So, I started filling out my eform 1 for my PSA glock lower, and stopped at the barrel length and overall length. I'm first trying to decide which size barrel to get, and I'm going to shoot for either 4.5 or 5.5. I'm leaning towards 4.5, but don't know of any pros/cons for 5.5 over the 4.5 inch. Also, unlike my 22 sbr, I'm going to do a shorty rail, that goes to the tip of the barrel, instead of the suppressor under the rail. I know there are 3 and 4 inch rails, so finding some isn't the issue.

So if this was going to be suppressed, which size barrel would I get the most benefit out of?

Also, what would the overall length be on the gun with a 4.5 or 5.5 inch barrel with a magpul MOE stock?

I'm thinking the length on a 9mm 4.5in would be the same as my 4.5in AR 22 SBR, because of the lack of a barrel extension.

The basic principle on what to put for barrel length is you want to put the shortest size possible. There's no rule on it being longer than what you put down as long as it's still considered short barrel.

So u could put 4.5 inch and put a barrel up to 15inch if u wanted.

The overall length you will probably have to build off specs or have someone give you the overall length of a similar setup. I already had my barrel and measured what the overall was and then measured the size of my moe stock off a different rifle and added it together.

On my mpx. I measured my mpx and then took the website specs off the manufacturers website and just for peace of mind I compared it to other people's OAL measurements on forums etc.

My mpx barrel size I put 4.5 inch since that was one of the options that's supposed to be available down the line.

On my other 5.56 pistol I put 7.5 inch becuz going shorter is pointless. Its crazy enuff with the 7.5

4.5

I think I put 23.5 on my Form1

The usual measurement is 19" + barrel length.

I checked my 4.5" 22 SBR last night. I put 21.50 on the Form 1, which is what it measures with the stock(m4) extended to the tip of the barrel. Seeing as to how a 9mm doesn't have a barrel extention, I would assume a 5.5" barrel would bump it up an inch. With the MOE stock, that 22lr comes out to 21.75, so with a 9mm I would think around 22.75.

Not sure why my measurements are a little shorter than everyone else's though.

Don't forget according to the ATF's standard for measuring barrel length (measure from the closed bolt to the furthermost end of the barrel or permanently attached muzzle device with a dowel rod) you would need to include the bolt chamber depth as part of the dimension for barrel length.