Discussion of how to get an 8.5" Barrel SBR AR15 to 29" OAL

[Hawkeye]

I've taken a six month or so forum hiatus, but I was browsing today and saw this thread bumped, so I'm back.

I've got a 9mm 8.5" barrel and I can't get close to >29". I'm using the VLTOR EMOD with a 15" LOP and I'm still and inch too short.

Hey Jim:

The trick that I found to getting my 8.5" (PSA nitride barrel) SBR to 29" was the combination of:

Magpul ACS / ACSL
Magpul extended buttpad (has to be the thickest one, they offer three sizes)
VLTOR 8 position A5 extended buffer tube

Each of those will add enough length that combined it should put you at 29" with an 8.5" barrel. I have a VLTOR emod stock at home, and when I was testing it wasn't as long as the ACS-L with the extended buttpad.

 

[j_h_smith]

I've taken a six month or so forum hiatus, but I was browsing today and saw this thread bumped, so I'm back.



Hey Jim:

The trick that I found to getting my 8.5" (PSA nitride barrel) SBR to 29" was the combination of:

Magpul ACS / ACSL
Magpul extended buttpad (has to be the thickest one, they offer three sizes)
VLTOR 8 position A5 extended buffer tube

Each of those will add enough length that combined it should put you at 29" with an 8.5" barrel. I have a VLTOR emod stock at home, and when I was testing it wasn't as long as the ACS-L with the extended buttpad.

I'll look into it. I guess another stock will soon be added to my collection. Hope it works.

Thanks!

 

[Squaregrouper]

Are you measuring from the end of your barrel or the end of the muzzle brake/flash hider? I've got a 9mm 8.5" barrel and I can't get close to >29". I'm using the VLTOR EMOD with a 15" LOP and I'm still and inch too short. Your ACS-L has a 14.9 LOP. Add the .7 buttpad and it would seem you're still going to be almost a 1/2 inch too short.

Does PSA make a 9.5" barrel? I have a 300blk upper that has a 9.5" barrel. It's not a PSA, but if you do have a 9.5" barrel, you should be fine.

Good luck either way.

Flash hider removed from both uppers (SBR is 10.5" 5.56), measured from the tip of the barrel, along the bore line to the end of the stock. I then took a parallel measurement from the top (longest part) of the stock to the tip of the barrel. This gave me 29.5". I then measured the difference between the uppers and the .300AAC was 2" shorter, giving me 27.5" OAL if the 8.5" barrel was installed.
The current stock is a MOE. Magpul lists it as 6.9" The ACS-L is listed as 8.0" + .7" for the extended pad.
8.0" + .7" = 8.7"
8.7" - 6.9" = 1.8"
27.5" + 1.8" = 29.3"

Is my math flawed?

 

[j_h_smith]

Flash hider removed from both uppers (SBR is 10.5" 5.56), measured from the tip of the barrel, along the bore line to the end of the stock. I then took a parallel measurement from the top (longest part) of the stock to the tip of the barrel. This gave me 29.5". I then measured the difference between the uppers and the .300AAC was 2" shorter, giving me 27.5" OAL if the 8.5" barrel was installed.
The current stock is a MOE. Magpul lists it as 6.9" The ACS-L is listed as 8.0" + .7" for the extended pad.
8.0" + .7" = 8.7"
8.7" - 6.9" = 1.8"
27.5" + 1.8" = 29.3"

Is my math flawed?

It would depend on where the pin is located in the stock. If it's located slightly off of where the MOE stock is located, you may not meet the 29 inches.

I just bought a Magpul ACS-L stock and extension to try. I'll let you know what I get ASAP.

Take care!

 

[Squaregrouper]

It would depend on where the pin is located in the stock. If it's located slightly off of where the MOE stock is located, you may not meet the 29 inches.

I just bought a Magpul ACS-L stock and extension to try. I'll let you know what I get ASAP.

