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Posted: 2/3/2009 12:54:54 PM EDT
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I'm having a barrel blank turned/threaded for my 6.5 BPC (grendel) build and I have a question regarding my Model1sales FF tube.
It's the kind that has an aluminum barrel nut that the tube screws onto. Could I slowly stone/grind off the front of the barrel extension to index the alignment of the FF tube (tighter barrel nut=rotation of the FF tube) so that a sling stud is out of one of the 'flutes' in the tube and dead 6 o'clock? How are extensions heat-treated? Case hardened? TIA for help |
| Not a good idea. Have you looked at the inside of the barrel nut? There is usually a shoulder machined into it that clamps the barrel extension against the receiver. Reduce the extension shoulder thickness and it may not tighten up. Anything done to index the handguard should be done to the handguard instead of the extension. Also stoning or grinding will not keep the extension shoulder square with either the receiver if removed from the back side or the barrel nut if removed from the front. |
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the threads of the FF tube are approximately .05" between eachother. <.05" won't cause the the nut to not have room to tighten.
I haven't drilled a hole yet for the stud. I'm not doing that until I have a rib on the exact bottom. There are 10 flutes and 10 areas that are normal diameter. 36 degrees between, center to center. Putting some real thought to this, the most I'd have to grind off would be .005".... Putting even more thought to it, It doesn't matter how tight the barrel nut is, it has to line up with a gastube hole... I think I'd have to lathe some off of the threaded section of the tube for what I want. The non-fluted areas would have to line up with the gas-tube holes, then it doesn't matter. The most I would have to take off would be 1/20th of .05" (20 gastube holes–– every other one lines up)... |
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Quoted:
I'm having a barrel blank turned/threaded for my 6.5 BPC (grendel) build and I have a question regarding my Model1sales FF tube. It's the kind that has an aluminum barrel nut that the tube screws onto. Could I slowly stone/grind off the front of the barrel extension to index the alignment of the FF tube (tighter barrel nut=rotation of the FF tube) so that a sling stud is out of one of the 'flutes' in the tube and dead 6 o'clock? How are extensions heat-treated? Case hardened? TIA for help Good luck! As long as you have enough metal left over to take the impact of the bolt closing you should be OK. I assume you do not intend to remove the barrel extension after chambering, but intend to stone the front lip that remains proud of the barrel. I used a file to take a cut the barrel shoulder of a FAL barrel to get it to index properly, and it shoots as well as I have a right to expect. All the same, I would rather stone the front of the reciever to accomplish the same thing. I would rather damage a $100 part that can be fixed instead of ruining your custom barrel.... heat treating? "Liquid carburize at 1550F for 1 1/4 hour, air cool. Stress releive at 550F for 1 hour. Rough machine, and then reheat to 1450 C, oil quench, then temper at 350F for an hour." I assume finish machining refers to grinding. If it is 8620, and it should be, expect 0.010-0.015" of case hardening. |
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Quoted:
Quoted:
I'm having a barrel blank turned/threaded for my 6.5 BPC (grendel) build and I have a question regarding my Model1sales FF tube. It's the kind that has an aluminum barrel nut that the tube screws onto. Could I slowly stone/grind off the front of the barrel extension to index the alignment of the FF tube (tighter barrel nut=rotation of the FF tube) so that a sling stud is out of one of the 'flutes' in the tube and dead 6 o'clock? How are extensions heat-treated? Case hardened? TIA for help Good luck! As long as you have enough metal left over to take the impact of the bolt closing you should be OK. I assume you do not intend to remove the barrel extension after chambering, but intend to stone the front lip that remains proud of the barrel. I used a file to take a cut the barrel shoulder of a FAL barrel to get it to index properly, and it shoots as well as I have a right to expect. All the same, I would rather stone the front of the reciever to accomplish the same thing. I would rather damage a $100 part that can be fixed instead of ruining your custom barrel.... heat treating? "Liquid carburize at 1550F for 1 1/4 hour, air cool. Stress releive at 550F for 1 hour. Rough machine, and then reheat to 1450 C, oil quench, then temper at 350F for an hour." I assume finish machining refers to grinding. If it is 8620, and it should be, expect 0.010-0.015" of case hardening. The problem with taking material off the receiver is that depending on how much the extension could extend over the back inside of the receiver where you would find M4 ramps. It would all depend on the tolerances as I have seen barrels that were flush and some were set a few thousands forward. Also the locating pin slot would need to be cut back the same amount. Timing the handguard by facing it off is the easiest and most cost effective thing to do. A few minutes on a lathe and it's a done deal. |
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