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Large frame question

jLorenzo

jLorenzo

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Feb 20, 2017
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If one was to build a .308 AR10 would a barrel change be all that was needed to move to 6.5 Creed? Bolts, buffers, etc all interchangeable? Assuming you might need to do a little fine tuning but over all they are compatitable? What other considerations should be made, for instance if one wanted to build a 6.5 upper and a 308 upper to use on the same lower?
 
jLorenzo said:
If one was to build a .308 AR10 would a barrel change be all that was needed to move to 6.5 Creed? Bolts, buffers, etc all interchangeable? Assuming you might need to do a little fine tuning but over all they are compatitable? What other considerations should be made, for instance if one wanted to build a 6.5 upper and a 308 upper to use on the same lower?
Click to expand...
The only thing you might need besides the 6.5 Creedmoor barrel is maybe a gas block. Everything else is good to go since the Creed's parent case is .308.
 
jLorenzo said:
If one was to build a .308 AR10 would a barrel change be all that was needed to move to 6.5 Creed? Bolts, buffers, etc all interchangeable? Assuming you might need to do a little fine tuning but over all they are compatitable? What other considerations should be made, for instance if one wanted to build a 6.5 upper and a 308 upper to use on the same lower?
Click to expand...
You’ll want to make sure you have a high pressure bolt. They generally have smaller diameter firing pin holes. But, that high pressure bolt can be used with 308/7.62x51.

Other than that, yes, all interchangeable. 6.5 CM does usually have more stable gas requirements across loads than 308/7.62, which vary widely due to the two different specs.
 
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The gas system is a, system that includes the buffer and buffer spring. It is possible- depending upon the configuration of the barrels- that the spring/buffer that is optimal for one is less than optimal for the other. You can likely find a happy medium with adjustable gas blocks/carriers.
 
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Grim's Reapers said:
The only thing you might need besides the 6.5 Creedmoor barrel is maybe a gas block. Everything else is good to go since the Creed's parent case is .308.
Click to expand...
Technically the parent case is the .30 Thompson Center. But, the point stands. Same rim diameter and nearly identical OALs. While 6.5 CM wasn’t created from a 308 case, it was created to be just a barrel change away from the 308.
 
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jLorenzo said:
If one was to build a .308 AR10 would a barrel change be all that was needed to move to 6.5 Creed? Bolts, buffers, etc all interchangeable? Assuming you might need to do a little fine tuning but over all they are compatitable? What other considerations should be made, for instance if one wanted to build a 6.5 upper and a 308 upper to use on the same lower?
Click to expand...
I've done exactly that without any "problems" for me . Now, if one was going to shoot factory ammo only or was planning to run near max handloads,I'd suggest an adjustable gas block as others have,for some adjustability insurance for possible ejector swipes. High pressure bolt as mentioned,headspaced to your barrel also. An easy to do project.
 
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If you are going to use the same barrel length and gas system, for the most part your existing lower should be fine.
You might want a Adj. GB... a different barrels / chambers / throats can be funny sometimes. ( Not to mention powder burn rate differences )
So don't be surprised if some fine tuning helps.

EDIT to add... make sure you use the same "Pattern".

There are two dominant patterns, DPMS pattern and Armalite pattern... they have subtle differences that matter.
 
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Grim's Reapers said:
No Mercy
Click to expand...
Screenshot_20240326_104253_DuckDuckGo.jpg
 
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@wvfarrier Just an aside, I had Douglas Barrels up in your neck of the woods put a 1:8 twist 26" heavy barrel on my Weatherby Vanguard (Howa 1500) 7RM action.
Had it back in just over three weeks, trued, blued, the whole 9.
They don't blue barrels at the shop, one of their employees does it on the side at his house. Charged me 40 bucks it and came out immaculate.

That thing shoots ridiculous groups.

I'm just one little customer and I know they make a ton of barrels for companies who build custom rifles and such, but they treated me like gold and I didn't have to wait months to get my newly barreled action back.

I will never buy a barrel for any of my guns from anyone else as long as they're around. 10 stars, two thumbs up
 
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jLorenzo said:
If one was to build a .308 AR10 would a barrel change be all that was needed to move to 6.5 Creed? Bolts, buffers, etc all interchangeable? Assuming you might need to do a little fine tuning but over all they are compatitable? What other considerations should be made, for instance if one wanted to build a 6.5 upper and a 308 upper to use on the same lower?
Click to expand...
Mechanically for basic fit, yes.

Functionally, there are several things to adjust due to it being a different animal with the reduced bore volume, and increased port pressure.

Generally speaking, you want to have a known range of ammunition you’ll be shooting with 6.5CM to control your port pressure.

When you push the long, heavy 140-147gr class with slower-burning powder, it can really spike your port pressure and make the BCG try to unlock early, which will work the brass too hard at a minimum.

You don’t want a high cyclic rate, but 6.5CM is a recipe for it without some significant adjustments to the overall set-up with the gas system.

The main approach is to push the gas port forward at least 2”, then spring the gun to handle whatever load is being shot.

I like sticking to 130gr or lighter for this reason, but most factory ammo is in the 140-147gr weight class.
 
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LRRPF52 said:
Mechanically for basic fit, yes.

Functionally, there are several things to adjust due to it being a different animal with the reduced bore volume, and increased port pressure.

Generally speaking, you want to have a known range of ammunition you’ll be shooting with 6.5CM to control your port pressure.

When you push the long, heavy 140-147gr class with slower-burning powder, it can really spike your port pressure and make the BCG try to unlock early, which will work the brass too hard at a minimum.

You don’t want a high cyclic rate, but 6.5CM is a recipe for it without some significant adjustments to the overall set-up with the gas system.

