What are the hardware differences in a 9mm upper and why?

[Whiterabbit]

Also, what is cross compatible, I am curious about too. At a minimum I am curious about:

Barrel extension, I think I understand. No need to engage the bolt since no gas system.

Bolt: is it the same as a 223 bolt? Different? what is different and why? Can I use a 223 bolt?

Buffer: same?

Buffer spring: same? I see bumpers I can buy for the back of the tube, are they really needed? What is the consequence of not using the bumper?

Anything else I need to be aware of?

[dyson]

Different bolt and buffer for sure. Not sure about buffer spring.

[Euphoria526]

When I ordered my kit it came with a "9mm lpk, bcg, buffer and tube"
Only thing I changed out was the upper and bolt. Everything else worked the same. But as I understand it, some might be more finnicky than others.
I got the Psa 9mm kit for reference

[264Grendel]

heavier buffer, search for 9mm buffer. different manufacturers have different weights.

You can use the same spring, but I was getting FTE's and stove pipes using the standard 223 spring. Switch the spring to a Wolff xtra power 9mm buffer spring to slow down the action. fixed the FTE's and stove pipes.

I would buy the spacer but I'm cheap so I use 5 quarters instead. The spacer is used to minimize the overtravel of the bolt, relieving unnecessary stress on the bolt catch on the last round.

You may need to find the right combination of buffer spring and buffer to get it to run reliably. I would start off using a standard buffer spring and a heavy buffer that u can pull from a 223 ar if you have one.

[Whiterabbit]

OK, I'm on board for "tuning" a buffer and spring, and adjusting overtravel to get it to run. 100% onboard.

That just leaves the bolt. I don't like the idea of not using a std bolt. Any reason I can't just use a regular bolt?

Edit: Nevermind, I see. It's a geometry issue. Even if I could get around the reciporcating portion, the bolt seems like it'll be too long. I assume I cant cut back the extension enough to make it work or make sense.

OK, so if I want to use a standard hammer and a standard upper and an off-the-shelf AR 9mm barrel, I need a new bolt. Do you guys have a suggestion for a reasonably priced 9mm bolt? I am accustomed to needing to polish parts, hand fit, etc to get 100% working. standard hammer OK and fits any upper receiver is what I would want.

[264Grendel]

sorry, I haven't done any searching lately for 9mm bolts. I think the cheapest I've seen is from JSE Surplus. Just make sure you get a ramped bolt to work with a standard 223 hammer.

You're also gonna need a magwell adapter or dedicated 9mm lower.

[Whiterabbit]

I've been reading about how to convert metal magazines to support 9m and plan to try that first

Thanks!

Anyone else have a good suggestion for a budget friendly bolt?

[GunnyUSMC]

The two things that will cost the most is the bolt and the lower. You need to decide which mags you wish to use, Colt type or Glock. The Colt style uses a mag-well insert on a standard AR lower.
PSA sales both types of lowers. Colt style go on sale for under $200 for a complete lower and the Glock mag complete lowers go on sale for $250.
BCG's (Glock & Colt Compatible) sale for about $180.
The upper is the easy part. Any standard AR upper can be used. If your looking to save money the Anderson slick side uppers or on sale at AIM Surplus. But if you want a dust cover, just get a standard upper.
A barrel, Handrail, charging handle and flash hider is all that is needed to finish.
Most places are out of 9mm barrels, but I did see that CBC Industries had some in stock for under $150.
I tried a few different buffers when I built mine. I found that the Rock River 9mm buffer worked the best.

[Whiterabbit]

I saw one for $180. So that's a pretty standard going price, huh?

So much money spent on equipment for saving money on ammo...

[AR-PISTOLCALIBER]

Also, what is cross compatible, I am curious about too. At a minimum I am curious about:

Barrel extension, I think I understand. No need to engage the bolt since no gas system.

Bolt: is it the same as a 223 bolt? Different? what is different and why? Can I use a 223 bolt?

Buffer: same?

Buffer spring: same? I see bumpers I can buy for the back of the tube, are they really needed? What is the consequence of not using the bumper?

Anything else I need to be aware of?

Start here.....

http://www.calguns.net/calgunforum/showthread.php?t=1098494&highlight=9mm

_

[ARDude]

Just as 264Grendal said...make sure you buy a 9mm bolt that is ramped. otherwise it wont work with a standard ar15 hammer.

[Euphoria526]

Check out Psa. They sell 9mm kits as a whole. And the do go on sale a few times a year, especially around this time of year.
Got mine for $499 I think a year or two ago. Came with the barreled upper, lpk,
Buffer spring and magwell insert.

[ARDude]

I've been reading about how to convert metal magazines to support 9m and plan to try that first

Thanks!

Anyone else have a good suggestion for a budget friendly bolt?

Are you talking about converting a standard .223 magazine to fire 9mm?

I've never heard of that.

You could buy a dedicated 9mm lower receiver for Colt or Glock mags.
Use a standard .223 receiver with a mag block for Colt or Glock mags.

[pacrimguru]

I have an old 9mm AR build thread that might be of some use to you:

http://www.calguns.net/calgunforum/showthread.php?t=250448

[Whiterabbit]

OK, I'm looking at last round bolt hold open, this is an important feature to me.

Just so I understand the baseline, If I take a stripped upper (plus CH) and insert the 9mm bolt, and put this on a standard AR-15 lower with no magazine (operate bolt hold by hand), will the bolt hold catch the bolt if I cycle the bolt back?