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Aero Precision M5 Build Help! .308 Conv to 6.5CM

ChristianPratt22

Private
Minuteman
May 7, 2020
2
0
Gilbert AZ
Looking for some guidance on part selection and compatibility for my Aero M5 build! Current build is complete and functional, but I'm swapping calibers(barrel) from .308 to 6.5CM as I was gifted a new Wilson Combat Match Grade Super Sniper 20" Barrel. The gun will be suppressed in about a year.

Link to barrel: https://shopwilsoncombat.com/Match-...-Fluted-Threaded/productinfo/TR-65CSSRG20FT8/

Current parts:
M5E1 Enhanced 18" .308 Rifle Length Complete Upper Receiver (w/ VG6, Black Nitride BCG (BCG is MPI/HPT) & Charging Handle)
M5 .308 Complete Lower With Carbine Buffer Kit (Geissele SSA-E FCG)
Magpul Furniture

What I need: Gas block/tube that's compatible with the WC barrel and Aero hand guard. Muzzle Brake (preferably SilencerCo compatible) Anything else I need to add or change? Any help is appreciated, thank you!
 
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I highly recommend an adjustable gas block like a SLR Sentry and a JP High Pressure Enhanced bolt carrier.

Actually, you just need the bolt, not the whole bolt carrier. JP sells just the bolt.

Click on the “High Pressure Bolts” tab:

 
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I second the vote for SLR and JP. A more economical bcg is the brownells 308 nitride bcg. It's significantly less money than the JP. I have several of both and the Brownells version does the job (also small diameter firing pin like the JP), but it's not as sexy as the JP. ;)
 
Deffff going to want a high pressure aka small firing pin bolt and def going to want an agb (slr as mentioned above) for shooting suppressed.

And imo a +2 gas system for 6.5 Creed is usually my norm but if you already have the barrel try the above first and see how it does
 
I have built countless 6.5cm gassers. I moved away from Rifle gas years ago. Not because they arent accurate, cause they are, but because how much it beats the shit out of brass. You will want to do everything you can to adjust that gas and lock time with rifle gas to mitigate that bolt unlocking early and ripping up your brass.

Adjustable gas block, I prefer Superlative Arms or JP these days. I am a huge SLR fan but I have a pile on the bench that are all seezed up. I dont find this happening anymore with the first 2 mentioned. SLR has great customer service and will send you rebuild kits but Im done with all that. If your existing 308 barrel has rifle gas than that gas tube will work just fine. If it doesnt, buy a rifle length gas tube which you can most likely buy from the same place you buy your gas block. If not, get one off Brownells, Primary Arms, etc...

Next thing that has to go is your carbine buffer kit. You will want JP SCS Heavy with spring kit. I have played with these and tested every spring and tungsten combo and you will want one of the 2 heaviest springs and tungsten on that SCS.

Lastly, you can pick up a JP or Rubber City High Pressure bolt and firing pin and put it in your existing bolt carrier. Or you can buy a complete High Pressure BCG from either JP or RCA. Ive built countless with both and they are both top of the line when it comes to BCG's.

The fun part, tuning it all to run reliably without beating your brass to death. With rifle gas you will be able to tune it pretty damn good with the above mentioned parts but you are still gonna get some brass swiping. No way around that. With +2 gas and the above parts, I have my 6.5cm gassers tuned to where the brass looks like it was fired in a bolt gun. No brass damage, swipes, rims ripping off, etc.

Good luck
 
I gotta say... consider building a complete spare upper in around the 6.5CM barrel, rather then swapping parts.

And given your barrel, a Adj. GB is even recommended by Wilson Combat.

Nowadays, I get the biggest ID handguard I can for Adj. GB builds... Aero makes an M5E1 one that is 1.70+ ish ID... while that sounds huge, you will have zero issues with the adj. GB bonking the handguard ( and messing with consistent precision )
 
I gotta say... consider building a complete spare upper in around the 6.5CM barrel, rather then swapping parts.

And given your barrel, a Adj. GB is even recommended by Wilson Combat.

