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MI, USA
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Posted: 12/9/2023 3:02:10 AM EDT
I am Building an 11.5 upper for my sbr I got a great deal ($75shipped) on a new BA barrel but it has no dimples. I was going to order a expo arms gas block from PA but do I also buy the slr dimple jig or just say screw it and put it together un dimpled. I have built a few uppers they all had pinned gas block faxon barrels from Aim but do I spend the money now and get a dimple jig I may only use a few times. I did call a couple places just to inquire they want $25-50 to dimple the barrel for me.
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OH, USA
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Posted: 12/9/2023 4:25:03 AM EDT
[#1]
I just dimpled a BA barrel tonight. Nitride is very tough... get carbide or cobalt bits. get Stub-length if possible or chuck up as far as you can on a jobber... too long and the curved surface will flex the bits to death.
I used a mill. I tried with a HSS 1/8" ball endmill first (because HSS was the only kind of ball endmills I have at the moment) and the ball endmill just skated around on hard ass curved surface of the barrel and then broke. It literally only scratched it up some. I had to spotface the locations with a 3/16" carbide 2 flute endmill to break through the nitride layer (you can hear the pitch change after several thousandths once you get to softer steel) and THEN used a HSS center drill to spot the set screw locations. |
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FL, USA
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Posted: 12/9/2023 8:58:34 AM EDT
[#2]
100% dimple. Anything doing is worth doing right.
Cobalt drill, a little bit of oil, slow speed and you're done in 5 minutes. Touch up with cold blue and voila. The price of a dimpling jig is negligible, especially for importance of a secure gas block |
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TX, USA
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Posted: 12/9/2023 9:04:17 AM EDT
[#3]
Quote HistoryOriginally Posted By JJL0325: 100% dimple. Anything doing is worth doing right. Cobalt drill, a little bit of oil, slow speed and you're done in 5 minutes. Touch up with cold blue and voila. The price of a dimpling jig is negligible, especially for importance of a secure gas block Bingo! |
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MN, USA
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Posted: 12/9/2023 11:01:20 AM EDT
[#4]
Meh! If the gas block is going to be shrouded by the handguard a dimple is not needed. If the gas block will be exposed, such as a FSB, absolutely dimple and even better, pin it.
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Posted: 12/9/2023 11:09:05 AM EDT
[#5]
Spend the $50 and send it to one of the highly regarded gunsmiths mentioned here all the time to pin it. And never have to worry about it again.
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Posted: 12/9/2023 11:54:04 AM EDT
[Last Edit: mudholestomper]
[#6]
I dimple every time. It’s a bare minimum thing for me. SLR is not the only jig out there, obviously. I use cobalt bits and they work easily. No oil needed. You’re just putting a dimple, not drilling a hole. The bit will spend maybe 10 seconds in the cut.
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Posted: 12/9/2023 12:43:51 PM EDT
[#7]
Yea, I would at least make one dimple, regardless if the GB is covered by the handguard or not.
Also, make sure you're using the correct GB screws. They should be knurled cup set screws. |
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Posted: 12/9/2023 1:05:04 PM EDT
[#8]
Quote HistoryOriginally Posted By JJL0325: 100% dimple. Anything doing is worth doing right. Cobalt drill, a little bit of oil, slow speed and you're done in 5 minutes. Touch up with cold blue and voila. The price of a dimpling jig is negligible, especially for importance of a secure gas block Doing it right still means a pinned gas block IMO but if you are going to go with a set screw type block then by all means, at least dimple it. |
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USA
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Posted: 12/9/2023 8:01:56 PM EDT
[#9]
Yes, dimple it. I've done one myself, just measured and eyed it, no jig, no problem.
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Posted: 12/9/2023 10:21:47 PM EDT
[#10]
Either pin or dimple.
If you dimple, dimple both. Use a jig if you are using a drill. Cupped set screws. Rockset. |
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Posted: 12/9/2023 11:07:46 PM EDT
[#11]
The dimpling was the easy part. Drilling the cross pin actually turned out to be not that difficult either. Or, maybe I just got lucky.
