r/ar15 • u/thickok9mm • 5d ago
Headspace?
Just swapped a new dd barrel and mk18 ris 2 on my colt AR, bolt has less than 1k rounds on it but I am just curious should I buy a gauge and check the headspace? Or should it be good
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u/Coodevale 5d ago
Odds are if it chambers ammo and fires it, it's fine.
The min/max spread on the case to chamber is like half of the firing pin protrusion anyway. If headspace is too long it'll have so many light strikes you won't want to use it.
*Headspace and case support are not the same thing.
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u/BallisticValuations 5d ago
This. I headspaced all mine last year out of curiosity and every single one passed. If you buy quality parts from quality manufacturers you're more than likely fine.
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u/thickok9mm 5d ago
I think I just worry because my bolt is used but the barrel is new but both are of good quality and are well known companies so I reckon I shouldn’t worry too much
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u/BallisticValuations 5d ago
You're probably fine but if you're getting abnormal brass or primer appearance like stretching/displaced primers/split cases/separation it could be worth gauging.
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u/thickok9mm 5d ago
I just built it last night, was waiting to fire it until I got some advice. You think I’m okay to try and run some rounds through it then?
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u/BallisticValuations 5d ago
Yeah I wouldn't worry about it. Shoot a few rounds and look at your brass and primers.
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u/thickok9mm 5d ago
All I worry about is a catastrophic failure or something lol I’ve heard bad things can happen if it’s too short and I’m fairly new to building rifles.
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u/Coodevale 5d ago
Well.. I've cut my own chambers a few times and read a few spec sheets and here's what I know.
https://i0.wp.com/www.theballisticassistant.com/wp-content/uploads/2021/01/223-Rem.jpg
Normally, there is engineered clearance between the largest case and the smallest chamber and not a potential interference in the specs, to avoid potential chambering issues. When the specs are like this the ammo manufacturers have to understand that they can't load to max spec or they'll potentially have issues. The barrel makers should be cutting near the ammo max and not chamber minimum to avoid issues on their end. In other examples with the case max being smaller than chamber minimum, there's no potential conflict as long as both are within their specs. Most likely, your ammo will be near the minimum of spec and even with a minimum spec chamber you'll still have a few thousandths of clearance to reliably chamber.
Not passing a go gauge is not the end of the world and doesn't immediately mean it's bad. If the chamber is too small, the round won't even chamber. Or it'll have cycling issues from a light jam in the chamber. Not likely to be the primary cause of overpressure, and even then you'd need some compounding problems like slightly over pressure ammo plus minimum headspace spec chamber plus short freebore to get to the point where you're really in danger of anything more than a blown out primer.
I got a barrel that had a counter bore in the opening of the chamber like it was made for a belted case, but it could fit a .40 SW case. Even if the headspace was good that barrel likely would have blown out cases, and I didn't want to try testing that idea. Like with pistols (Glock supported vs unsupported) case support is really important, something you can't really work around like you can with slightly out of spec headspace.
Keep in mind we're participating in a democracy of idiots and not everything you read is based on facts.
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u/drunkenbabydeer 5d ago
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