Take care!

Magpul's website has a 1.8" difference in LOP between the MOE and ACS-L + .7" extension. I will still have the same OAL.

 

[j_h_smith]

Flash hider removed from both uppers (SBR is 10.5" 5.56), measured from the tip of the barrel, along the bore line to the end of the stock. I then took a parallel measurement from the top (longest part) of the stock to the tip of the barrel. This gave me 29.5". I then measured the difference between the uppers and the .300AAC was 2" shorter, giving me 27.5" OAL if the 8.5" barrel was installed.
The current stock is a MOE. Magpul lists it as 6.9" The ACS-L is listed as 8.0" + .7" for the extended pad.
8.0" + .7" = 8.7"
8.7" - 6.9" = 1.8"
27.5" + 1.8" = 29.3"

Is my math flawed?

I understand your measurements, but I just put mine together with all the parts we've mentioned and I'm still 3/8" short and that's just to get to 29"..

8.5" barrel, measured by using a rod through the barrel, Vltor A5 buffer tube, Magpul ACS-L buttstock, Magpul .70 buttpad. All equal to 28 5/8" long. The ACS-L stock is 1/2" longer than the Vltor stock with the same buffer tube but I'm not getting to that magical 29" OAL with this setup.

 

[stringer bell]

You guys are way overthinking this.

Instead coming up with hair-brained ideas to get another inch or two to make the arbitrary, non enforced 29 inch length, simple get a pistol lower, put a PDW style brace lower on it and get what ever barrel you want. Done.

Functionally an AR with modern brace is no different than an sbr.

 

[erwos]

Functionally an AR with modern brace is no different than an sbr.

They are different - unless you like really bad stocks - and they look like ass. I'd rather pin-and-weld than use a brace.

 

[Wfilardo]

Pin and weld you better hope you don't have to mess with the gas block. Once it's on it's on. Pick a Brace there are dozens. There is no recoil anyhow so it's not like you need much.

 

[j_h_smith]

Pin and weld you better hope you don't have to mess with the gas block. Once it's on it's on. Pick a Brace there are dozens. There is no recoil anyhow so it's not like you need much.

It's a blow back 9mm SBR, so no gas block. I'm not giving up yet. I have a son who works for a really good fabrication shop. I just need to find a machine drawing of a buffer tube and I can have one made to the length I need. Since it's already a SBR, I'm going to try to make this work. I tried for almost a year to get my 10/22 to work with subsonic ammo. Then the Firefly bolt came out and I didn't need anything but to send in a check for what would now be easy for anyone to make them work with that ammo.

I'm not afraid to put in a little work. I'm not giving up yet....

 

[Hawkeye]

Honestly Jim, it may be easier to have a thicker buttpad made for it. Anyone with a 3D printer should be able to print one, or a good machine shop could machine a spacer that would fit between the stock and the pad you already have.

 

[j_h_smith]

Honestly Jim, it may be easier to have a thicker buttpad made for it. Anyone with a 3D printer should be able to print one, or a good machine shop could machine a spacer that would fit between the stock and the pad you already have.

Yeah, I'm going to have to think of a few options. One of them being putting that 10.5 inch barrel on the receiver and being happy with that.

Thanks!

 

[Squaregrouper]

I understand your measurements, but I just put mine together with all the parts we've mentioned and I'm still 3/8" short and that's just to get to 29"..

8.5" barrel, measured by using a rod through the barrel, Vltor A5 buffer tube, Magpul ACS-L buttstock, Magpul .70 buttpad. All equal to 28 5/8" long. The ACS-L stock is 1/2" longer than the Vltor stock with the same buffer tube but I'm not getting to that magical 29" OAL with this setup.

Mine arrives tomorrow. I will post my findings.
FWIW- I have a commercial buffer tube on my SBR. It is ~3/8" longer than my milspec buffer tubes. I do not remember who made it.

