I’m assembling an AR47 right now, putting a VG6 Gamma on it. It’s a 16" barrel, so no need to pin/weld.
I have crush washers, but no 5/8" peel washers. I don’t particularly like the look of crush washers. Is there any downside to timing it by sanding the back (on very fine paper) rather than using crush washers? Or I can always pick up a set of peel washers.
What’s a reasonable torque value for a 5/8-24 muzzle device on a 7.62x39 barrel? The barrel doesn’t have much of a shoulder if it matters.
Let me be the first to ask… WTF?
I think you would spend quite a bit of time, wasted time I might add, doing something like that. But to answer your question, I guess it would work. Never really pondered this particular situation. Those washers help keep it from loosening though too, so there is that to consider.
I thought it was actually common with 3 gun shooters to cut back on their muzzle brakes, but check Robb Jensen’s post here
https://www.m4carbine.net/showthread.php?26432-Flash-hider-installation-question&p=313145#post313145
I wonder why he considers it a hack job to remove material from the muzzle device.
I could chuck it up in the mini lathe (I think) and try to remove a little metal, or pay someone who knows what they’re doing. I don’t understand why removing from one side is hackjob and from the other is right.
My concern: lack of maintaining a perpendicular surface on the rear of the muzzle device. There is enough play in the threads to allow a baffle strike in a muzzle brake due to it being torqued against a non square surface (whether the rear of the device or the barrel shoulder).
Same reason that precision muzzle devices earn against using crush washers. The AAC shim set is cheap and functional. Gitchusum.
It’s a VG6 Gamma, not particularly long. I won’t be mounting anything else to it either. I could certainly chuck it up in the lathe, throw a runout gauge on to make sure it’s really square, then spin it and hit it with a flap disc or something. I’d make sure it was square after, too. I don’t think trying to cut it with anything else would work too well as it’s nitrided. I’d also consider taking off some of the shoulder on it, as the barrel’s shoulder is significantly smaller (there’s not much: http://www.blackriflearms.com/16-762x39-Mid-Length-4150-Nitrided-Barrel_p_168.html ).
I guess I’ll probably just pick up a shim kit, I just think it’s prettier with nothing there.
Well, seeing that you know your way around a lathe, that would work just fine. Just a lot of work, as you stated.
I think the AAC shim kit is around $12.
Also, which I haven’t seen mentioned… removing material exposes bare steel to the environment. Why would you not use washers? Correct timing, and coated device with minimal effort/cost. You may be able to do it yourself, but time is money. I can make my own soap. But I dont.
You run the risk of bottoming out the muzzle device against the muzzle when attempting to mount it without shims
I don’t know my way around it that well… I inherited a Chinese mini lathe a couple years ago. I’ve used it some but by no means am I a pro. I would NOT trust myself to bring the shoulder back on the barrel, taking a little material off the muzzle device is a lot easier though.
MegademiC, the VG6 Gamma is nitrided stainless so I’m not concerned about a raw finish (although I’d hit it with something to make it less ugly).
MistWolf, that’s a good point, I’ll have to check the depth of the female threads in the muzzle device vs the male threads on the barrel.
Custom bolt action riflesmiths often do what the OP is proposing- machine the muzzle device so it times correctly with the muzzle, no washers needed. As long as mating surfaces are square to the bore and threads, I think all is good.
If concerned about loosening, there are a number of threadlockers mentioned in other threads that will work. Torque should be no more than 25 ft-lbs I believe.
Mark, limiting the torque on the muzzle device threads is good enough, alone, to justify the use of shims or machining on as lathe IMHO.
What’s the best choice in order to keep it from loosening, Rocksett?
I’ll also probably build a decent 3 gun upper before too long… probably an 18" Faxon Gunner barrel, need to decide on the adjustable gas block, need to figure out what muzzle device is a good choice, maybe a JP LMOS BCG but maybe something else… that’s more likely to see advantages from accuracy improvement than something that primarily shoots steel case.
What the rifle smith should be doing is cutting the shoulder behind the muzzle threads so that that the muzzle device times TDC. They can do this with the barrel still in the lathe after cutting the muzzle threads. Cutting the muzzle threads and then cutting the muzzle device (unless it isn’t square at all) sounds bass ackwards.
Best solution for timing a muzzle device with a shim that I have found:
http://precisionarmament.com/product-category/muzzle-devices/accu-washers/
These should get you within an acceptable torque range pretty easily without any sanding or cutting. Also, once you bevel the inside edge of the shim that will face the barrel (not necessary if the muzzle threads have a relief cut) the shim and muzzle device will sit FLAT against the barrel shoulder and torque down consistently. I bevel the inside edges of mine with a Dremel and sanding wheel. Because they sit so flat and there is near zero room to squash, the torque values stack up pretty quickly, meaning it may take a lot more torque to get the device to turn the last few degrees. If that is happening, and you want to keep the torque minimal, sand down the shim on a flat surface. They are graduated in about 20 degree and 0.002-0.003" increments so you only need to take off about 0.001" to make a noticeable difference in the timing. It may sound like overthinking it, but really not complicated at all once you play with them for a little while. It may take a few minutes, but you should be able to get it timed dead nuts, with the torque value you want, very square to the muzzle, and be removable/re-useable for maintenance. Hope this helps.
I would guess that about 10 ft/lbs would be plenty tight enough without being too much torque.
Some people will never be happy with the simplistic nature of the AR and the lack of need to make specialized parts.
good luck cutting into a nitride treated part.
Going to take good carbide inserts in your lathe. You aint going to do shit to it IMO with a flap wheel or sand paper.
nitride is around 70 rockwell hardness. Not much out there harder than that.
Rocksett or Resbond Blue 907TS.