10mm AR

[ADIDAS69]

I recently was infected with a virus that is compelling me to build an AR pistol chambered in 10mm. Because “reasons” the Kriss offerings are not an option though i would like to use glock mags to match my Glock 40 (long slide 10mm). I am planning on using the 10.5 barrel offered by brownells matched with the Spartan Lower offered by Joe Bob Outfitters. If anyone would like to lend their $0.02 to the project with regard to potential pitfalls and so forth I’d be glad to hear it. Note that the virus has made me deaf to certain equine sound frequencies.

[Mobuck]

The AR pistol caliber uppers I've seen are "blow back" so how does that work with the much higher pressure 10MM?

[ADIDAS69]

There is one you tube video of a guy shooting a gas operated 10mm but I cannot find any ported barrels and or rotating bolts. With regard to recoil Joe Bob Outfitters actually has a notation on their site that a 10oz buffer weight is recommended. 10mm is surprisingly energetic MAC did a video showing that it is still accelerating out of a 16” barrel

[RickB]

The delayed blowback system used on the CMMG "Guard" PCCs seems interesting.
If I'm reading things correctly, it uses friction between the bolt locking lugs and barrel extension to slow unlocking, so it doesn't need a heavy bolt, or buffer, or stiff springs, or whatever other fixes are used in conjunction with straight blow-back.
Don't know if it will ever trickle down to components that can be bought separately?

A 10mm AR has been appealing, but mags seemed to be a problem, with modified grease gun or Uzi mags being the norm?
Glock mags with extended base pads make the concept more realistic.

[MarkCO]

RMW Extreme makes 10mm barrels and bolts for the AR pattern. They can be mated to Uzi Mag or Glock Mag lowers.

Mine is a QC10 Large frame Glock lower. The barrel, gas tube and bolt are from RMW. Everything else is standard AR15 parts. You can easily be under $1K, I used some premium parts and was just over. Shares mags with my G20SF.

Runs from 115 solids to 220 grain, 1300 to 2200 fps. With 180s at about 1500, feels about like the 9mm blowback PCCs. Very accurate, topped with a 1-4 MTAC, I can hold a 10" steel plate for 10 rounds at 300 yards with it.

I would not own a blowback 10mm anything.

[ADIDAS69]

MarkCO, thank you. I got in contact with 1/4 circle and am going to go with their kit. The brownells barrel they said should likely work but may need a little fitment re feed ramp but they said the same thing might be necessary if i used their barrel (they were out of 10.5”).

[ADIDAS69]

Ooh on second thought I may have Angstadt Arms sort out a “lower” for me.

https://angstadtarms.com/product/jack9-lower-receiver/

[MarkCO]

I have shot the Angstadts, they are good.

[ADIDAS69]

I offered them the monies but they said “no dice” to a jack lower for 10mm. Why doesn’t anyone care about awesome stuff? Everything is the worst.

[stagpanther]

I've built a 10mm AR--it's a "sometimes works, sometimes doesn't" proposition. In a nutshell the whole ejector/BCG rail dohicky I think is a bad design for a blowback AR--at least anything trying to cycle 10mm cartridges. I took a look at CMMG's design and would go that route in a heartbeat if I were do do it all over.

[MarkCO]

Originally Posted by stagpanther

I've built a 10mm AR--it's a "sometimes works, sometimes doesn't" proposition. In a nutshell the whole ejector/BCG rail dohicky I think is a bad design for a blowback AR--at least anything trying to cycle 10mm cartridges. I took a look at CMMG's design and would go that route in a heartbeat if I were do do it all over.

Yes, blowback and 10mm is not a good idea. The CMMG design looks good, but there have been some issues in 9mm and I would not go with it in 10mm after some work on it.

All two of the DI 10mm ARs I have shot have been wonderfully accurate and 100% reliable.

[ADIDAS69]

Re blowback type pistol caliber rifles is there something intrinsically hard about the AR15 chassis as it relates to reliability? For about 3500 rounds I’ve had zero problems with my CX4 Storm from Beretta it’s blowback and operates perfectly

[stagpanther]

Re blowback type pistol caliber rifles is there something intrinsically hard about the AR15 chassis as it relates to reliability?

IMO--yes. It boils down to pushing the AR lower into service to cycle very short pistol cartridges from Glock magazines. Purpose made designs like the barrette are different. The blade that functions as ejector, BCG guide and bolt stop in AR last shot hold-open designs is simply doing too much in a too-active environment IMO. There is also a "gap jump" between the magazine and chamber--if things go out of tune (or a bullet design hangs up at an angle) it can be problematic to chamber. And that bolt is not locking up--typically it's a lot of carrier mass that's banging away at the parts--especially the bolt catch if it's a last shot hold-open design (another "hardly pass the laugh test implementation" IMO).