 

[j_h_smith]

Mine arrives tomorrow. I will post my findings.
FWIW- I have a commercial buffer tube on my SBR. It is ~3/8" longer than my milspec buffer tubes. I do not remember who made it.

The VLTOR A5 buffer tube is 8 inches long. I believe it's the longest buffer tube you can buy.

 

[rayrevolver]

Why don't you pin a 3-lug adapter (adds ~0.8125") or whatever muzzle device you plan to use? That should get you there.

I just measured my 9" AAC barrel as best I could. Indexing off the muzzle brake shoulder, it was ~28.6" and once you add the threaded portion of the barrel (0.6") the total is about 29.2". I remember 29.1" so that jives. This is Vltor A5 and ACS-L with 0.3" pad that comes standard.

If your ACS-L pad is 0.7", you should be really really dang close to 29". Not sure what is going on.

 

[Squaregrouper]

Flash hider removed from both uppers (SBR is 10.5" 5.56), measured from the tip of the barrel, along the bore line to the end of the stock. I then took a parallel measurement from the top (longest part) of the stock to the tip of the barrel. This gave me 29.5". I then measured the difference between the uppers and the .300AAC was 2" shorter, giving me 27.5" OAL if the 8.5" barrel was installed.
The current stock is a MOE. Magpul lists it as 6.9" The ACS-L is listed as 8.0" + .7" for the extended pad.
8.0" + .7" = 8.7"
8.7" - 6.9" = 1.8"
27.5" + 1.8" = 29.3"

Is my math flawed?

I received the ACS-L and .70" enhanced buttpad today. My math was flawed. I didn't factor in removing the .35" buttpad that comes with the ACS-L.
My "final" measurement came in at 28-15/16". It was damn close to 29", but this is Marylandistan and I have seen the FL FWC lose it over lobsters that were 1/16" too short.
At this point, I'm seriously considering breaking off the .7" extension's tabs, finding longer hex bolts and mounting the .7" buttpad directly on top of the one that came with the ACS-L.

 

[outrider58]

I received the ACS-L and .70" enhanced buttpad today. My math was flawed. I didn't factor in removing the .35" buttpad that comes with the ACS-L.
My "final" measurement came in at 28-15/16". It was damn close to 29", but this is Marylandistan and I have seen the FL FWC lose it over lobsters that were 1/16" too short.
At this point, I'm seriously considering breaking off the .7" extension's tabs, finding longer hex bolts and mounting the .7" buttpad directly on top of the one that came with the ACS-L.

Can you cut an 1/8" piece of vinyl tile to the outline of your butt pad as a spacer? If so, I can provide...

 

[Squaregrouper]

Can you cut an 1/8" piece of vinyl tile to the outline of your butt pad as a spacer? If so, I can provide...

Sure, why not. I would rather go 1/4" so there is no question on legality.
I hear Kitchen Aid grinder attachments are good in Analpolis (sic) too bump.

 

[outrider58]

Sure, why not. I would rather go 1/4" so there is no question on legality.
I hear Kitchen Aid grinder attachments are good in Analpolis (sic) too bump.

Lol. You can double it.

 

[Squaregrouper]

I received the ACS-L and .70" enhanced buttpad today. My math was flawed. I didn't factor in removing the .35" buttpad that comes with the ACS-L.
My "final" measurement came in at 28-15/16". It was damn close to 29", but this is Marylandistan and I have seen the FL FWC lose it over lobsters that were 1/16" too short.
At this point, I'm seriously considering breaking off the .7" extension's tabs, finding longer hex bolts and mounting the .7" buttpad directly on top of the one that came with the ACS-L.

I'm now legal with an 8.5" PSA .300AAC upper with the original commercial buffer tube. 29-1/16 fully extended.
The threaded picture was taken vertically with the tape measure and buttstock on the ground.
The second picture is fully closed. (Yes, I'm wearing slippers- it is cold)