imschur Posted March 13, 2010 Report Share Posted March 13, 2010 I have one of these for my AR-15's. Does anyone know if there's a .308 AR version? Quote Link to comment Share on other sites More sharing options...
Jgun Posted August 22, 2010 Report Share Posted August 22, 2010 I don't know if this should be in gunsmithing or accurizing, but I was wondering if anyone can tell me how do you go about fitting the bolt to the barrel extension to obtain minimum safe headspace? As I understand it this is the main thing I can do (aside from using a match grade barrel and the appropriate load/bullet) to accurize my AR. Quote Link to comment Share on other sites More sharing options...
draco41 Posted August 23, 2010 Report Share Posted August 23, 2010 I don't know if this should be in gunsmithing or accurizing, but I was wondering if anyone can tell me how do you go about fitting the bolt to the barrel extension to obtain minimum safe headspace? As I understand it this is the main thing I can do (aside from using a match grade barrel and the appropriate load/bullet) to accurize my AR.Is it a completed barrel w/extension already installed? If so I don't think there is a way to change the headspace with out removing the extension and then even that would change everything else as well. (extension pin location, barrel gas port, etc. I'm pretty sure the only way to get a min length headspace is to start from a fresh barrel/bolt/extension. Quote Link to comment Share on other sites More sharing options...
imschur Posted August 23, 2010 Author Report Share Posted August 23, 2010 draco41 is correct. AR15barrels.com has a nice pdf that shows the relationship of the barrel, extension and bolt. Ive attached it too this post852_.pdf Quote Link to comment Share on other sites More sharing options...
survivalshop Posted August 23, 2010 Report Share Posted August 23, 2010 I have one of these for my AR-15's. Does anyone know if there's a .308 AR version?Not that I know of . I asked Brownells (I think they have them made ) & they said they had no plans to make one for a 308 , but that was last year . I have still have not seen them advertised. I lap mine my self using a different method . Quote Link to comment Share on other sites More sharing options...
survivalshop Posted August 23, 2010 Report Share Posted August 23, 2010 I don't know if this should be in gunsmithing or accurizing, but I was wondering if anyone can tell me how do you go about fitting the bolt to the barrel extension to obtain minimum safe headspace? As I understand it this is the main thing I can do (aside from using a match grade barrel and the appropriate load/bullet) to accurize my AR.Its not about acurizing , its about safety. Improper head spacing can be dangerous to the shooter. On the most part ,the head spacing should be OK , if all new componets , but its always good to check it if you are assembling a new barrel or for that matter a new bolt on a old barrel .If you have never done it before , you can read up on in a AR milspec tech manual , Google it or take your completed upper to a gunsmith to have them check it .I check all my builds ,just for piece of mind .I have go,no go & field gages for .223 & .308 and a few others , mostly military calibers. Quote Link to comment Share on other sites More sharing options...
Jgun Posted August 23, 2010 Report Share Posted August 23, 2010 So, if I undestand this correctly, headspaceing is accomplished by either machining the barrel/barrel extension mateing surfaces, or by adjusting the bepth of the reamer during chambering. If that is correct, then this is not something I can do myself if I have access to a lathe, right? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 24, 2010 Report Share Posted August 24, 2010 The headspace that you measure (with the gauges) is the relationship of the bolt to the barrel extension, closed on a chambered round (casing). The extension is sized and mounted on the barrel to acheive the proper headspace. After that, the mounting pin is emplaced, and the gas port drilled, so everything is centered up. After MUCH use, headspace increases, up to the point that the weapon fails the check on the Field gauge. It's armorer-time after that. Reaming the chamber can't fix that.Headspace gauges are about $30 each, and for new builds you'll need the Go and No Go gauges. For in-service weapons that have a pretty decent round-count on them, if they close the bolt on the No Go gauge, you'll need to purchase a Field gauge to be sure the weapon can/should be safely fired again. At any time, if a weapon closes the bolt on the Field gauge, don't fire it. There's a fella on AR15.com (username Cabinetman) that is lending out a full set of .308 gauges, just for the asking. If you're interested in that, the thread is in the "Varients" section, titled "Offer to any .308/7.62x51 owner," or similar to that. He sent me the gauges to use last March (?) and I sent them on to the next guy on the list. They've been going ever since. Free use, if you've got the time to wait for your name to come up on the list. <thumbsup> Quote Link to comment Share on other sites More sharing options...
