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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 10-26-2010, 10:25 AM
secamendsupporter secamendsupporter is offline
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Default Headspace on a DPMS .308

If I remove or replace the barrel on a DPMS .308 upper will I need to get the headspace checked? This is a new unfired upper.

Last edited by secamendsupporter; 10-26-2010 at 10:33 AM..
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  #2  
Old 10-26-2010, 10:33 AM
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Yes. Its very easy though. If its your first time, best way is to pick up a set of Go, No-go gauges. If you have done this before and have spent brass from the rifle you can use them to set your headspace.
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  #3  
Old 10-26-2010, 10:58 AM
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I just built a JD upper and lower with a DPMS barrel. Does it also need to be head spaced? If so anyone have a link on how to do this?
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  #4  
Old 10-26-2010, 11:29 AM
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Do you mean replace the barrel with a different one, or remove then replace the same one? As long as the barrel and bolt (that were previously know to be proper headspace) stay together, your fine. If you change bolts or barrels, then you should check the headspace.
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Old 10-26-2010, 11:36 AM
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I built the gun for the ground up so its all new.
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  #6  
Old 10-26-2010, 11:59 AM
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I check my headspacing out of the receiver to start. I verify the bot can freely drop into the barrel extension and turn into the lugs. I check for side to side free play when the bolt head is turned. If it looks ok I will take a home made dummy round (case bullet and spent primer) and test the fit of the bolt head within the round in the chamber. The bolt should drop in just fine and spin with little effort to engage the lugs. If it does not drop in that means your bolthead needs to be fitted by a gunsmith. If it does drop in a spin move on...

Next check you no-go. Using a 3x5 card, cut a small circle out that will fit in your bolt face. Try to insert and turn the bolt in the barrel extension now. You should not be able to get the bolt head to seat all the way. If it does not fit with the 3x5 paper in there you are GTG. If it does fit with room to spare you might want to get the looked at by a gunsmith.

99.9% of the time with new parts you will not have a headspace issue. Everything is made to spec and should work fine. Because headspacing is a safety issue I always recommend checking it yourself. Just like if someone hands your firearms and tells you its unloaded, you always check for yourself.
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  #7  
Old 10-26-2010, 12:28 PM
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How would you check a semi-auto like an AR-10?
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  #8  
Old 10-26-2010, 2:46 PM
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Default I am not an expert but...

It is my understanding that due to the way the AR style rifles have the bolt lugs in the barrel itself, and the fact that all bolts and chambers/bolt lugs are supposed to be machined the same, that all barrels are interchangeable. It certainly wouldn't hurt to get a headspace gauge but it shouldn't be an issue unless someone did something wrong, or the chamber or bolt have excessive wear. In many other rifles the bolt lugs are in the action and the barrel then screws into the action so depending on exactly how far you thread the barrel into the action the headspace is effected. The headspace in an AR style rifle (AR-15, LR.308, AR-10) is determined by the bolt and integral to the barrel bolt lugs, not by the threading into the receiver, so you actually can't do anything to effect the headspace (other than wear on the chamber and bolt/bolt lugs).

The idea behind this system rather than the system used on most bolt action rifles and even M1, Mini-14, maybe even AKs (I don't know about AKs) is that barrels, bolts, bolt carriers, everything, is interchangeable. I would guess that some really serious target shooters would want to match their barrel to the bolt and bolt carrier just to ensure that they were running the best possible matched everything, but I don't think it is required for normal rifles. I have seen some match barrels that come with the bolt they were chambered with, but generally this is not the case.

