Major difference in windage between 2 bullets

[brente4737]

Wondering if anyone can explain this. I have a Savage 10FCP in .308 1:10 twist. I have shot many handloaded 168 gr Amax and decided to try something else. I went with 180 gr. Nosler ballistic sivertips. After shooting about 20 Noslers I moved up to fifty yards where I finally hit the target. The noslers were going way left like 3 ft @ 250 yards. So to make sure it wasnt my scope I shot the amax, and dead on. My buddy shot the same rounds with his SCAR with the same results. His scar has a 1:12 twist. I know bullets can be off windage wise a little but this is over 1 foot @ 100 yards. My velocities are 2450 on the hornady, with superformance powder, and 2625 with the nosler with blc2 powder. Any insight would be great.

 

[Shynloco]

WELL...since nobody had chimed in, I'll take a stab at this one. I shoot strictly Benchrest and have a 1:10 MG barrel in my .308. Previous to a recent barrel change, there was also a 1:10 barrel on her and she loved 168 gr Sierra. And BTW, I shoot only 100 yds. But like you, got a hair and decided to try a heavier bullet (175gr) that Sierra recommended should I exceed 300 yds. Now I didn't have that radical a change, but my POI changed and the groups opened up at 100 yds. Changed back to the 168's and they were right on.

Based solely up my experiences, readings and suggestion by folks in the know, anytime you change the bullet weight, expect a change from what your rifle considers it's sweet load.

Another issue that you probably already know, if you don't work up a specific load IN YOUR PARTICULAR RIFLE, where there's been a major change such as bullet weight, powder/powder weight, you could incur a radical change simply due to velocity of the outgoing bullet. In looking in my Sierra Manual (and I use 42 gr of RE15 for 168 gr Sierra HPBT) and THEN looking at the recommended loads for Sierra 180 Gr HPBT, there is a drop of the powder load down to 41.3gr that is also accompanied by a drop in the Velocity. Hence both rifles you referred to are telling you that they really hate that patricular 180gr load you shot.

In another example, I decided to test 155gr Lapua Scenar's in that same 1:10 .308. Changed my powder load to the same expected bullet velocity as the 168 gr loads that I know she shots lights out with. The result of that change in bullet weight made my target @100 that I could 5 rds almost through the same hole (using 168 gr HPBT's that you could cover with a nickel), look like you used a shotgun on it at 100 yds. In others words, my rifle REALLY HATED 155gr Scenars loads I was using.

Hope that gives you some ideas of perhaps a way to explain that radical change you spoke about.

Alex

 

[brente4737]

Thanks for the input. I dont think my rifle hates the noslers cause it shoots just as good groups as with the hornadys. I just could never imagine that the noslers would shoot that far to the left. Im thought maybe it was the moly coating but my buddy shoots 168 moly noslers in his Scar.

 

[devin_hor]

I'll take a stab too, maybe that 1:10 twist is really spinning the 168's, making them drift right, so you dialed your scope left, now the 180's are spinning normal and hitting way left with the scope.

Are the velocities listed right? The 180 is faster than the 168?

Try shooting it ganster style(sideways) and see if they still go left or if they go down ;D

 

[nvjim]

You stated that your getting 2450 from the 168's and 2625 from the 180's. That seems backwards. Using a back-of-the-envelope power-vs-velocity estimator, you should be down to 2367 on the 180's for the same pressure, but you report 2625, that's quite a bit more pressure. In fact 2625 from a 180 is pushing the limits.

So, barrel whip differences come to mind. Also concerns over whether the scope is truly level (not canted to the gun, or to level when you are shooting).

Also, what sort of crosswind were you shooting into? Might have to do with the arc of the trajectory, though that would be one crazy wind.

Still, 1ft@100yds seems a bit beyond reason.

 

[KMart]

Changing ANY component can make for unpredictable results. Ond day I did a test between the 168 AMax and the 168 SMK. Everything was the same except the bullet. I shot the SMK first and had a nice little group at 100 yds. I then shot the AMax load and it shot low and to the right 7 inches from the other group. Granted, it wasn't 1 ft away, but 7 inches is a pretty good jump. The only thing I could attribute it to is the different ogive on the two brands resulting in different barrel vibrations.
Another thing, you indicated you changed powders as well from Superformance to Blc. If you didn't clean out the powder fouling between loads, that could contribute some to the problem.

 

[brente4737]

The velocities are correct, which is one reason why I wont buy any more superformance powder. Hornadys Superformance rounds say higher vel. but the powder isnt the same they use. They scope is true to the gun and one day was a left to right wind and the next it was a right to left. As far as the twist being too much my buddies Scar is a 1:12 and shot the same way.

 

[bigedp51]

In 1976 I had a Remington 788 in 6mm and was working up loads, I switched from a 100 grain Sierra flat base bullet to a Sierra 100 grain boat tail bullet and it hit two feet to the right of where it had been hitting before. (flat base vs boat tail)

Your two bullets are both boat tail bullets BUT the boat tails are shaped differently and both bullets are constructed differently internally. The muzzle blast can "push" bullets on a different path and your two bullets have a different shape base. (check your crown)

British .303 machine gun ammunition (ball Mk.8z) also used a rebated boat tail for greater accuracy. And was used only with single base powders on the ground and in aircraft.

 

[KMart]

The low velocity with the 168 gr bullet and Superformance can be attributed to the powder burn rate. Here is where Superformance sits on Hodgdons burn rate chart.

125 Hodgdon H4831 & H4831SC
126 Hodgdon SUPERFORMANCE
127 Winchester Supreme 780

I looked around and I couldn't find any reloading data for Superformance in 308. The powder appears to burn too slow for that application.

 

[sailhertoo]

In 1976 I had a Remington 788 in 6mm and was working up loads, I switched from a 100 grain Sierra flat base bullet to a Sierra 100 grain boat tail bullet and it hit two feet to the right of where it had been hitting before. (flat base vs boat tail)

Your two bullets are both boat tail bullets BUT the boat tails are shaped differently and both bullets are constructed differently internally. The muzzle blast can "push" bullets on a different path and your two bullets have a different shape base. (check your crown)

British .303 machine gun ammunition (ball Mk.8z) also used a rebated boat tail for greater accuracy. And was used only with single base powders on the ground and in aircraft.

Where can you get these rebated boat tail super bullets?

 

[bigedp51]

Where can you get these rebated boat tail super bullets?

Lapua makes more than cartridge cases.

http://www.lapua.com/en/products/reloading/bullets