Jgun Posted August 24, 2010 Report Share Posted August 24, 2010 I guess this is not going to be something I can do myself after I buy the barrel. I thought that there might be some way that I could machine the bolt or extension after the fact in order to acheive the dimension. I'm preparing to have a barrel made, and based on what your saying, I assume that in order to have it headspaced properly I'm going to have to supply the barrel maker with the bolt so that he can headspace it, is that correct? or are the bolts all pretty much the same size? By the way, Can you reccomend what brand barrel extension to go with, or are they, also, all pretty much the same? I'm going to go with a DPMS style BCG. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted August 24, 2010 Report Share Posted August 24, 2010 You can send the barrels maker a DPMS bolt for them to head space to the barrel . I have had no problems with them at all . I do have a spare as with my 5.56 AR's .Barrel extensions can be had from a lot of different places ,DPMS , Midway , SI Defence, Brownells , etc. . You can have a stainless steel or plain phosphated steel , your choice. Just to let you know ,I and others have had no problems with Fulton Armory , Krieger Criterion barrels . I have two and the both check out & shoot fine . Quote Link to comment Share on other sites More sharing options...
roberts Posted January 5, 2011 Report Share Posted January 5, 2011 Relative to the upper receiver lapping tool: Brownells says it's only cold rolled steel. Anyone with access to a lathe could turn one out in just a few minutes. Looking at it, I would make the pilot longer to ensure better alignment in the upper. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted January 5, 2011 Report Share Posted January 5, 2011 I'm sure it could be made & you can use the dimensions of your 308 upper to make one .If you know a good machinist or are one, it would not be that hard. I really have never came across a bad flange face on a upper receiver . They could be out there , though, because of all the mass production uppers that were made during the last couple of years.They are machined & should be square to mate with the barrel extension flange & should not need any facing . I mostly look for any coating from the Finnish that's put on the receiver & yes I do a very slight lapping to make sure the extension flange fits flush.I'm just not totally sure its needed in most cases. Quote Link to comment Share on other sites More sharing options...
elkbow Posted February 20, 2011 Report Share Posted February 20, 2011 i haven't built a .308 yet (have a POF), but built alot of other calibers, regular size receivers, I use a tool, also sold through brownells which is a cutter...with pilot, I used to lap, but if you are doing many upper receivers, squaring with a cutter is much quicker Quote Link to comment Share on other sites More sharing options...
hobbesgunner Posted March 11, 2011 Report Share Posted March 11, 2011 Funny ..I just made one of these for an AR15 couple weeks ago..building a mini sass..lathe and a piece of bar stock...didn't know anyone sold them.took idea from bolt action accurizing article. Figured if it works on bolt gun why not autoloader. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted March 12, 2011 Report Share Posted March 12, 2011 There's only one problem with those type of lapping tool's , you can not get away with out getting compound in places you don't want it .You don't want to lap the inside of the upper receiver where the bbl. inserts, only the face. You really can not do it , compound will get where you don't want it ,no matter what you do. Quote Link to comment Share on other sites More sharing options...
hobbesgunner Posted March 12, 2011 Report Share Posted March 12, 2011 Don't use lapping compound...I die cut 400 and 600 grit emery paper to fit tool..worked great Quote Link to comment Share on other sites More sharing options...
survivalshop Posted March 12, 2011 Report Share Posted March 12, 2011 Now that's a good idea ! Quote Link to comment Share on other sites More sharing options...
elkbow Posted February 13, 2012 Report Share Posted February 13, 2012 I know this thread is a bit old, but I haven't seen a tool to do the larger uppers. I do have the tools for the standard upper, and there are two that Brownells sells, one is a cutter and the other is a lapping tool.One word of caution, you want to do as minimal changes to the receiver face as to not change tolerances. I use the cutter slowly to see how unsquare the receiver is, and then lap it. As far as lapping compound in the upper, oh well, easy to clean out.I think the biggest advantage is to make sure everything is square. I have seen a receiver of a 6.5 Grendel that broke two bolts because the receiver was not square and putting torque in the bolt/extension, after squaring the receiver, no more broke bolts.here is some good explanation and how little material is removed:http://www.kiesfirearms.com/Centerfire.html Quote Link to comment Share on other sites More sharing options...
NoFail Posted March 12, 2012 Report Share Posted March 12, 2012 Lapping tool please!!!!! Really isn't there one for our .308's? Don't make me have to go and have one made!!!! Quote Link to comment Share on other sites More sharing options...
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