A BC for an LBT??

[longcruise]

I know this is an off the wall question, but if it can be answered, this is the place. 😀

I have a. 430 mold from LBT for a Wide Long Flat Nose (WLFN) bullet that I acquired in the mid '90's. It drops at 320 grains with WW. I'm trying to do some calculations for a load in a newly acquired CVA scout rifle and need a BC to do the calculations. If anyone can help with this I'd be very appreciative.

[Screwbolts]

If you have a chronograph you can record MV then move your crony to the 100 yard point by a target and get your true BC for the velocity you are shooting. There are readily available calculators for this.

[memtb]

I was curious about the same thing with some of my cast bullets. As a general statement .....for typical handgun ranges, the BC is relatively unimportant! All that said.....I did a little research and just called mine a 0.200 BC, assuming that it was “close enough for government work”! :bigsmyl2: memtb

[Tatume]

Try this. Using a ballistics calculator (I like JBM) Pick a reasonable velocity and other data, and put in three BC estimates. For a 43 caliber bullet at 1400 fps I used a 100 yard zero and 50 yard interval, with BC values of 0.15, 0.20 & 0.25. The drops in inches at 50 and 200 yards tell the story.

0.15 4.0 -12.7
0.20 3.7 -11.5
0.25 3.5 -10.7

The differences aren't enough to amount to a hill of legumes. So why sweat it?

[PositiveCaster]

The OP wants help with determining a BC for his bullet for use at the higher velocity from a rifle, not a handgun. Perhaps he’s interested in remaining velocity or potential wind drift, we don’t know. He really doesn’t need to be told he’s wasting his time.



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[memtb]

[QUOTE=PositiveCaster;5202225]The OP wants help with determining a BC for his bullet for use at the higher velocity from a rifle, not a handgun. Perhaps he’s interested in remaining velocity or potential wind drift, we don’t know. He really doesn’t need to be told he’s wasting his time.


“If” that was directed toward my post.....careful reading and comprehension would show that, I just recently had the same question! Though my velocities would only be around 1500 fps for 400 grainers from my 460 S&W!

“If” it wasn’t directed to me....then my apologizes are offered! memtb

[Tatume]

Don't worry about it. It was directed at me, and isn't worth any bother.

[longcruise]

I'm working on a load that will be Colorado legal for big game. The rifle is a CVA Scout with a 22" barrel. I have a chronograph but I don't trust myself to shoot over it at 50 or 100. :-(

For a rifle It will need to have at least 1000 fpe at 100 yards. If i use 44 mag load data for the 320 LBT in an 8.5" barreled pistol my max would be 1310 with Ramshot Enforcer. (the powder I know I'll have on hand before the season in September) I prefer H110 for the 44 mag but I have only a small amount and probably not enough to work up the load.

I would like to run the ballistics with the actual BC for the LBT but without it, my compromise on the BC is using the BC for a 300 grain XTP. I think it will be safe to go with that as far as accurate data goes although the LBT does have a pretty wide meplat. According to Point Blank I need to start it at 1385 fps to get to 1014 fpe at 100 yards. So I only need to pick up 75 fps to get there and I think it will be easy to exceed that.

I shoulda included this explanation with my original post. My apologies for neglecting to explain up front.

[versa-06]

longcruise; I just looked at some charts similar to your bullet design & it appears that with what I see your're really close at your stated 1385 fps to maintain that velocity of 1014 at 100 yds. 1385 may be slightly over the must have.

[Tatume]

The BC for the 300 gr XTP is 0.245, and I think that is very optimistic to the point of being unrealistic. A more realistic estimate was given by memtb above, 0.20. Personally, I think it's likely to be less than that.

The best approach is probably to forget about BC altogether. Most are based on the G1 model, which works for well-streamlined projectiles, but is not a good approximation for your bullet. Better would be to overcome your fear of shooting the chronograph and record some actual speeds at 100 yards. If you can keep your shots on a six-inch circle you can do it. When you find a load that satisfies the objective, write down the data and the calculation on a card and laminate it. The card will probably satisfy your game warden, who should be impressed with your sincere desire to obey the law.

[gpidaho]

longcruise: If your anywhere near a fellow Boolits member with a LabRadar that's your answer to the chrono at 100yrds. They can be programmed to give velocity at different distances. If you happen to be from S.W. Idaho we can use mine. Gp

[bluejay75]

I use .200 as a default BC with most of my FN boolits in almost every caliber I use...if its a short boolit. If its a long boolit (usually heavy for caliber boolits) I use .250. Out to 300 yards if you run in a Ballistic calculator you will be within 1 inch of the actual drops either direction.

Play with this calculator and you will see what Im talking about. Use HP or RN as your nose profile.

http://gundata.org/ballistic-coefficient-calculator/

[mattri]

If you have a chrono couldn't you just get your velocity then zero at 25, move to 50, 100 etc and then use your observed drops to work the numbers backwards in Hodgdon's or a similar ballistic program?

[Screwbolts]

Longcruise, you say you have a chronograph and you are working/listing pistol data for a rifle with a 22" barrel and no cylinder gap? Come on man, get off your butt and find what the load does from your rifle. You need to educate yourself on what your load will do from your rifle. Only you have the particular rifle, load, bullet and items needed to find all your answers.

If you do not trust yourself to shot at a target to verify zero and then set your Crony up in front of a proven zero, then how do you even expect to be able to hit an Elk with Elk fever in play?

BC varies dependent on velocity of the bullet. Oh that's right you have no idea what the velocity from your listed rifle is. To bad you don't have a crony, oh wait you do!

[memtb]

longcruise, Don’t give up on the forum......some of us are willing to help you. Not all of us are self-righteous, judgmental individuals.....that have forgotten what it was like to “not” have all of the answers! memtb

[longcruise]

Longcruise, you say you have a chronograph and you are working/listing pistol data for a rifle with a 22" barrel and no cylinder gap? Come on man, get off your butt and find what the load does from your rifle. You need to educate yourself on what your load will do from your rifle. Only you have the particular rifle, load, bullet and items needed to find all your answers.

If you do not trust yourself to shot at a target to verify zero and then set your Crony up in front of a proven zero, then how do you even expect to be able to hit an Elk with Elk fever in play?

BC varies dependent on velocity of the bullet. Oh that's right you have no idea what the velocity from your listed rifle is. To bad you don't have a crony, oh wait you do!

Wow! Condescension beyond comprehension! As well as indicative of a problem with reading comprehension. ��

So, one point at a time. The reference to pistol data was clearly for comparison and extrapolation to probable results from a 22" barrel.

Get off my butt?? That's a joke. This post is the beginning of the process. And it's not one viewed by myself as objectionable work but (one "t") fun times on and off the range.

I'll definitely not be setting up the chronograph at distance.

Tatume saw exactly what the whole point of the exercise is. It’s to establish a clear illustration of the legality of the firearm/load in case it is questioned in the field.

You seem to reaching pretty far for your ad hominens. After all it was just a simple question about a BC in case someone might have the information at hand. I could care less how the BC might vary at velocity. Like I said, the point is to establish the legality of the combo. A WCO in the field might question the legality but they won't be quibbling over the variations of a BC at velocity if it is legitimately supported by its source.

I never suggested that I would be shooting at an elk.

I'm not concerned with the adequacy of the 44 in terms of how it will perform. If it weren't for the legality aspect there would be no question.


I appreciate the well thought out suggestions that have been offered here. Thanks so much for those. :)

[kayala]

As gpidaho mentioned LabRadar would be ideal for your problem. It’s pretty expensive tool but you might find someone close by who owns one.