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Posted: 7/19/2012 10:13:55 AM EDT
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Never tackled an upper and have a question.
I have an A2 that I want to turn into a flat-top. For now I just want to use same barrel and handguards. How hard is disassembly and re-assembly? Will everything be headspaced properly when it goes back together or does it need go & No-go guages? |
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Everything should be ok. Head space is based off of the bolt and barrel extension. So you don't need head space gauges.
Use anti seize on the threads of the receiver extension. I don't think the front sight will work with a flat top if it is a A2 upper. You will probably need a F marked front sight base. Hope this helps you. |
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Quoted:
Everything should be ok. Head space is based off of the bolt and barrel extension. So you don't need head space gauges. Use anti seize on the threads of the receiver extension. I don't think the front sight will work with a flat top if it is a A2 upper. You will probably need a F marked front sight base. Hope this helps you. Use grease on the threads. The sights may work w/o an f marked fsb |
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Quoted:
Quoted:
Everything should be ok. Head space is based off of the bolt and barrel extension. So you don't need head space gauges. Use anti seize on the threads of the receiver extension. I don't think the front sight will work with a flat top if it is a A2 upper. You will probably need a F marked front sight base. Hope this helps you. Use grease on the threads. The sights may work w/o an f marked fsb Ignorance is not bliss, I've seen the F Marked FSB reference a thousand times and have no idea what the differences are. Anyone give me the scoop? |
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Quoted:
Quoted:
Quoted:
Everything should be ok. Head space is based off of the bolt and barrel extension. So you don't need head space gauges. Use anti seize on the threads of the receiver extension. I don't think the front sight will work with a flat top if it is a A2 upper. You will probably need a F marked front sight base. Hope this helps you. Use grease on the threads. The sights may work w/o an f marked fsb Ignorance is not bliss, I've seen the F Marked FSB reference a thousand times and have no idea what the differences are. Anyone give me the scoop? The F-marked FSB is .040" taller than a standard FSB. They can be beneficial to a flat top with a shorter than 20" barrel. There are longer sight posts (pins) available if needed to make a standard FSB work. 
You most likely have rifle ramps on your present rig. If so, be sure to grab a flat top receiver with no M4 cuts. PK Firearms had CMT A4 uppers with no M4 cuts in stock recently. So verify and make sure that your barrel extension ramps, which are probably "rifle ramps", match the receiver you plan to buy. |
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Check your feedramps and see if they are M4 or rifle. If rifle you need to get the unramped upper. If M4 you can use either but the matching m4 ramped upper is preferred. You can probably zero your rifle after swapping uppers without having to change anything. If not you can get the Bushmaster .040 over front sight post. Make sure you get a good barrel nut wrench. I use the Spikes wrench, but the damage industries wrench at aimsurplus looks pretty good for about $10 cheaper. I normally use Lithium grease on the barrel threads and torque 30-90 ft lbs. You can rent/borrow a torque wrench from your local auto parts store if you don't have one. The barrel nut should be tightened to 30 ft lbs 3 times then turned until the gas tube hole lines up. If you have a cheap wrench (like alot of the off brand combo wrenches) it may slip off or break barrel nut teath. Just cause a tooth breaks doesn't mean your barrel nut is bad. Occasionally you will get a really tight barrel nut (I had one that didn't want to come loose with 200ft lb of pressure on it). You can normally break them loose with heat. If not you will have to cut it off, but this is very rare. If you have any questions let me know and I will try and help.
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