What is the main difference between the oly and colt style 9mm uppers?  I just saw a socom sten mag block but was bothered that it only worked on Oly style uppers.  Is the bolt design different, the carrier, the hammer or something totally different?

Bolts are different, extraction is different, and the oly puts the mag in the front of the well, the colt is in the middle.

What is the benefit/problems with each system?

IMHO the Colt is better.  UZI mags are still "cheep" and available. Looks good too!!

That's a pretty long discussion but here's my possibly flawed thinking and why I chose a Colt pattern setup:

-25 round UZI mags, while a tad more expensive than Sten mags, are THE SHIT!  They're easy to load and are just about as close to 100% reliable as you can get.  I'm talking about IMI, FN and Lyttleton Engineering.

-That Oly extractor just looks wrong to me.  Maybe I'm just ignorant because they seem to be pretty much ok for those who have them.

-That Oly ejector just looks wrong to me.  Maybe I'm just ignorant because they seem to be pretty much ok for those who have them.  They are mounted on a boss in the upper that isn't part of Colt's original design and is pretty much just a long rivet.  They are also a wire spring.

-Oly uppers have a forward assist.  That's not a plus to me.

-The Colt pattern bolt is heavier.  

-With a good mag well adapter, Colt mags will hold the bolt open on the last round, like a Thompson or an MP5/40.

-Oly front sights are not forged.  This is a very small nit to pick but it matters to me.

-Oly seems to be experiencing growing pains.  This has apparently been going on since the early 90s.  Some people have better luck than others.  Buy your Oly stuff from a dealer (budam) on these boards.  Likewise RRA.  I got my upper from Pete-in-NH for a very nice price.

If you are buying a complete gun or an upper there are different issues. The Oly pistol caliber uppers use all of the standard 223 fire control and action parts. The Colt uses a 9mm specific hammer and buffer, so swapping between 9mm and 223 is not just a matter of changing uppers on the Colt system.

Sten mags are reliable and refinished mags can be had for as little as $6. With the Socom block, no mods to the mags are needed.

If you're looking for a Colt 9mm, one of the good local shops I frequent has a preban (early 90's) Colt 9mm in stock for $1250.  If you're interested let me know and I'll send you the contact info.

HI,
im just looking for an upper and not a complete gun.  It will have a dedicated lower so the fire control group wont be a problem

This block is only for the oly system so Im going to pass.  I have a ton of sten mags that i picked up for a little less than $3 each so im waiting for ProfGab or gloftoe to start selling their blocks so i can use these mags.
Thanks for the offer but I cant afford any more prebans now.  Im just going to wait a month or so til one of these guys makes their magazine block for the colt system

Question for JED, what is the price on the UZI mags?  How much are we looking at for each one here?  What modification is needed

Well... since Oly came out with the 9mm design first, Colt didn't follow Oly's original design with their stick ejector in the magblock.

The major difference in the designs is really that the Oly system uses a standard bolt carrier with a special 9mm bolt and barrel extension, with the feedramps on the barrel extension.  The colt uses a one piece bolt, which is basically a solid bolt carrier with a bolt face on the front, and an extension-less flat-faced barrel with the feedramps on the magblock.

An ancillary difference is that since the Oly uses sten mags, which have no provision for a last shot hold-open, the Oly system lacks that feature, while the Colt uses a mag designed specifically for the 9mm AR-15, and will operate the bolt hold open when used with factory Colt 9mm AR-15 magazines.

Yeah, that was badly written.  It's a good thing my income doesn't depend on my gunsmithing expertise, yet.  


HOPLITE,
DSA has used 25 round UZI mags for $11.  I bought two and got NIW Lyttleton mags.  Good stuff.

There are generally two cuts to modify an UZI mag.  Before I describe it, let me say that you should have someone like LRM modify them.
OK.
I made a cut in the back for the bolt holdopen catch.  If you have an ASA drop-in-the-top adaptor or another that doesn't have the bolt holdopen feature then this cut may be unneeded.
The next cut is the mag catch cut.  
In my experience, it's possible to insert an UZI mag farther into the uninstalled magwell adapter than is possible when the adapter is in the gun.  The idea is that the UZI mag should go all the way into the gun.  If everything is in spec then that shouldn't be so far that there will be malfunctions during extraction.  I marked my UZI mag after inserting it into the gun and used Ye Olde Dremel to cut the slot for the mag catch.  It's UGLY.  I did some caveman/redneck quality work there.  One of my attempts was just screwed.  The other works OK.  

