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Posted: 10/10/2013 4:54:25 AM EDT
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Are bolts or for that matter the entire BCG fairly generic in terms of replacing or changing them?
What I'm wondering is, can you buy a BCG or bolt if one breaks and just put it in or does it have to be from the same manufacturer or be fitted or something? Is it a good idea to keep an extra bolt or complete BCG in case one breaks? Can you take a BCG from one rifle and put it in another safely as long as they are both basically the same type if not the same manufacturer? The reason I ask is because I see BCG's for sale all over the place and also posts about having an extra bolt being a good idea since bolts do on occasion break. I asked someone else this question and he said maybe depending on the "head space" but did not have time to expand on that. So is the issue having the proper head space? And if so what exactly is head space and how does one check it? I just would like ot keep spare parts around that I can change out if need be but I don't want to get something unless I understand it and I'm sure that it will work correctly and safely. |
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The quality of BCGs can vary a lot.
Bolt carriers are low problem items in normal service; the gas keys however get a lot of posts here. Bolt carriers are also for practical purposes interchangeable and if a person has a problem with the key then having the ability to swap out the carrier can get the weapon back in service fast. Headspace is a chamber measurement. SAAMI is the source for civilian specifications for chambers and cartridges. The specs ensure a max tolerance cartridge will safely fit a min tolerance chamber and vise versa. Because of the modularity of the platform most of the time a new bolt and a new barrel are within safe limits on headspace, but not always. You are likely to be OK, but an actual headspace check leaves no doubt. Headspace is checked with gages. |
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Brownell's is the best source:
http://www.brownells.com/search/index.htm?k=head+space+gages&ksubmit=y Brownell's say you can use either a .223 or 5.56mm in a rifle, but I'd buy a 5.56mm. Usually you need two gages; one "Go" and one "No-Go". You can get by with a "No-Go". The bolt should NOT close on a No-Go. If it does the barrel-bolt combination has excessive head space and is not safe. To use, you very carefully and thoroughly clean and dry the chamber and locking lugs, and the bolt face and bolt locking lugs. Usually you remove the extractor and especially the ejector so they won't interfere with the measurement. You cannot accurately gage the assembly with the ejector in place, it has to come out. |
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That's more or less true.
Usually, if you have a quality barrel and buy a quality spare bolt, head space will be good. A lot of shooting schools report people having broken bolts and the school just installs a new bolt and gets them going again. Checking head space is always comforting, but if you have a quality, new bolt, you're good to go, but it is a comfort to at least be able to check it. Bottom line, a gage is an unnecessary expense with a quality AR, but it you have the money to waste and it'll make you feel better ............ |
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Quoted:
The original government specs required that Armalite rifles delivered for testing prior to adoption as our nation's rifle be able to swap bolts and other internals and still function. While all manufacturers have specs that they hold in house virtualy all new bolts and barrel extensions will work and headspace without issues. There is a .004" manufacturing tolerance between minimum allowable headspace and "no go" which simply means it can't be sent out the factory door as is. A "field" gage is actually .010" longer than minimum and if your rifle closes on that gage it should not be fired. It's time for a new barrel. Personally I have never seen an AR rifle with more than .008" and those have been run hard and put up wet for years. They still feed and function fine with new ammo. Reloads, depending on how many times they've been fired and if they have been resized to minimum headspace as they should be for any semi-auto may give up the ghost ahead of normally headspaced rifles. I would not be overly concerned with changing bolts, just be aware that tolerance stacking does occur. If you have a headspace gage use it. Hornady's Lock-N-Load system provides the cheapest way to gage fired brass. Mo DeFina makes the finest .001" increment drop in gages. RCBS makes a .001" drop in gage too, they cost more and aren't as nice as Mo's. These tools will let anyone follow and track the headspace wear on their rifles. Make sure you give any semi-auto .004" clearance between the fired measurement and your resized brass. |
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