So everyone is familiar with long vs short throating for specific bullets. For arguments sake say we are going for full dia bullet base seated to the bottom of the case neck. Now say for a given round the bullet starts tapering .300 past the case. We can measure and make all that work.... With a bullet 20gr heavier and same relation to the lands it may protrude .050 deeper in the case. So what angular relationship do you maintain between bullet taper vs throat angle? Change per bullet? How many shots until the erosion negates any matching?
Ogive vs lead angle
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MagnumManiac
Well-Known Member
Leade angle is different to throat taper. The throat is either parallel or tapered, the degree of taper may stay the same, but the length of it changes as the diameter is increased/decreased. For instance, a 300WM chamber has a 1º26'37" taper that runs from .315" down to .3095" above bullet diameter, then the leade has a 30º taper to the lands proper, as far as I can measure, anyway.
If cutting a custom throat, generally, it's only the length of it is what is of concern in regard to the bullet being cut for.
Nobody can say how many shots it would take to start to erode the throat enough to effect the angles, but tracking my own 1000yrd rifle, every 200 rounds down will have a measurable difference in length, it only minor, but it is measurable.
I don't worry about the length too much, but what concerns me is when the velocity starts to drop off.
When it does, I work back up to the previous velocity, pressure signs withsranding, of course, but generally this doesn't pose a problem becasuse the pressure drops when the throat lengthens.
Cheers.
gun)
If cutting a custom throat, generally, it's only the length of it is what is of concern in regard to the bullet being cut for.
Nobody can say how many shots it would take to start to erode the throat enough to effect the angles, but tracking my own 1000yrd rifle, every 200 rounds down will have a measurable difference in length, it only minor, but it is measurable.
I don't worry about the length too much, but what concerns me is when the velocity starts to drop off.
When it does, I work back up to the previous velocity, pressure signs withsranding, of course, but generally this doesn't pose a problem becasuse the pressure drops when the throat lengthens.
Cheers.
gun)
J E Custom
Well-Known Member
There is no reason to try and match the Ojive to the lead angle, In fact it is better for them Not to match or pressures will rise.
Most lead angles are set by the designer of the cartridge for other reasons and normally from 1o
to 2.5 degrees. for best engraving the bullet uniformly.
Study some of the chamber drawings and you will see many variations but none intended to match the bullet Ojive.
https://www.google.com/search?q=ptg...2010%2F09%2Fbasics-leade-angle.html;1600;1266
For best barrel life, slower rates of fire, lower temperatures, frequent cleaning and wider lands all contribute to better barrel life. lead angle may have a small effect on it but it is immeasurable.
Matching the angle of the lead angle to the bullet would make the bullet impact the lead angle in its entirety and lead to higher pressures and poorer engraving of the bullet in my opinion.
This is just my opinion on lead angle.
J E CUSTOM
Most lead angles are set by the designer of the cartridge for other reasons and normally from 1o
to 2.5 degrees. for best engraving the bullet uniformly.
Study some of the chamber drawings and you will see many variations but none intended to match the bullet Ojive.
https://www.google.com/search?q=ptg...2010%2F09%2Fbasics-leade-angle.html;1600;1266
For best barrel life, slower rates of fire, lower temperatures, frequent cleaning and wider lands all contribute to better barrel life. lead angle may have a small effect on it but it is immeasurable.
Matching the angle of the lead angle to the bullet would make the bullet impact the lead angle in its entirety and lead to higher pressures and poorer engraving of the bullet in my opinion.
This is just my opinion on lead angle.
J E CUSTOM
It just seems that for any given bullet/case combo there would be a throat/lead combo that gives you the best pressure curve. It would be interesting to see that data plotted for several combinations. I don't know if someone like sierra ever uses custom reamer designs during all their testing. I know i don't want to fund the testing!
jsthntn247
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I've seen reamers with an elliptical throat. They claim increased speed and barrel life. My 243 barrel has this throat in it and I'm able to get more speed from a 24" barrel than others report from a 27" with the same loads.
Hired Gun
Well-Known Member
I have never heard of an elliptical throat before. Can you go into a little more detail? Are you saying the throat is smaller at the neck area and get's bigger before it gets to the lead area?
To the OP. I have found that usually the heavier bullets are sharper shaped and need to seat to a longer OAL to maintain the same distance to the lands if you are inclined to do that.
To the OP. I have found that usually the heavier bullets are sharper shaped and need to seat to a longer OAL to maintain the same distance to the lands if you are inclined to do that.
Canadian Bushman
Well-Known Member
jsthntn247
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Not 100% sure because when you ask anybody with one about the specs on it and how it works they pucker up so tight they couldn't pass a cheerio and say it's proprietary. Google elliptical throat 6mm competition match reamer and you can find some info.
