Ar10 308, change to 6.5CM or 243 win, just swap upper or?

[ilikegunspdx]

What do I need to do if I have an ar10 308 complete lower and mags to change to 243 or 6.5CM? Is just swapping a complete upper enough?

With this ghost gun crap law potentially serializing uppers I may be ordering a shot load of them. If it's as easy as swapping out uppers I may add these 2 calibers.

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[kopcicle]

Well, there are a few other things potentially on the list.
You may want to investigate an adjustable gas block.
You will be juggling buffer and spring in any case.
I found that for little or no reason some .308 derivatives work in some magazines and not others. I mean the case body is the same but occasionally it gets unexplainable weird. This doesn't happen all the time or even often but be aware.

I'll see your 6.5Cm + .243 and raise you a .277-08

 

[Xaevian]

Ar10 lowers are not all the same. There are different patterns. That being said, .243 and 6.5CM share the same parent case as .308, along with several others. With a matching pattern upper to your lower, should be the same.

 

[kopcicle]

True, AR-10 as in Knights et al are different.
LR308 and the DPMS like patterns are mostly compatible, but...

There are so many different patterns that it defies standardization of any kind.

There's just enough difference between the DPMS, Colfax, and Anchor Harvy that I've used that I think I'll be making separate tooling plates, code, layout, and compatibility for each. And that's just the tip of the turd.

 

[ilikegunspdx]

Interesting about the lowers. It's regular aero M5 lower.

Just thinking about getting some inexpensive complete uppers for giggles if they are going to pass the law. Not excited by the ar15 options other than 300BO (ordered already) and 22 mag seems too expensive for direct blowback and proprietary mags.

 

[msgriff]

I would not mix manufacturers of uppers and lowers, regardless if they are of the same pattern. There are some exceptions that will work.
You generally don't want to share BCG/bolts between barrels. The smaller calibers are more prone to pressure signs/issues compared to the 30 cals and up. The 6.5 CM and smaller do better with actual high pressure bolts.
Get the longest gas system you can for the particular barrel length. Port pressure is higher than the same gas system length/barrel length of a larger caliber.

 

[kopcicle]

22 mag like the 17's is just too much more expensive for what?
A kind of jacketed +p 22LR with all the disadvantages and unreliability of a magazine fed of the 22LR. I just don't see it .

On the other hand, a dedicated single shot or bolt action in 22 mag has a place.
Even better a Ruger single six to pair with it.

Semi auto in 22 mag? not so much.

 

[ilikegunspdx]

22 mag like the 17's is just too much more expensive for what?
A kind of jacketed +p 22LR with all the disadvantages and unreliability of a magazine fed of the 22LR. I just don't see it .

On the other hand, a dedicated single shot or bolt action in 22 mag has a place.
Even better a Ruger single six to pair with it.

Semi auto in 22 mag? not so much.

Yea novelty factor is about it. Extended range if someone was shooting squirrels with a 22 maybe. If it was half the price then would be ok for novelty but a 22 mag complete upper costs a bit more than the 243 or 6.5 upper. I don't see it especially for simple blowback. 243 I like the round and already have 6.5 CM ammo. I think the uppers I saw for 243 was 24" and 6.5 CM was 20" or maybe 22" I don't recall.

 

[kopcicle]

@ilikegunspdx
This should be of some help.

AR-10 308 AR Compatibility Reference Guide | AR 308 vs AR 10

Compatibility Reference Guide - Understand and research the parts interchangeability and differences between the AR-10, AR-15, 308 AR and AR 308 rifles

308ar.com

 

[ilikegunspdx]

@ilikegunspdx
This should be of some help.

AR-10 308 AR Compatibility Reference Guide | AR 308 vs AR 10

Compatibility Reference Guide - Understand and research the parts interchangeability and differences between the AR-10, AR-15, 308 AR and AR 308 rifles

308ar.com

Thx! Interesting that POF is roller delayed bolt. I was always wondering why people said POF revolution was the lightest recoiling 308 they ever shot. I didn't know it had roller delay. Roller delay by itself doesn't guarantee much though, look at hk91 and clones, most people sell them after a while due to uncomfortable to shoot. I sure like roller delay in 9mm though. Nothing like it really that I have run into anyway as far as shooting experience for 9mm subguns.

 

[RyanG90]

.

 

[kopcicle]

My roller delay experience encompasses HK91, PTR, G3, CETME, and minor clones.
I have to add the original STG57 Swiss in 7.5mm in a whole separate vein because they got it right.

Back to the HK pattern. As designed and developed by HK roller delay works with two very important caveats. The geometry, metallurgy, and receiver support can not be compromised.

Enter the button counters, bean counters, manufacturing efficiency droids, and quarter by quarter investment capitol expectations and what you get is metallurgical failure waiting to happen.

The failure mechanism is as simple as it is complex. The rollers bust out of their normal operating positions and bulge the receiver. The reasons however are complex and worth a deep dive if you wish. I'll pass because I lived this and frankly It wore me out.

The STG57? Not so much. I'll leave it right there.

MP5 roller delay? Well known and just works.

This has zip, nada to do with a .308 change to 6.5 but someone delved into the veritable cesspool of my experience and touched on the question.

done

 

[ilikegunspdx]

My roller delay experience encompasses HK91, PTR, G3, CETME, and minor clones.
I have to add the original STG57 Swiss in 7.5mm in a whole separate vein because they got it right.

Back to the HK pattern. As designed and developed by HK roller delay works with two very important caveats. The geometry, metallurgy, and receiver support can not be compromised.

Enter the button counters, bean counters, manufacturing efficiency droids, and quarter by quarter investment capitol expectations and what you get is metallurgical failure waiting to happen.

The failure mechanism is as simple as it is complex. The rollers bust out of their normal operating positions and bulge the receiver. The reasons however are complex and worth a deep dive if you wish. I'll pass because I lived this and frankly It wore me out.

The STG57? Not so much. I'll leave it right there.

MP5 roller delay? Well known and just works.

This has zip, nada to do with a .308 change to 6.5 but someone delved into the veritable cesspool of my experience and touched on the question.

done

That stg 57 sounds interesting. Have never regretted anything I've ever bought that was Swiss made. Hell even my dog poop shovel is 1939 Swiss surplus! I assume those stg57's can't be found in usa except parts kits or whatever? Love that cartridge.

Was going to buy the ptr 12.5" 308 (can't recall name 51 maybe?) but they stopped making it a little before I wanted to order one and literally could not find a single one for sale anywhere. Didn't/don't want the 8" one. So I went with ar10 sbr instead.