Accuracy and Bearing Surface in neck
- Thread starter wboggs
- Start date
Only bearing surface could make neck contact and maybe the question is how much body in front of, or behind the neck as there is more body than neck in most cases. I’m not sure but as to accuracy, without being able to observe what is going on inside the barrel, I have formed the belief that the bullets that are less susceptible to asymmetrical damage as they are pressed from the rear into the barrel cylinder, in a way that would cause imbalance in flight, are tangent ogive.
Secant ogive bullets have a distinct angle interfacing with the chamber. Imagine laying a refrigerator down, that is “just” smaller than the doorway, and then pushing it from the bottom, six feet away from the passageway. If it a 1950’s style round top, it’s going to better self-align that final quarter inch, and if it’s a 1990’s rectangle, it’s going to grab at that angle’s contact, which can, for an instant, pull it even harder in that same misaligned direction.
If it were not for this effect, that can round off one side of the bullet, I don’t think it would matter much at all to accuracy, as all of the bullet has to go through all of the barrel, regardless.
There is lower peak pressure on brass if the bullet does not start from a hard jam, but gets more of a “running start.” There is also lower muzzle velocity, and this can allow guys to observe results and tinker with loads at the very last minute by seating bullets deeper, on the range.
Secant ogive bullets have a distinct angle interfacing with the chamber. Imagine laying a refrigerator down, that is “just” smaller than the doorway, and then pushing it from the bottom, six feet away from the passageway. If it a 1950’s style round top, it’s going to better self-align that final quarter inch, and if it’s a 1990’s rectangle, it’s going to grab at that angle’s contact, which can, for an instant, pull it even harder in that same misaligned direction.
If it were not for this effect, that can round off one side of the bullet, I don’t think it would matter much at all to accuracy, as all of the bullet has to go through all of the barrel, regardless.
There is lower peak pressure on brass if the bullet does not start from a hard jam, but gets more of a “running start.” There is also lower muzzle velocity, and this can allow guys to observe results and tinker with loads at the very last minute by seating bullets deeper, on the range.
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Chaotik
Gold $$ Contributor
My understanding is that the % of the neck that is sized (whether 50%, 70% or 100%) could have and effect on neck tension. So not all of the bearing surface in the neck may be making contact with the sized portion of the neck.
And there is no way to directly measure neck tension, which I believe would require some way of measuring the inward neck hoop tension with some sort of sensor; I am not aware of any commercially available options to do this.
And there is no way to directly measure neck tension, which I believe would require some way of measuring the inward neck hoop tension with some sort of sensor; I am not aware of any commercially available options to do this.
6BRA
Gold $$ Contributor
if you like bushing dies
Look at a few of the famous accuracy cartridges and the generally have long necks.
They definitely help keeping bearing surface out of the neck/shoulder junction is generally recommended, I have seen that effect accuracy but I’ve definitely seen it effects ES and at distance that’s a major factor.
It does make a difference, particularly with how the neck expands and seals off the chamber. But I haven't seen where any difference is universal for any load configuration. My main focus regarding how a bullet is seated in the neck is to be sure that the bearing surface isn't engaging the neck-shoulder junction, which is easy to do with a somewhat short freebore and a large/long projectile. So, I've got to be sure the projectile(s) I'm using will work this way in my chamber, or have the freebore lengthened for the projectile I insist on using.
There are examples of some really short necked cases that shoot very well. Neck tension can affect tuning, especially so when jumping the bullet but I don't think it's directly related to how much neck to bullet contact area it has or doesn't. You can still change tension with bushings.
DaveTooley
Gold $$ Contributor
I agree with what's been said but I'm more confident with medium to long necks and moderate throat lengths. I've never gotten consistent accuracy out of extremely long FB's but have never been handicapped by shorter FB's as long as the neck shoulder junction doesn't come into play.
Neck tension is something we talk about but you can only get so much because the bullet acts as an expander. Try this. Seat a bullet and note the force required. Pull the bullet then reseat it. The neck tension didn't change because you pulled the bullet but there will be a noticeable decrease in the required seating force.
Neck tension is something we talk about but you can only get so much because the bullet acts as an expander. Try this. Seat a bullet and note the force required. Pull the bullet then reseat it. The neck tension didn't change because you pulled the bullet but there will be a noticeable decrease in the required seating force.
Seems like it would vary by bullet and load. Our riflesmith is always a fan of cartridges that have as much neck/bullet contact as possible for increasing neck tension consistency.
ShtrRdy
Silver $$ Contributor
This is a good question. When you mention the tradeoff between how much of the bullet is in the freebore versus how much of the bullet is in the neck, there is something else to consider. The diameter of the freebore compared to the bullet diameter can be quite different. A couple examples the I'm aware of is the 223 Rem SAAMI chamber has a freebore diameter of 0.224", (the same diameter of the bullet), and the 300 Win Mag SAAMI chamber has a freebore diameter of 0.315", (0.007" larger than the bullet).
RickyK
Gold $$ Contributor
Dont understand why you say the bullet does not change neck tension . When you seat a bullet , it is going to expand the neck as an expander mandrel will .
Ned Ludd
Silver $$ Contributor
I have managed to obtain pretty decent precision with both .224" and .308" bullets seated having the boattail/bearing surface anywhere from well below the neck/shoulder junction to almost halfway out the neck. We're talking 0.25 to 0.3 MOA precision here, not BR level, but it's been more than sufficient for F-TR competition. The largest effect in this arena for me has always been effective case volume and operating pressure for a given load, rather than precision.
The only time I have experienced a bullet apparently not wanting to tune in that I believe might be from the amount of bearing surface in the neck was recently with a .308 Win F-TR rifle set up with a much longer than normal freebore for a longer heavier bullet. I also tried to develop a load with Berger's 200.20X bullet in this rifle, a bullet that typically tunes in extremely easily and well with about 3/4 of the neck length occupied with bullet bearing surface. In the rifle with much longer freebore, well under half a caliber of bearing surface was seated in the neck with the 200.20X bullet, and I could never get them to shoot reliably in that rifle. In fairness, I did not test a wide range of neck tension/interference fit during this process.
Unfortunately, that is a sample size of "1". I've heard many anecdotes from others suggesting that some bullets/loads can tune in quite well with as little as .050" to .010" bullet bearing surface in the neck. I suspect that there is no hard and fast rule, with different bullet/rifle combos each behaving in their own way. When setting up freebore length for a bullet I have not used before, I generally try to keep the bullet boattail/bearing surface junction visibly above the neck/shoulder, but not more than halfway out the neck.
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wboggs
Gold $$ Contributor
Thanks, I beginning to think there are no hard and fast rules
gawd no
no part of the base of the bullet should be near the neck/shoulder junction
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