Help me out with some inch by inch questions

HALL,AUSTIN · July 28, 2017, 09:29 AM

I've looked and looked but can't find any inch by inch velocity readings for 300blk or 6.8spc (either the original or spc II). I know the 300blk is pretty near topped out at ~9 inches but I'd still like to see some numbers corroborating that. I'd also like to see how short you can go with the 6.8 before you start to lose a bunch of velocity. Any help or data would be appreciated, so if you have either caliber please post your caliber, barrel length, velocity and load if you can. Again, thank you in advanced.

T. O'Heir · July 28, 2017, 10:59 AM

"...at ~9 inches..." Nine inches of what? Barrel? Depending on who you ask/believe velocity loss per inch can be 25 FPS to 100 FPS per inch. There was an article in one of the gun rags, years ago, where the guy(forget who and the cartridge used) cut 1" off at a time with velocity tests at each length. Results were 100 FPS loss per inch. Others are saying, now, with no documentation, it's 25 to 50.
Doubt you'll find anything like that for a specific cartridge though. The only rifle cartridge Ballistics by the Inch tested is .223 using 45, 50 and 55 grain bullets.

TheDevilThatYouKnow · July 28, 2017, 11:54 AM

I was going to say, 'go to BallisticsByTheInch.com but they don't seem to have .300Blk on there yet.
AR15.com has an article on it. Edit: Make that two, at least. As does 300BlkTlk.com.

Bartholomew Roberts · July 28, 2017, 03:07 PM

110gr VMAX and TAC-TX are both right at 2200fps even out of my 9" barrel measured with a Magnetospeed. Both rounds are marketed as being 2375-2400fps from a 16" barrel. So, a 9" barrel will get you about 92% of a 16".

jmr40 · July 28, 2017, 04:25 PM

Several things here. I haven't looked at any of these so I don't know if they are any good or not.

https://video.search.yahoo.com/searc...fr=tightropetb

Quote:

There was an article in one of the gun rags, years ago, where the guy(forget who and the cartridge used) cut 1" off at a time with velocity tests at each length. Results were 100 FPS loss per inch. Others are saying, now, with no documentation, it's 25 to 50.
Doubt you'll find anything like that for a specific cartridge though.

That test has been repeated thousands of times, the results have been documented and posted for anyone to look at.

Test results from 6.5 Creedmoor. It only lost 54 fps from 27" down to 20" with 142 gr bullets.

https://rifleshooter.com/2016/02/6-5...p-a-creedmoor/

Some 308 data

http://www.thetruthaboutguns.com/201...-and-accuracy/

This should keep anyone busy for a while that actually wants to learn.

https://search.yahoo.com/search?ei=u...e=23207_101916

ed308 · July 29, 2017, 10:10 PM

I've heard this from a barrel manufacturer that knows a thing or two about cartridges and barrels:

The 6.8 has quite a bit more power than a 300BO, 110s at 2550, 120s at 2460 out of a 16" barrel. The 300 is apx 100-150fps slower than a 7.62x39, 200fps slower than a 30-30 with the same weight bullets out of the same length barrel.

July 28, 2017, 09:29 AM	#1
HALL,AUSTIN Senior Member Join Date: June 23, 2011 Location: asheville north carolina Posts: 556	Help me out with some inch by inch questions I've looked and looked but can't find any inch by inch velocity readings for 300blk or 6.8spc (either the original or spc II). I know the 300blk is pretty near topped out at ~9 inches but I'd still like to see some numbers corroborating that. I'd also like to see how short you can go with the 6.8 before you start to lose a bunch of velocity. Any help or data would be appreciated, so if you have either caliber please post your caliber, barrel length, velocity and load if you can. Again, thank you in advanced.

July 28, 2017, 10:59 AM	#2
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	"...at ~9 inches..." Nine inches of what? Barrel? Depending on who you ask/believe velocity loss per inch can be 25 FPS to 100 FPS per inch. There was an article in one of the gun rags, years ago, where the guy(forget who and the cartridge used) cut 1" off at a time with velocity tests at each length. Results were 100 FPS loss per inch. Others are saying, now, with no documentation, it's 25 to 50. Doubt you'll find anything like that for a specific cartridge though. The only rifle cartridge Ballistics by the Inch tested is .223 using 45, 50 and 55 grain bullets. __________________ Spelling and grammar count!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

July 28, 2017, 11:54 AM	#3
TheDevilThatYouKnow Member Join Date: November 22, 2015 Posts: 89	I was going to say, 'go to BallisticsByTheInch.com but they don't seem to have .300Blk on there yet. AR15.com has an article on it. Edit: Make that two, at least. As does 300BlkTlk.com.

July 28, 2017, 03:07 PM	#4
Bartholomew Roberts member Join Date: June 12, 2000 Location: Texas and Oklahoma area Posts: 8,462	110gr VMAX and TAC-TX are both right at 2200fps even out of my 9" barrel measured with a Magnetospeed. Both rounds are marketed as being 2375-2400fps from a 16" barrel. So, a 9" barrel will get you about 92% of a 16".

July 29, 2017, 10:10 PM	#6
ed308 Senior Member Join Date: November 5, 2016 Location: DFW, TX Posts: 1,147	I've heard this from a barrel manufacturer that knows a thing or two about cartridges and barrels: The 6.8 has quite a bit more power than a 300BO, 110s at 2550, 120s at 2460 out of a 16" barrel. The 300 is apx 100-150fps slower than a 7.62x39, 200fps slower than a 30-30 with the same weight bullets out of the same length barrel.