6.5 and .308 buildouts

[Amac305]

I am in search of some confirmation bias for some builds in working on. In order to combat the general issue many folks have with large-frame build spec inconsistencies (especially when slapped together with parts lying around), I have a few questions that have come up in my research on here.

I have the following goals:

1. To make use of all the 6.5CM and 308 ammo I have lying around, I want to build out a 6.5 Manbun and .308 setup.
2. I’d like to make the most use of parts I currently have in my safe.
3. Buy parts that will allow me to operate these two calibers by utilizing the same lower and swapping out the upper receiver.

To that end, I plan on using only proof CF barrels (already have them in 6.5 and .308). Intended use is hunting (90%) and 800-1000 yd shooting (10%), both with NODs/Thermal when the coyotes get bad. When hunting, max range I would go would be 250 yds, so I don’t need same hole accuracy, but sub MoA would be ideal.

I also have a JP large frame BCG with a .308 bolt.

I currently have a GGP billet upper receiver and handguard lying around.

I am thinking I can purchase another GGP billet upper and lower receiever, and if the tolerance and spec gods are kind to me, said lower receiver set can serve as the common lower receiver for both the 6.5 and .308 upper.

To get around the headspace issue, since I would be using proof CF AR prefits and a JP BCG, I would just need to move the bolt and lower receiver from platform to platform when I want to go from real man (.308) to hipster (manbun).

Am I missing something here with this approach? Should I just stop being a cheap bastard and pay for two lowers? Before you chime in to say I’m trying to do something the platform was not designed to do, understand the goal here is to make use of the parts I have at my disposal while keeping capex at a minimum.

 

[sparky702]

It will never work .Any time I have tried to have one lower to share with two uppers results in a second lower .

 

[wade2big]

It will never work .Any time I have tried to have one lower to share with two uppers results in a second lower .

The man is using the same brand upper and lower. They will swap.

 

[wade2big]

Reading forums makes it seem like putting together one of these things is rocket surgery. It's not.

1. Use the same brand upper and lower.
2. Make sure the bolt headspaces (I haven't found a barrel that doesn't headspace to a toolcraft BCG).
3. Make sure the handguard is compatable with upper (DPMS low or high pattern, or proprietery like in the Seekins and Aero M5E1).
4. Rifle length extension, buffer, and spring is the easy button, but a Armalite/Vltor RE-A5 receiver extension, rifle spring, and H3 carbine buffer works well.
5. Also be mindful that a rifle length gas in a .308 can be slightly longer requiring a longer gas tube than a regular rifle length tube that would run on a 556. Fulton Armory is a good source for the longer tube. Check with the barrel manufaturer if you don't know. Faxon requires the longer tube for sure.
6. An adjustable gas block is almost required. Mandatory if a can is going on the end. Might as well figure on using one from the start or at least some other gas restricting method. I only have experience with the gas blocks.

There it is. All you need to know or at least close to it.

 

[Amac305]

@wade2big - thanks for this great info. Should have mentioned- I have two adjustable gas blocks, not the same make and model but figured this didn’t matter much as long as it fits in the handguard.

 

[Nbleak21]

The man is using the same brand upper and lower. They will swap.

Sorry @wade2big my experiences mirror @sparky702 .

OP just needs to bite the bullet and build a second lower.

One receiver just never works out. Murphy’s law is at play here abs Lots WILL go wrong:
1. The Gun case just doesn’t look right
2. The solo upper never stands properly in the safe
3. You bring all the 308 ammo to the range but forgot you’ve still got the 6.5 upper strapped to the receiver and didn’t bring the other upper to lighten your load
4. Most importantly, 2 guns are better than one.

/thread.

 

[wade2big]

Sorry @wade2big my experiences mirror @sparky702 .

OP just needs to bite the bullet and build a second lower.

One receiver just never works out. Murphy’s law is at play here abs Lots WILL go wrong:
1. The Gun case just doesn’t look right
2. The solo upper never stands properly in the safe
3. You bring all the 308 ammo to the range but forgot you’ve still got the 6.5 upper strapped to the receiver and didn’t bring the other upper to lighten your load
4. Most importantly, 2 guns are better than one.

/thread.

I missed @sparky702 sarcasm. Went right over my head.
For the record, I have an equal upper to lower ratio as well.

 

[Amac305]

1-2 are about looks only and #3 can easily be solved by the barrel difference (.308 is 16”, 6.5 is 22”). #4 I can’t argue with,

 

[Amac305]

Alternative is that I just sell the proof manbun barrel since it’s new. But I have a bunch of niiice 6.5 Nosler hunting rounds that really don’t deserve to be shot at paper.

 

[rpoL98]

OP should bite the bullet and buy a second (HP) BCG for your manbun upper. they're cheap enough. after a while, a bolt gets mated to the barrel extension, barrel.

 

[Nbleak21]

Alternative is that I just sell the proof manbun barrel since it’s new. But I have a bunch of niiice 6.5 Nosler hunting rounds that really don’t deserve to be shot at paper.

Don’t let the manbuns fool ya… 6.5CM is a good (great) round. I would not advise leaning towards whatever the blasphemous proposal this quote is suggesting.

Build ‘em both. If I had to pick ONLY one rifle caliber and SHTF ammo considerations wasn’t a concern, my pick would be 6.5CM, not .308

You’ll be thankful you did once you start to stretch to 1000.

 

[sparky702]

I missed @sparky702 sarcasm. Went right over my head.
For the record, I have an equal upper to lower ratio as well.

Sorry I forgot to mention I am a sarcastic bastard .

 

[bigjake83]

Da fuck is a ManBun?

 

[rpoL98]

Da fuck is a ManBun?

 

[bigjake83]

Looks like a prerequisite to join AR15.com

 

[Amac305]

I’ve always been one to go all in on something, I’m guessing I should start buying some expensive flannels and Stock my freezers with some beyond meat

 

[rpoL98]

OP should bite the bullet and buy a second (HP) BCG for your manbun upper. they're cheap enough. after a while, a bolt gets mated to the barrel extension, barrel.

... especially if you're the type to go all-in.

 

[FaithlessSaint]

My only advice would be to have 2 bcg's. My 6.5 is a double ejector. My 308 is a single...