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Newbie looking for advise on .308 build


Former 11H
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If this isn’t the right way to ask others for advise, please tell me. I’m happy to follow your protocol. 
I’m in the process of gathering parts for this AR .308 build and would like help in choosing and sourcing a few components. 
One of the reasons for this build is that I had major shoulder surgery in December, right side of course, and I would prefer an AR platform to replace my bolt action 308 deer rifle and hopefully have less felt recoil. I also want one with more oomph and a straighter trajectory than my 300 blk. 
I am starting with a stripped lower from 80% arms, a stripped M5 upper from Aero Precision, 16” barrel, BCG, low profile adjustable gas block .750, melonite gas tube, and upper parts kit, extended mag release button, all from Aero Precision. Lower parts kit and fire control group from 80% Arms. I’m waiting for the jig from 5D Tactical, and if that doesn’t come before the changes in definitions by that three letter agency, I’ll buy a serialized lower from AP. 

My first question is, can I run both super and subsonic ammo and sometimes put my Sig TI 7.62 QD can on it, and have it run reliably?
Second question, do need an adjustable buffer assembly? I know nothing about spring tensions and buffer weights, lengths etc.
Third question, has anyone used vented charging handles for running suppressed? Are they a gimmick or is it worthwhile getting one?

I haven’t ordered a barrel shroud yet. The one I want is back ordered at AP. Nor have I chosen a stock, although I’d like a collapsible one with an adjustable cheek pad. 
I started this with the intention of getting just enough components to make sure I could build this once the changes have gone into effect.  I figured, over time I’d buy more parts as I could afford them, but I’ve gotten carried away, as you do, with any new exciting project. 
Thanks for any help you guys can give me, and again, I really hope this is the right way to ask for help. 
 

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Perfect way to ask for help - you nailed it.  :thumbup:

What caliber?  You never mentioned it, besides talking about the 300BLK.  Many calibers in the Large Frame .308AR, we've done most of them, here. 

I ask that question because you directly asked about supersonic and subsonic ammo.  In the large-frame, many times, there's not many options for subsonic ammo.

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8 hours ago, Former 11H said:

Are they a gimmick or is it worthwhile getting one?

The only time I have ever had an issue with gas in my eyes to the point I couldn't see clearly for a bit was shooting full auto in the service. I guess if you plan on lots of rapid fire strings with the rifle it might be worth a special charging handle but I worry more about the ergonomics of the latch than the little gas that comes back. You can use rtv silicone to create a seal around the CH. Here is the instructions...... on Reddit , videos of the process on gootube as well.

 

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Thanks guys for the quick replies. 
This build will be a .308 What better place to seek advise than forum.308!
i do not expect to be doing rapid fire but was thinking more about a rapid follow up shot and having that wisp of smoke curling up towards my face and scope. I haven’t actually fired my 300blk suppressed since last summer, so I may be over thinking the charging handle bit. A dab of high temp RTV in the crescent seems like a great and simple solution. I have seen subsonic in .308 online. I’m not sure why I’m concerned about switching between super and sub, suppressed and unsuppressed. My 300 blk doesn’t care one bit and cycles fine. Still, I’d like to know if anyone has had issues in the tuning stage and what they did. 
That answered my third question. Two more to go. 
Thanks again

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11 hours ago, Former 11H said:

can I run both super and subsonic ammo and sometimes put my Sig TI 7.62 QD can on it, and have it run reliably?

I have a SDN-6 and have not been able to find one set-up to run both reliably in a 308AR, I've read many that have but I haven't. It always involves making a change in the recoil system for the load. I quit chasing the function thing, I have used a pile of 308 sub ammo trying different things but just can't see what advantage it has over my 300BO, same pill, same speed.

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11 hours ago, Former 11H said:

do need an adjustable buffer assembly?

