ballistic coefficient

[canuck4570]

would any of you know the ballistic coefficient of this RCBS 180 gr. bullet

https://shop.rcbs.com/WebConnect/images/rcbs/item/FullA/82020.jpg

[MtGun44]

It will be similar to any same caliber same wt jacketed bullet
with a roughly similar shape and plain base.

Ballistic coefficient is NOT constant. Identical boolits fired from different
guns will often exhibit significantly different ballistic coefficient, which
is one of the reasons that no bullet or boolit will every match the
calculated trajectory very closely.

Sad to say, I used to obsess about ballistic coefficients, and being a techie
used to fiddle around a lot with trajectory software. Eventually found
out that real worlkd testing NEVER matched the calcs, so I tend to
do more actual testing.

[Doc Highwall]

According to the RCBS cast bullet book the 30-180-SP is .293 and the 30-180-FN is .255. I am trying to find the BC for the SAECO #315 175gr TCGC.

[canuck4570]

According to the RCBS cast bullet book the 30-180-SP is .293 and the 30-180-FN is .255. I am trying to find the BC for the SAECO #315 175gr TCGC.

thanks Doc.....
trying to find something on the 315
this is a tapered bullet that is supposed to be shot has cast if I am not mistaken
if I see something I will let you know

[canuck4570]

Doc
found this on google

http://www.uslink.com/~tom1/cast_bc.htm

[David2011]

The ballistic calculator on Handloads.com has a BC estimator on the left side of the page. It uses general boolit shape, diameter and weight. The difference between a round nose a nd a Spitzer is big. The rnfp looking picture would probably fall somewhere between .230 for a round nose and .432 for a Spitzer.

David

[missionary5155]

Good morning
Absolutely deadly to any critter it hits out to 500 yards.
This is the boolit I use in all my caliber .30´s. It will flat smack down the 50 pound ram at 500 meters.
You already got the numbers so I thought to add the facts.

[canuck4570]

Ok I am willing to try this bullet but before I would like to know how you lube it since its a tapered bullet
the instruction says shoot has cast, OK that's fine but how do you put this lube?

also do you leave the grease grove outside the neck unlube ?

[onesonek]

Don't know how accurate it is, but at least it gives an idea. It calculates cast, but no plugins for lube grooves, so it don't account for everything.
http://www.uslink.net/~tom1/calcbc/calcbc.htm#calculator



It will be similar to any same caliber same wt jacketed bullet
with a roughly similar shape and plain base.

Ballistic coefficient is NOT constant. Identical boolits fired from different
guns will often exhibit significantly different ballistic coefficient, which
is one of the reasons that no bullet or boolit will every match the
calculated trajectory very closely.

Sad to say, I used to obsess about ballistic coefficients, and being a techie
used to fiddle around a lot with trajectory software. Eventually found
out that real worlkd testing NEVER matched the calcs, so I tend to
do more actual testing.

There's is alot truth to what MtGun 44 says here. BC's change with launch speeds, and with change of speed in flight. But the BC calculators do give one a starting point for testing. The other problem is, most that I know of are calculated to a standard of conditions at sea level. So if you use a ballistic program, it needs to have the capability to change conditions. Some do and some don't. Fortunately, flat base designs are pretty tough to fudge numbers on, where as boatails is a whole different story. But then if don't have accurate nose/ogive demensions, it's difficult to get an accurate BC from an estimator. But again, it'll will give you a starting point for actual test shooting.
If you don't have actual measurements,, as MtGun also saiad take a flat base spitzer, then I would subtract .05-.10 for the meplat, and .010 for each lube groove, and you be somewhat close.

Dave

[canuck4570]

ONESONECK
your are correct I have noticed this also about the ballistic program
use it only as starting or quide reference than mark the adjustment to be made

[Gohon]

Don't remember where I got it but for that same bullet I have 0.220 as a BC in my load program. As for lube, I use LLA on everything. Never had a problem with accuracy or leading but then I've only pushed it to a tad over 2000 fps from a 30-30.

[lawhetzel]

As has already been said, ballistic coefficient is a pretty slippery figure to get exactly right. It can vary depending on the barometric pressure, altitude, muzzle velocity, etc. That said, again as has already been said, a general figure is usually all that is necessary. I am not sure, for myself, how much difference in the second (hundredths) decimal is significant and perhaps even a tenth (first decimal place may not be significant out to 200 yards or so.
Really, the only way to get an accurate figure for your bullet, from your gun, with your load, is to chronograph the velocity at two known velocities, say muzzle and 100 yards, and plug those figures into your software. The older method based on profile can only give an approximation. At least that is what I think that understand from my reading on the subject.

[GabbyM]

Image in post one is of the SP bullet not the FN 180. I'd think the BC would be at least .250 in not over .300.

[Tom Myers]

Don't know how accurate it is, but at least it gives an idea. It calculates cast, but no plugins for lube grooves, so it don't account for everything.
http://www.tmtpages.com/calcbc/calcbc.htm#calculator

The BC Calculator on my Website is set up to calculate both jacketed and cast bullets so the calculations are not as precise as they could be if the algorithms were set up for just one type of bullet.

http://www.tmtpages.com/LinkSkyImages/forum_images/RCBS-30-180-SP-WebsiteBC.gif

The Precision Cast Bullet BC Estimator Software (http://www.tmtpages.com/cast_bc.htm) does a better job of estimating the cast bullet BC as it allows for a variety of ogive configurations (even Tangential and Truncated Cone nose shapes) Although, in this instance, they both return values that are reasonably close to each other.
I Scaled out the image of the RCBS bullet and entered the dimensions into the Cast Bullet BC Estimator with these results.


http://www.tmtpages.com/LinkSkyImages/forum_images/RCBS-30-180-SP-BC.gif

Hope this helps.

