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Posted: 9/12/2017 10:03:29 AM EDT
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Who has one that can supply accurate dimensions? Specifically, OD and bore. Thickness is 0.250", I know. I need to have some made up.
This: 
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I forget- does the ADCO spacer thread on (looking for minor and major thread dimensions?) or does it slip on (and looking for just larger than major of threads) dimensions?
I chopped the base off of an A2 flash hider to make my own spacer a couple years ago, but I have to admit the ADCO spacer looks mo betta |
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I forget- does the ADCO spacer thread on (looking for minor and major thread dimensions?) or does it slip on (and looking for just larger than major of threads) dimensions? I chopped the base off of an A2 flash hider to make my own spacer a couple years ago, but I have to admit the ADCO spacer looks mo betta I just need to determine, more than anything, interference fit between the threads and the inner bore dimension of the spacer. I do not want it having side to side slop thus ending up off center once the MD is tightened. I'd like to keep all measurements concentric with the bore. |
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I'm quite sure that ADCO, being the site sponsor that they are, will be happy to supply you with the complete set of blueprints, since you are not willing to spend $20, or use your brain to design your own spacer. @bigbore I want 8 of them, Mr. Helpful. And this is me using my brain, phase one. Some will be used on supressed weapons, used by a second party. Concentric alignment to the bore is paramount and dimesions are critical, I want zero misalignment. Check the profile at left...WELDER not MACHINIST. Baffle strikes=BAD. |
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.720-.730 o.d. with an i.d. of .502-.503(oversize reamer). The length appears to be .300 to .400. The material would be 4140 pre-hardened steel. You would need to chamfer the I.D. both ends 45 degrees by .030 and break the edge on the outside with a file. The usual thread length on 5.56 barrels is .600. This is not the exact dimensions of thier spacers but these dimensions would be very close.
ETA. Remember 1/2 inch O.D. threads don't measure .500. When finished they measure .496 |
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.720-.730 o.d. with an i.d. of .502-.503(oversize reamer). The length appears to be .300 to .400. The material would be 4140 pre-hardened steel. You would need to chamfer the I.D. both ends 45 degrees by .030 and break the edge on the outside with a file. The usual thread length on 5.56 barrels is .600. This is not the exact dimensions of thier spacers but these dimensions would be very close. ETA. Remember 1/2 inch O.D. threads don't measure .500. When finished they measure .496 Nom OD = 0.7390-0.750" Nom ID= 0.502- 0.506" **Barrel OD behind threads measures 0.700" on 3/5 of my M4 profile barrels. So long as the surfaces are machined square and the bore is concentric with the OD, I should be good? OAL @ 0.250"-0.300"( as you suggested) should be gtg for a P/W A2 MD on a 14.5" barrel. And thanks for pointing out the ID chamfering. 
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Actually Tig, all you should have to determine is the diameter of the shoulder on the barrel to know what your inner dimension would be for an interference fit. Unless I am not understanding your question?
I want the ID (bore) as close to the thread OD as possible and concentric. I figured that if I mimicked the ADCO dimensions, then I would have confirmation that I was gtg, that's all. I am going to P/W my MDs, so I want it right the first time, Dave. |
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@KarlSG1 I want 8 of them, Mr. Helpful. And this is me using my brain, phase one. Some will be used on supressed weapons, used by a second party. Concentric alignment to the bore is paramount and dimesions are critical, I want zero misalignment. Check the profile at left...WELDER not MACHINIST. Baffle strikes=BAD. If you want them to slip OVER the threads with a very slight interference fit, then you'll need to measure the barrels individually. If you want them to thread on, then the ID should be obvious since they'll be threaded. The simple answer is .500" ID, but measure the outside diameter of the muzzle threads of about five different barrels and I bet you'll find slight variances between them. This would make the spacers, if made to the same specs, a tight fit for some and a loose fit for others. Same goes for the OD of the spacers. If you want a perfect match between barrel OD and spacer OD, you'll need to measure each barrel. If you want a universal fit, than you should just make them .500" inside and .740/.750 OD or whatever your barrels mic on the OD and be done with it. 1/2-20 threads will measure just under .500". And if you want the spacer dimensions concentric, as you said, your thread OD can have no variance, and your spacer ID will have to coincide with this dimension perfectly. Just take the guns you'll be installing spacers onto with you and your machinist will know what to do. That way if it gets messed up, it's on him to correct since he made the spacers to his own determined specs, not yours. This is how I would prefer to do it if I were doing the work and the customer was looking for this amount of precision. Also, since ADCO sells these off the shelf, I can guarantee you they aren't held to the tolerances you're after. They need to have a built in margin of error since they are basically universal. You can even see in the pics they don't fit as well as they could if they were made to fit. You may have an in with whoever is making these for you, but I would be surprised if any machinist is willing to make these for less than what ADCO is asking per unit. |
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*Pulling measurements from crushwashers here: Nom OD = 0.7390-0.750" Nom ID= 0.502- 0.506" **Barrel OD behind threads measures 0.700" on 3/5 of my M4 profile barrels. So long as the surfaces are machined square and the bore is concentric with the OD, I should be good? OAL @ 0.250"-0.300"( as you suggested) should be gtg for a P/W A2 MD on a 14.5" barrel. And thanks for pointing out the ID chamfering. |
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If both sides are parallel and there is at least some clearance from threads that is all you need. I've got 2 pals that run supressor mounts that want to experiment, I don't want to be the fool that shitcans their cans, so to speak. |
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And I can have an 8 pack of these made for a case of Budweiser. Welders and machinists in the same building pays off.  |
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And from what I am told, so long as the threads on the barrel are cut concentric, then baffle strikes are not a possibility. |
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As long as they are surface ground square you'll be fine. Otherwise, if your threads aren't perfect, they will cant your muzzle device guaranteeing a baffle strike. Instead of looking for a way to remake, what I consider a band-aid to begin with, why not just get a barrel of the proper length and proper threads? As for the few running cans, KAC and LaRue barrels. No issues to date with baffle strikes. Concentric threading must be gtg. We have a surface grinder in shop, so that can be performed. |
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Concentric threads on a production barrel are very rare. Concentric threads, cut to the proper size, on a production barrel are basically nonexistent. That's why they need to make your spacers square, to at least stack those tolerances in your favor a tiny bit. I may shitcan the idea of having them made for others? Experimentation may be up to them. I do not run suppressors, so no worries there. |
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If both sides are parallel and there is at least some clearance from threads that is all you need. If the machinist has a surface grinder available, I would definitely grind the flats parallel. ETA: I send my stuff to Adco because they do this stuff for a living and have the reputation that they do for a reason. |
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This exactly.. If the machinist has a surface grinder available, I would definitely grind the flats parallel. ETA: I send my stuff to Adco because they do this stuff for a living and have the reputation that they do for a reason.
(My machinist does this for a living also. Man's got skills!) |
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