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Re: Bearing surface comparator
Posted: Sat Jul 09, 2011 9:35 pm
by Dougan
ovenpaa wrote:Today I finished off a Bearing surface comparator. This was a trial project that Mark (Spud) and I had been talking about,
6mmBR sum it's purpose up very nicely:
Why Does Bearing Surface Length Matter?
A bullet's bearing surface is the full diameter section that actually contacts barrel rifling. A longer bearing surface creates more friction which can lead to higher pressures. Also, when seating bullets close to the lands, large variances in BS can mean that some bullets engage the rifling while others do not, even with identical cartridge OAL. This can cause shot-to-shot pressure variances, increase Extreme Velocity Spreads (ES), and degrade accuracy, particularly at long range. Consistent bearing surface lengths help optimize ES and accuracy.
P1020094.JPG
The hard part is turning the internal diameter of the comparator surfaces top and bottom, the slightest slip and it they are oversize and scrap for this size bullet. I ended up building the top section in stainless and I am tempted to turn a stainless bush insert for the bottom section as it is easier to machine in some ways and means the bush can be swapped out for different sizes so you could measure say 6.5mm/7mm & .308
This is just taking the concept of 'consistency' to an extreme.....Love it
Re: Bearing surface comparator
Posted: Sat Jul 09, 2011 9:54 pm
by spud
Dougan wrote:ovenpaa wrote:Today I finished off a Bearing surface comparator. This was a trial project that Mark (Spud) and I had been talking about,
6mmBR sum it's purpose up very nicely:
Why Does Bearing Surface Length Matter?
A bullet's bearing surface is the full diameter section that actually contacts barrel rifling. A longer bearing surface creates more friction which can lead to higher pressures. Also, when seating bullets close to the lands, large variances in BS can mean that some bullets engage the rifling while others do not, even with identical cartridge OAL. This can cause shot-to-shot pressure variances, increase Extreme Velocity Spreads (ES), and degrade accuracy, particularly at long range. Consistent bearing surface lengths help optimize ES and accuracy.
P1020094.JPG
The hard part is turning the internal diameter of the comparator surfaces top and bottom, the slightest slip and it they are oversize and scrap for this size bullet. I ended up building the top section in stainless and I am tempted to turn a stainless bush insert for the bottom section as it is easier to machine in some ways and means the bush can be swapped out for different sizes so you could measure say 6.5mm/7mm & .308
This is just taking the concept of 'consistency' to an extreme.....Love it
thats the goal,