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fredriffle-
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rsterne
I assume you mean a faceted pyramid instead of a round cone?…. The possible designs could be anything from 3 to 6 sided, I guess, I have seen 5 sided ones…. I don’t know if they are any more effective than a cone or not, never tried them…. The limiting factor would be the largest diameter across the points, and I know that Al requires a 0.200″ Meplat for his RG style moulds now…. Instead of the HP pins being made on a lathe, they would have to be finished on a mill, I would think, adding one more setup to the process, another machine, and hence additional cost….
I would think some testing would be in order to prove that the concept has merit…. Take an RG pin and file or mill some flats in it, cast some bullets and test them to find out if it is worth it…..
Bob
fredriffle
Mike B.
There are a couple of items that one needs to try to observe when designing an HP pin… to have it made.
If you are also designing & having the mould made … one can figure out how much weight the HP pin will reduce the weight & then add ~ that much weight to the nose …
Take for instance a .173 or a .200 meplat, or something like a tapered truncated cone nose design with ~ that same meplat…
One can increase the meplat to ~.235 for ~ the first .310 of that cast products tapered nose … which will tend to increase the finish cast bullet product by ~ 10 grains…
Then one can reduce that weight back down to very close to the original cast bullet weight… without having to shorten the cast products OAL… with the HP pin…
Most hollow pointed cast bullets tend to have a decrease in predicted BC because of the fact that they tend to both the decrease in the cast bullets OAL to arrive at an ~ .2 meplat, & then add to the decrease in predicted BC by adding the HP pin to the equation… by the lightening of the end products weight with the addition of the HP…
The potential solution is to … as noted above… add the weight to the nose area by increasing the meplat as noted above… then install the HP pin … of approximately the same weight… & leave the products OAL alone…
You will end up with essentially the same predicted BC… as the non HP design format… plus potentially a bit more predicted BC out of the whole deal …
I know because I did the calculations then had the custom mould or moulds made, & then in addition had the HP pin made & installed to my own drawing specifications …
Taking an approximate 176 – 178 Grain bullet and increasing the meplat as noted above will get you something like a 186 grain cast product before hand … leaving the OAL @ ~ 1.000 inches… alone.
With the .200 HP pin diameter, stepped with an OD at an ~ .165 , & with a length of ~.250 on the HP pin taper plus an ~ .030 diameter radius at the nose one will end up with an ~ 175 – 176 gr bullet … once again that now is an HP version of that same basic design format …
One other thing when designing an HP pin… there are right angle triangle calculation on the internet where you can calculate the draft angle of the a right triangle … I try to keep that draft angle of the HP pin at at least a 7 degrees of taper … or more …
Why?
Because … That tends to help the cast product come off of the HP pins a bit easier …
Too shallow of a draft angle and the pin point will tend to cool off tiny bit too fast, & your cast product will thus tend to want to stick around & hang onto the HP pins…
Thus in addition to get good fill out at the cast products … at the nose end of the HP … you will most probably want have an HP wall thickness of ~ .025 at the meplat to ensure a good fill during the pour …. whether ladel or bottom pouring said end product mould.
That is another point of the equation, … that must be taken into account … in your calculations …
Thus all of the components of the HP equation must be taken into account…
1.The dome opening dia in relation to the end products meplat…
2. The HP pin length, & finally…
3. The diameter at the HP pin’s dome in that truncated cone calculation … also can come into play when designing a HP pin..
Each component of the equation has its plusses and minuses that one might wish to consider & weigh when designing a HP pin… Flat pin or a hemispherical pin when turning a pin to specifications
Too long a pin, & or … too shallow a draft angle tends to slow down the HP cast products through put…
Take Care, & Stay Safe…
The angle cut taper is basically figured per side so that the machinist can set up that angle to cut said taper …
If you look at an NOE dimensional sketch drawings you will see both the full depth of the HP and the depth of the truncated cone … shown on the RG moulds…
I have the same basic bullet design program that NOE proper is utilizing … ostensively from the same source…
Now to begin to answer your next potential question … in regard to the angle calculation…
The depth of the truncated cone forms one side of the right triangle… In the right angle triangle calculation program that I use this is the a side …
That depth dimension is normally shown below the bullet sketch as a dimension to the end of the truncated cone… the full depth of the HP is shown along the centerline of the dimensional sketch including the hemispherical cone point.
If one wants one can draw a dashed horizontal line from that depth to the HP opening
The other side of the 90 degree right triangle is formed by taking the R= radius of the hemispherical cone, & subtracting it from one half of the major diameter of the HP opening … This becomes the b side in that program…
That gives you the second side’s length of the right triangle…. Now that one essentially has both side lengths of a right triangle one can solve for the angle of the taper… using basic geometry…
It then becomes a simple matter to insert into an right triangle calculator program … the two side lengths a & b, and then set the precision (number of places) that you want the calculation angle & the hypotenuse to read out to… & let the free program do its work …
I normally use 14 places … a complete over kill I admit … but it tends to get the job done… for me at least …
The result give one the hypotenuse length of the right triangle, & more importantly the needed angle for the machinist to cut the HP pins taper to…
This intel I add to the machinists data that I send to my HP machinist for his setup,& the cutting of the HP diameter pins, & the pin angle …
The above set of calculations has worked many times for me, & has always has given me what the design Software predicts that the bullet weight will be … (All be it within a grain or two) provided of course that one uses the correct alloy during the production in in regard to the end product weight calculations…
The design software program also allows one to set the alloy type to increase the accuracy of the end weight prediction… I tend to believe from looking at the NOE proper drawings that only WW for the smokeless products, & pure lead for the air driven products …
It is what it is…
I sincerely hope that this long winded explanation helps you, & tends to answer your question…
Take Care, & Stay Safe…
HI Mike….
