Posted: 3/7/2009 12:03:28 AM EDT
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Question:
I had a student in my rifle course yesterday that has a DPMS, AP4 .308 Carbine with a 16” barrel, a 1/10 TW, and a Picky rail upper. The rifle came from the factory with a removable fixed A2 type rear sight and we attempted to do a BZO at 25 meters (not yards) with that removable rear sight. I took a cold bore shot and the rifle printed about 8-10 inches from my POA, and all the follow-up shots grouped well, but they were still 8-10 inches high. I applied all of my rifle BZO skills and I just could not get the rifle to print at my POA. I even put a removable A3 carry handle, off of my personal Colt M4 on the rifle, and although the groups were printing tight and almost going through the same hole, they were still high. This doesn’t seem right for an out of the box EBR and I am baffled. I also applied the front sight adjustment and I even did hold-over/under and although the impact shots were where they should be, that was fruitless for zero. I know a lot but I don’t know everything. Any input will be helpful. Thanks in advance. Be Safe. Joe |
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The easiest avenue is to use a laser boresight, then actual ammo use.
Raising the front sight to POI (point of impact) should suffice. Same lot numbered factory ammo and and inspection (FSB, mechanical integrity, etc) are also a given. If you are chasing the group around the paper, usual culprits are mechanical. Usually: 1. FSB secure/positioning problems 2. Barrel to receiver contact or lack there of (over or under torqued). 3. Loose or faulty rear sight 4. Muzzle crown flaw FYI... Best of luck with it. 3 weeks and I can look at it. V OUT |
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Quoted:
The easiest avenue is to use a laser boresight, then actual ammo use. Raising the front sight to POI (point of impact) should suffice. Same lot numbered factory ammo and and inspection (FSB, mechanical integrity, etc) are also a given. If you are chasing the group around the paper, usual culprits are mechanical. Usually: 1. FSB secure/positioning problems 2. Barrel to receiver contact or lack there of (over or under torqued). 3. Loose or faulty rear sight 4. Muzzle crown flaw FYI... Best of luck with it. 3 weeks and I can look at it. V OUT Thanks V, You have reaffirmed everything I could think of. I will try to get it squared away and if I can't, I'll call you when you get back. Be Safe. Joe |
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Joe, this also reminds me of a problem that some Stag rifles were having. From what I remember, some uppers were improperly machined in the area where the barrel/ext sits. It was causing the same problem and people were changing out iron sight combos left and right with no fix.
I tried to find the topic in the archives, but I suck. |
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Quoted:
Joe, this also reminds me of a problem that some Stag rifles were having. From what I remember, some uppers were improperly machined in the area where the barrel/ext sits. It was causing the same problem and people were changing out iron sight combos left and right with no fix. I tried to find the topic in the archives, but I suck. Wow! That would suck, because there is no real way to check for it. Great info Animus, I'll put it in my toolbox. Hey! I learned something today! Hope you, your spouse who is Fiesty (very punny, I know), your nose picker (who is probably driving by now) and Timmey (non-wheel chair type) are all well. I'll have to share a Stella Artois (in my garage already awaiting me) with you so we can bitch about this joint and not have to explain acronyms and such. TOPIC: SOFA and how it has fucked up this Not A War Anymore that is happening over here. V OUT |