.300 Win Mag ballistics, puzzling

A

AndABeer

New member
So I was trying to get my new 700P in .300 Win Mag dialed in and not having alot of luck. I had run through most of the 180 gr. loads I had, a variety of factory stuff as I don't have time to develop a handload. The best group I was able to manage was with the Winchester Premium in a Balistic Silvertip. It was the last four rounds of the box into a one inch group at 100 yds.

I start to pack up but then remember the 150 gr stuff I had at the bottom of my range bag. I decide to go ahead and try it. I figure it will print a couple inches higher than the 180 gr stuff but I'll still be able to shoot for groups. I have some Winchester Failsafe and Hornaday BTSP. As I load the fourth round topping off the rifle with the Hornaday, the Rangemaster calls one minute to cease fire. So I hunker down and crank off the four rounds in about 20 seconds. I am pleasantly surprised with a .5" group, once again Hornaday to the rescue. However, I am somewhat puzzled by the fact that the 150 gr. went to point of aim when the scope was set-up for the 180 gr. load. I suppose it is possible the Hornaday was not loaded very hot and the Winchester was but is there another explanation? At a 100 yds is the .300 powerful enough that the 30 gr. difference does not impact POI?
 
This sort of thing is not that uncommon. Different loads can set up slightly different vibrations in a barrel, SFAIK, and maybe that's part of the cause--regardless of what the book sez.

I was getting the same behavior with my '06 at 500 yards; I've gotten identical points-of-aim hits with my .243 with 70-grain and 85-grain bullets.

Ya never know until you've tested, which is the "why" of "One test is worth a thousand expert opinions."

But write down your discoveries. I'd guess you're best off with the combination of those two loads which DID give the best groups at the same point of aim and forget the rest.

FWIW, Art
 
Heck I try to do that. My reloading objective is to get everything to the same POI, as fast as possible. This may be the same issue that happens with certain handguns, in which the minute increase in muzzle flip overrides the minute difference in trajectory.
 
Actually the lighter bullets exit the barrel a tad quicker than the heavy ones during recoil causing the lighter bullet to hit lower at closer ranges. I have found the same to be true with handguns as well.
 
It's not a 300WinMag but my 308Win loves to do funky stuff.

My two most accurate handloads are both rock solid 1MOA performers(it's an AR with chrome lined barrel and regular handguards so it's good to me) and with my 165grn Noslers shooting to their zero, if I switch out to my 180grn Sierras not only does the load hit a few inches lower which is what I would expect but the 180s point of impact is also shifted off to the left by about 3 inches. First time I saw this I thought I was nuts, but doing it a couple times over showed that the rifle prints the two loads into two very different points of impact with the scope set to the same zero, it's dead solid dependable performance and it's all part of learning how your rifle performs. Watching my rifle do this completely shattered the notion that I previously had where I thought that just because one load uses a heavier bullet means that it should just print slightly lower in the same vertical line than where a lighter bullet would shoot with it's scope zero.

Barrel whip or barrel harmonics and where it prefers to put different loads is a fun yet wierd thing to witness.



As for your 300WinMag, don't know the twist rate on it but that isn't an absolute indicator to which bullets it will or will not like. From your tests out at the range maybe you should try finding some 165grn loads, Nosler Balistic Tips perhaps? Your rifle might have a sweet spot with bullets in the 150-165grn range, won't know tell you test them. Looks like the 180s weren't too much of a success.
 
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