  Attached File |
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Posted: 12/9/2023 11:10:09 PM EDT
[Last Edit: FoxValleyTacDriver]
[#12]
Honestly if you're only going to use the jig once or twice you should just sell the barrel and buy a dimpled one honestly. But I already have a pile of tools I've only used once so I try not to let it grow....
I only buy dimpled barrels now |
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Posted: 12/10/2023 10:12:09 AM EDT
[#13]
Quote HistoryOriginally Posted By FoxValleyTacDriver: Honestly if you're only going to use the jig once or twice you should just sell the barrel and buy a dimpled one honestly. But I already have a pile of tools I've only used once so I try not to let it grow.... I only buy dimpled barrels now My garage is full of once-used tools. I used to feel guilty about that inefficiency. But as we slide closer to third world operations, I don't feel so bad. |
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GA, USA
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Posted: 12/10/2023 12:02:58 PM EDT
[#14]
Quote HistoryOriginally Posted By sunnybean: The dimpling was the easy part. Drilling the cross pin actually turned out to be not that difficult either. Or, maybe I just got lucky. https://www.ar15.com/media/mediaFiles/96670/IMG_5343_jpeg-3055065.JPG What size drill bit you use on that cross pin hole? |
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OR, USA
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Posted: 12/10/2023 12:47:32 PM EDT
[#15]
I've never had a properly torqued gas block move with or without dimples. I've had two that weren't dimpled that were an utter bear to get off. However, whenever I can I dimple just in case.
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AL, USA
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Posted: 12/10/2023 12:50:00 PM EDT
[Last Edit: BhamAR]
[#16]
Originally Posted By DetroitDuramax: I am Building an 11.5 upper for my sbr I got a great deal ($75shipped) on a new BA barrel but it has no dimples. I was going to order an expo arms gas block from PA but do I also buy the slr dimple jig or just say screw it and put it together un dimpled. I have built a few uppers they all had pinned gas block faxon barrels from Aim but do I spend the money now and get a dimple jig I may only use a few times. I did call a couple places just to inquire they want $25-50 to dimple the barrel for me. Dimple and use Hot-Lock, I prefer it to Rocksett as it breaks loose easier. However, don’t buy from Amazon, too many people return bottles to them after they use them and it’s compromised. Rocksett fan bois will scoff, I’ve used them both extensively for muzzle devices and gas blocks, both perform their job extremely well, never had either fail. Hot-lock is just easier to break loose, if you need to. Video here on dimpling is extremely helpful, including a tip for breaking through the nitride. This is the way to go. This guy’s channel is awesome! He’s on here, I’d love to buy him a beer as he’s clearly a great American!  SLR Dimple Jig (used with Depth Limiting Collar) |
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Posted: 12/10/2023 2:29:53 PM EDT
[Last Edit: sunnybean]
[#17]
Quote HistoryOriginally Posted By OTDR: What size drill bit you use on that cross pin hole? Quote HistoryOriginally Posted By OTDR: Originally Posted By sunnybean: The dimpling was the easy part. Drilling the cross pin actually turned out to be not that difficult either. Or, maybe I just got lucky. https://www.ar15.com/media/mediaFiles/96670/IMG_5343_jpeg-3055065.JPG What size drill bit you use on that cross pin hole? 5/32” ETA. That is the size of pin that came with the Riflespeed gas block. |
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Posted: 12/13/2023 1:15:51 AM EDT
[#18]
Quote HistoryOriginally Posted By sunnybean: 5/32” ETA. That is the size of pin that came with the Riflespeed gas block. I use 1/8”. I wouldn’t want to go bigger. |
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Posted: 12/13/2023 11:59:01 AM EDT
[#19]
I have a lot of barrels, dimpled and undimpled, and on calibers that kick a hell of a lot more than the 5.56 or even the .458 SOCOM, and I have never had a gas block move on me. However, I dimple just because. I would never in a million years drill the barrel for a cross pin. I have heard people on here get their panties in a bunch saying set screws deform the barrel and hurt accuracy yet think that pinning does nothing? Get real. Most likely neither does anything to really hurt accuracy if done correctly but banging in an oversized taper pin in a hole right under the bore of the barrel does not seem like a good idea to me. Plus, I don't like holes in my barrels that don't do anything so far as I am concerned. It's not like its on a front sight tower that can get banged around, especially if the GB is under a handguard. Sort of like wearing a belt and suspenders and then super gluing them to you. Do it if it makes you feel all warm and fuzzy, but...
