BCG in new build

[pnutty]

I am building on a aero m5 receiver kit with a BA 6.5cm barrel, a local gun shop is selling DPMS 308 bcg for a good price. Is it required to have the “high pressure” dual ejector bolt with smaller firing pin for the 6.5cm round or would I be ok with the 308 bcg?

[98Z5V]

Should be fine.  I run regular .308 Win BCGs in my .260 Rem gas guns, so similar pressures and identical projectile - both those regular BCGs do just fine.  

[pnutty]

13 hours ago, 98Z5V said:

Should be fine.  I run regular .308 Win BCGs in my .260 Rem gas guns, so similar pressures and identical projectile - both those regular BCGs do just fine.  

Perfect, thanks for all the help you’ve given me. With any luck the rest of the parts should be here by this weekend and I will do a range report. 
 

Just one other question, when installing the barrel nut on ar15’s I always clamped the barrel in a barrel vice and tightened the nut that way. With the larger 308 platform, would it be better to sandwich the top and bottom ends of the receiver in a vice and tighten the nut that way?

[98Z5V]

10 hours ago, pnutty said:

Just one other question, when installing the barrel nut on ar15’s I always clamped the barrel in a barrel vice and tightened the nut that way. With the larger 308 platform, would it be better to sandwich the top and bottom ends of the receiver in a vice and tighten the nut that way?

Depends on the torque setting you're going for, but basically, Yes, you can do that. I would definitely pad them, even aluminum angle will work, no bare vise jaws.

When you're installing a barrel that way, the torque forces of clockwise rotation are working on the solid side of the upper receiver.   

You can't take a barrel off, in that manner - upper sandwiched in the vise jaws - because the counter-clockwise torque is acting on the weak side of the receiver - the bigass hole of the ejection port...  You'll crack the upper receiver.  Ask me how I know that tidbit of information...   

[pnutty]

21 minutes ago, 98Z5V said:

Depends on the torque setting you're going for, but basically, Yes, you can do that. I would definitely pad them, even aluminum angle will work, no bare vise jaws.

When you're installing a barrel that way, the torque forces of clockwise rotation are working on the solid side of the upper receiver.   

You can't take a barrel off, in that manner - upper sandwiched in the vise jaws - because the counter-clockwise torque is acting on the weak side of the receiver - the bigass hole of the ejection port...  You'll crack the upper receiver.  Ask me how I know that tidbit of information...   

That was an experience I bet, what is your suggested way of installing and removing barrels on these 308 uppers? 

[98Z5V]

1 hour ago, pnutty said:

That was an experience I bet, what is your suggested way of installing and removing barrels on these 308 uppers? 

Geissele Reaction Rod, all the way.  They make 2 of them, small-frame ARs and large-frame ARs.  Only way to go. 

There are others out there, copies, some good, some not.  When you start looking at the cost of a real Reaction Rod, factor in how many guns you think you're gonna build.  Cost-to-benefit ratio.  I make alot of guns for myself, and for friends, and I let my local Gun Pusher use my large-frame Reaction Rod - I go get it back from him when I need to assemble one of my own.  The cheapest I'd go would be the copy that Brownells makes.  Stay away from aluminum ones, unless it's a one-time build.

[pnutty]

13 hours ago, 98Z5V said:

Geissele Reaction Rod, all the way.  They make 2 of them, small-frame ARs and large-frame ARs.  Only way to go. 

There are others out there, copies, some good, some not.  When you start looking at the cost of a real Reaction Rod, factor in how many guns you think you're gonna build.  Cost-to-benefit ratio.  I make alot of guns for myself, and for friends, and I let my local Gun Pusher use my large-frame Reaction Rod - I go get it back from him when I need to assemble one of my own.  The cheapest I'd go would be the copy that Brownells makes.  Stay away from aluminum ones, unless it's a one-time build.

Good points on everything, the rods put the torquing stress on the steel barrel/extension instead of the aluminum upper receiver.

I do have to ask, have you ever had the index pin slot deform or get damaged using the action rod method? I read some stories about that happening but they were with the smaller platform and not the larger platform.

 

[98Z5V]

10 hours ago, pnutty said:

I do have to ask, have you ever had the index pin slot deform or get damaged using the action rod method? I read some stories about that happening but they were with the smaller platform and not the larger platform.

Never.  Never, ever.  Three reasons why.

1.  When you're putting a barrel nut on an upper receiver, you aren't putting any significant torque to the index pin. Muzzle devices?  Yes, kinda, but the barrel nut should have been locked down before you started messing with muzzle devices, in the first place.  

2.  Common misconception that the index pin actually pins the barrel extension to the barrel - it doesn't.  It's only in the barrel extension, and does NOT go through the extension, to pin the extension TO the barrel.  Just doesn't.  If it does, you have an improperly made barrel.

3. The barrel extension is torqued onto the threaded barrel at 175 lb/ft.  Not a typo.  If someone damaged the index pin into the slot into the upper receiver, either their barrel wasn't made correctly, or their torque wrench is a POS - they're going WAY too heavy...