How long does a 308 barrel need to be to reach max velocity

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Super cool!
I hope he took a stringed trigger shot before standing over the test shots, if he felt it warranted a barrel vise.

Definitely not what I expected to see.
I wonder what length barrel it would take to get the bullet to slow down.

I like stuff like this. Just imagine the work to line the rifling up between the two barrels, only to chop it all down, for science!
 
Did you see their “do scopes really need to be close to the barrel” test? It was another absurdism like this barrel - they made an optic riser block so tall, the gun had to be fired from the hip.

These videos they’re doing are kinda of like myth busters, for guns, but with a HEAVY dose of sarcasm - but not… I’m a fan.
 
If Shaq had a custom rifle built…..

Neat video. I learned a few things. I know they said POA shifted horizontally as they shortened the barrel but was there a change in precision?

Around 45” is where it maxed out on FPS. I can imagine the looks at an F Class match if someone showed up with something like that. :rofl: If he did well it wouldn’t take a month or two before there were 3 or 4 more guys copying him.
 
Their testing seems a little incomplete. If you go through all the trouble and expense of creating and mounting a 69" barrel why wouldn't you test the speeds with 125gr, 150gr, 168gr, 180gr and 200gr bullets?

I would have also liked to see a plot of group size vs barrel length vs bullet weight. Does the group size get small up to a point then start spreading? Kind of like a muzzle weight / harmonic balancer?

With that rig there is so much they could have done if they had taken the time to do it. How does point of impact change vs barrel length vs bullet weight?
 
Nature Boy said:
If Shaq had a custom rifle built…..

Neat video. I learned a few things. I know they said POA shifted horizontally as they shortened the barrel but was there a change in precision?

Around 45” is where it maxed out on FPS. I can imagine the looks at an F Class match if someone showed up with something like that. :rofl: If he did well it wouldn’t take a month or two before there were 3 or 4 more guys copying him.
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MikeInOr said:
Their testing seems a little incomplete. If you go through all the trouble and expense of creating and mounting a 69" barrel why wouldn't you test the speeds with 125gr, 150gr, 168gr, 180gr and 200gr bullets?

I would have also liked to see a plot of group size vs barrel length vs bullet weight. Does the group size get small up to a point then start spreading? Kind of like a muzzle weight / harmonic balancer?

With that rig there is so much they could have done if they had taken the time to do it. How does point of impact change vs barrel length vs bullet weight?
Click to expand...

well they were crowning the barrel with a portaband, so I’m gonna say any measurements of group size were not very relevant. Would have been neat to also see a 200 grain load
 
@someguy2800 thank you for sharing this video.
I'm a little surprised that they didn't gain a little speed after cutting off some of the barrel. The pressure must have stayed fairly consistent.
 
someguy2800 said:
well they were crowning the barrel with a portaband, so I’m gonna say any measurements of group size were not very relevant. Would have been neat to also see a 200 grain load
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If your going through all the effort mise well make a broad as possible test. The issue becomes once you change bullets then powder and which primer works best. Eventually we get to 50k in components.
 
A lot of folks are convinced that “300blk is optimized for 9 inches,” or “6.8 SPC is optimized for barrels under 16” while 6.5 Grendel needs >20”…” or that “308 is done by 20” and longer barrels are just a waste…”

It’s pretty telling when these bullets are still speeding up beyond ~45” with an asymptotic approach which appears it would carry for another foot or more… pretty obvious that there is no practical barrel length for any application in which a 308win wouldn’t keep gaining speed with increased barrel length. And the implications for cartridges which are burning ~25-30grn of powder instead of ~45-50, or burning 70-90grn+ powder is pretty obvious… we don’t use anywhere near to the maximum potential of these rounds in the barrel lengths we choose.

C5D4E71B-F1AE-476E-A2B1-066A3FEDE110.jpeg
 
The difference between 24" and 45", even 69", is somewhere less than 100 fps. REALLY. The temperature difference between a shot taken at 6AM vs 1PM could account for a bigger swing in velocity.

But I'm not surprised to see velocity increase well past the typical 24" even if the gains aren't really meaningful.
 
I just watched that video and WOW. That rifle makes the old Civil War rifles look small.

I was impressed that there wasn't much change between about 45 inches and 69 inches.
 
I wish I knew what powder they where using I would live to replicate this first in Quick loads then start optimizing.
 
I didnt watch the video. Not really a fan of most gun stuff on YT.

A few things i considered. First is cutting the barrel with a portaband is gonna cause the bullet to do all sorts of weird stuff. It'll be off-angle, not deburred, and not at the optimal 11° for gas expulsion.

Second is powder burn rate. For obvious reasons.

Also temperature. And did they let the barrel end cool after cutting?

The only cartridge i know of that is tuned to a specific length of barrell is the 30 Herrett. It will whoop its 30-30 parent out of a 10" barrel, but not out of an 20" barrell. Of course this also has to do with the powders chosen.

I will commend them for a cool idea for a video, but its hardly scientific.
 
BigBlue 94 said:
I didnt watch the video. Not really a fan of most gun stuff on YT.

A few things i considered. First is cutting the barrel with a portaband is gonna cause the bullet to do all sorts of weird stuff. It'll be off-angle, not deburred, and not at the optimal 11° for gas expulsion.

Second is powder burn rate. For obvious reasons.

Also temperature. And did they let the barrel end cool after cutting?

The only cartridge i know of that is tuned to a specific length of barrell is the 30 Herrett. It will whoop its 30-30 parent out of a 10" barrel, but not out of an 20" barrell. Of course this also has to do with the powders chosen.

I will commend them for a cool idea for a video, but its hardly scientific.
Click to expand...

I think you are way over thinking this
 
I threw it in Quickloads and I cannot get that particular load to show the plateau at the extreme barrel lengths. Interestingly QL with only minor tweaks reproduces the Hodgdon date for 4064 and 175gr bullet really well

Min charge is 41.5 gr 4064
Hodgdon: 45,200 psi 2500 fps from 24 inch barrel
Quickloads 45,400 psi 2503 fps

Max Charge is 45.6 gr 4064
Hodgdon: 59,500 psi 2728 fps from 24 inch barrel
Quickloads 61,493 psi 2734 fps

So I tweak the powder charge to get 2600 fps from a 24 inch barrel. But where they got 2784 fps from the 69 inch barrel QL predicts 3057 fps this tread of the prediction being fast holds until the lines cross ~24 inches. The the QL prediction starting coming in lower than the real world data. MDT got ~2568 at 19-inches and QL predicts 2471 fps.

QL predicts that the load had burnt 40% of the powder at peak pressure which occurs when the bullet has moved 1.4 inches down the barrel. 95% of the change is burnt by 13.2 inches of travel. The full charge is not burnt until ~48 inch of barrel length. Exit pressure is still ~2000 psi.

I suspect that either we are using the wrong powder and that load is actually using a faster powder or that QL friction model (both bullet on barrel and the friction of gases in front of and behind the bullet is not sophisticated enough for the extreme barrel length.
 
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