So I have 2 form 1s in right now both set at 10.3 inch barrels (one 5.56mm and one 300 blackout) in hopes to do both MK18 builds.

Everyone is out of stock of mk18 DD uppers.

Everyone is out of stock on 10.3 inch barrels.

Everyone is out of stock on RIS II handgaurds.

One option is to buy 2 MK18 Pistols and once the forms get approved, take the uppers off and put them on the SBR lowers.  I am regretting this... maybe I should of put 10.5 inch instead for barrel length?  Since the availability of parts is higher on 10.5 inchers

http://ballisticadvantage.com/10-3-inch-556-625-hanson-carbine-cmv-performance-barrel.html

I have two of these in 300blkout and love them.

I went with the slr ion series rail and absolutely love it. Feels great and the 9.7" version goes within an 1/8" from my suppressor when installed.

http://slrrifleworks.com/index.php?route=product/product&path=66_106_134_135&product_id=645


Top one is BA 10.3" barrel with 9.7" SLR ion lite rail and Specwar 762 suppressor.

Call Adco and see what they will do for you.  If they have the profile you are looking for they can cut and thread it to your length.


They did it for me.


 

Don't give a second though to the barrel length you put on your form.  You can use any length barrel you want.


When are your stamps due?  I bet you will still have a barrel before a stamp.  


I do understand, I am very impatient too.  After I made a thread like this, I had an 8" .45ACP upper in 4 days.......and no stamp yet.

I saw two MK18 uppers on the EE this morning FYI.

http://www.shop.blackholeweaponry.com/RTS-105-556-Standard-Carbine-1-2-Black-AR15-556-STD-C-1-2-B.htm

Ballistic Advantage has both 5.56 and 300 BLK 10.3" barrels in stock

This is correct. You can permanently change anything on your stamp including barrel length, rifle length, and even caliber at any point.

I sent in a form 1 as a 223 and immediately regretted not building it as a 300 blackout. I sent a nice letter the day my form 1 got back to the NFA branch just stating I had PERMANENTLY changed the caliber to 300 blackout.

They sent me a form stating that they have noted the permanent caliber change and thanking me for the letter. Note: You do not have to do this for temporary changes, but it is strongly encouraged for permanent changes if you are not planning on keeping the parts so you can return it to the original configuration.


Also, as stated above, Ballistic Advantage has both sizes in 10.3" and they are about as good of a barrel as you will find. They all come with a 1 MOA guarantee, which is well beyond how I expect to use my SBR (for home defense).

Only 5.56 barrels... all of their 10.3" 300 BLK are out of stock

At the time of my post there were 4 300BLK 10.3" barrels in stock

Anyway, there is definatly 10.5" in stock, I just looked

Heh, funny.  Someone who viewed this post must of bought em

So... 10.5.... Does it matter what I put on the form 1 then?  I mean I'll have to write the letter to the ATF for a permanent change correct?

You should call BA, I bet they will get you whatever you need and probably give you a discount. I bought mine over black Friday. Bought one for a discount, then after the deal was over regretted not buying another one. I called, and they honored the discounted price even though it was 2 days after the sale ended. They're great folks.

As for the letter. I don't know that changing the barrel length requires a letter, but anytime I change my AR to be different from what is listed on my form I notify them. It's not worth the risk for a stamp...

This is seriously a "beating a dead horse" issue with the F1 barrel length for a AR15...

The ATF's verbiage is very clear on the matter.  They request that you send a letter for a permanent change of barrel length or caliber.  Since a AR15's configuration can be changed with the click of two push pins it is not a permanent change.

Not only is it not even required by law in the first place, it's not really relevant to the AR15 platform

With that said, if your one of those people that worry about everything just type out a basic letter notating the change after your stamp comes back and drop it in the mail.  It cost you nothing but postage if it makes you feel better.

The later part of your post is the stance I have.

I understand your logic, but by the same logic there is no such thing as a permanent change because you can install a new barrel on every gun ever made.

The form 1 purpose is to help them identify the firearm. If it is going to be configured with a 10.3" barrel it needs to state that on the form or if it doesn't, you need to notify them. It's really pretty simple and doing this eliminates any questions of legality.

They have stated that temporary changes do not need to be noted, so if you're going to keep a 10.3" barrel then there is no need to tell them. But since it's hard to explain how your rifle is only temporarily a 10.5" barrel when you don't even own a 10.3", I think you could potentially have problems. More than likely, they're not going to give a shit, but why risk it?

Exactly how i see this.  I must have the 10.3 inch configuration in the first place before I can have a 10.5 inch.  That's how I understand it at least

You guys really think anyone is going to care about .2" ?   Esp. as you put the shorter length on the form and will run slightly longer in reality, that sounds far less nefarious than the other way around.  

Tell them you thought it was 10.3" when purchased.

Watching several dealers put OAL on forms throughout the years, I don't know if any of them got within .2" of actual OAL.

Came here to say this. I got mine on the EE but you can go straight to the source as well.

Actually, my entire MK18 came from the EE

10.3" SS 300 BLK back in stock

http://ballisticadvantage.com/10-3-inch-300-blackout-hanson-pistol-ss-premium-barrel.html