AR Sponsor
Posted: 1/19/2005 3:49:34 PM EDT
|
I just finished a recent build, and am looking forward to shooting it for the first time. I know there's really no way to adjust headspace on an AR-15 (short of swapping out lots of bolts, or changing the barrel extension), so it almost seems pointless to check headspace. However, I wanted just a little reassurance that it was OK before I pulled the trigger on a live round, so here's what I did in the absence of real headspace gauges: New Bushmaster 5.56 NATO barrel, New Colt bolt/carrier. Removed upper from rifle, stripped bolt (removed extractor and ejector) and reassembled bolt carrier. Reinserted carrier in upper, keeping upper separate from lower. Took a random round of Federal XM193 (LC 01 headstamp), and chambered it by hand. Bolt closed easily. Added two thin pieces of masking tape over the back of the round, and chambered it by hand. Bolt would not close with firm two thumb pressure. Removed both tape layers from round, replaced with one layer. Bolt closed with slight resistance. Removed all tape. Bolt again easily closed on round. Repeated tape test, same results. Reassembled bolt. Is this ineffective and uber ghetto, or is it an ok check? FWIW, on the last build I just locked and loaded live rounds, and kinda leaned away for the first shot. Checked the ejected casing for signs of overpressure or long chamber. Checked good, and ran fine since. Didn't feel quite as brave this time... 
|
Headspace as I understand it refers to the distance from the bolt face to a specific point in the chamber where the case shoulder meets the chamber wall. In the most basic terms, it measures how much room exists in the chamber for the cartridge. Too much room, bad stuff happens. Not enough room, bad stuff happens. The right amount of room =  A quick google search will yield lots of detailed and more technically accurate explanations. Fulton Armory has a pretty good breakdown.ETA: Why yes, I have been known to hang out at FALfiles. My first FAL build still soldiers on! |
|
Sort of. Make sure you remove the extractor and ejector first, as these *can* throw off your reading. Put the gauge in the chamber, and try to close the bolt/carrier. On a "Go" gauge, the bolt should go fully into battery. Bolt should not close on "Field" gauge. In a perfect world, it wouldn't close on a "No-go" either, but a field gauge tells you when it is bottom line unsafe to fire. ETA: make sure you clean the chamber and bolt face to remove any grit or oil before performing the check. |
|
Oh, and *gently* close the bolt. Take out the buffer spring. Don't let it slam home under spring pressure or you should consider your gage ruined. Don't knock this method. Personally, I prefer to use 3 unchambered match rounds selected at random, and marked and stored in my reference storage box. I've used it for building FAL's, checking M1 garand builds, and putting together a VZ-52 in 7.62x45. Try finding gages for that last one. |
AR Sponsor
Win a FREE Membership!
Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!
You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.