10mm AR question (UPDATED)

[Major Kong]

I'm building a 10mm AR SBR on a QuarterCircle 10 lower. My intention is to use one of the QC10 40S&W Glock-cut BCGs with a heavy buffer (7.5 oz) and a .308 spring.

I can't imagine that the extra pressure of the 10mm would cause any problems with the bcg but I can't seem to get a straight answer from either QC10 or the interwebs. Anyone have any experience with this situation?

Edited August 14, 2016 by Major Kong

[MacGyver]

I don't have anything to add.  But, I'm sure interested in what you find out!

Can't wait to see this one get up and running.

[Major Kong]

29 minutes ago, MacGyver said:

I don't have anything to add.  But, I'm sure interested in what you find out!

Can't wait to see this one get up and running.

Me too Mac! it will be a couple more months on the Form 1 so it'll have to start life as a pistol.

[MacGyver]

My 9mm DDLES variant shoots a lot softer than I expected.  I can't imagine you'll run into issues that a heavier spring and buffer won't soak up appropriately.

[Jct1911]

Blowback 10mm is iffy. Remember, springs work in both directions. Too much rear travel  leads to broken bolt catches upon return. You may also run into feeding issues as the bolt overruns the mags. 

[KKing]

My suggestion, which is what I'm running right now, would be to use this buffer + Wolff xp buffer spring. Reasoning is the buffer itself is longer which does away with the need for spacers and such when using a regular carbine buffer...so no broken bolt catches. Also, it's heavier, which you'll need in a 10mm
http://heavybuffers.com/9q.html

If not it, I would run their "T" version, which is even heavier.


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[Major Kong]

34 minutes ago, KKing said:

My suggestion, which is what I'm running right now, would be to use this buffer + Wolff xp buffer spring. Reasoning is the buffer itself is longer which does away with the need for spacers and such when using a regular carbine buffer...so no broken bolt catches. Also, it's heavier, which you'll need in a 10mm
http://heavybuffers.com/9q.html

If not it, I would run their "T" version, which is even heavier.


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This is the one I went with: http://www.joeboboutfitters.com/KVP_Solid_Stainless_Steel_Blowback_Buffer_7_5oz_p/kvp-buffer-7.5-9mm-ss.htm

If I have any trouble with it I'll look into the heavier ones. I'm hoping that this plus the heavier spring will do the trick.

[KKing]

This is the one I went with: http://www.joeboboutfitters.com/KVP_Solid_Stainless_Steel_Blowback_Buffer_7_5oz_p/kvp-buffer-7.5-9mm-ss.htm

If I have any trouble with it I'll look into the heavier ones. I'm hoping that this plus the heavier spring will do the trick.

Oh wow good call, $40 cheaper and only an oz. difference. I wish that had been an option when I built, I would have used it too!


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[1gewehr]

What are you using for magazines?  I've thought about a 10mm AR, but the lack of larger mags stopped me.  I've heard that M3 Grease Gun mags work with 10mm. Anyone know for certain?

[KKing]

What are you using for magazines?  I've thought about a 10mm AR, but the lack of larger mags stopped me.  I've heard that M3 Grease Gun mags work with 10mm. Anyone know for certain?

Not trying to speak for him but since he said he's using a glock cut bcg, the only reason to run one of those is for glock mags.

[Major Kong]

28 minutes ago, 1gewehr said:

What are you using for magazines?  I've thought about a 10mm AR, but the lack of larger mags stopped me.  I've heard that M3 Grease Gun mags work with 10mm. Anyone know for certain?

I've ordered a couple of these: http://www.brownells.com/magazines/handgun-magazines/magazine-parts/magazine-extension/g21-25rd-45acp-extension-for-glock--prod55111.aspx

With a little bit of modification they will work with the Glock 20 magazines.

[gjohnsoniv]

Tagged for reference and because I want to see how this turns out. 

[1gewehr]

11 hours ago, KKing said:

 

Not trying to speak for him but since he said he's using a glock cut bcg, the only reason to run one of those is for glock mags.

 

Hmmm, reminder to self:  Don't type with my foot in my mouth.  Doh.

[Dolomite_supafly]

If anything is going to happen it will be the case head ruptures because there isn't enough pressure/weight holding the bolt in place. I think you will have it covered with the heavy buffer. I have had experiments where the gun seemed to cycle fine. Was tossing the brass out perfectly but none of the bullets made it out of the bore. That was a blowback 30 Tokarev shooting 180 grain bullets.

If you need any help let me know.

[KKing]

Hmmm, reminder to self:  Don't type with my foot in my mouth.  Doh.

No worries, I often suffer from foot in mouth syndrome, just ask my wife!

[Dolomite_supafly]

Also, I can probably make you a much heavier buffer as well depending on recoil spring. If you have a flat wire I could make one that is much heavier

[Major Kong]

So, slight change of plans. I was able to get a 45acp bolt but the 40cal bolt is still out of stock. I had already bought barrels for both so I decided to go ahead and build the 45 first. Here it is, built as a pistol until my Form 1 comes back:

QuarterCircle 10 GLF lower

CMT UPUR 3 upper

QuarterCircle 10 45acp bolt

KAK Shockwave stock

Kaw Valley 8.5" barrel

BCM Enhanced LPK

Kaw Valley Linear compensator

Matrix Arms Charlie KeyMod Handguard

Aimpoint Comp M3 w/American Defense base

SGM Tactical 26 round magazine

Working this weekend but will hopefully be able to get it out next week and break it in.

 

[shotgunshooter]

So, slight change of plans. I was able to get a 45acp bolt but the 40cal bolt is still out of stock. I had already bought barrels for both so I decided to go ahead and build the 45 first. Here it is, built as a pistol until my Form 1 comes back:

QuarterCircle 10 GLF lower

CMT UPUR 3 upper

QuarterCircle 10 45acp bolt

KAK Shockwave stock

Kaw Valley 8.5" barrel

BCM Enhanced LPK

Kaw Valley Linear compensator

Matrix Arms Charlie KeyMod Handguard

Aimpoint Comp M3 w/American Defense base

SGM Tactical 26 round magazine

Working this weekend but will hopefully be able to get it out next week and break it in.

 

Are you planning on putting a can on there?

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[Mark A]

I have vowed to build no more AR's.

I sense a great disturbance in the force...

[dcloudy777]

We're it me, I'd probably put the heaviest buffer I could find/make in it.  If it short-strokes lighten the buffer until it runs reliably.

A heavy hammer spring helps slow the bolt down as well, without increasing the bolt's forward speed like a heavier recoil spring would.

[Major Kong]

7 hours ago, dcloudy777 said:

We're it me, I'd probably put the heaviest buffer I could find/make in it.  If it short-strokes lighten the buffer until it runs reliably.

A heavy hammer spring helps slow the bolt down as well, without increasing the bolt's forward speed like a heavier recoil spring would.

7.5oz buffer and a .308 spring. We'll see how it works this week and tune from there.

[Major Kong]

18 hours ago, shotgunshooter said:

Are you planning on putting a can on there?

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That's the plan. I let 41f creep up on me and didn't get it in on my trust. Figuring out how I'm going to proceed with suppressors from this point on.