Longest 300 BLK Barrel While Still Subsonic

[overmatch]

Looking to build a 300 BLK bolt gun for subsonic plinking around the backyard. Using factory subsonic loads, can anyone chime in on what the longest barrel is I can run while reliably keeping them subsonic? I initially thought about a 9" barrel for the sake of keeping it compact, but am now thinking I might want the extra barrel length if I decide I ever want to stretch its legs with supersonic ammo. Can will be a Nomad L.

This thread here raised the concern about 220 grain rounds going super out of a 16" barrel, so curious if anyone has datapoints on how much shorter than 16" I'd have to go to keep subs reliably subsonic.

 

[Merle]

Using Sierra reloading data for subsonic 300 blackout loads I have had no issues keeping them subsonic out of my 16" Ruger American Ranch rifle.

 

[overmatch]

Using Sierra reloading data for subsonic 300 blackout loads I have had no issues keeping them subsonic out of my 16" Ruger American Ranch rifle.

Thanks, that's very helpful. Do you know of a comparable factory loaded round that is similar or the same as what you're reloading? Due to current circumstances, reloading isn't an option for me (as fun as it would be), so I need to find a somewhat reasonably available factory load to stock up on.

 

[Merle]

Thanks, that's very helpful. Do you know of a comparable factory loaded round that is similar or the same as what you're reloading? Due to current circumstances, reloading isn't an option for me (as fun as it would be), so I need to find a somewhat reasonably available factory load to stock up on.

Sorry man. Can't help you there. I've never shot any factory ammo out of that rifle.

 

[J McGriddle]

Most of the published velocities will be from a 16" test barrel unless noted otherwise. Even the SAAMI drawing lists velocities without stating a barrel length.

If I was in your situation I would email the ammo company CS and confirm the test barrel length and the listed velocity before i stocked up on a bunch of it.

 

[cooper_257]

I have shot a couple boxes of HSM 220gr out of my Ruger American Ranchrifle with a 16" Barrel and a can. All of them stayed subsonic.

 

[Dead Eye Dick]

Our 300 Whipser/300/.221 XP-100 used a 15 inch barrel, the longest allowed in IHMSA. It was fine with Subsonic but we had issues with wide SD’s which made hitting targets at 200 meters a very real problem. It was a fun gun to shoot and when it did, hit those 65 pound rams, they fell like hit by a freight train. Spotters watched the bullets going down range.

But alas, it never shot a 40, a Beautiful Experiment. A costly experiment too.

So, getting back to the subject at hand, 15-16 inches with a suppressor should be fine. I may be wrong, but going much longer, while trying to stay subsonic with very heavy bullets, could lead to a bullet sticking in the bore.

 

[RossinFL]

I had my ruger american ranch 300 blackout out this past weekend. I was shooting 220 grain s&b. It was hot, about 98 degrees. All the bullets stayed subsonic. I did not chrono the loads so can't say what the velocity was.

 

[overmatch]

I had my ruger american ranch 300 blackout out this past weekend. I was shooting 220 grain s&b. It was hot, about 98 degrees. All the bullets stayed subsonic. I did not chrono the loads so can't say what the velocity was.

Great. It seems like the consensus is 16" is fine for keeping 220 subsonic, barring any crazy elevation or heat. Appreciate you guys all chiming in.

 

[monkeypunch]

Are you able to load your own? The real magic in a 300 blk bolt action is found rolling your own with pistol powders. Most of the factory ammo is geared to ensuring semi auto guns run, and are using slower burning powders. I'm currently running Hornady 190gr Sub X's with AA #9.

 

[Kadams1563]

Also a benefit to the 300 BO is the capability to run such a short barrel.

I’d do a 13.7 or a 14.5 with a pin and weld muzzle brake.

 

[overmatch]

Are you able to load your own? The real magic in a 300 blk bolt action is found rolling your own with pistol powders. Most of the factory ammo is geared to ensuring semi auto guns run, and are using slower burning powders. I'm currently running Hornady 190gr Sub X's with AA #9.

Reloading is on the roadmap, just unfortunately not anytime soon unfortunately. Great info to know though, thank you.

 

[JerkyFreak]

The speed of sound is directly related to the air temperature. So, provided the powder is not too sensitive for temperature, it is more likely for the ammo to stay subsonic as the temperature rises.