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View Full Version : Is it normal to buy upper with no BCG?


nrakid88
05-24-2009, 7:34 PM
I am just wondering, since I want to get a 16 inch midlength upper with gov profile barrel, I can only find a few BCM uppers, but these come with no BCG or charging handle... Does this mean I can buy any bolt and bolt carrier and the gun will have good headspace? I thought the bolts were mated to the guns individually.

evan69
05-24-2009, 8:24 PM
It depends on the feed ramps of the barrel. All I know is that m4 feed ramps will work with any BCG.

aplinker
05-24-2009, 8:50 PM
It doesn't matter. A properly made barrel will headspace correctly with a properly made bolt. Just buy them both from reputable sources and watch for signs of overpressure.

It depends on the feed ramps of the barrel. All I know is that m4 feed ramps will work with any BCG.

Then you don't know anything. ;) Feed ramps have nothing to do with BCG function.

Josh3239
05-24-2009, 8:56 PM
ARs shouldn't have headspace issues, they should all be made to the same spec. Stick with high quality and you shrink the already small chance. It seems with manufacturers trying to crank out things quickly lately that there have been more bolts (amongst other parts) than normal being out of spec.

I would say get yourself a good quality bolt as you'll kill 2 birds with one stone, you'll get something well made and in spec.

It depends on the feed ramps of the barrel. All I know is that m4 feed ramps will work with any BCG.

I think you are mixing up the issue of M4 feedramps vs regular feed ramps with regard to barrels and uppers.

joelogic
05-24-2009, 9:08 PM
To the OP, yes it is normal these days due to the prices and options available to you.

aplinker
05-24-2009, 9:12 PM
To the OP, yes it is normal these days due to the prices and options available to you.

It's been normal for a long time prior to that, as well.

LMT doesn't sell complete, either.

Addax
05-24-2009, 10:14 PM
It doesn't matter. A properly made barrel will headspace correctly with a properly made bolt. Just buy them both from reputable sources and watch for signs of overpressure.



Then you don't know anything. ;) Feed ramps have nothing to do with BCG function.

+1, Plinker's advice is spot on.

Wild Squid
05-25-2009, 1:17 AM
Can someone tell me if it would be ok to use the Noveske N4 Recce upper with a RRA BCG? I haven't put my rifle together yet so don't know how it will shoot.

aplinker
05-25-2009, 1:21 AM
Can someone tell me if it would be ok to use the Noveske N4 Recce upper with a RRA BCG? I haven't put my rifle together yet so don't know how it will shoot.

Why wouldn't it? Contrary to popular opinion, there's no magic in the Noveske. ;)

RRAs BCGs are most likely CMT (though they've been known to use others), which are what Noveske uses, as well.


How much did you (over)pay for that upper? :D

NeoWeird
05-25-2009, 3:15 AM
In case it didn't get through to people, since someone just asked a "well what about this combination..." question, let me try to explain it with a little more detail.

MOST companies, and I say most because as far as I know ALL of them do but there MIGHT be one or two morons out there who want to do things their own way, use standarized measurments off the same datum when it comes to the manufacturing process of AR barrels. These dimensions are USUALLY set forth by the military and the companies simply did the same for civilian rifles. The result is that ALL bolts, when new, will be within a tolerance range. The barrel extension will also be within a tolerance range. The barrel will also be within a tolerance range. If the military says it has to be 1.205" +/- .001" (or between 1.204" and 1.206" for those that don't understand tolerances) then that is what it has to be. Doesn't matter if it's a Colt, a RRA, Bushmaster, DPMS, etc. They will all fall within that range.

So even if you grab a DPMS barrel, a Bushmaster carrier, a Colt bolt, a RRA lower, a high standard upper, etc. etc. etc. they will all fit within a proper headspace range.

NOW A WARNING: firearms slowly get shot out, and things like extension elongation, chamber elongation, etc. can occure. By swapping bolts around rifles, or by using used parts with new parts, you could potentially find yourself with a dangerous setup. Always use new parts with new parts, and don't swap bolts and uppers. It can be done, but it's not a safe practice.