[Three44s]

What you lose in BC ....... you'll gain worlds in terminal ballistics.

I'd just put "boots on the ground" and have at it.

The terminal end of things trumps all at any reasonable range!

Best of luck

Three 44s

[NSP64]

Tom, I didn't know that was your website! TMT enterprises. Wow learn something new every day. Thanks, I use it all the time.

[Larry Gibson]

Having actually measured numerous BCs (Oehler M43) of both jacketed and cast bullets it is interesting what variances can be expected. The influences mention (atmospheric conditions and temperature) do have an effect but it is mostly with the 3rd (thousandth) number. The relevance of the third number is about as Dr. Oehler puts it; this relevance is about like thinking, is the deer 173 or 174 yards away. Any major difference between the 2nd number (hundredths) doesn’t become a factor until the practical range of 200 or 300 yards is exceeded, this with either cast or J bullets. Thus with the same muzzle velocity a difference between a .25 and a .26 or even a .28 BC will be difficult to ascertain when actually shooting the bullets out to 200. Yes you can point to the figures all you want but there are so many other influences that it becomes a somewhat moot issue. However, beyond 300 yards the higher the BC the better the bullets trajectory and wind resistance will be, the greater the range the greater the benefit of a higher BC.

There is one influence on the BC of a bullet that is often over looked; that is the influence the twist has on stability and the resultant BC. We often over look this simply because we shoot the bullets out of what ever the twist of the rifle happens to be. Many formula’s or programs that are used to determine the twist rate for a specific bullet will usually give 3 ranges of stability; marginal, stabile and over stabilized. Each bullet will have a particular twist rate where it fits into one of those ranges. I have run comparative tests of numerous same cartridge/different twist rifles to see this is common. Easiest examples are the .308W with 10, 12 and 14” twists and the .223 with 7, 9, 12 and 14” twists. Using various weight and designs of bullets in each we can readily see which bullets in which twists are stabile, marginally stable or over stabilized. This is readily apparent in the measured BC. Take a 55 gr FMJBT in the .223 for example; The lowest BC will come with the 7” twist then the 9” twist. Usually the smallest BC comes with the 14” twist. The highest BC is almost always with a 12” twist. Considering the RPMs involved the 7 and 9” twists are over stabilizing the bullet where as the 14” twist bullet is marginally stabilized. In the example of the .308W using M118SB with the 174 gr bullet we will find BCs of 10” twist rifles in the .47s, in the 14” twist the BCs are in the .45s and in the 12” twist the BCs are in the .51s. With that particular bullet we can say the bullet is probably stabilized in the 10 and 12” twist (the better being the 12” twist) and is marginally stabile in the 14” twist. I have found this to be the same with other cartridges and calibers of different twists. Each bullet will have a particular twist in which it will be best stabilized.

Now before anyone gets all raspy here and wants to show me 100 yard groups of 40 gr bullets out of 7” twists that are sub moa let me again say that the benefit of the higher BC is not going to be noticed until the ranges are long, 300 yards and beyond. This is particularly the case between bullets that are stabile and those that are over stabilized. If we are shooting cast bullets at longer ranges then the BC does begin to have an importance. With out going into the relevance of RPM to stabilization just let me finish by saying that the same cast bullet out of the same rifle that shoots moa will have a higher BC than the same bullet that is shooting 3 moa; the more accurate load is stabilizing the bullet better.

Larry Gibson

[Tom Myers]

Well said Larry.

I wish I could organize and communicate my thoughts in such a manner.

[onesonek]

I agree Larry,,,and Tom thanks for making that available,,,,I have use that calculator just as late myself just so I have an idea. Normally I don't give it alot of thought with the point blank ranges I hunt. The long range toys is another matter.

dave

[Doc Highwall]

Right now the best I can determine the B.C. of the SAECO #315 175gr TCGC from shooting with a 100yd zero and a 300yd zero is .300 to .320

[Marlin Junky]

Right now the best I can determine the B.C. of the SAECO #315 175gr TCGC from shooting with a 100yd zero and a 300yd zero is .300 to .320

Why not run three or so through the chronograph at 100 yards and see how much velocity is shed with respect to the 10' results?

MJ

[GabbyM]

Why not run three or so through the chronograph at 100 yards and see how much velocity is shed with respect to the 10' results?

MJ

You probably already know all this but here it is.

That would give one more data point. Although B.C. changes with velocity and stability. BC is dependant on stability also. Stability can and does change at range. Chronograph and bullet drop at 200 and 300 yards are good data points as long as you can get the wind to cooperate. Just need to get up at 4:00 AM to set up and wait for the sun to come up. I’ve shot over my Chrony at 200 yards. That’s far enough for me.

[Doc Highwall]

I plan on shooting over two chronographs this summer, one at the bench and the other at 300 yards. I feel the 300 yards is safe enough as the gun shoots better then 3 inch groups at 300 yards with my best at 1.600" for 5 shots. I will have my nephew in the pits with a walkie talky to coordinate the velocity at the muzzle and the velocity at 300 yards and know the actual velocity lost. The bullets will be shot over both chronographs first to show how close the two are in agreement with each other. I will have to get to the range early to put up my range flags and get everything set to go without any hitches. Here is a picture of four 5 shot groups at 300 yards and a close up of the 1.610" group.

[Marlin Junky]

Doc,

Excellent... keep us posted.

SAECO 315 is up there on my list of molds to acquire but I was wondering how it groups at about 2000 fps? Any input?

MJ

[Doc Highwall]

This velocity is above 1800fps I will have to get the chronograph out to check it later this year when the weather changes.