Looking for something out of the ordinary and I figured the arfcom hive is the place to ask.  I need a 9mm bolt that has locking lugs.  I'm building a lower that takes MPX mags to feed a suppressed barrel and in order to feed properly I'm anticipating i'll need a star shaped bolt.

Do you have a 9mm barrel with a "star chamber"?

Are you planning to run it as blowback or gas? If bb, doubt you will find anything unless you get a cmmg guard type bolt carrier and then as far as I know they don't yet make them for 9mm.
If you are planning to run gas/DI, you can use a standard 223 bolt and carrier. But it may need some tweaks as I have never tried to run a 223 bolt thru mpx mags and not sure if you will need to trim the lugs to do it?
Are you building the lower from scratch?  If not who makes it? Not sure if it would become a replacement for glock lower but is intresting.

Why are you screwing around with expensive MPX mags?
Scorpion mags are under $20 apiece.

You should be able to get a blowback bolt to feed from either one as long as you get the mag height and angle right.

I'm making the lower myself. I figured it would be easier to use compatible parts rather than fuck with making up some jankey mag release for scorpion mags.

The cost of the mags doesn't bother me. I'm willing to pay for better quality.

I guess I'll just buy a blowback bolt and barrel and see how it works. I must have been thinking of the old oly arms 9mm with the proprietary ejector.

MPX mags are $20 ea... Not sure if you're aware of that.

Sig MPX 9MM 30 Round Mags

The Gen1's are $20 on clearance, with known issues. Looks like they're trying to clear them off the shelves.
The Gen2's are still $60 apiece.

Not to say the Gen1's can't be made to work.

A 9mm direct impingement AR can be made, and there are one or two companies out there that will put one together for you on a semi-custom basis.

The problem is that they don't work all that well as factory ammo tends to gum them up pretty quickly.  If you get one, you'll want to hand load for it to keep it happy.

In contrast a blow back operated 9mm AR is dirt simple and when properly built will run extremely well.

I'm also not seeing the benefits of using MPX magazines, when Glock magazines are cheap, and colt pattern magazines are solid, reliable and Metalform magazines are only about $30 each if you shop around.

I believe a 5.45x39 bolt is what you seek. The AK guys building 9mm carbines say they share the same or close enough bolt face size.

You might want to contact Macon Amory.  He has a gas operated .45 upper, and I'm pretty sure I remember him saying that he's got a DI 9mm upper in production.  You want locking lugs, he's got 'em.

The mag lips are a hefty .985" wide with a slight rearward rake. The magazine seat depth is the same as standard nato mags.  The AK pattern mag cut looks like a good starting point.  Could you message me with your thoughts and price on bolt modification?  I haven't really had any time to take any engineering worthy measurements.

You might want to talk to RMW XTREME
http://www.rmwxtreme.com/#top

I would think a gas operated, locked bolt 9mm, would cough and sputter badly, depending on what powder was used in the 9mm ammo

most rounds, I suspect, would not have enough gas pressure by the time it got to the gas port.



maybe hot loaded handloads with a slower burning powder like Blue-Dot ?

. . or a custom gas tube that's only a few inches long ?



Why would you want to go in this direction ?


.

So,

I'll be going with standard 9mm blowback system.  Has anyone had experience with KM Tactical?  Getting a 5/8x24 threaded barrel to throw on the Silencerco Hybrid.

As well as a unique ejector sub-assembly, the Olympic Arms system uses a barrel extension and bolt face that have a unique conical interface.

What you have described in your OP sounds a lot like the modified "star" lug system recently introduced in .45 ACP in the CMMG Guard.  There is a discussion thread in this forum, in the the Armory tab, General Firearms forum, and the Industry tab in their forum.  CMMG has reported that they are working on another caliber (and they have a teaser video), but declined to indicate what the new caliber(s) are.

Best of luck with your project.

MHO, YMMV, etc.

People feel they need to reinvent the wheel.  Fuck, Metalforms can be had very cheap on sale and they run like gang busters. No magic bolt or barrel required.  Super easy to load. 

I don't need to reinvent the wheel. Just doing it because I can. I liked the mpx mags best of everything I looked at so I'm trying it out.

I know I wasn't thinking of the cmmg system, though I'm sure I'll eventually adopt it.

I was merely curious if there was a 9mm bolt with a star pattern face rather than the standard colt/glock cut because I thought it may strip rounds easier.

I will need to incorporate a feed ramp like the colt mag blocks, I think.

9mm DI requires a very short gas system to run. I have a 10.5" RMW XTREME DI 9mm that runs like a champ, if you use most factory ammo available it will run but the issue is factory ammo is dirty and you have to clean the bolt/carrier every 30-50 rounds or so in my experience. I have started load development using 165gr, 147gr and 124gr bullets and so far had 0 issues and ran thru 150 rounds without cleaning (165gr and 147gr bullets with several different powders and at standard pressures.) This is with a standard buffer and spring, my lower does not have last round bolt hold open so no lock back but I have had 0 feeding/extraction issues (except extraction with lite/starting powder charges.) I have also tested with and without a suppressor and it runs the same. Ron built a DI 9mm for himself and has run several thousand handloaded rounds FA without fail he has also run some factory ammo FA as well but had cleanings in between mags and let me tell you in FA there is no recoil at all. I see the DI 9mm as not for everyone, if you want to buy the cheapest 9mm and run 1000 rounds non stop you will not be happy but if you are willing to handload and tailor a load for it with a clean burning powder you will love it.

I've been over the measurements of my upper and there just isn't room for a DI setup, unfortunately.  Do you guys have a recommendation for 9mm bolts with a 556 style extractor?  I've found the colt extractors and they would work, but a 556 extractor would be a lot better.

NFA modular has one.

I guess I should have said plunger ejector.  I know wilson combat has them in the AR9 bolt but I can't seem to find any others.