starter · #1 ·
Well, I went to the range tonight with my XCR for the first time. Shot about 45 rounds, 20 of which were federal xm193, the rest some stuff I bought at Walmart. Gun ran fine. I learned that, when shooting in an indoor stall on gas setting 4, you can pretty much forget about collecting your brass. That stuff bounced hard off the wall and way out into the range. I also learned that a bob sled doesn't work in an XCR. I couldn't get the bolt into battery while it was inserted. I failed get my irons sighted in before I ran out of adjustment. I have an MI front and a matech rear. The front post is all the way down, and I'm still shooting about 3 or 4 inches too low at 25 yards. I had the matech set on 200. Anyone have any advice regarding what I'm doing wrong?
 

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I had the same problem. My XCR was hitting low even with the front sight all the was down(Samson front sight). I ended up filing it down till I was very close to right on at 25 yards and then I re blued the sight post. Be carefull not to file to much off or you will be high.

You can also but a set of front sight posts ans swap them out as needed.
 

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I think that's pretty common. I have the MI front and rear. Had to bottom my front post, which was 13 turns, to get it an inch low at 25yd, very close to dead on at 50yds with the large aperture. The small aperture shoots a little higher for me. Anyway, I'm happy with it now.
 

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I have Troy front and rear, and I just about had to bottom out the front to get it on target at 100yd with Q3131. I expect it probably has something to do with using sights designed for an AR15 height-over-bore, on an XCR where that dimension doesn't match.

Just remember they are called "Back Up Iron Sights" for a reason... and they will serve that purpose fine. I think the standard recommendation is going to be to get a red dot or other optic as a primary sight.
 

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Discussion Starter · #5 ·
But both sights are rail mount, so the position of the sight line on an M-16 isn't an issue, right? Is the nominal height of the sight line, above the rail, not more or less standardized for flat-top AR-15'sh rifles?
 

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With the Matech you need to have the range scale on "300" for an M4 and on the "line" for M16's. With a 16" barrel you'd be closer to the M4 setting. It might not make much difference but should help give a better BZO.

When "targeting" other rifles it's common to file the front sight post to maintain the capability of adjustment later on. File little, check often! But if you screw up, they're pretty cheap to replace.
 

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I have a GG&G flip up front and a ARMS 40L rear that cowitness with an Eotech 552. Front sight only had to go down one click and with the rear centered the rifle shot to the left about 6-8 inches. A few clicks to the right on the rear sight and it was dead on at 50 yds. (lg. aperture) Still has some room for windage adj. I would say your problem is inherent to the sights you chose.

Hope this helps,

Roy.
 

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But both sights are rail mount, so the position of the sight line on an M-16 isn't an issue, right? Is the nominal height of the sight line, above the rail, not more or less standardized for flat-top AR-15'sh rifles?
I wouldn't think so... think about an extreme case. Say the sights were a foot over the bore. Think about how far you would have to lower the front to get it on target at 25, or 100yd or whatever.... it would be well past impossible.

I believe the XCR places the sights a little higher than an M4 flat top type rifle. It stands to reason that you will have to adjust the front further down to get on target than you do on an M4.
 

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AR15 sights are .4" higher on the XCR. I had to rotate front sight post down 4 clicks to get it dialed at 50 yards.
 

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Discussion Starter · #10 ·
Ok, let's just run the numbers. Google says that the height above bore for iron sights on an M-4 is 2.6 in, and that the rail on an M-4 is 1.215 in above the bore. The front sight post provides about 2 MOA of adjustment per click. With the target at 25 yards, the angle between the bore centerline and the line of sight is approx. 10 MOA. If I assume that the sights on the XCR are a full inch higher (don't know this exact number, yet), then the angle, for an XCR, is approx. 14 MOA. If the distance between the front and rear sights are approximately the same for both the M-4 and the XCR, then I would need to adjust out the difference: 4 MOA, or about 2 clicks of the front sight post. I am, however, presuming that front sights for an AR-15/M-16/M-4 are generally designed such that the center position provides approximately the correct zero for that weapon, but even if the center position puts the line of sight parallel to the bore, it should only take about 7 clicks to get my XCR on target. It seemed like a lot more than that, but I don't remember the exact count. I'll check that again when I get home tonight.
 
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