fiddler Posted March 26, 2011 Share Posted March 26, 2011 So if I am getting a spare bolt do I need to check headspace? If I do, how do I do it? With one of these gauges from Brownell's? Link to comment Share on other sites More sharing options...
Dan Sierpina Posted March 26, 2011 Share Posted March 26, 2011 So if I am getting a spare bolt do I need to check headspace? If I do, how do I do it? With one of these gauges from Brownell's? You can check the headspace with another bolt. AR bolts are probably the closest tolerence parts used in firearms. Should you decide to get the gages to check, you need a set of 3. Go, No Go, and the Field. Remove the ejector from the bolt, start with the Go gage. The bolt should lock just fine with the Go gage. Next, the No Go gage. If the No Go still allows the bolt to lock, it's acceptable, no optimal. If the Field gage locks, try another bolt. In bolt guns, a Field gage would mean the headspace is totally out of tolerence. With an AR, you can try other bolts, but, I'd venture to guess, the Field gage would still fit. Link to comment Share on other sites More sharing options...
fiddler Posted March 27, 2011 Author Share Posted March 27, 2011 You can check the headspace with another bolt. AR bolts are probably the closest tolerence parts used in firearms. Should you decide to get the gages to check, you need a set of 3. Go, No Go, and the Field. Remove the ejector from the bolt, start with the Go gage. The bolt should lock just fine with the Go gage. Next, the No Go gage. If the No Go still allows the bolt to lock, it's acceptable, no optimal. If the Field gage locks, try another bolt. In bolt guns, a Field gage would mean the headspace is totally out of tolerence. With an AR, you can try other bolts, but, I'd venture to guess, the Field gage would still fit. I'm not sure what you mean when you say I can check the headspace with another bolt. Link to comment Share on other sites More sharing options...
slowsure Posted March 27, 2011 Share Posted March 27, 2011 I think what Dan is referring to is that if your bolt checks to big (larger than field) you can try another bolt, as the dimension between bolt face (where the cartridge face meets the bolt) and the back of the locking lugs can very by a few thousands and "sometimes" a different bolt will not close on the larger gauge. Link to comment Share on other sites More sharing options...
Dan Sierpina Posted March 27, 2011 Share Posted March 27, 2011 I think what Dan is referring to is that if your bolt checks to big (larger than field) you can try another bolt, as the dimension between bolt face (where the cartridge face meets the bolt) and the back of the locking lugs can very by a few thousands and "sometimes" a different bolt will not close on the larger gauge. That's what I meant! Link to comment Share on other sites More sharing options...
fiddler Posted March 28, 2011 Author Share Posted March 28, 2011 So if the bolt closes on the field gauge headspace is incorrect? Seems like that can't be right. Link to comment Share on other sites More sharing options...
want2race Posted March 28, 2011 Share Posted March 28, 2011 It's called a Field Reject gage. If it closes on the Field gage, it fails headspace. If it fails, change bolt and cam pin and retest. I always change cam pins at the same time as they wear too. I've never seen new parts fail HS. Usually, if the gun fails the HS gaging the barrel will also swallow the throat erosion gage (unservicable barrel). Link to comment Share on other sites More sharing options...
Dan Sierpina Posted March 28, 2011 Share Posted March 28, 2011 So if the bolt closes on the field gauge headspace is incorrect? Seems like that can't be right. You may not think it's right, but, it is. A No Go gage is .004" longer than a Go gage. A Field gage is .004" longer than a No Go. Ideally, the bolt should close only on the Go gage. Link to comment Share on other sites More sharing options...
fiddler Posted March 28, 2011 Author Share Posted March 28, 2011 (edited) So if the bolt closes on the field gauge headspace is incorrect? Seems like that can't be right. You may not think it's right, but, it is. A No Go gage is .004" longer than a Go gage. A Field gage is .004" longer than a No Go. Ideally, the bolt should close only on the Go gage. Sounds like I need a Go and a No Go gauge. ??? Do I really need anything? Can I assume that if the bolt closes on sized ammunition and everything works and the rifle is accurate that headspace is good? Edited March 28, 2011 by fiddler Link to comment Share on other sites More sharing options...
Dan Sierpina Posted March 28, 2011 Share Posted March 28, 2011 Actually, if you want the gages, you need all 3. You can not adjust the headspace anyway, as it's controlled during chambering. You can control the amount of sizing you do to the brass, which is what folks refer to as checking headspace. If your ammo runs fine, and doesn't separate, you'll be fine. Link to comment Share on other sites More sharing options...
caspian guy Posted March 28, 2011 Share Posted March 28, 2011 (edited) Absolutely correct about there being 3 gauges and the order of use. Edited March 28, 2011 by caspian guy Link to comment Share on other sites More sharing options...
fiddler Posted March 28, 2011 Author Share Posted March 28, 2011 Okay. I think this makes sense now. If I want to check the headspace of the rifle I need all three gauges, Go, No Go and Field. If I want to make sure my ammunition is in spec I need a sizing gauge for that. If the rifle runs fine its headspace is probably fine. Thanks for all the replies. I like learning new things. That's one reason I decided to try Multi Gun. That and all the cool new toys. Link to comment Share on other sites More sharing options...
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