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Posted: 4/15/2008 7:27:08 AM EDT
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I've been around rifles all my life, but I'm new to ARs. I've lurked here for some time, sucking up knowledge from you guys. A couple months back I obtained my *first* AR. I'm happy. Now I've got a couple of stupid questions that I don't see clear-cut answers to around here. For instance... yesterday on a different AR site, I saw an instructional document on how to change barrels. It didn't mention ANYTHING about what the nut should be torqued to, or more importantly, it never mentioned headspace. In my experience with rifles, you might say that headspace is a critical thing to check! Now, for you experts: What can I change without the services of a gunsmith with a headspace gauge, or the ability to professionally fit parts? Can I change a barrel by simply bolting it on there? Can I change a bolt without checking headspace? Can I safely change the carrier and/or bolt by just dropping one in? Pardon me for covering such basic things. I'd like to know what I can do safely, by myself. Thanks. Roger NRA Lifer since 1975 (when it was cheap!) |
| Well, as it happens, I'm really handy with tools. I just thought someone might be able to answer those short questions. I've looked through a lot of the references on this site but like I said, didn't see anything (I could have missed it of course) that addressed them. The search function pretty much sucks. |
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This tacked thread in the Build It Yourself section should answer most of your questions. Assemble Your Own LOWER, UPPER, FREE FLOAT, TRIGGER, GAS BLOCK - Step by Step Instructions! - link |
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Using the above link you can build an AR from a completely disassembled bucket of parts. Barrels are all headspaced using a semi-permanent barrel extension. The bolt is set to a standardized dimension, that matches to the barrel extension. So, you can buy a Colt bolt and use it in a E.R. Shaw barrel without issue. I bought a set of head space gauges a few years ago....never had any combo that wasn't correct. |
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IMO, you'll need a bench vise, alluminum barrel blocks, a ar15 armourers wrench (for the barrel nut) and a hammer and set of punches for knocking out the gas tube roll pin and those special pliers for removing the lock ring on the delta ring are handy. A lot of people will tell you to get an upper receiver block, but my Colt manual shows the barrel blocks being used so that's what I use. It works. |
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If your looking for manuals, try here: www.ar15.com/forums/topic.html?b=3&f=7&t=349784 |
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Can I change a barrel by simply bolting it on there? Yes. You will need a sturdily mounted bench vise (4"-6"), an action block (no vise jaws, though you need those for other jobs), a barrel wrench, and torque wrench. Well, I don't use a torque wrench, but you can do so if you want. Can I change a bolt without checking headspace? Yes, I have done so many times, but it was with new or near new bolts and barrels that I knew the age and usage. I have swapped around parts many times with no problem. Can I safely change the carrier and/or bolt by just dropping one in? Carrier, yes, and it has NO effect whatsoever on headspace. And for the most part, unless a barrel or bolt were very well worn, you can drop in those, too. What you didn't ask... What if the headspace is off, how do I adjust it? You can't. There is nothing in installing the barrel that has any affect on headspace. That is machined into the barrel/barrel extension and bolt. If the barrel is in spec, and the bolt, together they are in spec. Torque... there are stickies on how to assemble an AR-15, including barrel mounting. There is no magical "correct" torque number where everything lines up right. It all depends. There is a RANGE of torque, 30 ft-lb being the minimum, but if you have ever put a nut on a bolt, you know when the barrel nut is snug enough. So, you get to that 30 ft-lb minimum (with threads lubed with moly grease... aka ordinary wheel bearing grease, NOT Neverseize) and you check to see if the notches in the barrel nut line up so that you can insert the gas tube into the upper receiver. No? Then back it off and torque up a little more. Try again. After 3 or 4 back off, torque up, (and I don't use a torque wrench, just a 1/2" drive breaker bar plus barrel wrench), you should soon be able to line up the notch. You will have to fiddle the gap in the delta ring spring and snap ring around to the top each time. All in all, this is really an easy operation, and people make more out of it than there really is to it. |
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Good information, thanks guys. Now that I've read all the info, I understand how the headspacing works in an AR. Pretty basic, really. That's why it's kind of curious that in the military manuals it says something like, "don't switch bolts with your buddy because something bad could happen". Can't remember exactly. The Marine manual talks about using a max headspace gauge after installing a barrel, but I suspect now days it's not really necessary. I suppose in the bad old days it might have been more of an issue - when bolts might have had more variation. Now I feel confident that I can slap on another configuration and have a whole different rifle. I think I'll go have fun ordering cool new tools to put in the reloading shop, for the AR. What could be more fun than new tools? :) |
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..That's why it's kind of curious that in the military manuals it says something like, "don't switch bolts with your buddy because something bad could happen". Can't remember exactly. That is correct. When NEW everything will work out fine. But after a firing thousands of rounds you can drop in a buddy's bult and have TOO MUCH headspace. PUtting in a new bolt in a used barrel is never a problem. Put in a used bolt in a NEW barrel may have excessive headspace - check it with a Field Gauge. Putting in a used bolt in a used barrel increases the risk of excessive headspace, again check it with a field gauge. In the Military rilfes are periodically checked with a field gauge (see chapter 2 in the manual QUIB linked to). If the rifle fails, then a new bolt is procured and the rifle is tested again; if it passes it's good to go. If it fails then a new barrel is tried (see the -23 for details on how this progresses). Bolt carriers are NEVER an issue, as they don't factor into the headspace. Keep the bolt with the barrel. Swapping bolts between barrels will wear it quicker and over time you could develop a headspace issue. |
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