What in Tarnation is happening to my bullet?

[Dimner]

Going back to the bullet that I discussed in this post: https://www.artfulbullet.com/index.php?threads/maths.8809/ , the NOE TL-310-178

It has been working well for me through my initial tests with my Winchester 94 and my M1 Garand. Accuracy at 50 yards is promising. Holes touching or nearly so with the Garand and open sights. Holes touching or even overlapping with the 94 and a scope. Holes nice and round (I can post pics if it's helpful)

However, something is happening with the bullet that is greatly affecting the actual Ballistic Cooeficient vs the Estimated BC based on form factor and sectional density.

Okay, calm your man boobies (as my daughter tells me). Yes I said BC. That always send the people in a flurry. I know in the real world BCs are different than estimations. I also know the BC isn't an end all be all number that we should hold in our dear hearts as something very important. I didn't buy the mold for it's BC. However, in this instance, the rather large deviation from the expected vs reality is telling me something is happening to the during ignition, barrel travel, and/or launch. I'm just not experienced enough to understand what that is.

Sure, so far accuracy looks good, but this is something I would like to solve.

Using my labradar and it's ability to measure velocity at multiple distances for each shot, I'm getting BC calculations of 0.190 to 0.210 with different powders with the 94 and Garand. The estimated BC for this bullet by NOE is 0.3337. That seems like a very large difference. I tend to trust NOE's estimate. BC estimation is done by SD divided by Form Factor. The only way to bungle an estimation would be to get their Form Factor value wrong. Sectional density is a straight forward calculation. Anyway, for this discussion, I'm thinking we should say NOE's estimate is within reason of what could be expected.

So why is the BC of my bullet reducing so drastically? I have a boatload of data I can sift through, just need to know what to look for. I put 75 rounds down range yesterday with various powders, all tracked by the labradar.

My first hunch is possible the alloy?

 

[popper]

BC is a function of fps.

 

[Ian]

BC is a function of fps.

Bingo.

 

[Dimner]

I'm not following what you guys mean.

 

[Jeff H]

For a given bullet, the stated BC is the BC at a specific velocity.

The BC of the same bullet is different at different velocities.

 

[Dimner]

Sorry, I should have been more clear. I understand how BC relates to velocity. But I do not know how the answers above stating that pertain to my issue.

I'm calculating my actual BC using actual measured velocities at different distances. The recorded shots, distances and velocities range from 1800 fps to 2200 fps. All calculated BCs are within .190-.210. There is no practical velocity that could be mocked up to achieve a BC near the estimated 0.3337. Therefore, the only thing left has to be some sort of alteration to the physical bullet.

 

[Dimner]

Examples with 30wcf

Shot ID	V0	V10	V25	V40
1​	2161​	2121​	2061​	2001​
2​	2164​	2125​	2065​	2011​

Shot ID	V0	V10	V25	V40	V50
1​	1978​	1942​	1887​	1833​	1797​
2​	2021​	1984​	1928​	1873​	1838​
3​	2008​	1972​	1918​	1864​	1824​
4​	1989​	1952​	1897​	1844​	1808​

Examples with M1 Garand:

Shot ID	V0	V10	V25	V40	V50
1​	2239​	2199​	2139​	2080​	2041​
2​	2259​	2219​	2157​	2096​	2058​
3​	2231​	2191​	2130​	2070​	2030​
4​	2251​	2211​	2150​	2091​	2052​

Shot ID	V0	V10	V25	V40	V50
1​	2232​	2192​	2131​	2070​	2029​
2​	2233​	2194​	2133​	2074​	2036​
3​	2210​	2170​	2110​	2051​	2012​
4​	2207​	2168​	2108​	2049​	2007​

 

[RBHarter]

Altitude , barometric pressure , and humidity .

Live example with a .160 250-260 gr SWC . At 4000-4500' MSL , 24-27% humidity , 25-27.5 in hg , and a 1240 MV I shot the load 75 yd with soft ball to honey dew accuracy based largely on the trigger operator at 78-82 yd it all came undone which was a product of gyroscopic stability and transsonic buffeting . No my example and findings arent up for discussion . With the same MV and bullets in a faster twist I didn't get this result . Also not going supersonic removed the issue . Moving along .
Taking the load to 110' MSL , 70-80% humidity , 29.6-31 in Hg the bullets were making ovals at 55 yd . 20 yd is a long ways when we're talking about 25% of the gross proof range .

