What’s the benefit of having a long necked cartridge?
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MudRunner2005
Well-Known Member
What I've always heard is that you should have as long a neck, as your bullet's diameter. So if you're shooting a .30 caliber, your cartridge's neck should be .308" long. 6.5mm should be .264" long, etc..., etc...I've been mulling this over (based on what I was taught as a young man) and have finally formulated a question for you guys so you can "straighten" me out.
How much of a factor does neck length play into bullet alignment with the bore? Swamplord I'm not picking a fight, but your post was the one that got me to thinking the most....It seems to me (and I'm probably wrong, just trying to figure out where) that a "concentric" neck that was slightly longer would "hold" a bullet true longer (and I realize that this time is minimal), the SD's make sense to me but I've used graphite for years to cure that ill, and velocity would be a function of how much you were jumping.
Like I said, not wanting to pick a fight, I'm just wanting to learn/understand a little better.
I'm most likely going to have multiple other questions on this topic, so please bear with me
Disclaimer, I'm not saying this is fact, just what I've always heard to go by as the rule-of-thumb for wildcatting.
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MudRunner2005
Well-Known Member
What most people think of when they say the chamber's "throat" is actually called the "leade". It's where the bullet first makes contact with the lands and grooves. The throat is the first few inches of rifling. This is the way it was described to me by a BR shooter who was showing me how to borescope a barrel, and what to look for. He showed me how the leade moves forward over time from wear & tear (erosion), and how the throat fire-cracks from the concentrated flame and bore pressures. Both of these can be exacerbated by shooting long shot strings without letting the barrel properly cool...Especially in magnum cartridges, and cartridges with a small bore & a large case capacity (like the .22-250).
"THEY" have never heard of a 300 Winchester Magnum. One of the most successful and easy to tune cartridges ever does not even have a .308" long neck.
MudRunner2005
Well-Known Member
I'm well aware... See the last sentence of my post...
Thanks MudRunner, you explained both of those topics almost exactly as they were explained to me 25+ years ago. I was just wondering if I had forgotten something or was missing something. (These topics were explained to me by a BR shooter as well)
What confuses me to a degree (looking for feedback here), is I have scoped rifles with excessive fire cracking with little to no (relative to number of shots down bore) erosion, and I have seen barrels that are eroded beyond belief (again relative to shots) with absolutely no fire cracking.....so is this all in the cleaning regimen?
I'd say barrel material/ bore finish, amount of powder burned and the heat of explosion of the powder and a combination of these things as well as how cool the barrel is kept ( minutes between shots.
I get firecracking before throat erosion in most of my barrels. I usually shoot one every five minutes or so.
I get firecracking before throat erosion in most of my barrels. I usually shoot one every five minutes or so.
MudRunner2005
Well-Known Member
Just my thoughts, and I'm no pro, but I think powder burn rate might have a big factor on the fire-cracking part. The slower (cooler) burning powders might have slightly cooler flames, which will lead to less/no fire-cracking. And of course, proper cool-down times. It's just a theory, as I have no proof of this.
As for throat and rifling erosion of some barrels and not so much on others, I think it's a combination of the barrel's steel type (CM, SS, etc...), bullet construction (how thick the jacket is, and what the alloy mixture of, or material, the jacket is made up of), and how hot the barrel gets while shooting. When steel is heated, the molecules start moving around faster. And when they get moving around fast enough (from high heat) steel can easily be manipulated, cut, and eroded (think of blacksmithing, or oxy-acytalene torches). So, as the bore gets hotter, even a more malleable material (like copper) can eventually begin to slowly erode the much harder steel. This is also just a theory.
Rifleman97
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Interesting topic change, if I had the money I'd build a test rifle in a heavy overbore caliber such as 26 Nosler or something and burn out one barrel with fast burning powders and then replace the barrel and burn it out with slow burning powders, and see which causes which, and see if there's a way to lengthen barrel life overall
J E Custom
Well-Known Member
You are absolutely correct. It was hammered into my head by all the "Old Timers" when I was a young pup. What changed was because of the quest for more velocity and more powder choices. Once we demanded more speed, more case capacity was needed and the 300 Win Mag is an example of increasing the case volume without having to Increase the action length.
As wildcatters, we are constantly pushing the boundaries of all the old
norms and getting away with it because we have better chambers, bullets, powders and reloading dies that can load ammo more precisely in short necks. (How many remember when you started to seat a bullet and then rotated it in the die before it was to finished length/depth to keep it straight) things have changed for sure.
After many years of trial and error designing and building wildcats that would perform better that the parent cases this standard had to be altered. This doesn't make it a bad rule, in fact it is still a good guide line for small caliber cartridges and very usable for the mid caliber rifles
It does have a point that it is not practical in the truly big bore bolt rifles because of cartridge length. the old doubles can and still use long necks because lots of them don't size the case and just crimp the case to hold the bullet and they are single loaded.
J E CUSTOM
WildRose
Well-Known Member
The throat area is what is exposed to peak heat and pressures due to the way the bullet engaging the lands and seals off about 99.9% powder preventing it from escaping ahead of the bullet. That is where the pressure spike occurs as the reaction accelerates.
Pressure creates heat, heat creates pressure.
Slower powders reduce that peak and keep burning adding push all the way down the tube compared to faster burning, higher pressure generating powders.
WildRose
Well-Known Member
Fire cracking looks like reptile skin. When you see it your throat is either gone or about to be.
Big chunks start flying off and the lands begin rapidly eroding away.
I've seen .204 Rugers and .220 Swifts go from being nail drivers to 3+ MOA guns over the course of just a few days of prairie dog shooting.
Never get one hot and keep shooting and you can extend barrel life a very long time as the hotter the chamber/throat area gets the more erosion and firecracking accelerates.
WildRose
Well-Known Member
Just a guess but probably more to do with your powder choices and how hard you push the upper ends of velocity.
More heat, more pressure, more pressure, more heat, faster powders, max loads = max heat and pressure.
Seating bullets into the lands makes a big difference as well because of the increased pressure spike due to so much less powder getting out ahead of the bullet.