If I were going into combat and the only tool I had to change out a tank tread was my gun barrel, maybe I'd think differently about pinning, but I'm not, so I don't. |
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Posted: 12/15/2023 9:27:25 AM EDT
[#20]
Quote HistoryOriginally Posted By Big-Bore: I have a lot of barrels, dimpled and undimpled, and on calibers that kick a hell of a lot more than the 5.56 or even the .458 SOCOM, and I have never had a gas block move on me. However, I dimple just because. I would never in a million years drill the barrel for a cross pin. I have heard people on here get their panties in a bunch saying set screws deform the barrel and hurt accuracy yet think that pinning does nothing? Get real. Most likely neither does anything to really hurt accuracy if done correctly but banging in an oversized taper pin in a hole right under the bore of the barrel does not seem like a good idea to me. Plus, I don't like holes in my barrels that don't do anything so far as I am concerned. It's not like its on a front sight tower that can get banged around, especially if the GB is under a handguard. Sort of like wearing a belt and suspenders and then super gluing them to you. Do it if it makes you feel all warm and fuzzy, but... If I were going into combat and the only tool I had to change out a tank tread was my gun barrel, maybe I'd think differently about pinning, but I'm not, so I don't. It is not about the "kick". It is about the heat. Heat is what contributes to failure. It is very unlikely that a .458 SOCOM is subject to full auto or multiple mag dumps. It never sees the heat. It is not likely to fail. Banging on an oversized taper pin is a strawman argument. Best practice is to use a stainless coil pin. Neither a roll pin nor a coil pin will deform a barrel. It is the pin that is deformed. Which is why you never reuse the pin. I work at a range and attend several AR based classes a year. I see AR rifle failures almost every week. The most common cause that takes a rifle out for the day is a gas block installation failure. |
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Posted: 12/15/2023 9:02:55 PM EDT
[#21]
Quote HistoryOriginally Posted By xciapup: It is not about the "kick". It is about the heat. Heat is what contributes to failure. It is very unlikely that a .458 SOCOM is subject to full auto or multiple mag dumps. It never sees the heat. It is not likely to fail. Banging on an oversized taper pin is a strawman argument. Best practice is to use a stainless coil pin. Neither a roll pin nor a coil pin will deform a barrel. It is the pin that is deformed. Which is why you never reuse the pin. I work at a range and attend several AR based classes a year. I see AR rifle failures almost every week. The most common cause that takes a rifle out for the day is a gas block installation failure. Roll/coil pins are what I use. |
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USA
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Posted: 12/16/2023 10:47:09 AM EDT
[Last Edit: Bebop_941]
[#22]
Quote HistoryOriginally Posted By xciapup: It is not about the "kick". It is about the heat. Heat is what contributes to failure. It is very unlikely that a .458 SOCOM is subject to full auto or multiple mag dumps. It never sees the heat. It is not likely to fail. Banging on an oversized taper pin is a strawman argument. Best practice is to use a stainless coil pin. Neither a roll pin nor a coil pin will deform a barrel. It is the pin that is deformed. Which is why you never reuse the pin. I work at a range and attend several AR based classes a year. I see AR rifle failures almost every week. The most common cause that takes a rifle out for the day is a gas block installation failure. Quote HistoryOriginally Posted By xciapup: Originally Posted By Big-Bore: I have a lot of barrels, dimpled and undimpled, and on calibers that kick a hell of a lot more than the 5.56 or even the .458 SOCOM, and I have never had a gas block move on me. However, I dimple just because. I would never in a million years drill the barrel for a cross pin. I have heard people on here get their panties in a bunch saying set screws deform the barrel and hurt accuracy yet think that pinning does nothing? Get real. Most likely neither does anything to really hurt accuracy if done correctly but banging in an oversized taper pin in a hole right under the bore of the barrel does not seem like a good idea to me. Plus, I don't like holes in my barrels that don't do anything so far as I am concerned. It's not like its on a front sight tower that can get banged around, especially if the GB is under a handguard. Sort of like wearing a belt and suspenders and then super gluing them to you. Do it if it makes you feel all warm and fuzzy, but... If I were going into combat and the only tool I had to change out a tank tread was my gun barrel, maybe I'd think differently about pinning, but I'm not, so I don't. It is not about the "kick". It is about the heat. Heat is what contributes to failure. It is very