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Posted: 12/7/2012 3:04:35 PM EDT
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My brother asked if I would build him a carbine upper, and shipped me some el cheapo M4 profile barrel and separate FSB (a-frame) from midway.
Being that they arent mated, the FSB has no taper pin holes, and neither does the FSB. Is it possible to spot weld the FSB to the barrel to secure it? It fits on but is a little loose and wont stay in place on its own. I'm not sure what else I can do at this point, aside from spot welding it or swapping for a low profile, but he already bought 2-piece rails. |
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I wouldn't weld it for a few reasons. The main two being:
1. You can warp the barrel. 2. When you need to remove it you'll have to grind it off, again damaging the barrel. The only real solutions are to drill/taper your own taper pin holes. Modify it for setscrews. Or tell him to send it back and buy a clamp on gas block. If you don't have some machining experience I would go with the last option. It's better for him to spend an extra $20 then to risk ruining a barrel and doing a sub-par job by welding something on that was never designed to be welded on. |
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If he wants the A2 style I think Armalite is the only one who makes a clamp on A2. But there's a few low profile or railed clamp ons around.
Here's the Armalite. |
Yea the FSB is pinned  how did you come up with welding??? They are not bad to do with the right tools and a little common sense….. take a look at this article http://www.ar15.com/archive/topic.html?b=3&f=123&t=470461
EDIT: yours would be even easier because your FSB doesn't have pre drilled holes. |
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If you want to do it yourself, here is my post in the building thread.
I used the thread above and some others as source material http://www.ar15.com/forums/t_3_4/226782_Assemble_your_own_LOWER__UPPER__FREE_FLOAT__TRIGGER__GAS_BLOCK___Step_by_step_instructions_.html&page=25#i5724417 |
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Quoted:
If you want to do it yourself, here is my post in the building thread. I used the thread above and some others as source material http://www.ar15.com/forums/t_3_4/226782_Assemble_your_own_LOWER__UPPER__FREE_FLOAT__TRIGGER__GAS_BLOCK___Step_by_step_instructions_.html&page=25#i5724417 Thats a good write up AIP. I just did my 1st a few days ago. I like the tip tapping the hole and using a screw to hold the FSB. I didn't switch to an end mill, I went straight through with the drill bit to no ill effect, just went slow. I have a DD barrel…. I think it would be necessary for a pre drilled FSB though. I used about 900RPM too, with the bit I used it went through super easy. |
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Thanks
I was concered with how hard the nitrided barrel might be, hence the end mill to give a square landing area for the bit. I used a brand new TiN drill, and it was like butter. I don't think I mentioned it in the other post, but I used the sling swivel holes to help align the assembly on the drill press. I put a drill bit in the hole and then used that and a square on my table to make sure the asembley was square in the vice and to the press table/bit. I checked it by chucking a bit in the press and comparing that with the bit sticking up and out of the sling swivel holes. That assums the sling swivel holes are square to the FSB of course. |
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Quoted:
Thanks I was concered with how hard the nitrided barrel might be, hence the end mill to give a square landing area for the bit. I used a brand new TiN drill, and it was like butter. I don't think I mentioned it in the other post, but I used the sling swivel holes to help align the assembly on the drill press. I put a drill bit in the hole and then used that and a square on my table to make sure the asembley was square in the vice and to the press table/bit. I checked it by chucking a bit in the press and comparing that with the bit sticking up and out of the sling swivel holes. That assums the sling swivel holes are square to the FSB of course. Yea thats the issue. I like your idea with the set screw to hold it then its just a matter of getting it perpendicular to the bit, IMO probably the easiest part. I made this simple block to help me out…. 
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Quoted:
Yea the FSB is pinned how did you come up with welding??? They are not bad to do with the right tools and a little common sense….. take a look at this article http://www.ar15.com/archive/topic.html?b=3&f=123&t=470461
EDIT: yours would be even easier because your FSB doesn't have pre drilled holes. Ive only taken them off, never had to put one on so I didn't even think about it until it all showed up. |
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Quoted:
Yea thats the issue. I like your idea with the set screw to hold it then its just a matter of getting it perpendicular to the bit, IMO probably the easiest part. I made this simple block to help me out…. https://lh6.googleusercontent.com/-fE0dmyTbk4E/UMKqW3CQo2I/AAAAAAAABak/7w1mADOtc8o/s1024/_W0A7195-1.JPG https://lh4.googleusercontent.com/-nqQYr42vhi4/UMKqZqjPuPI/AAAAAAAABas/6l2ja8REJdQ/s1024/_W0A7196-2.JPG What pin does that index on? |
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Quoted:
Quoted:
Yea thats the issue. I like your idea with the set screw to hold it then its just a matter of getting it perpendicular to the bit, IMO probably the easiest part. I made this simple block to help me out…. https://lh6.googleusercontent.com/-fE0dmyTbk4E/UMKqW3CQo2I/AAAAAAAABak/7w1mADOtc8o/s1024/_W0A7195-1.JPG https://lh4.googleusercontent.com/-nqQYr42vhi4/UMKqZqjPuPI/AAAAAAAABas/6l2ja8REJdQ/s1024/_W0A7196-2.JPG What pin does that index on? The barrel extension pin |
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Quoted:
Quoted:
Quoted:
Yea thats the issue. I like your idea with the set screw to hold it then its just a matter of getting it perpendicular to the bit, IMO probably the easiest part. I made this simple block to help me out…. https://lh6.googleusercontent.com/-fE0dmyTbk4E/UMKqW3CQo2I/AAAAAAAABak/7w1mADOtc8o/s1024/_W0A7195-1.JPG https://lh4.googleusercontent.com/-nqQYr42vhi4/UMKqZqjPuPI/AAAAAAAABas/6l2ja8REJdQ/s1024/_W0A7196-2.JPG What pin does that index on? The barrel extension pin Good idea, thanks. |
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