I went shooting today and my Colt mag ran flawlessly for the first time.  My ejector problems are solved.  I used the same approach I've used in the past for tweaking 1911 ejectors to clear a scope when ejecting.  Brass now rains out in a little one foot wide pile about 7 feet away.  Much nice! No more brass marks anywhere except on the brass deflector either.
My UZI mag was another story.  Since the rounds don't sit up quite as high and are not canted up as far as with the Colt mag I started grinding some channels into my feedramp.  The UZI mag works better but not 100% yet.  I keep getting rounds with the nose wedged up above the chamber.  Someone (David H probably) posted a pic over on snobguns.com of a Colt style mag block with two giant funnels cut in the feed ramp for curing this exact problem.  In my own stone-axe way, I'm doing the same thing but slowly.

Someone was saying that you MUST have a 9mm specific hammer and it precludes switching uppers.  AFAIK, you can grind the autosear notch off of the back of an M16 hammer and use that for both uppers.  I use a RRA 5.7 oz steel carbine buffer for both my 9mm and 5.56mm uppers and both run great.  There is a wierd Colt-pattern flat notched up 9mm hammer and possibly even a plastic one.
OK, I'm ready for another smack, Circuits!

I'll have some pics (evidence?) later.

My $0.02 worht.....



I have a Cavalry Arms lower with an ASA (Colt style) and I'm using the standard 223 buffer and hammer.  The hammer MUST be the type that has the rounded top, not notched or the 9mm upper will not work.  This has been covered many times.

Uzi mag are resonable in price now.  The idea of having to use the Sten mag in the Colt sytle is still "sweet" (as I have a custom block).  It position the mag in the center and they work great.  It functions simlarly to the South African mags that were manufactured for the Colt system.

I do not care about having the last round hold open.  As long as it feeds and ejects good, I'm happy.  Some people point out that they have to have it...okay...

I've used J_E_D's method to mark my Stens.  It works, but it take some time.  If I get bulk stuff done, I'll end up having a shop do it.

No smacks :)  The special 9mm hammer (or bobbed .223 hammer) is only needed if using a Colt pattern semi-auto bolt.  A full auto pattern bolt is a little lighter than the semi bolt, because it's cut to clear a full auto M16 hammer, and will take just about any hammer.  The semi bolt is closed on the top to leave some extra mass, and requires a shortened .223 hammer or the special 9mm hammer.

The original Colt 9mm design used pinned-in magblocks, and required a special extended bolt catch to work with the Colt 9mm mags.  Later designs use a bolt hold-open 'activator' built into the magblock, and they work with the standard short .223 bolt catch.

As has been noted, the biggest disadvantage of the Colt system is the cost of the mags, where even converted Uzi mags are 3x the cost of new in wrap sten mags.

If you're handy with tools or like supporting your local gunsmith, you can have a magblock made or modified to use sten mags with the Colt system.  I've personally made a magblock set to use the regular mag catch with sten mags in my Oly 9mm conversion.

I've even designed a bolt hold-open for sten mags, but it's complicated (translated, "expensive") enough that you might as well stick with Uzi mags and welded tabs to get the bolt hold-open to function.

Do you have pictures?!  Does it keep the mag in the front of the well or is it mid-well?!

So does the RRA 9mm upper require a different hammer in one of their .223 lowers, or can it use the .223 hammer?  This UZI magwell adapter has me tempted.

GR

Find a hammer that looks like this, and use it for all 3 caliber (22LR-223-9mm) -- basically an M16 w/the lug removed. [b]The std AR hammer with the "notch" will lock up right now as soon as you release the charge handle with 9mm, unless your bolt is "ramped". [/b]


[img]www.imagestation.com/picture/sraid58/p7a21929478de21856da2653f457a76fc/fc681fb2.jpg[/img]

Gotcha, and thanks for the pic!  I will have to keep an eye on the Uzi mag-well adapter.  Seems like a really good idea for a Colt-style setup like I am wanting.

GR