unlikely that a .458 SOCOM is subject to full auto or multiple mag dumps. It never sees the heat. It is not likely to fail. Banging on an oversized taper pin is a strawman argument. Best practice is to use a stainless coil pin. Neither a roll pin nor a coil pin will deform a barrel. It is the pin that is deformed. Which is why you never reuse the pin. I work at a range and attend several AR based classes a year. I see AR rifle failures almost every week. The most common cause that takes a rifle out for the day is a gas block installation failure. Geniune question cause I'm curious to learn from your experience: What causes the failures you see? Not cleaning the threads, not using the correct thread locker (or no thread locker), not torquing to at least 25 in/lbs, or the barrel not being dimpled? What would you say the ratio of gas block failures with dimpled vs. non dimpled barrels is? I'm genuinely curious since I have barrels that are dimpled and some that aren't. I've run some of them hard and with proper installation, I've never had one fail. With all the variables listed above, I'm just curious how much can actually be attributed to not dimpling. Another thing to consider is that if a set screw loosens or backs out, whether or not the barrel is dimpled really doesn't matter as to whether or not the gas block will shift and fail. The dimple may give you a little more time before the screw clears the dimple to catch the issue but if the screw backs out, it's an issue, dimple or not. I agree dimples help mitigate shift from impacts but as many have stated, if it's under a handgaurd, that's a moot point. If you think I've missed something, let me know but dimpling (to me) seems to be a redundant process except when the gas block is exposed. Edit: another benefit of dimpling (if done properly) is indexing the gas block for installation. |
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AL, USA
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Posted: 12/16/2023 10:56:05 AM EDT
[#23]
Depends on the purpose of the rifle. Just wanna shoot it a lot and not risk having problems, pin it.
Life or death go to gun including SHTF, pin it, dimple at least one set screw, & use a dab of Hot-Lock on the screws. Guaranteed to be bulletproof with those three things. If you can dimple one, you can pin one. |
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MN, USA
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Posted: 12/16/2023 11:27:03 AM EDT
[#24]
Another thing to consider is that if a set screw loosens or backs out, whether or not the barrel is dimpled really doesn't matter as to whether or not the gas block will shift and fail. The dimple may give you a little more time before the screw clears the dimple to catch the issue but if the screw backs out, it's an issue, dimple or not. I agree dimples help mitigate shift from impacts but as many have stated, if it's under a handgaurd, that's a moot point. All well said. I would add that a dimple doesn't make a set screw hold tight any better than not. A dimple might keep a gas block from shifting position IF the setscrew(s) loosen, note plural, as in BOTH, but if the setscrew(s) loosen it won't matter if the gas block shifts or not as you will have lost the gas seal and the gun will no longer function as it should. |
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USA
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Posted: 12/16/2023 11:32:03 AM EDT
[#25]
Quote HistoryOriginally Posted By s4s4u: All well said. I would add that a dimple doesn't make a set screw hold tight any better than not. A dimple might keep a gas block from shifting position IF the setscrew(s) loosen, note plural, as in BOTH, but if the setscrew(s) loosen it won't matter if the gas block shifts or not as you will have lost the gas seal and the gun will no longer function as it should. Quote HistoryOriginally Posted By s4s4u: Another thing to consider is that if a set screw loosens or backs out, whether or not the barrel is dimpled really doesn't matter as to whether or not the gas block will shift and fail. The dimple may give you a little more time before the screw clears the dimple to catch the issue but if the screw backs out, it's an issue, dimple or not. I agree dimples help mitigate shift from impacts but as many have stated, if it's under a handgaurd, that's a moot point. All well said. I would add that a dimple doesn't make a set screw hold tight any better than not. A dimple might keep a gas block from shifting position IF the setscrew(s) loosen, note plural, as in BOTH, but if the setscrew(s) loosen it won't matter if the gas block shifts or not as you will have lost the gas seal and the gun will no longer function as it should. 100% agree. |
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OH, USA
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Posted: 12/16/2023 1:59:12 PM EDT
[#26]
I dimpled and pinned a Geissele gas block last weekend, (My 3rd one). Just gotta take your time, and triple check before you commit to sending the drill bit in.