Thanks for the detailed explanation…. I also have the same software as NOE, plus a 2D drafting program, and I use both…. I specify my boattail angles as the angle of one side from the centerline, I just wanted to make sure you were measuring your 7 deg. the same way…. The TMT software, as you know, has suggested HPs, but the angle changes, and with long slender bullets, I’m pretty sure they would not release from the pins…. Since you know that 7 deg. works, I will make sure I don’t have less than that….
Bob
Air guns also are also setup … If I am not mistaken to run on essentially on pure lead … which does not tend to fill out the mould to the same point as an alloy would …
Thus the need for tin and antimony each of those elements tends to have their own purpose… in a lead alloy.
If you wish to use a 5 degree slope for one of your an airgun designs … then please do…
Take Care, & Stay Safe…
I usually use 40:1 (2.5% tin), because it fills out the mold great, without being too hard for airgun use….
It is entirely possible that with a harder alloy, your 7% taper is likely spot on…. I was not arguing, I was merely making an observation that some of Al’s molds (even those intended for PBs) have less taper…. but work fine with airgun suitable alloys….
Bob
Did you truly mean 2.5% Lead … instead of Tin…
I am not trying to argue either …
I just thought that you might wish to look at your latest posting … in regard to the 40:1 reference…
In reading the historical postings I have seen postings with many topics & references to product sticking on the HP pins…
It seems to me that a notation in regard to the taper angle was in order … to attempt to get that intel out to the general membership so that hopefully they would have potentially a broader understanding of the RG options..
You and the other administrators all seem to have the ability to manufacturer what accessories that you need for your own personal use … if the historical postings are correct…
Many of the members do not have that luxury …
However it is what it is… with no one being able to convince anyone else about what they have determined is the correct path to take on a specific subject …
That is as it should be… allowing different ideas and formulas to be expressed on the open forum … in such a way that the membership in general can look, & if they so choose, hopefully ask a question to get answers that they can consider and ruminate on.
Hopefully the goal is for each member to read & decide to try the different options presented, & get their own test results … should they decide to choose to …
It is what it is …
Take Care, & Stay Safe…
You are correct, 2.5% Tin, I changed the post, thank you for noting the error…. Recently there has been a problem with some slugs sticking to the pins, and some of that is due to ridges on them…. This is something Al is constantly chasing….
I am not an Administrator, Al asked me several years ago to design slugs and pellets for airgun use, and I have provided him with many more designs than are currently in production….
You are doing a stalwart job of helping people, and deserving of being an Administrator, IMO…. I will suggest that to Al, I think it would be a great addition to the Forum….
Bob
In the for what it is worth department : The R= dimension is (I tend to believe) the most critical dimension here…
In that a rather small decrease in that radius dimension downward, by comparison … tends to make a rather larger difference in the draft angle taper (assuming of course that the polishing is uniform) along the entire length of the taper… that it is calculated geometrically on … with from what I have found is a minimal decrease in projected cast bullet weight… (Please understand that if 5 degrees works for pure lead then by all means go with it…)
It is also why when the 20th century rolled around, & cartridge designers started to make cartridges like the 30-30 that those cartridges were tapered…
They also found out much to their consternation that the original cartridge case material (of copper and zinc) tended to solder itself to the rifle, when they first started out trying to come up with a jacketed bullet material to allow one to push the lead projectiles faster with the new smokeless just being developed…
This cartridge taper was ostensively also designed into the new cartridge case designs … so that it only took what amounted to a minuscule of cartridge case rearward extraction to free the cartridge case from the chamber … because of that new cartridge case design’s taper…
Thus one had longer cartridge with longer lengths … like the 300 H&H coming into existence…
The more recent longer and straighter cartridge cases now tend to take more effort by comparison to extract as the taper angle on those cartridge cases now tends to be a much shallower angle … if indeed they are potentially tapered at all…
The 223 at first tended to get stuck until the chamber etc.. until the AR’s were chrome lined… corrosion, & powder residue … to push a round to 3000 fps …
As did the 45-70 which tended to get stuck in Custer’s newly issued trap door Springfield carbines when they got hot.. & filled with holy black residue… It tended to slow down the rate of fire for those troopers having to pry those spent cartridges out of their carbines chambers with their issued knives … to reply to those Native Americans … with their now surplus Civil War firearms…
Nuff said.
Take Care, & Stay Safe…
rsterne
Kitisarke
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