10mm AR SBR

[36g]

Latest project - 10mm AR SBR. Getting close to finishing. Need to drill and pin front sight, test fire, and Duracoat.

Lower receiver is JoeBob Outfitters (Glock mag version) as is barrel. Stock flat top upper with A2 carry handle. Extra heavy buffer and spring. Triangle carbine length handguards.

Nice companion to 10mm M&P or Glock.

Don't worry - 07 MFG, SOT.

[Iron369]

I like that. You might have just inspired my next project.

[buyobuyo]

Very nice. I've been contemplating a pcc SBR, and 10mm is very intriguing. Haven't moved on anything yet, though.

[45workhorse]

Nice set up!
Let us know how it shoots.

[Baltimoreed]

Never shot a .40 or 10mm but I like my 45 acp PCC sbr and rifles. Pure fun.

[armoredman]

10mm is MADE for subguns, nice project, sir.

[36g]

10mm is MADE for subguns, nice project, sir.

Made for subguns unless you are the FBI and intent on using it in an MP5 - they didn't last long...

[Plate plinker]

Made for subguns unless you are the FBI and intent on using it in an MP5 - they didn't last long...

What’s the problem with a 10mm mp5??? Please elaborate.

[36g]

What’s the problem with a 10mm mp5??? Please elaborate.

My understanding is that the FBI had excessive breakage rates on their MP5/10s from the outset. Even had developed two sets of rollers to deal with high pressure and reduced pressure loads. If I understand correctly HK discontinued production of the MP5/10 and the MP5/40 somewhere in the mid '90s.

[sawinredneck]

Had the chance to buy an MP5 10mm back in the 90's, select fire, all the springs and I think around 15 mags. A local gun store was closing up and he offered it to me for a buy as he knew I loved 10mm. Unfortunately it was bad timing, newly married and my wife had just lost her job. Still wish I'd had made that happen!
Nice build!

[Plate plinker]

My understanding is that the FBI had excessive breakage rates on their MP5/10s from the outset. Even had developed two sets of rollers to deal with high pressure and reduced pressure loads. If I understand correctly HK discontinued production of the MP5/10 and the MP5/40 somewhere in the mid '90s.

Well, there is a hi impulse and low impulse locking piece for that format. The rollers may change when those are switched I don’t know. Rollers change bolt gap.

[36g]

Did a test fire this afternoon. Quite spicey...

Using Blazer 180 grain FMJ flat tip ammo and ETS polymer magazines.

Noticed a difficulty inserting empty mags on closed bolt. If starting with bolt open, mag inserted okay. Upon hitting bolt release bolt closed okay but noticed a shaved spot on right feed lip. After several cycles and letting the bolt modify the feed lip was able to insert the mag on a closed bolt. Same for several mags.

There is a tendency for the third or fourth round to strike the feed ramp and jam. Was not able to fire more than 4 rounds without stoppage. Probably will need to polish feed ramp.

As a straight blowback the cocking process is stiff due to heavy springs and buffer. Kind of reminds me of an Astra Model 600 pistol in that regards.

As a general note, my general routine is to test fire a new build without any lubrication. Theory is to more rapidly wear off rough spots or parkerizing without lube then add lube. Will need to run a hundred or so rounds through it.

Need to add a white or fluorescent red tip to the front sight post as the black post was difficult to pick up against a target in the afternoon shadow with the sun in ones eyes.

Bullet strikes on the backstop at 50 and 100 yards were positive and indicative of some serious energy left at those ranges.

Rifle is quite handy and I'm looking forward to getting it broken in and more appropriately sighted in.

I'll get some Duracoat on the front sight base and barrel tomorrow. The barrel was for a pistol build and had the front sight base shoulder at about the mid point. I made an aluminum sleeve to move the shoulder forward to yield a carbine length handguard shoulder for the handguard cap and handguard before pinning the front sight base.

[Baltimoreed]

I’m sure that the 10mm in a blowback AR is very spicy on both ends. My first 45 acp pcc builds were Olympic blowback with grease gun dedicated lowers but the last two were cmmg rotary bolts. The difference is night and day. Neat build.

[36g]

Polished the feed ramp tonight. Got to thinking that bullet shape may be coming into play also. Have some hard cast loads somewhere - will try to find some of those as well as some other factory ammo.

[Lloyd Smale]

what are you using for a buffer and spring. my 9mm wouldnt run good enough to use a binary trigger until i used 7 once buffer and a 308 ar10 carbine spring. 10mm must need a serious buffer to slow down that bolt enough that it doesnt beat itself to death in a few thousand rounds

[36g]

Spring is a Kaw Valley Precision .308/Pistol Caliber Extra Power Carbine Buffer Spring.

Buffer is a Kaw Valley Precision AR-15 Solid Stainless Steel Blowback Buffer - 7.5 oz.

[Baltimoreed]

The big advantage I’ve found is the ability for a straight blowback to feed anything. My cmmg rotary bolt builds are picky in what they feed. Of course the bad side is the blowback’s extra weight.

[cwlongshot]

There is hood reason there isn't many blow back 10mm rifles...

They are usually very heavy and can be hard to cock...

Personally Id love a 357 Sig too but another BAD choice for a blow back. The delayed blow back or full gas gun is the way to go here for these two.

CW

[Lloyd Smale]

Spring is a Kaw Valley Precision .308/Pistol Caliber Extra Power Carbine Buffer Spring.

Buffer is a Kaw Valley Precision AR-15 Solid Stainless Steel Blowback Buffer - 7.5 oz.

no expert but 7.5 oz buffer seems light. ive been told by guys that know more then me that its on the light side for a 9mm.

[cwlongshot]

IINM My 40 has a 9oz...