I've owned all at once 06' , 308 , and 30-30 rifles with 1-8.5 , 1-10 , & 1-12" twists . The 1-12" 308 refused to shoot any bullet over 175 gr without regard to shape or length , 172 gr 301618 no problem , 180 Hornady RN nope not fast or slow , not on a paper plate at 50 yd and it is shorter than the preferred 150 SPBT which would cover 5 pretty regular with a quarter at 100 . The 1-8.5" 06' wanted everything under 2700 fps MV and it was happy I had a hobby drill press 200 gr Spitzer PB 1900 fps MV was just out of reach and what I needed . The 301618 wouldn't do it either . Alloy I suspect but I needed expansion on impact . So it is what it is .
1-10" 06' and 30-30 ...... Well the 06' rifle in and of itself is a huge PITA and has a factory match chamber PP is out of the question and cast is marginal to chamber but the 30-30 will hold 8" at 50 with the NOE version of the 310-230 spire point so there's that it doesn't shoot anything else outside of 3" despite my best efforts .

I don't even want to open the alloy door but I did and it's an entire thread just getting through 12 ways to get 18 BHN and have 12 different target results and why 4 of them leaded badly with the same charges for all .

What it comes to is that some parings just aren't going to talk to each other even if they're close to ideal .

2,3,4,6 groove rifling , exit dia , top band shape at exit , base shape at exit , nose engraving ........

NOEs shop and offices are located at almost 5000' MSL just north of Salt Lake City on the East side of the Great Basin Desert about 80 miles from the Bonneville salt flats home of very nearly 3/4 of all land speed records not needing a left turn . So his estimated BC is probably closer to accurate out his back door than you might find on your range .

Trues story .
Speer couldn't figure out why a bullet they had , I think it was in the 270 circa 1955 , measured out for a BC but wouldn't get even close on the range . Drift was where it should have been but drop was way off . Everything trapped was destroyed so no help there . The superior flat shooting certain death of the 06' and all they couldn't just say " well this is what it's actually shooting " . With the implementation of shadow photos they discovered that their nifty high speed low drag pointed SP in flight had become a 1R RN in the barrel . So began the learning curve about jacket performance in both internal and target ballistics .

 

[Tomme boy]

Also why hornady changed the plastic tip formulation. The heat from the flight of the bullet was melting the tip changing the bc of the bullet going down range. They were never able to measure this before they got the radar chrono. So my guess is your bullet is changing shape in flight.

 

[Snakeoil]

We all know that soft bullets bump up and fill the bore when fired. So, depending on how hard/soft your bullets are, it could be they are compressing in the barrel enough to turn them into a wad cutter of sorts. What is the NOE bullet in question?

Have you taken the specs for the bullet and done the actual hand calcs to come up with a BC? It could be that NOEs numbers are a bit optimistic. He could also very well be simply using the Lyman BC numbers for those he is duplicating. And if I am not mistaken, there are multiple schools of thought on developing a BC for a bullet and it will change depending on which you use. I found a very simple calc online that used meters instead of yards. I simply used your numbers and converted to meters and MPS and got a BC of .206. So, I'm in the same range that you are calculating.

I think I would try to calc the expected BC from the bullet specs in the NOE drawing. It's a bit tedious. I Googled the subject and there is a wikipedia article that walks you thru the calcs. Might turn out that the BC you are getting from your range results are the correct BC for the bullet.

I don't do enough noodling on cartridge performance to have a good feel for what a common bullet shape should have as a BC. So, I did a quick search and found this great list published by Sierra. Looking down that list at all those very slippery jacketed bullets with names like Matchking, and in the .30 cal range, there are quite a few under 0.3. Yes there are many in the .4 and .5 range. But again, we are taking slick boattail jacketed spitzers. So, to think that some lead slug out of a mold is going to have a better BC than a jacketed spitzer is wishful thinking. I've attached the link to the chart for your reference. I'm not trying to be a know-it-all here. My knowledge on this subject is very shallow. I dug into it only to educate myself and try to figure out what was going on in your case. Thought I'd share what I found and what thoughts it generated.

https://www.sierrabullets.com/wp-content/uploads/2019/10/BC-chart-rifle.pdf#:~:text=Ballistics%20Coefficients%20-%20Rifle%20Stock%20%23%20Dia.%20%28inches%29,Point%201515.243%20Spitzer%20Boat%20Tail%20Blitz%201520.243%20Spitzer

 

[fiver]

see where that COG is.
your not having an internal ballistics problem.

 

[Tomme boy]

That bc is off by a large amount. You found out first hand. Noe has it wrong

 

[Spindrift]

To me, your Labradar BC values look realistic, considering the shape and weight of the bullet. The NOE estimated BC looks too optimistic.