No, this Armalite recoil system is bulletproof, if you want to rule out spring and buffer weight issues it is the kit to use. You can get the same combination a few different ways, some searching here will show you what others did to get there but this kit is the short answer. I recommend you do lots of reading on the subject here before buying.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201

You might find the kit with other vendors, many have luck when they call Armalite and express the need they have. 

But if you plan on doing a number of builds and want to tune the rifle to the load specifically then adjustable buffer wouldn't hurt a thing.

Edited by jtallen83
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We'll get @Matt.Cross in here - we shot his .308 Win AR last fall suppressed, with subsonic ammo, and it was amazing!  Prior to playing with the subsonic ammo, we've shot it suppressed with match ammo for years and years.  His gun handled it fine.  Those subs were wild to shoot - hollywood-guiet.

Edited by 98Z5V
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On 6/11/2022 at 11:10 AM, Former 11H said:

All good advise. I’d love to hear from Matt Cross too. Thanks

Happy to chime in, been watching the thread with great interest. I think the only (possibly a non-issue, as long as you're aware of it) issue you might not have expected is that in a DI system you can expect the semi-auto function to be forfeit with subsonic ammo. Blackout is amazing in that the gas systems are built from the ground up to cycle subsonic ammunition, and the supersonic excels by virtue of always having an excess in terms of what's necessary to operate the system.

Large ARs on the other hand, are designed and built around functionality for supersonic ammunition of varying weights and applications. This makes a transition to subsonic get really interesting, because none of the current factory gas systems are designed with cycling subsonic ammo in mind. This is true of specifications such as gas system length, gas port size, and system inertia metrics like spring strength, spring length, buffer weight, BCG mass, etc. All this becomes much more feasible in a piston system such as what you'd find in LWRC, POF, and GA Precision's large AR systems, but those are off-the-shelf spec systems not intended to be purpose modified, and generally prohibitively expensive in terms of experimenting towards success.

All that said, if you can live with, or build towards the expectation of setting up a system to utilize both super and subsonic with no substantive change to the system, you can do so quite happily with the understanding that subsonic rounds will almost certainly need to be manually cycled. I'll discuss some potential exceptions in a minute.

My rig is a Mega Arms MA-TEN matched set with the monolithic upper, an 18.5" mid-weight profile Titan barrel from Fulton Armory, rifle-length gas system with a .093" gas port and .936" gas block journal, and SLR Sentry adjustable gas block. An Ops Inc .30 cal 12th model suppressor/brake combo completes the muzzle package. I shoot primarily Federal Gold Medal Match 175gr through it, and when suppressed the muzzle report with supersonic ammo is fairly well on par with .22LR from a standard sporting length rifle. Many here on the forum have both shot this rifle and heard it fired and can attest to the accuracy of that description (or inaccuracy if they wish). I've also in recent times had the pleasure of running Ruag (Swiss) 200gr subsonic rounds through it, as well as varying brands of 175gr SMK subsonic, in which case as has already been stated by @98Z5V it's literally "hollywood quiet". The only caveat with subsonic is that it has to be hand-cycled, but very well worth the trade-off for me.

I'll wrap up with my thoughts on what would give you your best chances of successfully cycling subsonic in a large AR: 

#1. A standard length barrel with a short gas system. The idea here is to get as much gas into the system as possible before the bullet exits the muzzle.

#2. The largest possible gas port, I think .125" is as large as a gas block will permit.

#3. As little weight/spring pressure as possible in the reciprocating mass of recoil system and BCG. It's gonna suck for supersonic, but that's the price of cycling subsonic.

 

There ya have it, my thoughts on the matter! Welcome to the forum, and looking forward to learning from what your build ends up teaching us all!

