Mr. T (MrT4) said:

Why do you think subsonic 9x19 let alone 45acp would be quieter than subsonic 300BLK ?  The important advantage 300BLK holds over 9mm is that subsonic 300BLK  has about as much KE at 400+m  as 9mm has at the muzzle, 9mm and 45acp are both shedding KE at much higher rates due to low BC bullets  while 45ACP could run with 300BLK to about 120m , it lacks the capability of .300BLK to go much hotter with supersonics. Not to mention as crap as .300BLK design is, it can be much more accurate at range not to mention 45acp is at present less common in service use than 300blk

.300blk is undeniably the more lethal, better caliber for SF / Covert Assassin use.

I make the suggestion of a 9x19 option that uses Glock mags from a US sales standpoint, rather than a terminal effectiveness standpoint. 

-There's already a number of existing mini .300blk bolt guns on the US market:

https://www.recoilweb.com/best-300-blackout-bolt-action-pistols-175502.html

-There's no 9mm bolt action rifle of any description (other then a custom conversion project) on the US market.

-9mm 147gr Subsonic is very inexpensive on the US market (~$0.25-0.35) whereas .300blk subsonic is around $0.8-$1 per shot

-9mm subsonic from a bolt action is 'Hollywood quiet' :

https://youtu.be/83Nkn3LrinQ?t=161

I just think it would prove an attractive niche with less competition and more US civilian interest. 

Mr. T (MrT4) said:

De Lisle, if it was made today to modern specs, would not be in 45ACP , 45APC was just the most practical off the shelf subsonic round at the time and Lee Enfield by virtue of rear locking and swappable boldface the easy action to make work.Even today there is no easier bolt action to convert to 45acp than lee enfield.

This dug up a painful memory.  15 or so years ago a large quantity of Lee Enfields hit the US market ($99 each) and there was a company that made conversions to 45 ACP and 7.62x39.  They went out of business just as I was about to place an order.  I have regretted delaying my order ever since.

Don't forget the US version of the De Lisle, which saw some experimental use in Vietnam chambered in .458" x 1.5" Barnes (11.6 x 33B) which was basically a shortened version of the .458 Winchester big game cartridge. It fired a standard 500 grain bullet at just below the speed of sound. It was unpopular because it was fitted with a long, heavy target barrel which along with the suppressor made it very cumbersome.

B&T SPR 300 is so far the only rival on the LE&Mil market.  Mini Fix is the only one in that lineup that could be considered a competitor

CZ600 had the potential to be the king of the market , but lucky for me ,its a bit of a mess and military tests did not go to well.

Well needless to say I hope the rifle is a smash success here in the US.

Back in the 90s, J.D. Jones showed off an AR in .300 Whisper at a subgun match I attended. Shut the gas off, and FFFTH was all you heard.

Thats very cool. Were you a subgun shooter? 

It would be nice if more semi auto rifles had the ability to turn the gas off like that. The AUG has a 'grenade' setting that turns the rifle into a straight pull bolt action style, but not aware of any factory guns in .300 with that option.

Yep. Still have my Sten, take it out about once a year and run a few mags through it.

I think there's a few ARs from smaller companies that offer gas blocks with shutoff, but mostly 5.56 instead of .300.

Farmplinker said:

Still have my Sten, take it out about once a year and run a few mags through it

Super cool. Very jelly. 

Sorry I have not been here in years, I may have missed the discussion somewhere. If I did could you point me in the right direction?

After all of the HK versions and designers moving to SIG, is the SIG MCX Spear LT the best design currently available to civilians?