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Posted: 9/5/2006 11:50:12 PM EDT
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Had a customer send in a pencil carbine barrel to have the moderator removed and a more historically correct one installed. This is for an XM177 clone project. Anyways, I take off the old moderator to find this conglomeration:  There are SEVERAL things going on here and I will explain each of them... First, the threads are nowhere near full length. I suspect this was because the first shop turned a shoulder at thread minor diameter to help him align the DIE that he used to cut the remaining threads. I commend him for wanting the threads straight, but I scold him for not single-point threading. Second, the solder joint was quite weak. With the moderator in the lathe chuck, it only took a little leverage on the FSB to break it all loose. While the solder probably meets the 1100 degree rule, it was a pretty weak job. This brings us to the rust, likely a by-product of the flux that's necessary to help the solder flow. Of course once the solder cools, it's not like you can clean out the remaining flux. Given some time, lots of rust will grow as a result. So now I ask this queston to the super anal folks who worry about parkerizing under the FSB... What's the better permanent attachment method, blind pin/weld or 1200 degree solder? |
I always believed that the blind pin method was the best but use to think that the silver solder method was a valid alternative. No more.|
I don't follow Arfcom screennames that close, but I don;t think this is Dump1567's barrel. I did his a while back though. I have not done final measurements to determine if I can shorten the barrel 1/4" or so and time some new threads back a 1/4". As bad as it looks, there are actually some threads there still, but they are clogged with solder and rust. The owner has already offered to just buy a new barrel, but I'm a glutton for punishment so I am going to see if it can be saved before admitting defeat. 
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I have soldered, and removed the same soldered muzzle attachments for several years on many barrels, and have never seen anything like that. You could tell something was horribly wrong with that barrel without taking it apart because of the visible rust on the exposed part of the barrel. So that gives me the impression that the execution was incorrect, not the general method. The muzzle on my AR-10 was pretty messed up from the weld and pin method employed. Far as weld vs solder, their both stupid, just a matter of degree of stupidity. |
There was no exposed rust. The grenade ring in the picture was slid back over the 0.600" part of the barrel. That rust that looks like it would have been exposed was indeed covered. The worst of the rust on the threads was directly under the grenade ring. I should also add that this barrel was probably re-parkerized after it was soldered because there was no sign of heating. It's quite likely that the park bath was not able to be cleaned out under the threads and also contributed to the rust. Of course any barrel brought to 1200 degrees for soldering is likely to need to be re-finished. The spray-on finishes would be preferred so that there's no park bath chemicals caught in the junction. I'm not generally a fan of spray-on finishes, but here is a good use for them. |
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I recall back in the early 80's some rust from "un-neutralized bluing salts" creeping out from under the pinned front sight on my refinished Mini-14. A few shots of WD-40 after removing the visible crud cured it eventually. My 'smith back then also did the FIRST "permanently attached by silver soldering" AR-15 Flash Hider to keep the local law dogs from being unhappy with the folded length of my "truck gun". Paladin |
Ah, I get it, they are not usually put on correctly so did not think about that part of the barrel being covered.
Agreed, does like a improper post park treatment. On AR's I have been able to attach without doing a refinish. On FAL's back during the ban would do the paint job after the solder job.
I mean welding something to a barrel is stupid, and so is attaching something to a barrel with 1,100 silver solder. |
Help! Historical correctness is NOT my thing. Which way is it supposed to be? Customers always send me pictures where the chamfer is facing the moderator and the sleeve part slides back over the barrel. Is this backwards? |
This is correct assembly: 
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Ok, thanks. That's how I have been doing them. That's also how this barrel came to me. In the rusty picture at the top, we are looking at the chamfered side which faces the moderator. The other side of the grenade ring is counterbored and slides BACK over the barrel. That counterbore is what was covering the visible rust on the barrel. Should there be a lockwasher in that counterbore, or does the moderator simply capture the grenade ring against the barrel? Thanks for the education. |
If you're pinning, I'd say the lockwasher is unneccesary if the mod is tightened up against the ring and the pin is precise enough to not allow any wiggle at all. |
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I know I don't NEED a lockwasher as it's put together tight and pinned. No slack in the pin fit at all. I was just asking if there would BE a lockwasher inside the grenade ring on a historically correct upper. I should think not, but colt has done strange things in the past... |
Now I'm all confused?? Is it a standard A1 style lockring? If not, that's one tiny-ass washer! The small step at the bottom is where my Bushie SL bbl. fits into.  The space used up (recess) by the lockring in pic is where I thought the launcher hooked into... |
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Here is how to do it: LINK to PIN thread Silver solder is a bad way to go. |
While I agree that Rocksett is wonderful stuff, the BATF does NOT consider it an acceptable method. This leaves us with the 4 standard methods: Blind pin & weld 1100 degree+ solder 4 welds equally spaced around the circumference 1 continous weld covering at least half of the circumference. Exposed welds are ugly, so we rule the last two out on anything but an AK. 1100 degrees is bad for heat treating and will generally require re-finishing a large heat affected area. This logically leaves us with the blind pin & weld method that's most popular. I wish Rocksett were acceptable. It would make the job so much easier and cleaner. |
Realistically, none of the industrial adhesives--even Rocksett--can withstand the BATFE permanence test: an extremely long breaker bar. 
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The solder job pictured above came off very easily. I clamped the moderator in the lathe chuck. Put a roughly 12" long bar through the FSB and twisted. It popped loose really easy and unscrewed by hand. |
Oh I have no doubts that it did, but try telling that to the BATFE.  They're like a bunch of children; sticking their fingers in their ears and yelling at the top of their lungs whenever someone tries to challenge their "wisdom." |
Are you sure that's how they test them? If so, I can't see any solder job as being strong enough. I know that a pin would gall up and lock up the threads. But even with a long enough bar, you would just rip the end of the barrel off while twisting on it. I know this to be the case because customers have sent them to me after doing this. It's nasty what you can do to metal with enough leverage. And Rocksett is much worse/harder to take apart than silver solder. |
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It's what I've been told. I read it not too long ago, when several people were discussing approaching the BATFE about considering Rocksett as a viable permanent attach method. I'm not surprised that Rocksett is more difficult to loosen than silver solder; it takes over 2000* F (1100* C) to melt it. 
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Oh, that's nothing. I'm talking people that did not KNOW there was a pin there that went to town with a BIG pipe wrench. They oblong the pin hole, then the pin mashes over, then everything galls together. They usually stretch out the index slot in the receiver as well. |
So I chased the nasty threads and glass bead blasted them to take off all the rust. I took pictures the other night, but I have not pulled them off the memory card yet. Stay tuned and I will post them here tonight. I'm up-in-the-air about whether you should just replace the barrel (do it right) or try it out as it is. There are some threads left, enough that I could put it all back together and nobody would know what's under there. That's just not my style though. It should be as good as I can make it and there's not much more I can do with them the way they are now. One other thing, the barrel nut was loose on the upper.
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