Wild Squid
05-25-2009, 1:06 PM
Thanks for explaining NeoWeird. Let me ask something else. So why do some people that sell uppers mention that the BCG that comes with the upper is properly fitted or headspaced? If going by your logic then all that had to be done was they use new bolt carrier groups and all would be well? Or does any seller actually shave like 0.001" off the bolt to get some kind of perfect fit? And what I mean is, does anything ever have to be done to properly headspace a BCG to an upper that were purchased new separately?

NeoWeird
05-25-2009, 2:00 PM
Thanks for explaining NeoWeird. Let me ask something else. So why do some people that sell uppers mention that the BCG that comes with the upper is properly fitted or headspaced? If going by your logic then all that had to be done was they use new bolt carrier groups and all would be well? Or does any seller actually shave like 0.001" off the bolt to get some kind of perfect fit? And what I mean is, does anything ever have to be done to properly headspace a BCG to an upper that were purchased new separately?

Because semi-autos have relatively loose chambers to facilitate cycling. Match rifles have intentioning minimized tolerances to ensure the firearms locks up as close to the exact same way as possible - if there is only .0005" clearance between the bolt and extension then it's hard for the bolt to close .002" away from the extension on the first round, .003" on the next, .001" the one after that, etc.

In the case of the specially fit bolts, it's almost always a normal bolt, a normal barrel extension, and usually a normal or top quality barrel bank. The only difference is SOMETIMES they use a specific chamber (for example they may use a .223 Wylde chamber instead of the 5.56 NATO - close the same and can shoot the same ammo, but the Wylde is more geared towards competition shooters) and then the REAL difference is the firearm is chambered to a minimum headspace to that specific bolt, extension, barrel setup. Sometimes they may even go further by having matting surfaces and engagment lug surfaces precision grounds to ensure lockup is square and there are no high spots - again to ensure that lockup is as close to the exact same way every time. Accuracy is not in the parts, but how consistant the rifle is.

In these setups you shouldn't change to the bolt, or use the bolt in other guns, because you may have a bolt on the tight end of the tolerance range, which then gets ground on the faces a little, so now it's undersided. It's fit to it's barrel so everything is good, but you may put in a bolt that's on the high end of the tolerance range and it will now have too little headspace. The cartridge may get forced closed into the chamber and create DANGEROUS pressures.

It's just best to make sure that bolts and barrels that are fitted to each other stay with each other.

aplinker
05-25-2009, 6:52 PM
eh... part of it is just "marketing."

Because semi-autos have relatively loose chambers to facilitate cycling. Match rifles have intentioning minimized tolerances to ensure the firearms locks up as close to the exact same way as possible - if there is only .0005" clearance between the bolt and extension then it's hard for the bolt to close .002" away from the extension on the first round, .003" on the next, .001" the one after that, etc.

In the case of the specially fit bolts, it's almost always a normal bolt, a normal barrel extension, and usually a normal or top quality barrel bank. The only difference is SOMETIMES they use a specific chamber (for example they may use a .223 Wylde chamber instead of the 5.56 NATO - close the same and can shoot the same ammo, but the Wylde is more geared towards competition shooters) and then the REAL difference is the firearm is chambered to a minimum headspace to that specific bolt, extension, barrel setup. Sometimes they may even go further by having matting surfaces and engagment lug surfaces precision grounds to ensure lockup is square and there are no high spots - again to ensure that lockup is as close to the exact same way every time. Accuracy is not in the parts, but how consistant the rifle is.

In these setups you shouldn't change to the bolt, or use the bolt in other guns, because you may have a bolt on the tight end of the tolerance range, which then gets ground on the faces a little, so now it's undersided. It's fit to it's barrel so everything is good, but you may put in a bolt that's on the high end of the tolerance range and it will now have too little headspace. The cartridge may get forced closed into the chamber and create DANGEROUS pressures.

It's just best to make sure that bolts and barrels that are fitted to each other stay with each other.