View Full Version : BCG break-in?
In my conquest to build an AR the right way, I was finally able to order and received a BCM bolt carrier group. This was, I think, the last piece to replace cheap parts in my carbine.
When I got it and installed it, the first thing that jumped out at me was how tight the gas rings were. I had to remove and re-insert the bolt into the carrier like a man. Pleasant surprise.
The second thing that jumped out at me was how freaking tight the extractor pin fit. Impossible with the supplied O-ring (I stashed it after reviewing parts diagrams in a mild panic to see if it *had* to go in there, heh).
The third thing I noticed was that when I rode the charging handle forward all the way, the bolt would not lock up under the pressure of the action spring.
All this after a healthy application of Slip EWL (liberally coated, sat for a day, wiped, reapplied).
Took it out and shot it yesterday to verify function. Was pleased that it threw the brass just to the rear edge of my peripheral vision consistently--Federal XM193, American Eagle .223, Federal XM855, and Monarch steel-cased .223. I did have 2 short strokes on the Monarch-steel-cased .223, but when it did shoot it had the exact same ejection patterns as anything else I tried.
After I got home and during cleaning, I noticed a few interesting things:
* bolt fit inside the carrier was still tight but not as tight as it was
* extractor pin was still tight but no longer challenged my manliness
* riding the charging handle all the way forward would now result in the pressure of the action spring sending the bolt into batter
The obvious answer is that the BCG has to break in, but the direct question in this post is: how long does that period usually take?
For a full picture of what's going on here, I'm running a 16" DD barrel with a carbine-length gas system, brand new BCM BCG, blue Sprinco action spring, and H3 buffer in what was a stripped DPMS upper. Can provide more specs on request, but I don't think I missed anything relevant to the BCG going back and forth.
Just shoot it. If it functions fine now it will wear in as you go...no worries...don't clean it...shoot it 250-300rds before it "wears" in
You can't rely on cheapo russian ammo for diagnosing short strokes and such...you can actually hear sometimes how much each round differentiates from each other because they are not always loaded the same way.
One time I had a TulAmmo that sound almost suppressed:agree:
Part of your problem is that you are riding the charging handle forward.
if you feel the need to "break it in" short of shooting it. Drown the bolt in some motor oil and run the charging handle a few thousand times. that will smooth up the surfaces, wear down the anodized finish. Keep it wet. same with shooting it. keep it wet.
Not during normal operation. It gets let go like a sling shot. I just ride it when I'm closing the bolt on an empty chamber, like clearing it or spreading some lube.
Definitely plan to keep shooting it, but also curious to know how long I should wait before I start monitoring it and tuning it for the widest range of loads (if I decide to pursue that, or just say "screw it, 5.56 or nothing").
Once again there is no need to to ride it forward. There is also no need to tune it. Put an H2 in it and you should be just fine with most ammo.
Not during normal operation. It gets let go like a sling shot. I just ride it when I'm closing the bolt on an empty chamber, like clearing it or spreading some lube.
Definitely plan to keep shooting it, but also curious to know how long I should wait before I start monitoring it and tuning it for the widest range of loads (if I decide to pursue that, or just say "screw it, 5.56 or nothing").
Meh, not to get stuck on a qualitative detail, but thanks for the tip. I'll chalk that up there with dry firing and staggered gas rings for this platform.
What's telling you an H2? Experience, or do you have some more methodical recipe? What's telling you the H3 is too much in this system, especially with the steel cased stuff showing a very similar ejection pattern when it worked (which would tell me, as thehun pointed out, the ammo most likely has inconsistent charges)?
Once again there is no need to to ride it forward. There is also no need to tune it. Put an H2 in it and you should be just fine with most ammo.
I personally wouldnt run an H3 buffer...I shoot variety of ammo and with you running a blue spring with H3 leaves very little wiggle room.
My old setup used to be your barrel and DD used a milspec spring with H buffer...it ejected perfectly...
Iraqgunz has lots of experience and I would listen to him...
Yeah, definitely plan on listening to him especially, which is why my questions are not a sign of resistance but a sign of acceptance; I plan to get all the information I can out of anybody anywhere close to his experience level. The more I can understand "why", the less often I have to ask "what".
Meh, not to get stuck on a qualitative detail, but thanks for the tip. I'll chalk that up there with dry firing and staggered gas rings for this platform.
What's telling you an H2? Experience, or do you have some more methodical recipe? What's telling you the H3 is too much in this system, especially with the steel cased stuff showing a very similar ejection pattern when it worked (which would tell me, as thehun pointed out, the ammo most likely has inconsistent charges)?
The fact that his title is "Industry Professional" should answer your question. The forum doesn't hand out those titles to just any Joe Dickhead. If you're not gonna take the advice of an IP, there's really no point in asking questions.
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yhmspecter
10-20-13, 16:17
IG is the person to listen too, when I first got here I was sporting a YHM rifle and he helped clear the shit out of my head.. I wouldn't over think much this weapon system is G2G with minor break in.. Lube and ammo will get it done, you have a carbine gas
system it will run all..
Right on, thanks.
For clarification: I'm not saying IG is wrong or challenging his answer. I'm trying to understand why his answer is right so that I can make sure my shit is squared away in my next build or when I help somebody else out.
I don't want to be one of these dudes who just repeats what I've heard. For example, maybe 6 months and $200 later I decide to put a can on it and all of a sudden I'm putting way too much gas in my system (or worse, somebody else's) because I didn't understand why one setup worked and why it didn't before going and changing things again.
Hope this clears up some of the confusion.
Because his the man :thank_you2:
The Colt M4 carbine 14.5" is shipped with an H2 buffer and it works. The Colt 6920 is shipped with an H and it works.
Both have the same gas port size- the difference is that the M4 carbine will also be fired in burst or auto.
So assuming that the DD carbine length barrel uses a similar gas port and based upon your current shooting of the set up now, I would default to the one that will function without the possibility of sacrificing reliability.
Right on, thanks.
For clarification: I'm not saying IG is wrong or challenging his answer. I'm trying to understand why his answer is right so that I can make sure my shit is squared away in my next build or when I help somebody else out.
I don't want to be one of these dudes who just repeats what I've heard. For example, maybe 6 months and $200 later I decide to put a can on it and all of a sudden I'm putting way too much gas in my system (or worse, somebody else's) because I didn't understand why one setup worked and why it didn't before going and changing things again.
Hope this clears up some of the confusion.
Heavy Metal
10-20-13, 17:23
In my conquest to build an AR the right way, I was finally able to order and received a BCM bolt carrier group. This was, I think, the last piece to replace cheap parts in my carbine.
When I got it and installed it, the first thing that jumped out at me was how tight the gas rings were. I had to remove and re-insert the bolt into the carrier like a man. Pleasant surprise.
Take the cam pin out of your BCG, re-insert the bolt and see if it spins freely when fully inserted in the carrier, if it does not, remove the extractor assembly and try it again.
Sometimes, tight gas rings aren't.
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