AR10 - can 6.5CM and 308Win uppers use same lower (buffer/spring)?

[RABAZ]

built an AR10 last year, and have 2 uppers - 308win and 6.5CM. probably only have a hundred rounds or so through each upper. 308win upper cycles pretty reliably, but more trouble with jamming on the 6.5CM upper. question - am I trying to do something that won't work (i.e. - common lower for both uppers)? Does the cycling action of the two differ enough that i need different lowers for each? Kind of a newbie, so don't know what i don't know. thanks for any help.

 

[cohunt]

As long as they are the same "pattern" you can swap lowers. Might need to adjust the buffer or spring though depending on how they cycle

Most common 2 different styles are the "armalite/ar10" and "dpms/lr308/sr25"


Armalite has more of a diagonal mating area to it just in front of the buffer tube --- the dpms has more of a radius profile to it

Most likely your cycling issue lies in the gas system

 

[FreeNHim]

I know that you can use the same lower with multiple uppers on a Daniel Defense DDM5, because I do without an issue.

Do both uppers utilize the same BCG? You might need to change out the buffer if the mass is different, but that's beyond me. I've never built one.

 

[RABAZ]

I know that you can use the same lower with multiple uppers on a Daniel Defense DDM5, because I do without an issue.

Do both uppers utilize the same BCG? You might need to change out the buffer if the mass is different, but that's beyond me. I've never built one.

Nope - 2 sep BCGs purchased with and supposedly specific to the uppers

 

[FreeNHim]

In my limited knowledge, that could be your issue. If the mass is not the same for each BCG, then things may not time correct using the same buffer.

I know that there are those on this forum who are a lot more knowledgeable than me. Someone will help you.

 

[TeamCarnage]

Yes, you can use the same lower as long as you stay in the same pattern. Recommend you use adjustable gas blocks on both uppers, that way you can adjust the needed volume of gas to properly cycle the BCG's. Also, the only thing differing in the BCG is the bolt itself. If you are on a tight budget you could swap the bolts between BCGs That said a complete BCG with bolt is not that expensive and will save time in swapping over. I like to stick with one manufacturer when doing this to avoid compatibility issues.

 

[M1A1ABRAMS]

built an AR10 last year, and have 2 uppers - 308win and 6.5CM. probably only have a hundred rounds or so through each upper. 308win upper cycles pretty reliably, but more trouble with jamming on the 6.5CM upper. question - am I trying to do something that won't work (i.e. - common lower for both uppers)? Does the cycling action of the two differ enough that i need different lowers for each? Kind of a newbie, so don't know what i don't know. thanks for any help.

You may find this thread helpful. These guys can help you out. unfurl="true"]https://www.longrangehunting.com/threads/completed-ar10-builds-6-5-creedmoor.319421/post-2698859[/URL]

 

[Zen Archery]

Yup good to go.

 

[brcfo_outdoors]

When you say "jamming" could you be more specific? Also do you know what buffer weight your lower is using?

 

[RABAZ]

When you say "jamming" could you be more specific? Also do you know what buffer weight your lower is using?

with the 6.5CM: either failure to fully lock into battery, or failure to eject properly and getting jammed w subsequent round. Also, sometimes is prone to not locking back w an empty mag.

 

[RABAZ]

You may find this thread helpful. These guys can help you out. unfurl="true"]https://www.longrangehunting.com/threads/completed-ar10-builds-6-5-creedmoor.319421/post-2698859[/URL]

thanks, will ck it out!

 

[buckbrush]

What direction is fired brass being ejected?

 

[RABAZ]

What direction is fired brass being ejected?

hmmm - i think the 308 goes slightly backward, say, to 4 o'clock; while the 6.5CM goes forward at 2 o'clock, if barrell is 12 o'clock.

 

[brcfo_outdoors]

Based on your description of the jams and direction of brass, it sounds like your bolt is moving too fast when shooting 6.5. Since your buffer weight seems to be spot on for the .308 which would be a heavier recoiling gun, I would assume your 6.5 upper is over gassed. Does it have any kind of adjustable gas block?