The main approach is to push the gas port forward at least 2”, then spring the gun to handle whatever load is being shot.

I like sticking to 130gr or lighter for this reason, but most factory ammo is in the 140-147gr weight class.
Click to expand...
^^^^^ ^^^^ exactly ,my experience with factory loads (140-147) . My "no problems " comment in above post, seems to contradict the agreement with this post. It doesn't ,because I knew or was very confident that I could produce handloads that wouldn't cause the described issues quoted above. And I did by using 40.5 grains of H4350 with 140-142 bullets. FPS is slower than factory loads by a tad ,but groups tighter......I'm happy. No buffer /spring changes or adjustable gas block happened with this project ,just the ability to tweak the load and it runs fine . I'll be testing / loading 130s this year ,to bump fps up a tad and compare performance against the 140s.

Conclusion : heed the advice quoted and of others above ,it is sound. Headspaced bolt / barrel combo as mentioned also.
 
Uppers are pretty cheap. Why barrel change? Just build a 6.5CM upper and you can change in 20 sec. I have never changed a barrel on an AR. But I have several several uppers for different lowers.
 
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Fig said:
Uppers are pretty cheap. Why barrel change? Just build a 6.5CM upper and you can change in 20 sec. I have never changed a barrel on an AR. But I have several several uppers for different lowers.
Click to expand...
Throw in a handguard too and it adds up.

Rough numbers:

Let’s say the barrel is $300-400

Upper is $200-$300
Handguard is $200-$300

Total, you’re looking at $700-$1k now instead of $300-$400. You’ve more than doubled your spending. And let’s not fool ourselves, as soon as you get the new upper, you’re going to also be picking up a new BCG and charging handle.







LRRPF52 said:
…

When you push the long, heavy 140-147gr class with slower-burning powder, it can really spike your port pressure and make the BCG try to unlock early, which will work the brass too hard at a minimum.

…

The main approach is to push the gas port forward at least 2”, then spring the gun to handle whatever load is being shot.

…
Click to expand...

6.5 CM is rated for those higher pressures and why I recommend a high pressure bolt.

I don’t think the early unlock is too much of an issue with longer barrels. But is definitely something to consider with barrels trying to use mid-length gas systems for 6.5 CM. Though it seems like companies that made those have corrected their ways and gone to at least rifle length. But some still do, looking at you Ballistic Advantage with your mid-length 18” 6.5 CM and carbine-length 14.1”.
 
Top 5 list of things I don’t want to do before going to the range. No particular order.

1. Tax audit
2. Root canal
3. Colonoscopy
4. Disassemble an upper in order to instal a different barrel.
5. Ok, I could only come up with 4.

Honestly, even having multiple uppers for 1 lower doesn’t make that much sense to me. The lower is the least expensive part of the gun.
 
PappyM3 said:
I don’t think the early unlock is too much of an issue with longer barrels. But is definitely something to consider with barrels trying to use mid-length gas systems for 6.5 CM. Though it seems like companies that made those have corrected their ways and gone to at least rifle length. But some still do, looking at you Ballistic Advantage with your mid-length 18” 6.5 CM and carbine-length 14.1”.
Click to expand...
Dwell time matters.

ETA: the urgi testing showed increased reliability and less parts breakage with M4’s just by moving from carbine to midlength. The shorter the gas system, the higher the port pressure.
 
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LRRPF52 said:
Mechanically for basic fit, yes.

Functionally, there are several things to adjust due to it being a different animal with the reduced bore volume, and increased port pressure.

Generally speaking, you want to have a known range of ammunition you’ll be shooting with 6.5CM to control your port pressure.

When you push the long, heavy 140-147gr class with slower-burning powder, it can really spike your port pressure and make the BCG try to unlock early, which will work the brass too hard at a minimum.

You don’t want a high cyclic rate, but 6.5CM is a recipe for it without some significant adjustments to the overall set-up with the gas system.

The main approach is to push the gas port forward at least 2”, then spring the gun to handle whatever load is being shot.

I like sticking to 130gr or lighter for this reason, but most factory ammo is in the 140-147gr weight class.
Click to expand...
I was thinking shooting 120-130s mostly as well. Maybe try some 140s. I shoot 155s mainly with 308.
 
hlee said:
Top 5 list of things I don’t want to do before going to the range. No particular order.

1. Tax audit
2. Root canal
3. Colonoscopy
4. Disassemble an upper in order to instal a different barrel.
5. Ok, I could only come up with 4.

Honestly, even having multiple uppers for 1 lower doesn’t make that much sense to me. The lower is the least expensive part of the gun.
Click to expand...
Im not talking about taking the upper apart. I am talking about having 2 complete uppers that can be swapped onto the same lower. Couldn't be any easier.
 
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Fig said:
You’re not wrong, but I have three uppers for every one lower. Who has one AR15 or AR10? Those things multiply in the safe like rabbits.
Click to expand...
It’s the warm and dark environment. I really can’t blame them. Puts me in the mood too.
 
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jLorenzo said:
If one was to build a .308 AR10 would a barrel change be all that was needed to move to 6.5 Creed? Bolts, buffers, etc all interchangeable? Assuming you might need to do a little fine tuning but over all they are compatitable? What other considerations should be made, for instance if one wanted to build a 6.5 upper and a 308 upper to use on the same lower?
Click to expand...
For the most part, its just a barrel, but with all builds, stuff may not play well together as this is not a large scale "milspec" that manufactures use as a template. Some bolts work better than others based on firing pin hole size.
 
I have LMT MWS guns and my spare barrels have turned into guns. I will admit it was when spare parts were more plentiful but dont trust yourself. Just buy another upper if you wanna save a few bucks.

PB
 
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