mikecr said:OBT is about dimensional change in bores -sweeping back & forth breech to muzzle to breech, etc.
But on firing barrel/bore straightness changes as well. The barrel straightens from rest condition like a newly pressurized hose. It untwists a bit from the counter energy of spinning up the bullet, this also applies through bedding and on down the fore arm to lift the gun in torque against the bag. The bore expands directly behind the bullet as it travels down the barrel. The powder burn rate changes with pressure and heat as the bullet travels down the bore. And there are pressure nodes, which trump many things, as timing is set way into diminished returns, and it's hard to change this even if you tried -by then. Pressure nodes are like an OCW, only at extreme peak pressures as is common with competitive underbores.
Given all this, there is a lot going on at the muzzle before, during, and after bullet release. And there is a lot going on as extended over more time with a longer barrel(like slower motion). So if we're to pick a place for the muzzle to be on release, a longer barrel will make the precise timing of this easier. But it's even more important that we do so here, because any off timing will have a larger affect, because some of the movements are way bigger with longer barrels.
With a shorter barrel, slight mis-timing is less damaging, because some of the movements are a lot less. This is a good thing because it's more difficult to nail timing with enough precision with shorter barrels, because there is less time to do so(like fast forward).
Muzzle pressure is that slapping the back of bullet bases on release. It's a disturbance to stability if nothing else. With big boomers and short barrels(like 26") muzzle pressures can reach extremes(12-15Kpsi) and this does nothing good for results. A competitive 6PPC, even with it's ~22" barrel and extreme pressure load, produces low muzzle pressures(~8Kpsi). This helps while shooting light boat tails. FB bullets are less susceptible to muzzle pressures either way.
More powder burning produces more gasses that if not extended inside the bore will release at the muzzle. And I believe there is a price to pay here.
I notice 6Dashers shooting really well in 30" barrels, and I wouldn't be surprised if some of that is due to low muzzle pressures. Most of it is the shooters, and it's a damn good cartridge, but you might think there would be some detriment(price to pay) for such long barrels with such a small cartridge.
It's interesting to me.
I'm referring to all the muzzle movements that are beyond OBT. As in OBT is just one factor.jlow said:it would seem that if accuracy is only lost when the dimensional change is happening at the crown, it would mean that you are safe and in the accuracy node most of the time.
There is a thread around here somewhere about powder burn percentage(that got really ugly). It didn't conclude with consensus about the cause of muzzle fireballs & secondary pressure peaks -whether powder burn or secondary gas burn off. But I think most would agree that the main contributor is a relatively short barrel for capacity.jlow said:I am also wondering how muzzle pressure is a slap in the back of the bullet, it would seem that this is a constantly building pressure that is always there as soon as the powder starts to burn.
Steve Blair said:Did Virgil compete at 1000 yards?
Steve Blair said:It is not impossible, but a barrel that short would be a significant disadvantage. Longer barrels allow large capacity cartridges, slower powders, higher B.C. bullets and higher muzzle velocities while keeping muzzle pressures reasonable with prudent component selection. Long barrels can also shoot quite well. My 34" .300 WSM will agg 5-shot, 100 yard groups ~.22" and I am a mediocre benchrest shooter shooting from a flexible, wooden bench. [br]
I have no doubt when the demands of long range shooting are removed, a short, very stiff barrel will produce more reliable results. When all of the problems between muzzle and 1000 are considered, it is not the best choice.
jlow said:I did some simulation using QL. ... So as you can see, with an 18†barrel, you really only have two nodes (6 & 7) that you can reach and the powder weights are either 42.3 grains or 45 grains.
I suggest you read this review:brians356 said:jlow said:I did some simulation using QL. ... So as you can see, with an 18†barrel, you really only have two nodes (6 & 7) that you can reach and the powder weights are either 42.3 grains or 45 grains.
In the interest of maximum clarity, could you define "node" WRT QuickLoad?
jlow said:I suggest you read this review:brians356 said:jlow said:I did some simulation using QL. ... So as you can see, with an 18†barrel, you really only have two nodes (6 & 7) that you can reach and the powder weights are either 42.3 grains or 45 grains.
In the interest of maximum clarity, could you define "node" WRT QuickLoad?
http://www.accurateshooter.com/gear-reviews/test-quickload-review/
A node is a powder weight that produce a tight group. With any caliber/bullet/powder/case/temperature/seating configuration, there are discrete powder weights that gives a tight group. We call them accuracy nodes.brians356 said:jlow said:I suggest you read this review:brians356 said:jlow said:I did some simulation using QL. ... So as you can see, with an 18†barrel, you really only have two nodes (6 & 7) that you can reach and the powder weights are either 42.3 grains or 45 grains.
In the interest of maximum clarity, could you define "node" WRT QuickLoad?
http://www.accurateshooter.com/gear-reviews/test-quickload-review/
Thanks. But there is not one occurrence of the word "node" in that review - unless my Firefox page search has a gaping hole in it.