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short necks.....what problem?

 
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  #15  
Old 08-30-2013, 06:57 AM
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Re: short necks.....what problem?

I can picture neck length becoming a factor for some cartridges & their chambers.
You always want as much powder burned in the chamber as you can achieve,, not further down a bore,, not at the muzzle.
Well a 300WM has a lot of slow powder to burn, and it's low shoulder angle lends to funneling a good bit of unburning powder down the bore as added mass to a bullet(increasing recoil and muzzle pressure). This reduces it's potential.
To combat this, I'm sure folks seek extremes in neck tension. Effective tension here comes from neck thickness, length sized, spring back(hardness), or jamming of bullets.
If best seating isn't jammed, that's one less option.

Maybe this is where the notions of longer necks & accuracy come about.
But it won't apply so much with the better cartridge designs available(like a 300WSM).
This, because better case ratios bottleneck a charge to burn inside the chamber, reducing recoil, muzzle pressures, and increasing efficiency.
How you gonna do this with a 300WM without a death grip on the bullet?

But like I said, load development leads to the best from it one way or another. Just a matter of 'best' being good enough.
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Old 08-30-2013, 08:54 AM
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Re: short necks.....what problem?

Quote:
Originally Posted by Sully2 View Post
I didnt mention neck tension being consistent...but if you have "X" tension for a neck .25 long...then compressed at the same rate the tension will be MORE in a neck say .30 or .35 long
two ways to think about neck tension on a bullet.

1. this would be that actual "bite" on the bullet from the neck ID to the bullet OD. Or often stated as the difference between the two in thousandths of an inch

2. but the above is actually somewhat incorrect unless every neck length was the same. A longer neck with the same interference number will actually have more surface tension than a shorter one. I suppose that one could get by with a slight bit less tension on the bullet with a longer neck (be a good experiment). Your dealing with a little more square inches of area to actually grab the bullet. It's also a well known engineering fact that larger diameters require less tension (or interference) than smaller diameters of the same length. But also doubt we'd see a lot of this unless maybe comparing a .223 diameter to something like a .375 diameter.
gary
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Old 08-30-2013, 11:24 AM
RTK RTK is offline
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Re: short necks.....what problem?

Does neck tension make that big of a difference when it comes to the burning of powder and where it takes place??? The bullet is going to stop when it hits the lands anyway and pressure builds from there until it starts it's move again.. Am I Right??? or Wrong??
I would think neck tension plays a minor roll.
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Old 08-30-2013, 02:14 PM
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Re: short necks.....what problem?

I would say very minor affect on pressure and amount of powder burn overall.
It directly affects the pressure peak, and tune. So you need it consistent.
The higher the neck tension, the higher it's variance. Consistency comes with lightest tension that adequately grips a bullet.

But if you're load is based on reaching the highest pressures, you'll reach for anyway to get there.
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Old 08-31-2013, 01:57 AM
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Re: short necks.....what problem?

Quote:
Originally Posted by Mikecr View Post
I would say very minor affect on pressure and amount of powder burn overall.
It directly affects the pressure peak, and tune. So you need it consistent.
The higher the neck tension, the higher it's variance. Consistency comes with lightest tension that adequately grips a bullet.

But if you're load is based on reaching the highest pressures, you'll reach for anyway to get there.
That is what I'm saying, I use .0015" under bullet diameter across the board, it's ample for all of my rifles, except my 375Weatherby where I run .002" under bullet diameter, just for piece of mind.

I think people misunderstand where the powder burns in general, most large cases have significant amounts burning in the throat, no matter the shape of the shoulder or the length of the neck, in smaller cases I believe this notion to be true, especially in the 222 based cases where the flamefront stays in the case and Ackley based cases. It may be true in the WSM's, but slow powders don't propogate the flame through them easily which in most cases would cause a plug of unburned powder to be travelling into the throat behind the bullet.
I may be wrong about this, but I've never seen it testing a few WSM cartridges on my Pressure Trace equipment, peak pressure appears to occur around the same point in either 300WinMag or 300WSM.

Cheers.
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  #20  
Old 08-31-2013, 08:17 AM
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Re: short necks.....what problem?

