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Posted: 8/30/2016 1:03:00 AM EDT
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Hello, all. A couple days ago, I asked you guys for advice, and have been persuaded to purchase a LaRue barrel and handguard. Again, thanks for the help. Today, I've got another question. I'm not incredibly familiar with the construction of the AR-15; I bought mine as a whole rifle, and I know it well enough to break down and clean it when necessary, but what I don't know about is the gas block area.
If I bought an A2 style front sight base, does that fit around the gas block, or do I need to do anything special? Never really had a chance to eyeball a rifle that had one, so I'd appreciate your help once again. |
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Unless you specifically search out a "clamp on" style FSB, you'll have to have a standard A2 FSB taper pinned to the barrel of your choice. Sounds like that work is well outside your area of expertise, so you'll have to send it somewhere to have it done.
ETA: I just found your other thread. What length rail did you purchase? |
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An A2 style front sight base is a gas block. Any other gas block would have to be removed. The standard installation of a front sight base requires drilling and reaming holes for taper pins which generally requires a jig for support and is not a trivial machining operation.
The only clamp-on A frame style front sight base that was on the market is apparently out of production and unavailable. There are clamp-on gas block/front sight bases with fold down front sights on the market. Some barrels are designed for low profile gas blocks only and do not have a journal long enough for a standard front sight base. Barrels with a nitrided type finish treatment will be very difficult to drill for taper pins. |
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A2 front sight is also the gas block. The standard model is pinned with taper pins. It needs to be installed by someone with the capabilities to drill and ream the holes. Also because it is the sight it needs to be aligned perfectly.
Another issue is drilling a Nitride treated barrel. Nitride is a surface hardening and very difficult to drill. Most gunsmiths won't attempt to drill it. A quick search found http://www.shop.dezarms.com/product.sc?productId=27. Also your rail needs to be short enough to fit behind the A2 sight. What size rail did you buy? If you go with a set screw style gas block you ideally want to find one the has the correct spacing for LaRue barrels. Any will work but the barrel comes dimpled and of course just a little better if the screws sit in the dimples. Not a maor issue if it doesn't. I believe SLR makes one with the LaRue spacing. |
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Thanks for the information, guys! To answer the question several of you asked, I purchased the 12-inch rail; I believe that should provide enough clearance for an A2 front sight / gas block. Having learned the answer to my initial question:
Does anybody have any recommendations for an A2 sight base? Or are they all basically the same quality? |
| No matter what you chose to do with your gas block, you will need a gas tube that matches your barrel's gas system length (carbine, mid, rifle, etc.) and a roll pin that holds the gas tube to the gas block. Pay attention to descriptions of the parts you order, some tubes/gas blocks come with the pin, some don't. |
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You'll need a barrel with a rifle length gas system to be able to put an A frame front sight in front of a 12" rail.
Maybe if you tell us what your goals/intentions are we might be able to suggest some alternatives. You'll quite possibly spend more getting a front sight installed than you did on the barrel. If you're looking to create a traditional AR15 barrel configuration, that's not going to work since Larue barrels have the shoulder on the barrel set up for a gas block/FSB only, without the space for a handguard ring. Larue doesn't say what their materials or processes are so I can't tell you if the barrel is nitrided or not. |
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What barrel length do you have and what gas block location does it have. Chances are very high that the block is back under that rail. If so, there is no way to install a true A2 sight. The rail will be in the way. In his original thread, he said he was looking for a 20" barrel, so I'm assuming that's what he purchased which will mean a RLGS. If so, everything should work fine with an A2 FSB. FWIW, though, getting a FSB pinned to a barrel typically isn't very cheap. I'd personally just go with a LPGB. |
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Quoted:
In his original thread, he said he was looking for a 20" barrel, so I'm assuming that's what he purchased which will mean a RLGS. If so, everything should work fine with an A2 FSB. FWIW, though, getting a FSB pinned to a barrel typically isn't very cheap. I'd personally just go with a LPGB. Quoted:
Quoted:
What barrel length do you have and what gas block location does it have. Chances are very high that the block is back under that rail. If so, there is no way to install a true A2 sight. The rail will be in the way. In his original thread, he said he was looking for a 20" barrel, so I'm assuming that's what he purchased which will mean a RLGS. If so, everything should work fine with an A2 FSB. FWIW, though, getting a FSB pinned to a barrel typically isn't very cheap. I'd personally just go with a LPGB. Thanks, I missed reading that. With a 20' barrel and rifle gas block location and that rail, it is possible. I agree, though that he is not likely to have the skill and equipment to install a true A2 FSB over the gas port, line it up properly and drill and ream the block and barrel. I recently did install an A2 FSB from scratch on a carbine barrel. I do have the equipment to do it, including the proper jig, a good drill press, the right size drill bits, drill and tap oil and the 2/0 reamer. It takes a lot of planning and time if you are not a professional gunsmith. Mine turned out great, but it was a slow, tedious and careful process for most of us. Many who do it end up with a sight that is canted to the side, even when they have a gunsmith do it because he did not line up and mark everything precisely and did not keep it aligned when in the drill press. I was using a nitride barrel, too. Penetrating the nitride makes things more difficult, too. Anyone doing this should plan on needing to replace bits at least once. Pleased with the result but not excited about trying to do this again anytime soon. 
