Posted: 2/1/2008 10:28:42 PM EDT
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Need some help with headspace. I finished building a 24" Varmint AR15. I bought the Forster .223REM GO and NOGO headspace gauges and checked the chamber tonight. The GO Gauge has 1.4636 and the NOGO has 1.4666. I could not close the bolt on either the GO or the NOGO gauge. Below are the rifle's details: DPMS lower with Rock River Arms LPK and two-stage trigger kit. RRA A4 Stripped Upper with charging handle and foward assist DPMS 24" Bull Barrel with Extension installed. JP Enterprise free-float handguard DPMS flat top gas block and gas tube Mil-spec BCG Magpul PRS stock with Rifle buffer tube, spring, and buffer I separated the upper and lower receivers. I then removed the extractor and ejector. I placed the bolt back into the bolt carrier. Installed the key, firing pin, and retaining clip into the bolt carrier. I inserted the GO gauge and then slide the BCG into the upper. I pushed the BCG forward and saw that the bolt started to rotate about 10 degrees and stop. The NOGO gauge was about the same. I then grabbed another BCG that has seen about 350-400 rounds. I only removed the extractor as I was having trouble getting the ejector roll pin out. I then installed this BCG assembly into the upper. I applied more pressure than before as I could feel the ejector spring compress. The bolt then snapped into battery. I then tried the NOGO and it too snap into battery with about the same pressure. I figured I was pushing too hard in order to overcome the ejector spring and concluded that this test was no good. I then spent some more time on the used BCG and finally got the ejector roll pin out. I then tried it back in the DPMS 24" upper. This time the bolt closed on the GO gauge but it still took more pressure than I thought should be used. Shouldn't I see the bolt rotate easily on the GO gauge? Next I tried the NOGO gauge on the used BCG. The bolt started to rotate a few degrees but then stopped. I then tried the brand new BCG on the older upper. This is a J&T kit upper with a 16" barrel. The new BCG would not close on the GO or NOGO gauge. So it looks like my chamber and bolt are too tight. Doesn't the GO gauge measure maximum SAMMI length. Should I not run any ammunition through the new AR? Should I try some other bolts? UPDATE: I also tried the stripped bolt and carrier in a brand new Armalite upper with 16" barrel. This upper assembly came from Armalite headspaced and unfired. The bolt would close on both the GO and NOGO gauge. I also measured the overall length of both gauges with my micrometer, they both measure 1.658". Shouldn't there be a difference in length? |
| I don't really know much of anything at all about headspace but are you sure that it's not a problem with the gauges your using? I never checked the headspace on my new upper before I started shooting. I would do it if I bought some milsurp rifle but not on a brand new AR. |
How exactly do you perform the check? Do you rotate the loose bolt within the receiver extension? I did have the ejector and extractor removed on the BCG and upper I was checking. There was only one time that I tried another BCG and did not remove the ejector because the roll pin was too stubborn. I finally got the roll pin out, so I made the check with two different BCGs, one brand new the other with about 450 rounds through it. You're right I don't want to take the barrel out of the receiver now that it has been installed. |