AR-10 build... .308 vs 6.5CM gas system

[Charlie98]

I just came off building a .308 AR-10 with a mid-length gas system... it works well enough but I think it's overgassed.

Question: I'm fixing to build an AR-10 in 6.5CM, this rifle will have a full-length gas system. Will a standard gas block work alright with a standard BCG and buffer, or is an adjustable gas block a better choice?

 

[troy fairweather]

It's always a good idea to have a adjustable gas block, there not much more money either

 

[Blue68f100]

When I got into building my AR-10 (6.5 CM, 24" heavy barrel, min spec chamber) I found out there was 2 different gas/port used depending on mfg build. One uses larger ports than the other. What I ended up doing was going a heavy buffer and adj gas block. I've since gone to a silent capture setup with H3 weighted buffer. Still use the adj gas block.

 

[Charlie98]

I found out there was 2 different gas/port used depending on mfg build.

Are you talking the barrel port?

 

[Blue68f100]

Yes, Since there is no Mil spec on the AR-10. There are 2 different setups, which use different bolts and barrel extension nut. One is not very common but it's out there.

 

[Charlie98]

Yes, Since there is no Mil spec on the AR-10. There are 2 different setups, which use different bolts and barrel extension nut. One is not very common but it's out there.

Like the last one, this one will be Aero Precision... so DPMS. I'm also using the standard M5, not the enhanced... the barrel mount up is simpler, and easier to lap.

 

[mpofficer31a]

I always use an adjustable gas block on large frame ARs. There are so many potential variables between the bolt weight, barrel gas port diameter and the specific round (a 243 has a completely different gas functionality than 358, even with basically the same brass). I have built a few 6.5 CMs and I think an adjustable gas block is worth the expense for that round too. I really like the SA gas blocks, but they're always on back order.
https://suparms.com/collections/adjustable-gas-blocks-direct-impingement

Just about any quality adjustable gas block will work. They're worth the few extra $$, especially when you consider how much they can affect things on a rifle that costs about 10x more than gas block itself.