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Quoted:
In his original thread, he said he was looking for a 20" barrel, so I'm assuming that's what he purchased which will mean a RLGS. If so, everything should work fine with an A2 FSB. FWIW, though, getting a FSB pinned to a barrel typically isn't very cheap. I'd personally just go with a LPGB. Quoted:
Quoted:
What barrel length do you have and what gas block location does it have. Chances are very high that the block is back under that rail. If so, there is no way to install a true A2 sight. The rail will be in the way. In his original thread, he said he was looking for a 20" barrel, so I'm assuming that's what he purchased which will mean a RLGS. If so, everything should work fine with an A2 FSB. FWIW, though, getting a FSB pinned to a barrel typically isn't very cheap. I'd personally just go with a LPGB. If the LaRue barrel wasn't on sale, I may agree. Taking a quality barrel on sale and adding less than $150 to get it where you want it isn't crazy to me. ADCO charges $90 to install a FSB if you provide the sight. Let's say you can pull it off for $125. You've got a quality barrel for $350. That's not terrible if you have the money and want a quality barrel with a FSB. For reference, a comparable Ballistic Advantage barrel would run you $310 without any sales, if you order from them and have them install the sight. |
| The basic idea is just your average long gun. 20" heavy-ish barrel, quad rail, and iron sights to supplement my 4x scope. My preference for the A2 sight block mostly comes from the bayonet lug, but I'm really starting to think it's not worth it and I should just get a good set of flip-ups to replace the cheapo $50 flips I have right now, and call LaRue to order a 13.2 inch quad instead of a 12. |
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Quoted:
If the LaRue barrel wasn't on sale, I may agree. Taking a quality barrel on sale and adding less than $150 to get it where you want it isn't crazy to me. ADCO charges $90 to install a FSB if you provide the sight. Let's say you can pull it off for $125. You've got a quality barrel for $350. That's not terrible if you have the money and want a quality barrel with a FSB. For reference, a comparable Ballistic Advantage barrel would run you $310 without any sales, if you order from them and have them install the sight. Quoted:
Quoted:
Quoted:
What barrel length do you have and what gas block location does it have. Chances are very high that the block is back under that rail. If so, there is no way to install a true A2 sight. The rail will be in the way. In his original thread, he said he was looking for a 20" barrel, so I'm assuming that's what he purchased which will mean a RLGS. If so, everything should work fine with an A2 FSB. FWIW, though, getting a FSB pinned to a barrel typically isn't very cheap. I'd personally just go with a LPGB. If the LaRue barrel wasn't on sale, I may agree. Taking a quality barrel on sale and adding less than $150 to get it where you want it isn't crazy to me. ADCO charges $90 to install a FSB if you provide the sight. Let's say you can pull it off for $125. You've got a quality barrel for $350. That's not terrible if you have the money and want a quality barrel with a FSB. For reference, a comparable Ballistic Advantage barrel would run you $310 without any sales, if you order from them and have them install the sight. I completely agree, if you absolutely have to have a FSB. For me, personally, I use optics almost exclusively, so I don't really have the need. That's why I said personally I'd just go with a LPGB. It's up to OP to decide if he absolutely needs a barrel mounted front sight. |
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Quoted:
The basic idea is just your average long gun. 20" heavy-ish barrel, quad rail, and iron sights to supplement my 4x scope. My preference for the A2 sight block mostly comes from the bayonet lug, but I'm really starting to think it's not worth it and I should just get a good set of flip-ups to replace the cheapo $50 flips I have right now, and call LaRue to order a 13.2 inch quad instead of a 12. That's what I would do, personally. The cost will be roughly the same. |
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Quoted:
The basic idea is just your average long gun. 20" heavy-ish barrel, quad rail, and iron sights to supplement my 4x scope. My preference for the A2 sight block mostly comes from the bayonet lug, but I'm really starting to think it's not worth it and I should just get a good set of flip-ups to replace the cheapo $50 flips I have right now, and call LaRue to order a 13.2 inch quad instead of a 12. If it helps you decide, my 12 inch rail was on backorder when I got my 20" barrel, so I switched to a 13.2 and it was in stock, as of a couple weeks ago anyways. I put the ARMS flip ups on mine. I like them more than my KAC sights. |
| So, I just talked to the gunsmith down the road from me. To install and check headspacing on the barrel, handguard, and gas block, it looks like it'll cost about $200. This is all after buying the parts, of course. So, overall, about $800, if you factor in shipping on the parts. If I go with the regular gas block, it drops to about $600. I dunno. Does this sound reasonable to you guys? |