In comparison, the Hornady .30- cal 170grs flat point has a stated BC of 0.189.
The NOE number roughly equals the listed BC of the Hornady .30 cal 150grs spire- point flat base.

I don’t think the gap between estimated and measured BC is caused by major geometric change to the bullet. I think the estimated BC is far off.

Excellent results, by the way! And thanks for sharing these interesting observations!

 

[Bret4207]

Who came up with the original BC? You or the mould maker? 2nd question, if you smack a lead alloy bullet hard they deform. That happens in the throat too, so could the shape be altering enough to cause the BC change from what you expected?


ETA- Huh, I wrote that last night but must not have hit the post button. I see others have the same idea I was thinking.

 

[Dimner]

Snakeoil, and Spindrift. You speak sense in a language I can wrap my brain around. Thank you for that I think everyone is right, NOE just has a very far off estimation for the BC. The NOE method for that estimation makes sense, reading through it, but I think they are far off on how they are coming up with 'form factor'

Here's a blog of theirs on how they estimate the BC: https://noebulletmolds.com/site/using-our-products/faqs/
I'm guessing that the way they come up with 'form factor' works on paper and with the maths but the real world has something different to say.

Reminds me of an anecdote of my son's Junior year in high school physics project. He built a trebuchet. He had it all designed to the nth degree in CAD and with his graphing calculator. It was estimated to be able to launch a golf ball a million gazillion yards, okay maybe like 150yds. But the big lesson that I hope he learned is: Going from CAD and calculators to building something using a circular saw, 2x4s, drywall screws, lead ingot counter weights and all the friction and lack of extreme build precision, the results are going to be very different. It ended up slinging that golf ball in an arc about 30-40 yards up, and only 25 yards forward.

I should have remembered that lesson here.

For those who are wondering, this is the bullet: And Spindrift..... I use that 170 hornady bullet quite a bit. That example made the lightbulb go off in my mind.

 

[Snakeoil]

If you want a great shooting .30 cal bullet, try this one. It's an old Lyman design. I shoot it in a .314 size in my 03 with excellent results.

311-206-RN-K2 | NOE Bullet Moulds

noebulletmolds.com

That bullet you are shooting is a semi wadcutter. It should have about the same BC as a garbage can with the handles removed. That said, if you use this for hunting, I understand the preference for a large flat nose.

 

[Snakeoil]

I just happened to look at the BC for my bullet versus yours. Mine is only a tad better than yours on the NOE drawing. But I struggle with a bullet with a sleek nose like that only being slightly better than a bullet that is the lead version of a Winnebago.

 

[Dimner]

If you want a great shooting .30 cal bullet, try this one. It's an old Lyman design. I shoot it in a .314 size in my 03 with excellent results.

311-206-RN-K2 | NOE Bullet Moulds

noebulletmolds.com

That bullet you are shooting is a semi wadcutter. It should have about the same BC as a garbage can with the handles removed. That said, if you use this for hunting, I understand the preference for a large flat nose.

For the 30wcf, yes it's being used as a hunting bullet. That large flat nose beats out any gain in BC of other bullet designs. Especially since I plan on using it only with open sights. Also, it's one of the few bullet designs that fits well in my Friday afternoon built 1970's Winchester 94.

For the M1 Garand, I'm using it for CMP High Power format shooting at my club each week. We shoot at 100 yards with the CMP reduced targets. So the bullet is perfect for my application. a) A mold with many cavities b) Easy to cast c) Makes nice distinct holes on paper.

I like that bullet you posted, it would probably be that one or something very similar if I were shooting the M1 at any distance greater than 100.

 

[Dimner]

I just happened to look at the BC for my bullet versus yours. Mine is only a tad better than yours on the NOE drawing. But I struggle with a bullet with a sleek nose like that only being slightly better than a bullet that is the lead version of a Winnebago.

Oddly, the estimate for my TL-310-178 is 0.3337
The SP version of the NOE 311-206-RN is 0.3235?!

That's saying my TL-310-178 is more aerodynamic?





Makes me wonder if this is simply a case of a typo. Should the TL-310-178 be 0.2337?

This weekend, I will be shooting my type 99 Arisaka with the Lyman 314299. I'll circle back to this thread afterward and provide some data on what the BC of that bullet performed at.

 

[Snakeoil]

This weekend, I will be shooting my type 99 Arisaka with the Lyman 314299. I'll circle back to this thread afterward and provide some data on what the BC of that bullet performed at.

That is the Lyman number for that bullet I posted. That's the bullet I shoot in my 03. I think the NOE number is 314210.