View Full Version : BCG head space?
I got a complete BCM upper a year ago that came with a bcg and charging handle. I was wanting to buy another bcm upper with no bcg and handle my question is can I take my old bcm bcg and handle and put it into the new bcm upper and not worry about head spacing issues? I was told to buy some sort of tool to measure it to make sure but is that necessary? Also will a psa bcg work in any mil spec upper or do I need to headspace it?
You can use your BCG however it amounts to putting a used BCG into a new barrel. All of mine have names and dedicated components and nothing ever gets interchanged. Even though you probably won't have headspace issues it's a good idea to check headspace so purchase the gauges and later on charge your buddies for checking theirs.
No issues with the CH. And probably no issue with the old BCG. How many rounds on the old BCG?
I got a complete BCM upper a year ago that came with a bcg and charging handle. I was wanting to buy another bcm upper with no bcg and handle my question is can I take my old bcm bcg and handle and put it into the new bcm upper and not worry about head spacing issues? I was told to buy some sort of tool to measure it to make sure but is that necessary? Also will a psa bcg work in any mil spec upper or do I need to headspace it?
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Pretty much agree with everything above. Odds are, you should be just fine. I personally avoid swapping used BCGs between uppers. Every chamber will wear on the bolt differently. The differences might be small, even insignificant, but no two are the same. So, in theory, a used bolt that's been "seasoned" by a given chamber could be problematic if run in a different chamber. Still, the chance of actual problems arising is pretty slim.
Like many other things, it boils down to your actual application. If your "old" bolt only has a few hundred rounds on it, then repurposing it in a new upper warrants very little concern. If that "old" bolt has thousands upon thousands of rounds on it, I'd be a stronger advocate for going a different route.
Ultimately, with the way the market is today, purchasing a new BCG/Bolt for this scenario is a no-brainer. And, the PSA you mention will work just fine in any upper that's not defective. If you go that route, it might be worth waiting a few weeks. I can't imagine how low the Black Friday prices will be this year :D
I never shot the other bcm bcg I had just put the bcg and put it in the safe.
If there are no rounds on the “old” BCG you have zero issues or need to worry about headspace in the new upper.
I never shot the other bcm bcg I had just put the bcg and put it in the safe.
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The only rounds that were fired through it were at the factory as test fire would that make a difference?
No difference whatsoever. All BCM BCGs are going to be test fired from the factory. Placing a previously purchased factory new BCM BCG into a recently purchased factory new BCM upper assembly group is absolutely good to go. Technically, you can't be 100% about anything unless you headspace the setup, but personally, since everything you are running is new, i would run with the stated setup and be completely confident.
Regarding an additional BCG, I'd wait until black Friday and see if BCM places their BCGs on sale. You have two factory built BCM uppers, one with a factory new BCM BCG. You might as well finish everything off with another BCM BCG in the other upper group...but that's just me.
There is a lot of garbage posted whenever this topic comes up, and it does on a regular basis. I'm not going to type out a huge reply again, but I'll condense it to try and be of some help.
I spoke with the person at an upper end weapon manufacturer who did not make their own bolts. The person stated roughly 10% of the bolts they headspaced to barrels did not make the cut. Since they had a large bucket of bolts, they would simply grab a new bolt, and check it. There was almost never an issue with the next bolt. Sometimes tolerances just stacked the wrong way, that didn't make any of the bolts bad, nor did it make any of the barrels bad.
For some person here to tell you without doubt there is no problem, I would flag that person as someone who was playing parrot to what they had read online, and didn't actually know what they were talking about. There is no guarantee. That being said, the odds are strongly in your favor that if you purchase a QUALITY (not bottom feeder) bolt, you shouldn't experience any issues though the bolt may be a bit loose or tight.
I think a gauge from Brownells is like $23 and takes about 30 seconds to check. At that price and time investment it’s a no brainer to me.
I am just going to pick up a no go gauge and check just to be safe how do you use these gauges and what should I look for?
I've always read to remove the ejector and extractor for an accurate measurement. Is this not true?
