300 Blk subsonics destabilizing

Be careful -- low-volume ratio loads can detonate. Mangement not responsible for load data. Use at your own risk.

Moderators: mpallett, bakerjw

Post Reply
AKsnowman
New Member
Posts: 2
Joined: Sat Feb 03, 2018 3:16 am

300 Blk subsonics destabilizing

Post by AKsnowman »

What would cause factory 220gr subsonics to keyhole at 25yds out of a 7.5" 1:7 twist barrel? Would a suppressor make the velocity increase to supersonic, causing destabilization? It's sounding louder than my 10" 223 and 7.5" 7.62x39.

I plan to reload. Will I be able to handload 220gr subs that stabilize or should I start with getting a new barrel?
User avatar
doubloon
Silent But Deadly
Posts: 11897
Joined: Wed Dec 31, 2008 11:02 pm
Location: Houston-ish

Re: 300 Blk subsonics destabilizing

Post by doubloon »

Does it keyhole without the suppressor at any yardage 25, 50, 75, 100?
http://www.youtube.com/watch?v=BDtd2jNIwAU MUSAFAR!
http://www.youtube.com/watch?v=8CrOL-ydFMI This is Water DavidW
Complete Form 1s http://www.silencertalk.com/forum/viewtopic.php?f=10&t=79895
User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 7:15 pm

Re: 300 Blk subsonics destabilizing

Post by fishman »

Did you do an alignment check?
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647
AKsnowman
New Member
Posts: 2
Joined: Sat Feb 03, 2018 3:16 am

Re: 300 Blk subsonics destabilizing

Post by AKsnowman »

Yes, I checked for alignment. I didn't try supersonics because I don't really plan to shoot anything but subs through the suppressor. I set up my reloading station last night and started prepping cases. I have some Nosler 220 subsonic green tips to try out.
r
Silent Operator
Posts: 74
Joined: Thu Jan 12, 2006 7:47 pm

Re: 300 Blk subsonics destabilizing

Post by r »

you are shooting a really long bullet is a short barrel. 223 in a 10" barrel or 7.62x39(what weight bullet?) in 7.5" barrel are scale wise a lot higher barrel length/bullet length ratio. I shoot 240/250grain 308 in 308x1.5" BARNES(1 in 8") and also do 240grain 308 in handy rifle with 1 in 10" with suppressor but each of these are normal length barrels. I think your 7.5" barrel isn't imparting enough spin on that longer 220 grain bullet even though it is of the correct rated twist, to give it stability.
User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 7:15 pm

Re: 300 Blk subsonics destabilizing

Post by fishman »

r wrote:you are shooting a really long bullet is a short barrel. 223 in a 10" barrel or 7.62x39(what weight bullet?) in 7.5" barrel are scale wise a lot higher barrel length/bullet length ratio. I shoot 240/250grain 308 in 308x1.5" BARNES(1 in 8") and also do 240grain 308 in handy rifle with 1 in 10" with suppressor but each of these are normal length barrels. I think your 7.5" barrel isn't imparting enough spin on that longer 220 grain bullet even though it is of the correct rated twist, to give it stability.
What the hell does barrel length to bullet length ratio have to do with anything? A 7.5" barrel Is plenty long enough to get a 300 blackout bullet up to velocity. Velocity * twist rate = rpm. Twist rate is constant and velocity should be fine. A 2" barrel will stabilize a bullet as long as it can get it up to speed.
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647
User avatar
doubloon
Silent But Deadly
Posts: 11897
Joined: Wed Dec 31, 2008 11:02 pm
Location: Houston-ish

Re: 300 Blk subsonics destabilizing

Post by doubloon »

fishman wrote:...
What the hell does barrel length to bullet length ratio have to do with anything? A 7.5" barrel Is plenty long enough to get a 300 blackout bullet up to velocity. Velocity * twist rate = rpm. Twist rate is constant and velocity should be fine. A 2" barrel will stabilize a bullet as long as it can get it up to speed.
Maybe it's a Franklin barrel.
http://www.youtube.com/watch?v=BDtd2jNIwAU MUSAFAR!
http://www.youtube.com/watch?v=8CrOL-ydFMI This is Water DavidW
Complete Form 1s http://www.silencertalk.com/forum/viewtopic.php?f=10&t=79895
User avatar
DKDravis
Silent But Deadly
Posts: 170
Joined: Mon Jan 17, 2011 9:28 am

Re: 300 Blk subsonics destabilizing

Post by DKDravis »

Progressive twist barrel, cut too short??

Did you actually measure twist rate? I was defrauded once by a gunsmith who was supposed to install a new barrel on one of my rifles, he was supposed to deliver a brand new 1:12 twist in .224 cal, but instead reworked an old 1:14 twist factory barrel that he had removed from another customers rifle.. The idiot did not think I would measure the twist .. :evil: Then the idiot tried to run away from it, by referring to the bill, which did not state the delivered twist rate, saying that I "Never specified the twist rate"
Fortunately I had a photo of the original order slip ... on the guys own headed paper .. :mrgreen:

Did you TESTFIRE the setup (Gun+Barrel+ammo) without the suppressor installed .. I have never had better grouping or improvement in "wobbly" bullets from adding a suppressor .. Don't think that can ever happen.. but I may be wrong .. :wink:
DKDravis

"Sapere Aude": Dare to KNOW!
"Do not adjust your mind, there's a fault in reality!"
"When Wrong becomes Right, Resistance becomes our duty!"
Postal code 8541
Post Reply