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Wow. Thank you for that very thorough explanation. 
It seems as though I have a choice to make between hoping to get it to cycle on subsonic combined with hard recoil on supersonic, or accepting manual cycling on subsonic and reasonable recoil on super. 
That’s an easy choice for me to make. My first priority is to reduce felt recoil as much as possible due to recent major shoulder surgery that will only bring it’s functionality back to 80% of what it once was, when finally healed this Fall. I have to prevent further damage to it. This build will take the place of my bolt action.308 deer rifle. There really are people that need an AR for hunting. 🙂
Another reason for taking this route is that I have already bought pretty much everything but the buffer assembly, as far as functionality is concerned. I’d hate to have to shelve most of that and start this expensive endeavor from the drawing board. 
So, with all of that in mind, how would you recommend I reduce the felt recoil as much as possible without sacrificing reliability  when shooting supersonic? This rifle will also be on hand for defensive purposes. What would you suggest for the buffer kit?
Thanks again, Jeff

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37 minutes ago, Former 11H said:

My first priority is to reduce felt recoil as much as possible due to recent major shoulder surgery that will only bring it’s functionality back to 80% of what it once was, when finally healed this Fall. I have to prevent further damage to it. This build will take the place of my bolt action.308 deer rifle. There really are people that need an AR for hunting. 🙂
Another reason for taking this route is that I have already bought pretty much everything but the buffer assembly, as far as functionality is concerned. I’d hate to have to shelve most of that and start this expensive endeavor from the drawing board. 
So, with all of that in mind, how would you recommend I reduce the felt recoil as much as possible without sacrificing reliability  when shooting supersonic?

I can stop this whole thing right here, and tell you "it's buffer WEIGHT" that will do what you want it to do.  There's only one buffer that will do it, too. Click the link below.  We work backwards from that part, right there.

Buy the 10oz Rifle buffer that's the first thing on this page:

https://heavybuffers.com/ar10rifle.html

This one:

XH%20Rifle%20Buffer.gif

 

Reduces felt recoil and makes the gun operate more smoothly. Many customers use this buffer in .308 ARs to make shooting more comfortable for their spouses and youngsters. Great for use with suppressed weapons. Also popular with those shooting magnum calibers.

I strongly recommend this buffer if any of the following conditions apply:

  • If you will be shooting with a suppressor. (Your gun will still run fine unsuppressed with standard ammunition.)
  • If you will be shooting hot handloads or very heavy bullets.
  • If you want maximum recoil reduction.

 

I recommend using AR10 rifle buffer springs (#EA1095) with these buffers. OEM springs from other manufacturers or aftermarket springs may cause malfunctions. 'Flat-Wire' springs are not recommended.

Edited by 98Z5V
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@Former 11H, read this longass post - it will explain alot.  This the the "why and because" for alot of problems with .308ARs.  This was years in experimentation, and development, across multiple calibers, on the large-frame AR platform.

 

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On 6/12/2022 at 12:29 AM, Former 11H said:

What would you suggest for the buffer kit?

I would echo what @98Z5Vsuggested in this post, as it's what resides in my MA-TEN and is exceptional:

On 6/12/2022 at 1:07 AM, 98Z5V said:

Buy the 10oz Rifle buffer that's the first thing on this page:

https://heavybuffers.com/ar10rifle.html

This one:

XH%20Rifle%20Buffer.gif

 

Reduces felt recoil and makes the gun operate more smoothly. Many customers use this buffer in .308 ARs to make shooting more comfortable for their spouses and youngsters. Great for use with suppressed weapons. Also popular with those shooting magnum calibers.

I strongly recommend this buffer if any of the following conditions apply:

  • If you will be shooting with a suppressor. (Your gun will still run fine unsuppressed with standard ammunition.)
  • If you will be shooting hot handloads or very heavy bullets.
  • If you want maximum recoil reduction.

 

I recommend using AR10 rifle buffer springs (#EA1095) with these buffers. OEM springs from other manufacturers or aftermarket springs may cause malfunctions. 'Flat-Wire' springs are not recommended.

 

To this I will add the following: Don't bother with "hydraulic buffers" either, while they advertise softer recoil and reduced reciprocation, they are in fact nothing more than an expensive malfunction guarantee.