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AL, USA
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Posted: 12/16/2023 2:01:11 PM EDT
[Last Edit: BhamAR]
[#27]
Quote HistoryOriginally Posted By Bebop_941: Geniune question cause I'm curious to learn from your experience: What causes the failures you see? Not cleaning the threads, not using the correct thread locker (or no thread locker), not torquing to at least 25 in/lbs, or the barrel not being dimpled? What would you say the ratio of gas block failures with dimpled vs. non dimpled barrels is? I'm genuinely curious since I have barrels that are dimpled and some that aren't. I've run some of them hard and with proper installation, I've never had one fail. With all the variables listed above, I'm just curious how much can actually be attributed to not dimpling. Another thing to consider is that if a set screw loosens or backs out, whether or not the barrel is dimpled really doesn't matter as to whether or not the gas block will shift and fail. The dimple may give you a little more time before the screw clears the dimple to catch the issue but if the screw backs out, it's an issue, dimple or not. I agree dimples help mitigate shift from impacts but as many have stated, if it's under a handgaurd, that's a moot point. If you think I've missed something, let me know but dimpling (to me) seems to be a redundant process except when the gas block is exposed. Edit: another benefit of dimpling (if done properly) is indexing the gas block for installation. Couple of good responses to you already. I’d add one more benefit that hasn’t been mentioned yet. If dimpled correctly, it assures perfect alignment of the gas block. Just saw your edit, disregard…  |
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IN, USA
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Posted: 12/17/2023 12:28:24 AM EDT
[#28]
You don't need a jig. Align the gas block and tighten ONE of the screws. You can use a center punch to mark the spot to dimple in the other hole. You don't NEED a center punch, but can help. Anyway ... just drill the dimple in the other hole. Now tighten the screw in the dimpled hole. Remove the other screw and dimple that one. Super simple. Don't over-think it.
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MO, USA
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Posted: 12/18/2023 9:17:40 AM EDT
[#29]
I have been rebuilding my older AR's. None of my older barrels were dimpled. I used a dimpling fixture to make sure that I had the alignment of the dimple opposite the gas port hole. The advice that I got was to only dimple the rear set screw (Opposite gas port hole), as the front set screw can be in different locations depending on the gas fixture that you are using. If you dimple both holes, and decide at some later date to change gas fixtures for some reason, you could have an issue with the second dimple. Doing my updating/rebuilding I reused three barrels. I changed gas fixtures on all three from what they had originally.
Bob R |
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Posted: 12/20/2023 1:20:58 AM EDT
[#30]
It’s so easy to dimple with a fixture, why not.
I’ve always been intrigued by Lilja barrels and the flat that they machine opposite the gas port. The set screws will favor truing up the gas block alignment on the flat. |
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Posted: 12/20/2023 6:15:40 AM EDT
[#31]
Quote HistoryOriginally Posted By alpha0815: It’s so easy to dimple with a fixture, why not. I’ve always been intrigued by Lilja barrels and the flat that they machine opposite the gas port. The set screws will favor truing up the gas block alignment on the flat. Interesting, I had no idea... We are milling a narrow flat on the bottom side of the gas port section for set screws used with some types of gas blocks. This prevents marring of the .750″ or .936″ diameter by the set screws and helps align the gas block with the gas port hole.  Attached File |
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Posted: 12/20/2023 9:02:50 PM EDT
[#32]
I use the factory dimple once I verify that it all matches up perfect....using the line method
then I snug the dimple screw, snug the other screw, that scores the barrel, remove it. center punch, drill with 5/32 bit, just the tip just for a second, now its dimpled. 18v drill works fine. dont need no fancy jigs. |
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Posted: 1/24/2024 9:58:38 PM EDT
[#33]
Quote HistoryOriginally Posted By GrizzlyAdams: Spend the $50 and send it to one of the highly regarded gunsmiths mentioned here all the time to pin it. And never have to worry about it again. This 100x |
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