I think a gauge from Brownells is like $23 and takes about 30 seconds to check. At that price and time investment it’s a no brainer to me.
This link has what you need to know in the Learn tab.
https://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/5-56mm-maximum-headspace-gauge-prod6646.aspx?psize=96
I am just going to pick up a no go gauge and check just to be safe how do you use these gauges and what should I look for?
Oh, this game. Your conversation with “the person” at an upper end weapons manufacturer was somehow was more accurate than the conversation I had with “the person” at an upper end weapons manufacturer...
No, there is no guarantee. Never is with much in life. But by your logic the tens of thousands of BCG that come sealed in their little plastic bags that all of us get from various high end manufacturers, including BCM, and drop into our new uppers without head spacing, are inexperienced, uneducated, idiots.
Yeah, it appears you’ve got a lot of experience based on all your time and posts on this forum, good on ya. But with all due respect, do not assume I don’t know what I am doing or have no experience based on a post in some forum. Very unprofessional and liberalesque.
Back to the question by the OP, it’s his decision to do what he’s most comfortable with based on the input provided. If it were me, and it has been me, I wouldn’t worry at all about your “old” unfired BCG going into your new upper.
But don’t take mine or anybody else’s word for it on this forum. Email BCM and see what they recommend. If you go that route, I’d be interested for you to post the results of the conversation.
Squawk... Polly wanna cracker? Squawk...
There is a lot of garbage posted whenever this topic comes up, and it does on a regular basis. I'm not going to type out a huge reply again, but I'll condense it to try and be of some help.
I spoke with the person at an upper end weapon manufacturer who did not make their own bolts. The person stated roughly 10% of the bolts they headspaced to barrels did not make the cut. Since they had a large bucket of bolts, they would simply grab a new bolt, and check it. There was almost never an issue with the next bolt. Sometimes tolerances just stacked the wrong way, that didn't make any of the bolts bad, nor did it make any of the barrels bad.
For some person here to tell you without doubt there is no problem, I would flag that person as someone who was playing parrot to what they had read online, and didn't actually know what they were talking about. There is no guarantee. That being said, the odds are strongly in your favor that if you purchase a QUALITY (not bottom feeder) bolt, you shouldn't experience any issues though the bolt may be a bit loose or tight.
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I've always read to remove the ejector and extractor for an accurate measurement. Is this not true?
Yes generally it’s recommended that the extractor and ejector be removed. Someone used to make field gauges with a cutout for those features. If you leave the ejector in there you run the risk of a false reading due to the spring pressure. You can use more pressure on the BCG to overcome the extractor spring, but if your chamber is soft you may damage it as the tool is hardened I believe.
I’m tempted to buy another one, bring it to work and milk a pocket for the extractor in it.
I did email bcm and I got back what I figured I would. They said they test fire all bcm bcg with complete uppers and there shouldn't be issues however they said there is never a guarantee and to be 100 percent it would be a good idea to get a no go gauge so that's what I did 30 bucks for piece of mind is worth it IMO.
titsonritz
11-03-17, 12:41
I did email bcm and I got back what I figured I would. They said they test fire all bcm bcg with complete uppers and there shouldn't be issues however they said there is never a guarantee and to be 100 percent it would be a good idea to get a no go gauge so that's what I did 30 bucks for piece of mind is worth it IMO.
You do not want an "no-go gauge" you want a field gauge. The link is listed above.
RVTMaverick
11-03-17, 13:11
Yes generally it’s recommended that the extractor and ejector be removed. Someone used to make field gauges with a cutout for those features. If you leave the ejector in there you run the risk of a false reading due to the spring pressure. You can use more pressure on the BCG to overcome the extractor spring, but if your chamber is soft you may damage it as the tool is hardened I believe.
I’m tempted to buy another one, bring it to work and mill a pocket for the extractor in it.
Hey TAZ,
I fixed it ;)for you...:D
Doc Safari
11-03-17, 15:59
"Best practices" would suggest that headspace be checked as a quality control and safety assurance, if nothing else.
Murphy's Law also predicts that the one you do not check will be the one that has the problem.
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