I'm thinking of building a .300 whisper SBR upper (on a Form 1) but want to hear from others experienced in this caliber before proceeding.

I had planned on about an 11" barrel with a mid-length handguard.

This should be enough length for the .300 whisper to attain the proper subsonic velocity of about 1040 fps, right?  

Who's suppressors are usually recommended for this caliber?  

Will a standard 9mmm subgun suppressor work?  

Are any modifications to the magazines needed?

Anything in particular I should be on the lookout for?

I've checked out SSK's page as well as Quarterbore's 300 whisper page.  Any other links will be appreciated though.

Thanks!

So you are going to have mid-length handguards on it with a pistol length gas block under the handguards like a dissipator?

Yeah, that is enough barrel.

Suppressors?  I have no idea

Yep, you will definitely want the gas port back at the pistol (not carbine) position if you want subsonics to cycle without a can.  With that short a barrel, it might not even cycle subsonics with a can (if the gas port was in the carbine position).

A nice touch is to add a gas regulator of some sort.  That lets you reduce the gas flow when using supersonic loads (to avoid excessive force in cycling the action) or turn it off completely to turn the rifle into a straight-pull bolt action (and thus significantly reducing action noise).

I assume you're planning on reloading?  If so, you can tune your loads to stay subsonic for any barrel length.

My GI & thermold 30-round mags all work great.

I've heard of people using Gemtech TPR-S cans & Joe Gaddini's (SWR) .30 cal can with the 300 whisper.  I've also heard of people using 9mm cans with good results.  Once I get the time, I'm going to build the 9mm can I've had approved for months.  I'm designing it to mount easily on my 9mm SBR and my 300 whisper upper.

One more comment:  In order to feed the big fat subsonics (220 gr), I found the need to put M4 style feed cuts in the upper.  Once I made them large enough to feed the blunt 220s, the rifle cycled flawlessly.

Fiz,

It sounds like you're just the person who has the info I'm looking for.

I just purchased my first suppressor on a form 4 this year.  It's probably the most fun thing I've ever owned.  

You didn't specify, but do you have a suppressed .300 whisper?  How effective is the suppression on this caliber,  does it reduce the sound signature to levels less than an unsuppressed .22 LR rifle?  

Also,  sounds like you've built an SBR.  Let me see if I've got this process straight:

You just fill out a form 1 and submit it in duplicate with fingerprint cards, CLEO signature and check for $200 to the ATF office in Chicago like you would a Form 4 correct?  Once it comes back approved about 4 months later, you can "make" your SBR, right?

I had planned on using a carbine barrel with standard-position gas-tube (7-inch) and a mid length handguard (9-inch) which means there would be about 5-inches of barrel in front of the gas port.  

That should be sufficient shouldn't it?  particularly if I use an enlarged gas port..?

Thanks for the info!

Yep, I've done 4 Form 1's (2 cans & 2 sbrs).  You've got it right except for:
1) You need to fill out the citizenship card (5330.20) and include that in your application.

2) Form 1's go straight to DC; the address is on the form.

Did you get the latest forms from [url]titleii.com[/url]?

I haven't suppressed my whisper yet.  I should be able to finish my can in a couple of weeks here.  That'll be great!

I don't know if the regular carbine position will work with a barrel that short.  I couldn't get subsonics to cycle the action when I had a carbine position gas port on a 16" barrel.  Supersonics were fine.  Subsonics might have been ok with the added backpressure from a can, but I didn't have an opportunity to try.  Opening the gas port only helps you so much.  I still couldn't cycle subsonics with a .125" port, and that's the size of the gas tube.  Moving it back to the pistol position worked like a charm.  That's when I decided I really needed the adjustable gas system, because supersonic rounds were really slamming the bolt back.  

Thanks for the info.

I'll probably have the upper made by KKF or some similar person experienced with this sort of thing.  

Do you like the 300 whisper?

Artifex,
   I might be able to help you out.  I've got a 20" upper for sale.  It has the gas port in close (pistol length) and is turned down to .700 from the gas block forward.  The upper is setup for subsonic, but I'm more interested in supersonic stuff and want the longer gas block setup.  If you want to turn it into an SPR, all you have to do, once your approval comes back, is cut the barrel down to whatever length you want.  I've got an ad in the parts exchange forum.  I can also send you pics if you're interested.  I would also consider doing just the barrel & gas block, if thats all you're interested in.

VSP

I have one from SSK that I will sell 11" barrel and a friend is selling his ssk suppressor for 500 dollars.I will sell just the barrel with gas system for 500 or all the upper for 1100(swansleve,leas bear handguard & gas shut off)

Hmmm....

Why are you getting rid of these units?  Lost interest in the 300 whisper?  Performance not what you were looking for?   Ammo availability problems?

Artifex,
    I originally put the upper together for use in IPSC 3 gun competition (Various reasons, another topic).  When I ordered the barrel, I didn't make it clear that I wasn't really interested in sub-sonic ability.  All of my shooting was going to be done with full power supersonic loads, some would be borderline "hot" handloads.  The gas block is located in the pistol upper position for both sub & supersonic loads.  I started to get some pressure and speed cycling problems and had to adjust other parts to get the rifle to handle and shoot correctly for competition.  There's nothing wrong with the upper, its just not the correct setup for what I'm interested in.  I have shot heavy subsonic loads and it is sweet to shoot, but once again, its not what I intended on, so I need to sell it and basically start over.