I’d been wondering this for awhile. I want to get the Miad Core Insert that carries the Xtra BCG and thought I’d see what tweaking needs to be done.
If you have a spare BCG for your M4 does it need to be fitted, headspaced or what? Is it like having a spare fitted 1911 extractor or just plug-n-play?
Should it be or would it be best to have an “exact” duplicate?
My general advice is not to swap bolts around in weapons and if you REALLY find it necessary then they should be checked with the appropriate gage. If you are talking about TEOTWAWKI use then I wouldn’t be overly concerned unless you are putting lots of rounds down range.
I agree on not swapping bolts for shits-n-grins, but only for a SHTF situation but then I do want it to work. Thanks:)
Forgive me,but here is one of my OCD thoughts on replacement bolts.
As far as bolt brand or design…the only concerns I have about replacement bolts is those that are designed with a relieved lug as what is seen with Armalite “improved bolts.”
My thinking is that if a new barrel extension is worn into a relieved lug type bolt design,that the area of the relieved lug on the barrel extension would not have been burnished/worn and therefore possibly cause some uneven loading if a standard full lug contact bolt is installed as a replacement.
On the flip side if a barrel extension is worn in with a standard full lug contact design bolt I would think a relieved lug bolt such as the Armalite “improved bolt” would work fine as a replacement as the barrel extension lugs would have been worn in evenly and therefore no uneven loading.
Now whether there is actually anything to that or not Im not sure as I tend to over analyze just about everything.But is a theory I have.
Maybe one of the professionals can comment on that.
That said,to satisfy my own mind I only use USGI standard LMT or BCM bolts in all the new uppers I have/get,as those are the bolts I prefer to use and keep as spares.
But if I have to replace the bolt in say my old Armalite A2 NM(well used) that has had an Armalite “improved bolt” in place since birth,I’ll use a new Armalite “improved bolt” just for that reason.
You should be ok to use a new bolt (good quality) in a low round-count gun. New bolt in a well used weapon should be gauged.
While I agree that it’s never a bad idea to check headspace, a new bolt will always tighten up headspace in any rifle, therefore checking headspace is not really necessary if replacing a used bolt with a new one.
Exactly how did you reach that conclusion? Are you talking about a weapon that has 500 rounds through it or 5000? Do you know why headspace is checked?
Do you agree that the contact surfaces on both barrel extension and bolt lugs wear through use, gradually increasing headspace over time? What happens if you replace a bolt with one that has more material on the lugs than the one being replaced? Headspace is tightened, whether the rifle has 5 rounds through it or 5000.
If you were not having any problems with excessive headspace prior to swapping bolts, you should be fine after swapping bolts. Let me clarify and say I’m talking about replacing a worn bolt with a new bolt. And yes, I am aware of the reason for checking headspace.
MBR
I’d say chances that a new bolt would not meet the correct headspace is minimal,but could be the case if say the new bolt had an out of spec condition due to manufacturing defect or huge tolerance stack within the components themselves.Which could easily happen with what Ive seen with various parts these days…
As far as the barrel extension wearing the same as the bolt,I’d say there are several variables to consider.Namely material differences and manufacturing specifications such as tolerance,final finish and heat treat.
Afterall,as they say here “parts aint parts” and neither are some of the builds coming from some of these manufacturers.
Personally I think its corner cutting not to check headspace when swapping bolts as it has minimal cost factor and a huge safety factor.That does not even consider the expense of replacing a KB’d weapon.
You really dont get the point until you have a magazine blow to pieces out the bottom of the weapon and a nice tan on your face from being gas etched and peppered with pieces of your beloved firearm…
My opinion though.
As I said above, its never a bad idea to check headspace, but I would not call it absolutely necessary. Also as mentioned previously, this only goes for swapping a used bolt for a new bolt. ALWAYS check headspace if using a worn bolt in any rifle other than the one it came out of.
MBR
I know what happens. My point was that in the TM there is a set of procedures to follow in a particular order. I happen ot believe that the way it is outlined is the most logical. I guess I am just OCD or anal and always will check the headspace as well as firing pin protrusion when I replace or need to swap a bolt.
Thanks for that, Blankwaffe! I like the way you think and it never hurts to reason out issues like that. Thanks for other tips on ArmaLite, too!
Iraqgunz,
I’m not the OP in this thread but can you explain why headspace needs to be checked - that’s an area I know less about than usual in rifles.
Thanks
If Gunz says not to swap, don’t swap. There are several members here that know their sh** in reference to armoring and he is one of them. The others have not chimed in which I am assuming means there is agreement on this.
Hell, he’s only worked on thousands of guns. No way he knows what he’s talking about.
For me, and many others, what IG says is GTG. Period.
Because too tight of headspace or excessive headspace is dangerous. There may be differences in manufacturer tolerances, something that is out of spec., etc…
It’s also not rocket science and the gage is available. This person has the original GI gage. http://www.billricca.com/collectors_corner.htm.
6933
This site is not for emphatically dogmatic statements to shut someone up and send them on their way with a modicum of unexplained knowledge just to get them by… no matter how accurate said knowledge is. This site is for the sharing of knowledge and free discourse between M4 fans of ALL skill levels. Please allow discussions to take place so that as much info as possible is shared.
OK so, what happens if headspace is to tight or to loose, is there anyway to fix this or simply try another bolt or swap barrel’s or what is the solution or is there one?
maybe my head is too stuffed up right now but am i reading that carrying an extra bolt is a bad idea? or that swapping one now and again is the issue? i keep a spare bolt/pin in my MIAD for classes/training sessions/ etc should the bolt go down so i can make a quick swap and keep shooting…
If carrying a spare bolt would it also be wise to have a field gauge? Would a go or no-go be better? Obviously if a bolt breaks the gun it out of commission. A spare bolt is a quick swap. I have all three gauges. Which gauge should go in my shtf kit?
Does it need to be “fitted?” Should the head space be checked on a barrel with a high round count? Yes.
C4