I got out to the range this afternon to try a new load in my 257 AI. The bullet is a 90gr Sierra BTHP Gameking on top of IMR 4320.
 
 The first pic is of the first 5 rounds. This load was with 46.0gr of powder and the average velocity was 3301fps. This was the most consistant load speed wise with a spread of 23fps. But, it measured 1.89"
 
 
 
 This pic is of the next 5 rounds with 47.0gr of powder. The average speed was 3454fps with a spread of 75fps. It measures 1.26". Better but I know that both the rifle and I are capable of better. Maby if I play with seating depth I might shave a little off that but I won't be happy unless I get it under an inch.
 
 
 
 With the next 5 things start to go down hill in a hurry. This is with 48.0gr of powder. Our average speed is 3452 with a spread of 72fps. One more grain of powder and the same speed? The worst thing is that this group measures 1.487" verticly by 2.840" horizontally! To say that I'm not impressed at this point would be an understatement.  
 
 
 
 This brings us to our last group of 5. By this time some clouds had moved in and it was too dark for the chronograph so I was unable to get the speeds but by looking at the group it's pretty irrelevant as I won't be tryign this load again anyway. Can you say horizontal stringing? Sure. I knew that you could. This group measures 2.75" horizontal by .94" vertical.
 
 
 
 If I can consistantly get the 47.0gr load to group an inch or less with that kind of speed I'll be happy. I don't know how much I can shave off, if any, by toying with the seating depth. Also it's been a little while since I've been out but I don't think that I'm that out of practice. Any hints or insight that you guys have would be greatly appreciated.

h'bug,

That is a great bullet and was the most accurate out of my 257AI...that said, however, H-4350 was my powder of choice...groups under 1" were the norm and not the exception.  I tried 4320 but it was just a bit "quirky" as to groups...one day pretty good, next day.........."shotgun" groups....never had it over a chronograph however.  Give H-4350 a chance and see what it does for you.
 
Ol' John:cool:

OK, I will try the H4350. What kind of speed do you get? I'll be interested to hear if gitano has any insight to offer.

QuoteI'll be interested to hear if gitano has any insight to offer.

Sorry to say not much HB. My experience with the .257 is fairly limited. I've been shooting three bullets: the 85 grain Combined Tehnology Silvertips, the 100 grain Speer large-meplat HPs, and the Hornady 75 grain HPs. Because I'm a little 'gun-shy' of boat-tails, I've concentrated on the 85 grain CTBs and 100 grain Speers. The CTB is a boat-tail design, but it's not nearly as severe a boat-tail as the Sierras are.
 
I've been focused on Vihtavouri N-150, and H-4350 for the 85 and 100 grainers. I used I4064 for the 75 grainer. Here are the charges I have settled on so far and thier resulting velocites. I'll have to get my targets out, but as I recall, these are all doing MOA or better.
 
Hornady 75 grain HP - 47.0 grains of I4064 - 3764 f/s. I haven't made any effort to tune this load yet.
 
CTB 85 grain - 45.5 grains of N-150 - 3469 f/s. (More accurate than I4350.)
 
CTB 85 grain - 50.5 grains of I4350 - 3472 f/s. This is the hottest load tried and the most accurate but not as accurate as the N-150.
 
Speer 100 grain - 47.0 grains of H4350 - 3117 fps. Hotter loads were faster, 3274 f/s, but this was the most accurate.
 
I'll scrouge the targets up and post them too if there's any information of note there.
 
I'm pretty sure I'll be fiddling with 4350 some more for the 85 grainer because it gives a higher load density. Plus, I'm a little uncomfortable about how 'finicky' Vihtavouri powders are turning out to be in my cartridges. I may also try some 4831 behind the 100 grainer, but I'm not optimistic about MVs with it. The 75 grain holds some promise by virtue of the 3700+ MV. We'll see.
 
In the end, I'd suggest what John did, and you've already said you'd try - 4350. However, I'd also suggest that if you're really looking for accuracy and boat-tail bullets are frustrating that effort, you might try some flat-based bullets. Flat-based bullets have substantially reduced my level of frustration with handloading for precision.
 
Paul
 
PS.
 
Oh yeah... I was going to comment on your last target. Take one shot out of that 5-shot group, the left-most shot, and there is NO horizontal stringing.
 
Paul