Nowadays, I get the biggest ID handguard I can for Adj. GB builds... Aero makes an M5E1 one that is 1.70+ ish ID... while that sounds huge, you will have zero issues with the adj. GB bonking the handguard ( and messing with consistent precision )

The handguard ID has always been an issue with large frame gassers and AGB. Ive bought and tried them all. JP and Odin Works both make a huge one to give plenty of clearance around AGB so you arent hitting it under recoil and causing flyers.

I recently tested some SLR 308 MLOK designs and they give plenty of clearance and dont hit under recoil. When you have a round handguard you need the 1.75" ID for the clearance. But this SLR is shaped to give plenty of clearance around my .936" SLA AGB. I LOVE this handguard. Its the SLR 16" ION Lite M-LOK .308 DPMS High handguard. Been running it for about a year now.

 
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I have built countless 6.5cm gassers. I moved away from Rifle gas years ago. Not because they arent accurate, cause they are, but because how much it beats the shit out of brass. You will want to do everything you can to adjust that gas and lock time with rifle gas to mitigate that bolt unlocking early and ripping up your brass.

Adjustable gas block, I prefer Superlative Arms or JP these days. I am a huge SLR fan but I have a pile on the bench that are all seezed up. I dont find this happening anymore with the first 2 mentioned. SLR has great customer service and will send you rebuild kits but Im done with all that. If your existing 308 barrel has rifle gas than that gas tube will work just fine. If it doesnt, buy a rifle length gas tube which you can most likely buy from the same place you buy your gas block. If not, get one off Brownells, Primary Arms, etc...

Next thing that has to go is your carbine buffer kit. You will want JP SCS Heavy with spring kit. I have played with these and tested every spring and tungsten combo and you will want one of the 2 heaviest springs and tungsten on that SCS.

Lastly, you can pick up a JP or Rubber City High Pressure bolt and firing pin and put it in your existing bolt carrier. Or you can buy a complete High Pressure BCG from either JP or RCA. Ive built countless with both and they are both top of the line when it comes to BCG's.

The fun part, tuning it all to run reliably without beating your brass to death. With rifle gas you will be able to tune it pretty damn good with the above mentioned parts but you are still gonna get some brass swiping. No way around that. With +2 gas and the above parts, I have my 6.5cm gassers tuned to where the brass looks like it was fired in a bolt gun. No brass damage, swipes, rims ripping off, etc.

Good luck

So are you running the original 3/1 tungsten SCS, or all tungsten and no stainless steel weights??
 
Don't 308 and 6.5Creeds share the same bolt? Why does he need a dedicated 6.5 bolt?

This is copied from the JP website and explains why it’s best to have a high pressure bolt. Of course, these will work with a 308 as well.


High Pressure EnhancedBolt™

  • Allows reliable AR functional with previously incompatible over-pressured loads such as 6.5mm or 6mm calibers
  • Virtually eliminates primer flow and pierced primers
  • Reduced firing pin mass improves lock time and ignition reliability with hard primers
  • Features same quality construction and advantages of other JP EnhancedBolts
  • Backwards compatible with standard .308 ejectors, extractors and gas rings
  • Lifetime bolt warranty

For anyone using .308/7.62 AR-type rifles, it is common knowledge that many factory rounds exhibit excessive primer flow and/or ejector smear. At its core, this is a result of ammo development being done by manufacturers only for manual platforms without testing in semi-auto platforms. Some rifle manuals even record the maximum recommended load data beyond the functional range of these rifles. Unfortunately, these issues will persist until the manufacturers of ammunition realize that an AR platform requires a unique pressure curve to allow for both accuracy and reliability.

Manufactured to the exacting standards of our standard bolt offerings, the High Pressure EnhancedBolt™ design represents a giant leap forward in alleviating the problems traceable to over-pressured loads—namely primer flow, ejector smear, extraction issues, and ignition reliability. In combating these problems, this new bolt design opens up a much broader range of ammunition compatibility and load density in the AR .308/7.62 and other variants such as 6.5mm or 6mm calibers in this platform.