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Hi Admin, I don’t see the last posting I made. Is it possible to type something and after submitting reply, have it go poof, into thin air? Or perhaps I lost it before hitting submit, or maybe I just completely forgot to hit submit reply. 😞

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On 6/12/2022 at 4:13 PM, Former 11H said:

Hi Admin, I don’t see the last posting I made. Is it possible to type something and after submitting reply, have it go poof, into thin air? Or perhaps I lost it before hitting submit, or maybe I just completely forgot to hit submit reply. 😞

All of the above is possible if not probable. Think of it as a 2nd chance to be even more eloquent and long winded..... :laffs:

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Ok, I’m back. I think this will be an abbreviated version of what was lost. I can always post more later. 
I will order the recommended buffer and spring. Money is getting tight. I’ve already dropped $1,350 into this and expect to spend another  $650 just to get the buffer system, furniture, and the Sig QD taper-look muzzle brake on it. That includes the small router and mag well vise block. I have a big router but it’s not compatible with the lower milling jig. What’s one more tool, right?
On Aero Precision’s website, I only found one gas tube that fits the M5 upper in .308 that is rifle length. It states the buffer length is 6”.  Can I use a shorter one or is that the one to go with?

The 16” barrel has a gas port of .0730” Can you advise on how to adjust the gas block?
Thanks guys, I’m getting there. 

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I'll ad to what @98Z5V and @Matt.Cross are saying about buffers. Slash's "Heavy Buffers" are all I run in all of my AR-10's. From my 12" SBR, to the 20" SASS. All of mine are setup to be able to be run suppressed. And they run flawlessly with these buffers. Many of these guys have run multiple mags through them.

Even the two a$$holes noted above. (said with love of course) :laffs:

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On 6/12/2022 at 4:26 PM, 98Z5V said:

It can happen.  It usually waits until you have a really good, long, detailed post ready to go - and the forum eats it...   :lmao:

Most forum software has a timeout for posting.

Tip for all:  If you think you are going to be typing out a long post, it can be helpful to type it in your word processor first, then copy and paste it into the forum when you are ready.

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That’s so cool. I haven’t seen or thought of speed racer since I was a kid!
Glad to hear more positive feedback on the heavy buffer. I will definitely go with that. Does it require the 6” tube?
Does anyone have advise as to gas block initial setting?
Thanks

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1 minute ago, Former 11H said:

Does it require the 6” tube?

Rifle receiver extension.  This recoil system that you need will be a fixed stock - this will not be a carbine, collapsible stock setup.

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2 minutes ago, Former 11H said:

Does anyone have advise as to gas block initial setting?

All adjustable gas blocks should be started WIDE OPEN.  All the way.  That's the only way you'll ever know if the gas port in your barrel is big enough, without wasting a ton of ammo as an expensive experiment - before you find that out.

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Posted (edited)

All upper components are from Aero Precision. Gas port in barrel is 0.0730”As far as the tube and stock, receiver extension  will be Aero Precision 6” rifle, and Magpul PRS or PRS Lite. 

Edited by Former 11H
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2 hours ago, Former 11H said:

All upper components are from Aero Precision. Gas port in barrel is 0.0730”As far as the tube and stock, receiver extension  will be Aero Precision 6” rifle, and Magpul PRS or PRS Lite. 

16" is gonna be midlength gas for the Aero/Ballistic Advantage barrel.  18" midlength gas needs a gas port that's 0.085" or damn close, and the 16" has a little less dwell time over that 18".  I'm gonna go out on a limb here and state that your gas port is going to be too small, and will need drilled.  Try it first and report back, but it'll need to go up.

FWIW, there is no 6" receiver extension, or buffer, for a .308AR, so a link to what you're getting might help.  Internal depth of a rifle receiver extension is 9 11/16".  If we can see it, we'll know better what to suggest.

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