AR Sponsor
Posted: 10/16/2007 8:18:59 AM EDT
|
Hey guys, I have a question about a build I did several years ago. When I completed the build, everything was good and my "no go" gauge would not go. Now, several years later, the "no go" gauge will go. The rifle still functions perfectly and I see no damage to the fired cases. I haven't looked at them in detail, but nothing is obivous. What other checks can I make, or what should I look for? Should I be concerned even though I see no problems? What could have worn to cause this? By the way, the barrel is a .223, not a 5.56. Any help would be appreciated. Thanks |
|
Throat erosion won't affect headspace, the gauge is indexing off the shoulder portion of the chamber, and measuring to the bolt face. Having a bolt close on a NOGO gauge doesn't mean the headspace is in the dangerously excessive zone, only that it is greater than what you would want with a new bolt assembly. Find a .223/5.56 FIELD gauge and check with that. If you can turn the bolt closed on that, then your headspace with that bolt is excessive and a new bolt is indicated. |
| I am having the same problem, I am looking to replace my barrel because my daughter shoots the gun during deer season. I don't have a field gauge, my no-go is for .223 and measures 1.470 and with out even letting the charging handle go at full extension it will close on the no-go. Is there a chance that I could replace the barrel and not fix the problem. |
Interesting Can you ellaborate some more Paul? Is it always the bolt that causes excessive head space? I had it in my brain that excessive headspace could also be a chamber issue? If it is the bolt I'm assuming that it's the rear of the lugs that have worn? Could the barrel extension wear equally meaning even a new bolt won't solve the problem? These aren't loaded, I'm very ignorant on this subject. Thanks |
|
sorry for not providing a more complete answer. I was only speaking to two specific issues. One, erosion in the throat won't affect headspace, as the throat is forward of the shoulder of the chamber, which is where the gauge ends. Two, since AR bolts are easily replaceable, if a chamber is stretched to the point that headspace is dangerously excessive, replacing it with a bolt that reduces headspace back to a safe length is a convenient way to fix it. This does not always work, especially if you don't have access to a large supply of bolts, but it can be a simple fix. Bolt lug and/or extension lug wear can contribute minimally to growing headspace, but stretching of the chamber, due to high pressure inside the chamber during firing, is usually thought to be the major contributor. The hotter the ammo you shoot, the higher the pressures are that the chamber is subjected to. The hotter the chamber gets under sustained firing, the more effect higher pressures can have. Back to the gauges, depending on which actual NOGO gauge was used, a .223/5.56 chamber that barely lets the bolt close on a NOGO gauge could be as much as 0.006" shorter than what would be considered "excessive". Generally speaking, NOGO gauges are used when chambering as an upper length limit for a new chamber. Go gauges are the lower length limit. FIELD gauges are, again generally, at or near the upper limit of safe headspace. If you can close the bolt easily on a FIELD gauge it's time to get something done. Headspace is very possible dangerously long. |
|
simplicity Who is the manufacturer of the no-go gauge you have? If it is 1.470" that indicates it is a 'field' length gauge, unless ofcourse if it is a Military 'no-go' gauge (1.4706"). The headspce issue does not necessarily mean the bolt is the part that is out of spec. The chamber may have been cut to the 'no-go' gauge length and have worn due to several factors. Or the chamber was cut or or originally headspaced incorrectly. I have a 6x45 that I have used both no-go and field gauges (Forster) that the bolt will close easily on either. Tried 6 different bolts w/carriers all of which will close on the field gauge. This positively indicates that the headspace is way beyond SAAMI specs and the bolt has nothing (or very little at best) to do with same. For some further info concerning AR15/M16 headspacing you might check out Randall's website ar15barrels,com as he has an entire page devoted to this matter. Hope this helps Art |
|
The gauge doesn't have a manu. on it. It just says 1.470 nogo, but A friend of mine has an ar15 and tonight I went to his house and tried his bolt and carrier and it didn't close on the nogo gauge and it closed on the go gauge. Am I correct in thinking that the bolt is the problem? Can I just purchase a new bolt and fix the problem or do I need to buy a complete bolt and carrier assembly? P.S. the barrel is a DPMS .223 1:9 twist. I do appreciate all the help. |
The possible causes of excessive headspace are the bolt AND/OR the barrel. You might get lucky and fix this by just swapping bolts. You may need to change both bolt and barrel. The bolt carrier doesn't have anything to do with headspace. BSW |
|
Simplicity Well that is encouraging. It would indcate that you could go ahead and get a new bolt and tighten up the headspace in your weapon. However, if we return to the original post by jwcrabb, if your weapon is not beating up the brass (read bright ring forward of the case head or in the mid-section) and it is still grouping in a satifactory manner, why incur the cost of the new parts? Further when your weapon was headspaced, they might have used the no-go gauge, so the possibility exists that there is not really a headspace issue. Pertaining to the gauges, I use Forster and they allow a safe margin on their gauges, ie: the no-go gauge is 1.467" and the field gauge is 1.4696". So going on what you indicate your gauge is (1.470") you would need to find/use either a military field gauge (1.4730") or a Colt field gauge (1.4736") to really determine if there is a headspace issue. Hope this helps Art |
AR Sponsor