AR-15 Barrel Installation

[Sheriff9mm]

Good evening all...

I'm in the process of putting together a second M4gery for me and I've decided that I'm going to build the whole thing from scratch. While I've put together lowers many times before, this is the first time I'll be assembling the upper. I have all the necessary tools and just ordered a 16" M4 barrel kit that I'm going to convert to AWB compliant.

My question is this: While installing the barrel onto the upper receiver, am I to worry about checking the head-space even while using all brand new parts? Also, I'll be installing a new post-ban Front Sight Base on the barrel. Are there any special tricks to make sure that the FSB lines up properly and not canted to one side? Thanks in advance.

Parts in Hand:
-DPMS lower assembled from DPMS lower parts kit
-KNS Hammer and Trigger pins
-Bushmaster pinned carbine style stock
-Yankee Hill Machine A3 upper assembly

Parts on the Way:
-Delton M4 chrome lined barrel kit
-AWB Front sight base
-Branson A2-style compensator
-Lewis Machine and Tool Bolt Carrier Assembly

 

[wheelgun]

Nope. The headspace is set by the barrel manufacturer when they attach the barrel extension to the barrel. But you certainly can check it if you like....

The FSB should line up pretty well since it's alignment is determined by the barrel index pin. The important thing is to use an upper receiver clamping block while tightening the barrel nut to minimize the chances of bending the pin.

 

[vellnueve]

I disagree, wheelgun. If the BCG is not properly matched to the barrel/receiver combo, the headspace will be affected.

 

[MassMark]

I disagree, wheelgun. If the BCG is not properly matched to the barrel/receiver combo, the headspace will be affected.

I disagree with your disagreement... Unless the Bolt/BCG is way out of spec or he's dealing with a used barrel, then headspace is not an issue. When selecting my BCG for my NES build, (BCM), I asked two different builders, (Jon and Grant) if headspace would be an issue and both replied "no". If there's something in print that challenges this - I'd like to see it.

 

[bpm990d]

I would check it with either a NoGo or Field Gage.

B

 

[vellnueve]

I disagree with your disagreement... Unless the Bolt/BCG is way out of spec or he's dealing with a used barrel, then headspace is not an issue. When selecting my BCG for my NES build, (BCM), I asked two different builders, (Jon and Grant) if headspace would be an issue and both replied "no". If there's something in print that challenges this - I'd like to see it.

I disagree with your disagreement of my disagreement. Although pretty much all new manufacturers of BCGs build them close enough that headspace shouldn't be an issue, everyone who builds a rifle from parts should have the proper gauges to check. $10-20 is really a small price to pay to make sure that everything is in order.

 

[7.62x39]

While I agree that ALL new builds should be checked with go and no-go gages, I also agree that it shouldn't be an issue on a AR build.
Where are you going to get a go and no-go for $10-$20? I have them for 7.62x39, 5.45x39, 5.56x45 and 7.62x51 all of which were in the $60-$70 range

 

[vellnueve]

Forsters are available at Midway for under $20 apiece.

 

[cdkayak]

It's worth checking and it's short money to prevent an accident. Any manufacturer can make a mistake when reaming the chamber in the barrel.

 

[LoginName]

Two good tutorials on building your upper...

http://www.snipercentral.com/forums/viewtopic.php?t=1871&sid=589f9efa367fb2f6a5ee61e8a5210c4d

http://www.ar15.com/forums/topic.html?b=3&f=4&t=226782

Just one question: what do you mean by an "AWB front sight base"?

A gas block/picatinny type that uses allen screws to secure it, or a traditional A2 triangular shaped sight tower (with no bayonet lug), that's secured with taper pins?

Reason I ask, is if it's the latter, I think you could have a problem with proper alignment/timing. This is usually set by the manufacturer. Ever notice that practically every aftermarket AR barrel out there already has a front sight tower already attached?

Mind you... I'm not 100% certain of that being an issue. YMMV.

As for headspacing... I'm with most here that it shouldn't be an issue. I've built 3 uppers, never checked the headspace and I still have 10 fingers and two functional eyes.

Still... if you want piece of mind, it's the kind of thing that no harm comes from checking it.

 

[vellnueve]

AWB FSB refers to non-lugged

 

[Sheriff9mm]

Thanks for all the replies. Whereas this is the first upper I've built, i think i will check the head-space just to be sure. I have a buddy that has a set of gauges that he can loan me.

Two good tutorials on building your upper...

http://www.snipercentral.com/forums/viewtopic.php?t=1871&sid=589f9efa367fb2f6a5ee61e8a5210c4d

http://www.ar15.com/forums/topic.html?b=3&f=4&t=226782

Just one question: what do you mean by an "AWB front sight base"?

A gas block/picatinny type that uses allen screws to secure it, or a traditional A2 triangular shaped sight tower (with no bayonet lug), that's secured with taper pins?

Reason I ask, is if it's the latter, I think you could have a problem with proper alignment/timing. This is usually set by the manufacturer. Ever notice that practically every aftermarket AR barrel out there already has a front sight tower already attached?

Mind you... I'm not 100% certain of that being an issue. YMMV.

As for headspacing... I'm with most here that it shouldn't be an issue. I've built 3 uppers, never checked the headspace and I still have 10 fingers and two functional eyes.

Still... if you want piece of mind, it's the kind of thing that no harm comes from checking it.

Thanks for the great resources, they were quite helpful.

My plan is to remove the lugged front sight base and replace it with one that would be Mass-compliant. It should be an easy swap. I could just grind off the bayonet lug from the one that comes with the barrel kit and re-parkerize it, but i'd rather spend the extra $40 than do extra work refinishing (especially when I haven't done it before).

 

[bpm990d]

If you check it, you really only need the No Go gauge. You can use a cartridge as a Go gauge.

B

 

[MassMark]

According to an armorer in Iraq, using new components, you should be fine. Still he errs on the side of caution, (in case parts are out of spec) and uses a field gauge he bought from Bushmaster for $30.00.