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Posted: 11/29/2011 7:06:42 AM EDT
I'm building a 9mm AR pistol and it just dawned on me... how would I check headspace on this? I've never seen a 9mm headspace gauge. Is it as big a deal as on a 5.56 build?
Link Posted: 11/29/2011 8:15:36 AM EDT
Link Posted: 11/29/2011 9:49:20 AM EDT
I assume 99.9% of people who build their 9mm AR's put the parts together and shoot it without worries.

If the barrel and bolt are both from a quality manufacturer you shouldn't have any problems.

If the bolt marks the barrel face, you should be perfect.

Someone had pictures ...
Link Posted: 11/29/2011 11:29:42 AM EDT
Thanks on both replies
Link Posted: 11/29/2011 5:35:08 PM EDT
You do not need gauges for the blow back AR-15 in 9mm.. all you need is a sample of ammo assortment of various headstamp flavor and eyeball..

I prefer the depth micrometer method myself.. common case length falls in the .744/.748 range.. so use shortest case you have for measures,, longer is fine after that, as the cartridge will be firmly held by bolt face and case mouth with cartridge chambered

Std bolt pocket depth is .125",, that is common.

Measure how far the case sticks out of the end of the barrel.... common sense would tell you case need to stick out .125" from bolt face for bolt to sandwich case firmly at both end and fire pin get good hit.. I set mine to typically .135" )involves lathe/measuring skills)... this holds bolt off barel face approx .010", and less to no clunk noise of bolt close on live cartridge when using suppresor... only time bolt clunck barrel face is empty chamber ( I use Hy-Tech block with UZI mags,,, no bolt hold).

You can visual it with good results also,,, remove the extractor, drop case or cartridge in the chamber, close the bolt, and have a look (DO THIS INSPECTION WITH UPPER SEPERATED FROM LOWER)

With bolt shut on case/cartridge, look to see that case is held firmly in place ––> good to go

If you see clearance between case head and bolt face (gross amount).. then we can maybe have problem with fire pin hit primer firmly (been there with barrel made for me by a former vendor here),, I had to repair barrel make it run

Link Posted: 11/29/2011 6:15:48 PM EDT
SBR7_11, that's some great info. Thanks!
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