Come to think of it, if your barrel is already fully chambered I am not sure what you could do about it if the headspace was wrong. I suppose that if the headspace was tight you could have the chamber reamed but if the headpspace is too long on a new barrel all you could do would be to search around for a bolt that might fit in a little tighter to close the gap.
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Old 10-26-2010, 2:56 PM
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Quote:
Originally Posted by captbilly View Post
It is my understanding that due to the way the AR style rifles have the bolt lugs in the barrel itself, and the fact that all bolts and chambers/bolt lugs are supposed to be machined the same, that all barrels are interchangeable. It certainly wouldn't hurt to get a headspace gauge but it shouldn't be an issue unless someone did something wrong, or the chamber or bolt have excessive wear. In many other rifles the bolt lugs are in the action and the barrel then screws into the action so depending on exactly how far you thread the barrel into the action the headspace is effected. The headspace in an AR style rifle (AR-15, LR.308, AR-10) is determined by the bolt and integral to the barrel bolt lugs, not by the threading into the receiver, so you actually can't do anything to effect the headspace (other than wear on the chamber and bolt/bolt lugs).

The idea behind this system rather than the system used on most bolt action rifles and even M1, Mini-14, maybe even AKs (I don't know about AKs) is that barrels, bolts, bolt carriers, everything, is interchangeable. I would guess that some really serious target shooters would want to match their barrel to the bolt and bolt carrier just to ensure that they were running the best possible matched everything, but I don't think it is required for normal rifles. I have seen some match barrels that come with the bolt they were chambered with, but generally this is not the case.

Come to think of it, if your barrel is already fully chambered I am not sure what you could do about it if the headspace was wrong. I suppose that if the headspace was tight you could have the chamber reamed but if the headpspace is too long on a new barrel all you could do would be to search around for a bolt that might fit in a little tighter to close the gap.
The fitting would be done on the bolt head, not the barrel. If its too tight the bolt head would need to be trimmed. If there is too much play then you are kinda SOL and would need a new bold head.
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  #10  
Old 10-26-2010, 3:04 PM
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Default Curious, why not ream the chamber?

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Originally Posted by Bug Splat View Post
The fitting would be done on the bolt head, not the barrel. If its too tight the bolt head would need to be trimmed. If there is too much play then you are kinda SOL and would need a new bold head.
Why would you adjust headspace with the bolt and not with a reamer like on a bolt gun? The problem I see with adjusting the bolt is that now you have an upper that will only work with that bolt or bolt carrier group. If you were to finish ream to the correct headspace then in theory every standard bolt would fit that upper.
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  #11  
Old 10-26-2010, 3:08 PM
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Quote:
Originally Posted by captbilly View Post
Why would you adjust headspace with the bolt and not with a reamer like on a bolt gun? The problem I see with adjusting the bolt is that now you have an upper that will only work with that bolt or bolt carrier group. If you were to finish ream to the correct headspace then in theory every standard bolt would fit that upper.
If you are setting up a match gun there is no such thing as interchanging parts. You build the rifle for one thing, accuracy. When the barrel or bolt are worn you gut it and rebuild . I built a Ar that would shoot sub 1/4 MOA and used it in benchrest matches for fun. The bolt was hand fit to give me the best fit and accuracy. When I retired that barrel, out went the bolt head with it.
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  #12  
Old 10-26-2010, 3:16 PM
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well, there is more than one way to skin a cat I guess. You could removed the barrel extension and ream the bore. For me it seems like less work to just mod the bolt. Its easier to work with and does not require a large lathe.
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  #13  
Old 10-26-2010, 4:39 PM
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Sorry if OT. What if I were to remove the barrel for some kind of work, or if I loosen the barrel nut and replace it with those free float rails, will head spacing be an issue as well? the rifle has around 2k rounds through it.
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Old 10-26-2010, 5:15 PM
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Quote:
Originally Posted by gemini1 View Post
Sorry if OT. What if I were to remove the barrel for some kind of work, or if I loosen the barrel nut and replace it with those free float rails, will head spacing be an issue as well? the rifle has around 2k rounds through it.
No it will be fine. Only time it would be an issue is if you got a new barrel or a new bolt. Again its rare for two new parts to not fit correctly. Maybe I'm just an untrusting person and have to check things myself.
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Old 10-26-2010, 7:40 PM
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Oh okay, thanks for the info.
So should my bolt breaks and replace it with a new one, I should check the head space? Is there a simple way of checking it without using the gauges?
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