The critical advancement of this bolt comes in the reduced diameter firing pin orifice that precisely accommodates the .062" tip of our proprietary low mass firing pin. This modified relationship virtually eliminates primer flow and the possibility of pierced primers on any SAAMI or NATO specification ammunition while the reduced mass of the firing pin also improves lock time and ignition reliability with hard primers due to the concentration of kinetic energy on a smaller impact area. This is especially advantageous with some aftermarket match-type fire control systems that may use reduced-power hammer springs.

Among its other enhancements, the .308HP bolt features an improved ejector pin hole and modified ejector to mitigate case head extrusion and frequent brass shavings. The JP Enhanced Extractor eliminates virtually all extractor-related failures while the JP Enhanced Gas Rings provide a more reliable, lower friction gas seal with longer lifespan.

While ultimately every end user needs to be aware of the ammunition limitations of their large-frame AR, the JP .308HP bolt offers multiple advancements to vastly increase the ammunition and operational abilities of the platform.
 
Don't 308 and 6.5Creeds share the same bolt? Why does he need a dedicated 6.5 bolt?

Exactly my thoughts, in the parts description of my post I listed my BCG but I'm not sure anyone paid close enough attention.
Here's the specs on my bolt

DESCRIPTION
Our .308 / 7.62 Bolt Carrier Group is the perfect firing mechanism for your big-bore rifle build. This high quality BCG features a Black Nitride finish, is MPI/HPT and now includes a laser engraved Aero Precision "A" logo!
Carrier Features:
  • Material: Billet carrier machined from 8620 steel and case hardened
  • Finish: Black Nitride - advanced lower friction coating that minimizes the need for lubricants and cleaning
  • Gas Key: 4130 Steel attached with Grade 8 hardware and properly staked
  • Firing Pin: Machined from 8740 steel and hard chrome coated
  • Forward Assist serrations
  • Laser engraved Aero Precision logo
  • Carrier fits AR .308 compatible style AR Uppers and Rifles
Bolt Features:
  • Material: Case Hardened 9310 Steel
  • Finish: All bolt components are shot peened and black nitride coated
  • Extractor: Machined from 4340 Steel with double o-rings and double springs
  • Magnetic Particle Inspected and High Pressure Tested
  • High pressure bolt - external surfaces are CNC ground after heat treat for a precision fit and firing pin hole diameter is reduced to .070"
  • Multi-caliber bolt designed to function with .308, 7.62x51, 6.5 Creedmoor, .338 Federal and other .308 based cartridges.
 
@ChristianPratt22 I have that same WC barrel and Aero upper combo. I recently also swapped barrels from a 308, didn't change anything else aside from agb due to the .875 size.

swap barrels and try it.

If there is an issue, deal with it accordingly.
 
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I paid attention to your parts list, but I did not realize that your bolt already had the reduced firing pin size that works better with a 6.5 CM. I thought it was a standard 308 bolt. That’s good to know as I’m betting it’s not as expensive as the JP. I would use it and I doubt you’ll have any problems, if you do, you can try a JP as the firing pin is even smaller at .062”.



  • High pressure bolt - external surfaces are CNC ground after heat treat for a precision fit and firing pin hole diameter is reduced to .070"
  • Multi-caliber bolt designed to function with .308, 7.62x51, 6.5 Creedmoor, .338 Federal and other .308 based cartridges.
 
The handguard ID has always been an issue with large frame gassers and AGB. Ive bought and tried them all. JP and Odin Works both make a huge one to give plenty of clearance around AGB so you arent hitting it under recoil and causing flyers.

I recently tested some SLR 308 MLOK designs and they give plenty of clearance and dont hit under recoil. When you have a round handguard you need the 1.75" ID for the clearance. But this SLR is shaped to give plenty of clearance around my .936" SLA AGB. I LOVE this handguard. Its the SLR 16" ION Lite M-LOK .308 DPMS High handguard. Been running it for about a year now.



Good too know, thank you for the info. I have a .936 GB'd barrel waiting to be assm.d... I was looking for another Lancer CF hand guard.. was.