Velocity not making sense.

[SaskShooter]

Loading ammo for my .243 Winchester, I've been trying a bunch of different bullets. Several different kinds shoot sub-MOA, some shoot under half-MOA, some can't make 2 MOA.

But that isn't my problem, my problem is that I can't find a load that gives both good external ballistics/terminal performance AND accuracy. For example- 70 grain Nosler Ballistic Tips pushed to 3400 FPS over a 40 grain charge of Varget give me all the flat trajectory and terminal oomph that I could ask for, but accuracy is JUST below MOA.
On the other hand, 69 grain Berger High BC FBs can only be pushed to MAX 3100 FPS with 41 grains of Varget, but they shoot close to 1/4 MOA.
Ditto the 85gr Sierra HPBTs. Max charge of Varget- topping out at 2950 FPS- very close to 1/4 MOA, but dropping like rocks past 250 yards.

I don't understand why I can push 70 grain bullets at 3400 easy, but 69 grain bullets (with an extra grain of Varget behind them) only do 3100 max.

There isn't THAT much extra bearing surface on the Bergers over the Noslers.

 

[green 788]

When chronograph data doesn't make sense, 9 out of 10 times it's the chronograph... lighting issues... maybe too close to the muzzle and you're getting powder blow thru...

Your speed on the 70 grain Noslers is about right. The accuracy load is 42 grains of Varget, per Nosler--and it works... so you might dial it up a bit, so long as you're using Winchester brass.

Dan

 

[SaskShooter]

Well, I might just try loading up a few more 70 grain BTs with 42 grains then. I only loaded to 41 because my Lee loading manual states that as a "Do not exceed" load.

My chronograph is about 8 feet from muzzle, so it shouldn't be powder blow-through, although stranger things have happened. I guess I'll have more testing to do yet.

 

[Joe King]

If you want the best of both worlds your probably want to try a slower powder, Ramshot hunter shows the highest velocities for 243 with a 69gr Berger, the second thing you'll want to do is try different seating depths, third is try different primers. Some times you can just assemble components and get what your looking for but it generally doesn't happen that way.

You did stop at with a charge that was listed in your reference material as being max and that's the smart thing to do. But there's a lot of different powders, bullets cases, and primers. carefully finding the combination that gives you what your looking for with out going in to the "I'm trying to blow my gun up" area is load development, and it can be a lot of fun and pretty satisfying.

So keep researching, buy manuals, and books, keep visiting places like this and ask lots of questions. there's a massive amount of information easily available now than what there was when I started reloading.

 

[Gunpoor]

Just one point of correction in thought on this subject. More bearing surface with similar or same weight bullets increases pressure over less bearing surface bullets, and therefore velocity should increase similarly with the increase in pressure. Sometimes the bullets that give the best muzzle velocity, because of the longer bearing surface, don't have the highest BC and lose velocity quicker.

BTW, I wil take more accuracy over smaller gains in velocity every time.

 

[Joe King]

Just one point of correction in thought on this subject. More bearing surface with similar or same weight bullets increases pressure over less bearing surface bullets, and therefore velocity should increase similarly with the increase in pressure. Sometimes the bullets that give the best muzzle velocity, because of the longer bearing surface, don't have the highest BC and lose velocity quicker.

BTW, I wil take more accuracy over smaller gains in velocity every time.

Not necessarily, Before Berger announced the Classic Hunter (they where still calling it the SAAMI Hybrid) I emailed Walt asking about reloading them Vs. the VLD. What could I expect to see, pressure differences ect. he said the only difference I should notice is slightly less velocity due to the longer bearing length.

Seems that like many other things with reloading and shooting, there isn't a really much of a hard fast answer, just best fit answers (maybe, could be, who knows, try it and see). The things about the bullet that can effect vel being of the same weight, are jacket material, jacket thickness, bearing length, composition.

 

[Sully2]

Just shoot the Bergers and dont worry about it!

 

[FEENIX]

For example- 70 grain Nosler Ballistic Tips pushed to 3400 FPS over a 40 grain charge of Varget give me all the flat trajectory and terminal oomph that I could ask for, but accuracy is JUST below MOA.

I don't want to assume anything but have you tried different seating depths to find the sweet spot for your set-up. It's not NBT but NAB but here's my experience off my SAKOM995 in .300 Win Mag:

(1) 70.5 H4831SC 200 NAB CCI250 @100 yards

(2) 71.0 H4831SC 200 NAB CCI250 @100 yards

(3) 71.5 H4831SC 200 NAB CCI250 @100 yards



(1) Is one of many .010-.020 off the lands is the best group.

(2) and (3) are touching the lands.


My chronograph calls for a min of 10 feet from the muzzle.

Good luck!

Ed

 

[SaskShooter]

Thanks for the help, guys.
I've already fiddled with seating depths and I think I've found the sweet spot as far as that goes. I'm not sure as to how far off the lands I am, because my digital caliper went on the fritz and I haven't gotten a new one yet.
I think I might just try that Ramshot Hunter powder, because it seems fairly easy to find. Varget isn't too difficult to find out here, but when there's a powder shortage, Varget is the first to disappear!

Also, what about Hodgdon 4831? It's also listed as one of the higher velocity powders for light bullets in .243.

 

[Ridgerunner665]

Sierra 70 grain BlitzKings...using Varget, I can get the to 3,300 fps from a 20"barrel (youth rifle)...outstanding accuracy and terminal oomph!

And its not all about bullet weight...bearing surface matters

 

[SaskShooter]

While I have the ear of these brilliant LHR members, I have another question- how picky should I be when I sort my brass?

Right now I use fired factory cases, and keep all my brass separated by brand, lot, and number of times fired.
I know all the REALLY hardcore guys will probably just tell me to use Lapua brass, but my money-tree didn't fare too well this year, and Lapua isn't cheap.

 

[JeffP40]

I don't pay any attention to the book, except for starting loads. I load to the rifle and the brass. I don't think I have a rifle that will not go to , or exceed "book max", and that charge varies with the different manufacturers books. They are very conservative with their numbers. I don't have brass issues, primer pockets stay tight, and no, you don't have to worry about blowing anything up. The rifle will take much more pressure than the brass. It will tell you when it's had enough. I would up the powder charge and see what happens. It will tel you when it wants to quit.