With pressure trace I would think you'd see higher muzzle pressure from WM over WSM.
But it's very hard to setup apples/apples calibration & comparison.

I'm a follower of Gibb & Ackley efforts in case designs.
There is potential for a lot of powder in large cases of high body taper & low shoulder angles chasing the bullet down bores. Some of it's burning as it travels, but at a slower rate given reduced pressures on it so far past the peak & away from the chamber. Pressure affects burn rate.
If we were to employ Gibb's front ignition, we would see all this go away, and common loads would be completely different today.

Overbore efficiency isn't just case capacity to bore capacity, but can also be case diameter to bore, or powder burn rate to bore.
WSM ratios are an attempt to bottleneck a charge, to gain efficiency in burn. While the patent on these ratios amounts to no more than larceny and corruption, the WSM is still a sound approach.
In WSSM the ratio results seem amplified. I had to adjust weighting factor in QL to calibrate my results(+180fps for capacity) with a 26WSSM.
QL weighting factor represents efficiency from bottlenecked/overbore cartridges.

Yet underbore cartridges of correct capacity can pull off the same trick. Most represented today are the 6PPC, 30br, and 6.5x47L. These shoot so well because they are so efficient in burn, -with faster powders than normal for bore, at very high to extreme peak pressures. There is Little to no powder chasing bullets here.
You could reach this efficiency once with a WinMag, with a lot faster powder than H1000, but you'd have to pick up all the pieces and put frankenstein back together for the next shot!
A 300WM is opposite of efficient.

Reviewing IBS 1kyd overall results at the world open, I see the 300WSM out-numbering the 300WM 15:1
2013 World Open Standings
There is a reason for this, and you should see it on your pressure trace.
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  #21  
Old 08-31-2013, 11:15 AM
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Re: short necks.....what problem?

Quote:
Originally Posted by MagnumManiac View Post
That is what I'm saying, I use .0015" under bullet diameter across the board, it's ample for all of my rifles, except my 375Weatherby where I run .002" under bullet diameter, just for piece of mind.

I think people misunderstand where the powder burns in general, most large cases have significant amounts burning in the throat, no matter the shape of the shoulder or the length of the neck, in smaller cases I believe this notion to be true, especially in the 222 based cases where the flamefront stays in the case and Ackley based cases. It may be true in the WSM's, but slow powders don't propogate the flame through them easily which in most cases would cause a plug of unburned powder to be travelling into the throat behind the bullet.
I may be wrong about this, but I've never seen it testing a few WSM cartridges on my Pressure Trace equipment, peak pressure appears to occur around the same point in either 300WinMag or 300WSM.

Cheers.
some folks say the hottest point of the ignition is at the T.P. Can't prove it by me, as I simply don't know. But longer necks are well known to be beneficial, and short necks are not. I think that the grand idea that very long necks help guide the bullet into the lands is somewhat over stated, but it does a little.

Peak pressure should not occur when the primer goes off, but as the bullet strikes the riffling. The gas pressure is at it's peak and then pretty much squares itself with the increased resistance from the riffling. This all occurs in milliseconds. The powder burn continues as the bullet enters the lands, and may go all the way out to the end of the barrel. Depending of course on the case capacity. You take a small case like the .250 Savage using a .257" bullet, and I doubt there much burn inside the barrel. Yet you take a 25-06 or a .257 WBY mag, and you see a different ball game. I'd guess the powder burn is at least half way thru the barrel with some of the slower burn rates. Yet as the bullet passes thru the barrel the increased volume of the gas cylinder pushing it will in turn decrease in pressure. A given cubic inches of gas under a given pressure in a given volume will decrease as the cubic inches of volume increases. That's one of the laws of pneumatics.

Proponents of longer necked cases have long included a lot of well respected shooters from the past. You can add folks like Mike Walker, P.O. Ackley, Ferris Pindell, M.L. McPherson over the last thirty years or so. People tend to listen to what those folks say or did say. Yet each of these guys differed from the others in their thoughts and ideas otherwise. Ackley was big on the 40 degree shoulder angle, but the others were not. Ackley was big on getting a complete powder burn, and for the most the others are as well. Walker liked a caliber and a half if possible for the neck length. The others were a little less in length, but still long neck proponents.
gary
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