[MarkCO]

Originally Posted by ADIDAS69

Re blowback type pistol caliber rifles is there something intrinsically hard about the AR15 chassis as it relates to reliability? For about 3500 rounds I’ve had zero problems with my CX4 Storm from Beretta it’s blowback and operates perfectly

Not really, but aas stagpanther stated, there are set-up and tune issues that trip people up. IMHO, there is not one on the market yet that is "proper" all-around. It is a crazy space with manufacturers and consumers jumping on the wagon without a good understanding of the AR15 pattern, the tunes that work, the ammo that works, the parts that play nice together. I have built about a dozen with the same basic parts and they all run like a champ. But I learned a good bit from a few guys that have been running them for 20+ years and got to do T&E on several before they hit the market.

The ability to "tune" the AR9s is both a benefit and a bane. I have seen many that have tried to go light for speed and ended up with a mess. There are a lot of "products" on the market that lack any solid engineering, testing or development and those are creating issues as well.

In a blowback with a 16" barrel, you want a lighter bullet with a faster powder. That lets the pressure drop sooner, which mitigates a lot of the case separation, battering and ejection issues. I also think a two stage buffer (Blitzkreig or Tactical Innovations) are a very good help.

[stagpanther]

Keep in mind--a 10mm in an AR is a different ball of wax than a 9mm--just as it is in pistols.

[RickB]

Not to get too far afield, but how different are the internals of a 9mm MP5 and a 10mm MP5?
Was that a major reengineering, or "just" a heavier bolt and springs?

[stagpanther]

Not to get too far afield, but how different are the internals of a 9mm MP5 and a 10mm MP5?
Was that a major reengineering, or "just" a heavier bolt and springs?

The 10mm is going to be closer to a 40S&W in case and bolt face dimensions--and is MUCH more powerful than a 9mm. The lowers are set up to the same presentation of a Glock magazine--IMO you cannot necessarily expect the 10mm to feed in the same way or as reliably as the 9mm. Case support issues are the same as they would be in a pistol for the 10mm--but now your basically "swatting" the cartridge in from a Glock mag that is not "presenting" the cartridge close to the chamber face--and it's going in at an exaggerated angle at that. You need that big carrier mass to perform alignment duty when the angled cartridge meets the exaggerated radiused chamber opening--sorta like a big forcing cone on a revolver.

Until the "slavery" to the idea of a pistol cartridge AR MUST use Glock mags interchangeably with pistols--these fundamental issues will never go away IMO. If someone can point out even ONE LE or military unit that uses a 10mm Glock and AR where this is mandatory--I'd sure like to hear about it.

[MarkCO]

Which is why my 10mm AR is a DI gun.

[stagpanther]

Which is why my 10mm AR is a DI gun.

Wisdom.

[CowTowner]

Just because no one else has mentioned it - Once upon a time........
http://www.olyarms.com/shop/pistol-c...bines/k10.html

[4V50 Gary]

I wonder if weight may be added to the bolt carrier to make it a reliable blowback? A bolt carrier (minus the bolt) the weight of a short Glock slide should work.

[MarkCO]

Originally Posted by 4V50 Gary

I wonder if weight may be added to the bolt carrier to make it a reliable blowback? A bolt carrier (minus the bolt) the weight of a short Glock slide should work.

Of course, in terms of delay enough for the pressure to drop, but the weight becomes excessive, thus; unpleasant to shoot, tolerances need to be loose, wear increases. It has been done, and blowbacks for artillery have even been done. But there are better systems for firearm actions once you get past 9mm.

[stagpanther]

Catastrophic failure behavior is also a big "unknown." Lacking a DI gas system--presumably ALL that over-pressure is going to be driving that big carrier mass straight back at your face which is inches away from the chamber.

[ADIDAS69]

MarkCO, is your bolt a proper ratating bolt or just gas operated? RMW Extreme is light on pictures and descriptions.

[RickB]

Not to get too far afield, but how different are the internals of a 9mm MP5 and a 10mm MP5?
Was that a major reengineering, or "just" a heavier bolt and springs?

The 10mm is going to be closer to a 40S&W in case and bolt face dimensions--and is MUCH more powerful than a 9mm. The lowers are set up to the same presentation of a Glock magazine--IMO you cannot necessarily expect the 10mm to feed in the same way or as reliably as the 9mm. Case support issues are the same as they would be in a pistol for the 10mm--but now your basically "swatting" the cartridge in from a Glock mag that is not "presenting" the cartridge close to the chamber face--and it's going in at an exaggerated angle at that. You need that big carrier mass to perform alignment duty when the angled cartridge meets the exaggerated radiused chamber opening--sorta like a big forcing cone on a revolver.

Until the "slavery" to the idea of a pistol cartridge AR MUST use Glock mags interchangeably with pistols--these fundamental issues will never go away IMO. If someone can point out even ONE LE or military unit that uses a 10mm Glock and AR where this is mandatory--I'd sure like to hear about it.

Sorry, I was talking about H&K MP5 that was modified from 9mm to 10mm for FBI use in the 1980s; how much work was reguired to make the change?