What are your guys thoughts on headspacing . I know you can drop in most quality BCG into a upper and be good to go . Is there any concerns about accuracy , reliability, safety, ? Thanks for any input.
Nope, none, nada…
Forget about headspacing. You cant find it or change it. You have to trust that the manufacturers you purchased from built it right.
Exactly.
You can get field guages if you want to check but its not something you can change at home. If the headspace is off its back to the manufacturer.
Or check headspace per 23&P…
Exactly what I was thinking. When we talk about “trusting” manufacturers we really need to think about that. There are some that I would probably trust without question.
However, we all know there are some who shouldn’t be trusted at all. And remember that ANYTHING made by man and machine is susceptible to being screwed up.
I do as ToddK and Iraqgunz says and follow the -23&P as if were a religion.Thats two professionals giving professional recommendations on proper assembly and safety that should be heeded by all…and they are not selling headspace gauges.
I trust the manufacturers I buy from but I also inspect parts and verify headspace.
In fact I have yet to talk to a manufacturer in regards to swapping/installing bolts that did not specifically mention that the headspace should be checked during installation and before use.
For instance,in LMT’s case Gene Swanson even went as far as to mentioned the specific gauge dimensions that should be used,and detailed the headspace inspection process.
Its done at the factory level during assembly,so it should also be done at the individual level as well.
So yeah as a CYA,you should examine the bolt for visual defects,check fit of parts,firing pin protrusion and headspace.
Ive had two bolts that had issues other than headspace in the last three years.One the bolt had a cupped/erosion bolt face at the firing pin port from what looked like primer or primer pocket failure during HPT or test fire,and another at the bolt tail that allowed excessive firing pin protrusion slightly beyond max.Both returned and replaced by the manufacturer without question.
So its always good to double check anything your planning on using for both your own well being and as your investment in both cases.
I searched but didnt find anything. What is 23&P?
TM 9-1005-319-23&P
Links to the manuals are provided here:
https://www.m4carbine.net/showthread.php?t=35490
Post three contains a link to the newest version Change 8.
Thanks for all of the info . I am currently running all colt auto BCG’s except 1 thats a Stag mp tested semi auto that I have a auto colt on the way to replace it . I should have no problems at all with the Colt’s 
I know this is a really old thread but I have a question pertaining to this subject. I have a Rainier Arms Upper, a BCM FA chromed BCG, and a PSA 16" chrome lined barrel (all quality parts from trust-worthy manufacturers). I put an empty cartridge with a bullet just barely seated into the brass and let the bolt go forward to see how far it would seat the bullet into the brass (a make-shift head space test). It didn’t seat the bullet quite far enough.
My main questions: Does this test tell that the head space is too long? Should I use some shims to push the barrel back?
I think you need to read up on what headspace is. :eek: Headspace has nothing to do with the bullet.
So… I should be fine?
And yes, I know head space has nothing to do with the bullet.
You can do a rough headspace check with an unfired cartridge as a substitute gauge. Take all precautions to avoid a negligent discharge
I’ve never heard of doing this before. What exactly are you looking for when you use a live cartridge?
I’ve seen some people use a fired case for this. I kind of thought it a little dangerous. Better than no check at all, but can this get you close enough to go-no go gauge check?
A bolt should NEVER close and lock on a USGI FIELD or Colt FIELD II headspace gauge, if it did try a new bolt and if that one does you need a new barrel.
It’s so easy to check with a USGI field gauge, which is cheap, that I can’t imagine why you would’t do it.
I know I can get a real USGI field gauge from Bill Ricca’s, but they’re $60 plus shipping. I’m not familiar with the Colt Field II headspace gauge. I know this isn’t it exactly, but how would it compare?
http://www.brownells.com/.aspx/pid=6646/Product/5-56mm-223-HEADSPACE-GAUGE
I am going to search this, but when some match type barrels say they come with a fitted bolt, does that mean it is towards the minimum headspace dimension? Also, does it really gain you anything in accuracy?
Cartridge does not have to be live. A properly sized dummy round will work just as well. A fired case has expanded to the size of the chamber it was fired in and will give a false reading. What you are looking for is that the bolt will close on the case with light thumb pressure.
Keep the upper separated from the lower if using a live cartridge to test headspace.
It depends on who is fitting the bolt. It isn’t always wise to headspace to minimum, especially on a self-loading rifle, as it could lead to sticking with some lots of ammo.
I haven’t test it for myself, but some claim they get better results with fitted bolts. That’s using loads tailored for the rifle, not ordinary combat ammo. If using ordinary combat ammo, it’s unlikely the shooter will see any advantage to a fitted bolt.
My Lothar-Walther barrel is very accurate with quality precision ammo. I’ve only shot the rifle with the fitted bolt so I don’t know if there would be any difference in accuracy. I got the barrel for $325 delivered, bolt included and I’m very satisfied with price and performance