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So, I just talked to the gunsmith down the road from me. To install and check headspacing on the barrel, handguard, and gas block, it looks like it'll cost about $200. This is all after buying the parts, of course. So, overall, about $800, if you factor in shipping on the parts. If I go with the regular gas block, it drops to about $600. I dunno. Does this sound reasonable to you guys? Sending it to ADCO for tear down and install would probably be cheaper. ETA: Upper disassembly-reassembly at ADCO is $50 and if you decide to go with the FSB, it's $105 to have it taper pinned. Still cheaper than $200 and ADCO is a known quantity when it comes to AR work. If you use a regular low-pro gas block it'll just be $50. |
| The concern I have with ADCO is that they won't do hardened barrels, which they define as barrels with a nitride, Melonite, or other non-phosphate/parkerized finish, and since LaRue won't tell you what the story is on the barrel, I don't want to end up paying for shipping and not be able to get the process done. On top of that, it's $90/$105 before shipping, and insured shipping ain't cheap. |
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The concern I have with ADCO is that they won't do hardened barrels, which they define as barrels with a nitride, Melonite, or other non-phosphate/parkerized finish, and since LaRue won't tell you what the story is on the barrel, I don't want to end up paying for shipping and not be able to get the process done. On top of that, it's $90/$105 before shipping, and insured shipping ain't cheap. Have you asked Larue? It may not be listed on their website, but I have a hard time believing they won't at minimum confirm or deny that their barrels are melonited. ETA: From what I'm reading, Larue barrels use an IonBond finish, not melonite. I'd confirm with Larue and ADCO, but that's what I'm seeing. In either case, if you just skip the FSB and go with the 13.2" rail/LPGB, you avoid the issue altogether. |
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Not cheap, but you could get a clamp-on JP and have the added benefit of adjustable gas. And it would probably end up being less then buying a FSB and having it pinned.
http://www.midwayusa.com/product/413559/jp-enterprises-adjustable-gas-block-with-a2-front-sight-ar-15-lr-308-standard-barrel-750-inside-diameter-stainless-steel-matte |
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Not cheap, but you could get a clamp-on JP and have the added benefit of adjustable gas. And it would probably end up being less then buying a FSB and having it pinned. http://www.midwayusa.com/product/413559/jp-enterprises-adjustable-gas-block-with-a2-front-sight-ar-15-lr-308-standard-barrel-750-inside-diameter-stainless-steel-matte I actually thought about that before doing it myself. It became a personal challenge. I already had the barrel and wanted one rifle with an A2 FSB. My concern with a clamp on is that despite the clamping force, it might still move if hit hard, as often happens with FSB sights, since they are always exposed. Even slight movement would screw up your zero. Tapered pins through the edge of the barrel pretty much prevent that. The JP design does seem to be the best of the clamp ons, though, and would be cheaper than sending it out for pinning. Just don't knock the crap out of it after sighting in. Hit hard enough and the gas port opening could get blocked too, then the rifle is just a club. I think the JP FSB is designed for National Match competition shooting where a FSB barrel is mandatory and perfect sight alignment is essential. Those barrels are babied. |
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My concern with a clamp on is that despite the clamping force, it might still move if hit hard, as often happens with FSB sights, since they are always exposed. Even slight movement would screw up your zero. Tapered pins through the edge of the barrel pretty much prevent that. Quoted:
My concern with a clamp on is that despite the clamping force, it might still move if hit hard, as often happens with FSB sights, since they are always exposed. Even slight movement would screw up your zero. Tapered pins through the edge of the barrel pretty much prevent that. It's already been proven through testing that a clamp-on gas block will withstand enough torque to twist the barrel in the receiver and shear the index pin on an installed barrel. The concern about bumping one and it moving is imaginary. The JP design does seem to be the best of the clamp ons, though, and would be cheaper than sending it out for pinning. Just don't knock the crap out of it after sighting in. Hit hard enough and the gas port opening could get blocked too, then the rifle is just a club. I wasn't aware of the JP unit, it is very expensive but should work fine, with the advantage of being able to be reused on another barrel later on. Just keep in mind that with a Larue barrel, you apparently can't use a standard handguard ring. For the cost of that JP fixed sight, if it was me for a primarily optics-sighted rifle, I would probably get an ARMS fold-down FSB. |
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Wow, I like that ARMS folding sight! And it just clamps on with hex bolts? No need to visit an armorer? No. You'll only need a gunsmith if you want to pin a fixed front sight to the barrel. If you want fixed sights (clamp on the rail, don't fold), my favorites have become the Rock River Arms fixed A2 style rear sight (better than LMT) and a Daniel Defense fixed front sight. |
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One more option, kind of interesting. Would need a gas block to go with it:
http://www.brownells.com/rifle-parts/sights/front-sights/ar-15-fixed-clamp-on-front-sight-prod85934.aspx |
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