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Old December 10, 2018, 06:45 PM   #1
308Loader
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ar gas block change

so I want to free float my ar. I picked up all the parts I need and have the barrel nut changed out and the old front sight / gas block removed. this is the first time I done a project like this. every thing went smoothly, but I have one question before I install the gas block. the A2 front sight was pined on so I got the longer low profile gas block to cover the pin holes. it has 3 set screws, will I need to dimple the barrel for the 3 set screws. the rearward most hole hits the old pin cut out. the other 2 can be dimpled I think. I've never done this before but have read to use this type of block dimpling needs to be done, right? whos jig do you all like? or is their a better way?
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Old December 11, 2018, 03:03 AM   #2
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No need (unless you want to).
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Old December 11, 2018, 05:10 AM   #3
Nathan
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I cannot really answer that for you. Many people tighten the set screws and think they are fine. At some point, I’m sure their gas block comes loose. It is just a reality of heat cycling.

Applying rockset helps. It is like super high temp locktite.

IMO, cutting the sight part off your FSB and putting it back on is your best bet. Then you have a pinned gas block. Pins have proven reliable.

Or you could pin the new block on, but that adds another hole in your barrel.

I have a clamp on type on an accuracy rifle. It seems fine for now, but I worry I will find it loose someday.
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Old December 11, 2018, 08:53 PM   #4
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"IMO, cutting the sight part off your FSB and putting it back on is your best bet."

BINGO
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Old December 12, 2018, 11:19 AM   #5
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Dimpling is unnecessary.

I've never seen a properly-installed gas block come loose unless it was subjected to extreme heat* and abuse. *(We're talking 'melt your gas tube' levels of heat.)


But if you are worried about it, the FSB chop is a cheap solution.

I liked this one enough that I actually replaced it with a cheap aluminum gas block before selling the rifle, and stuck the DYI 'lo-pro' in the parts box:



Hacksaw, file, a quick hit with 120 grit, a cold blue touch-up, and an oil douche. Good enough for me.
The finish doesn't match, but I don't care and no one ever noticed, either.

Even more material could have been removed - especially in front of the gas tube - but I was after function. I wasn't trying to impress anyone.
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Old December 12, 2018, 04:35 PM   #6
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Since I don't know what I'm doing, I followed the instructions when I just recently changed out my OEM AR556 stuff with a STNGR FF hand guard and all that entails. They said nothing about dimpling anything so I didn't. Guess I'll find out if it ever thaws out and the snow melts.
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Old December 12, 2018, 07:20 PM   #7
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Thanks for the input guys. FrankenMauser, your cut down block does look nice. considering giving it a go with my old one. seeing as the barrel is cut for that exact pin spacing, nothing to chance. the new one looks pretty slick as installed, covers the pin holes, ok finish for something hiding under the hand guard.
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Old December 12, 2018, 09:04 PM   #8
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Quote:
Applying rockset helps
Never apply Rockset to anything you may want to disassemble at any point in the future.
Quote:
At some point, I’m sure their gas block comes loose.
Quote:
I've never seen a properly-installed gas block come loose unless it was subjected to extreme heat* and abuse.
I agree with Frankenmauser. Over the past 30 years as a gunsmith, I have built many dozens of ARs.. Never had one come loose. Set screws have teeth on the end and bite into the barrel when properly tightened, kind of like a lock washer.
Quote:
the FSB chop is a cheap solution
Done that several times. Looks OK.
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Old December 13, 2018, 07:30 AM   #9
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" the FSB chop is a cheap solution."

Back in "the old days" it was the ONLY solution. As was milling off the carry handle and attaching Weaver bases to the stubs.
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Old December 13, 2018, 07:44 AM   #10
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Quote:
I agree with Frankenmauser. Over the past 30 years as a gunsmith, I have built many dozens of ARs.. Never had one come loose. Set screws have teeth on the end and bite into the barrel when properly tightened, kind of like a lock washer.
How did you account for the differing rates of thermal expansion an the lack of anything to hold the set screw in place? Do you stake them? ....or just tighten some and hope for the best?
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Old December 14, 2018, 02:42 AM   #11
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Quote:
How did you account for the differing rates of thermal expansion an the lack of anything to hold the set screw in place?
Not sure I understand your question. Steel gas blocks expand at the same rate as steel rifle barrels. The teeth on the end of the set screw are designed to hold the screw in place when tightened, same as sheet metal screws have, same as flanged self-locking nuts have. The teeth work just like a lock washer.
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Old December 15, 2018, 07:16 AM   #12
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I'm pretty sure gas blocks aren't made of the same material as set screws and will expand at a different rate than those screws.
Heating even slightly dis-similar metals can cause loosening of the threaded parts--that's why I keep an acetylene torch handy. So, the likelihood of getting the gas block
THAT HOT can (and should) be minimized.
I've only had one set screw located gas block move and then only because it wasn't tightened adequately by the builder. I re-set it and it hasn't moved again. Still, I prefer clamp on blocks.
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Old December 16, 2018, 03:53 AM   #13
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No need to dimple. In fact, if your barrel is melonite treated if might be really hard to dimple the barrel. Just install the new gas block and tighten the gas block screws adequately. I’d use blue Loctite too.
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Old December 16, 2018, 04:33 PM   #14
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100 rnds through it today. Two 10rnd mag dumps and some double taps to get it nice and warm near the end of shooting session. Zero cycling and feed problems. Brought it home, removed the hand guard and checked everything. All seems to be right and tight. Must have done something right.20AR2.jpg

Thanks again for the reply's.
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Last edited by 308Loader; December 16, 2018 at 04:50 PM.
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Old December 17, 2018, 05:03 AM   #15
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Quote:
Not sure I understand your question. Steel gas blocks expand at the same rate as steel rifle barrels. The teeth on the end of the set screw are designed to hold the screw in place when tightened, same as sheet metal screws have, same as flanged self-locking nuts have. The teeth work just like a lock washer.
Maybe rate of thermal expansion is the wrong word since they are both steel, but I was thinking more about the heat flowing from in to out and how the barrel would get warm first, then when not shooting it would cool, then warm again shooting. The gas block would be cooler, but temps would vary between the 2 parts causing heat cycling at the boundary. Probably somebody smarter than me can tell it torque on the set screws is stable in this joint.

Unsure, I pinned mine.
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