[Beladran]

As i laid in bed sick last night (i think i was tripping out on to much tylenol pm and sinus meds) i couldnt sleep so i flipped the light on and grabbed my reloading manual and starting thinking of a load for my new 308. I have a springfield armory scope im going to put on it but its bullet compensated for 168gr match loads making 2550 fps.
well i dont have a cronny any more so i figure there has to be a relationship between amount of powder to the ammount of fps 1 gr makes. so i look at 168grbthp in the lapua reloading section go over to N550 and get the suggested start load and divide fps by grains(57.18). then i got the max load and did the same thing(57.81). there was only a .63 fps per gr difference between the start and max load. So i need about 44.5 grains to get me my 2550 fps. But thats not the point of this post. I began looking at other Vihta powders i used and started to compare their gr to speeds. I found that all the NN500's have the least gap between start and max, while the NN100's had the greatest gap (3fps per gr). also noted that the 100's made more fps with less powder and the more powder you add the lower the fps per gr went. With the 500's it was the exact opposit. :thinking: :scratch: maybe if you look at other powders this trend will show up to. I bet i could graph this out an show a point of diminishing returns on some of these powders and show what a "optimum" powder charge would be... lol this is gonna sound stupid but i think the heavier the bullet the more effecient the powder burns :scratch:

 

[jbpmidas]

In general, aren't the heavier for caliber bullets more efficient? Don't they have the highest ballistic coeffiecient? So they should be the most efficient!

 

[Beladran]

yea the high bc bullets are effecient but im saying heavy bullets enhance the powders.. im guessing they stay in the gun longer giving a better burn

 

[jbpmidas]

I believe the BC has more to do with it than weight. You should load a similar powder charge behind two different shape but same weight bullets. For example, I load some 220 gr. Sierra Matchkings for my .30-06. I would like to know the result of the same powder charge behind a 220 gr roundnose.

 

[nonnieselman]

A 220gr Roundnose vs a 220gr SMK makes a big difference in a Subsonic load, the RN takes more powder to get it to 1050 where a SMK doesnt take as much. Thats all know..

Ive never looked into it like Beladran has..

 

[Hammer]

A 220gr Roundnose vs a 220gr SMK makes a big difference in a Subsonic load, the RN takes more powder to get it to 1050 where a SMK doesnt take as much. Thats all know.. Ive never looked into it like Beladran has..

Thats cause he has way too much free time!

 

[Beladran]

thats like comparing a dart to a brick.. i looked at the 06 bullets 167,185,190 hpbt and the heavier the bullet the lower the fps per grain goes which is the opposite of a 308 case? idk now im confused and my head hurts lol 308 is more effcient with heavier bullets than 06 is??

 

[jbpmidas]

I believe the .308 is more efficient, but the .308 won't push a given weight as fast as the '06 will.

 

[jbpmidas]

How much powder does it take to push a 150 gr bullet 2700 fps out of each?

 

[Beladran]

ok i did this on a scratch pad going by the numbers on lapua website for both N550 for 06 and 308 using 150gr sierra hpbt to make 2700fps out of each

308 --47.42
30-06 -- 54.46

308 makes 56.94 fps per gr of N550
30-06 makes 49.58 fps per gr of N550
granted this math was done in my head so add a fudge factor of 10% lol

 

[jbpmidas]

.308 is much more efficient for that weight and powder! How about some other comparisons?

 

[nonnieselman]

Dont forget Primers can make a 100fps change in Velocity also.. Just something to think about..

 

[PhillipM]

.308 is much more efficient for that weight and powder! How about some other comparisons?

True, but a .30-06 with imr 4350 and that bullet just shines! Keep it out of an M1 garand though, it will bend the op rod. Ultimately as proven out in the national matches, a .308 is more accurate than a .30-06, they had to shrink the bullseyes down because everyone was cleaning the targets.

As to the 220 spire vs 220 round nose, you really need to look at how much of the bullet bears on the lands.

Hope you feel better soon!

 

[Beladran]

compared 180 barnes in 06 and 308 at 2400fps
308--42.26
06--47.21

so the gap just closed from a 7 gr difference to a 5gr difference between the two

 

[jbpmidas]

I wonder if the comparison should be % of case capacity instead of grains. The '06 is at a disadvantage when being compared to the .308 because of its increased case capacity.

 

[ftsibley]

I think i may go dose myself with a heavy shot of Nyquil and re-read this post, bet i will figure it all out once the Nyqil kicks in.

 

[Beladran]

dont forget to mix a shot of Jack in with that nyquil

 

[bubbat]

I think i may go dose myself with a heavy shot of Nyquil and re-read this post, bet i will figure it all out once the Nyqil kicks in.

:lol:

 

[Scharfschütze]

Don't forget ambient temperature (sorry, had to throw the calculus into the works). Remember, apples to apples...

 

[Beladran]

I wonder if the comparison should be % of case capacity instead of grains. The '06 is at a disadvantage when being compared to the .308 because of its increased case capacity.

ok after re reading my ballistics book this is how you calculate cartridge effeciency...
general rule of thumb if you dont know what the energy per grain is of a powder use 1gr of powder =200 ft/lbs of energy
your standard 30 cal M-2 ball ammo has 50gr of powder and has a muzzle speed of 2,800fps and a muzzle energy of 2,643 ft/lbs. its powder produces 178ft/lbs per gr of powder so multiply that times powder used(178x50=8,900ft/lbs) then find percent 2,643/8,900x100=29.7% that is how effecient that is