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Posted: 5/17/2010 7:18:41 PM EDT
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I may be sounding like a perfectionist here, but my FSB is 2-3 degrees crooked. It's a new Spikes M4 LE. I would post pictures, but it would impossible to notice with my iPhone camera and inferior photo skills. Anyone know of quick way to fix this? I really don't want to pay a gunsmith to fix a week old gun...it just bugs the piss out of me.
ETA: It's canted to the left...if that matters. |
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I just had this same problem, bought a M4 upper from a reputable co (Not going to mention names as they are bending over backwards to make it right) and the FSB was canted 2-3deg to the left. in my case it looked like someone tried to drive the drift pins the wrong way...and when they didn't seat...they hit it with a BFH.
I'm sure Spikes will make it right for you also..and imho that is the "fix" |
| We drill all FSB's in very expensive custom fixtures that we make. They locate the dead center of the front sight base (where the post is installed) and the indexing pin. I've seen slight variation in the front sight base forgings themselves, sometimes they are not perfectly symmetrical, a little thicker on one side than the other, it makes the front sight look canted but the sight post which we locate off of is dead center. Each front sight gets checked 3-4 times during assembly to make sure they are not canted. I'm pretty picky about having straight front sights. It's always best to shoot it to verify if it is indeed canted. If it is we will send you a new upper with an RMA for the old one, no questions asked. |
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We drill all FSB's in very expensive custom fixtures that we make. They locate the dead center of the front sight base (where the post is installed) and the indexing pin. I've seen slight variation in the front sight base forgings themselves, sometimes they are not perfectly symmetrical, a little thicker on one side than the other, it makes the front sight look canted but the sight post which we locate off of is dead center. Each front sight gets checked 3-4 times during assembly to make sure they are not canted. I'm pretty picky about having straight front sights. It's always best to shoot it to verify if it is indeed canted. If it is we will send you a new upper with an RMA for the old one, no questions asked. Well my eyes are certainly no measure of exactness. Perhaps the forging is just slightly off. I shot it this past weekend from a bench, but only had xm193...groups were too sporadic with the 55 grain and BUIS to tell much. I'll get some others opinions and shoot something heavier this weekend for a 50 meter BZO before I ask for anything drastic like that, but thanks for he excellent customer service response. |
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Very common with the AR. No, it's not. Actually it is. Ive seen Colt's with canted FSB's It's not much but enough to notice. Maybe 1-2 degrees. It's a battle rifle, not a sniper rifle. It's not going to affect accuracy, he just needs to adjust his rear sight accordingly. |
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I may be sounding like a perfectionist here, but my FSB is 2-3 degrees crooked. It's a new Spikes M4 LE. I would post pictures, but it would impossible to notice with my iPhone camera and inferior photo skills. Anyone know of quick way to fix this? I really don't want to pay a gunsmith to fix a week old gun...it just bugs the piss out of me. ETA: It's canted to the left...if that matters. It's can't be fixed because the FSB is drilled onto the barrel. Each FSB is unique to each rifle. Trying to adjust it could make the holes on the bottom of the barrel larger, then you have a bigger problem which is a loose FSB. I wouldn't worry about it, It's not going to affect anything, just adjust your rear sight. |
| There are a couple of things you can do to see if things are askew. First option is to shoot the rifle. If it takes more than 10 clicks of windage to zero, then send it back. Second option is to put a fixed rear sight on the rifle (i.e. a carry handle, LMT BUIS, Larue BUIS, etc.) and flip it upside down on a flat surface. If all four corners of the sights are touching the surface, then you should be good to go. This is assuming you have a quality FSB with symmetrical ears. |
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There is nothing you can do to fix it if it is really canted. ONLY If you dont know what you are doing, or dont have the proper tools it cant be fixed. An FSB that was installed canted can be reinstalled properly on the same barrel. Quoted:
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There is nothing you can do to fix it if it is really canted. No. it's repairable. Have you ever pulled a barrel ? Thus the term "you." If someone is posting asking about a canted FSB, then they probably can't fix it. If they knew how and had the proper tools then they could and probably wouldn't be asking about it. See where I am going with this? |
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Very common with the AR. No, it's not. Yes, it is quite common. Quoted:
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Very common with the AR. No, it's not. Actually it is. Ive seen Colt's with canted FSB's It's not much but enough to notice. Maybe 1-2 degrees. It's a battle rifle, not a sniper rifle. It's not going to affect accuracy, he just needs to adjust his rear sight accordingly. Well color me wrong.  But seriously, if you think about the number of AR's produced in relation to the number that have significantly canted FSB's, it might not seem to common.
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| Ok, I work in a geotechnical engineering firm. I had the lab measure the wings on the FSB with NIST traceable calipers. The right wing is .0482 inches taller than the left. I know it doesn't seem like much, but this must be the reason it seems canted. So, no crooked FSB. Sorry to Spikes for the false accusation. |
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