Refresh me - why the faster 300gr shoots lower than the slower 405gr in 45-70?

[tacotime]

Sighted in the 45-70 at 100 yards with the factory Rem 405 gr at about 1330fps, right on. 

Then for reference at same range and no scope adjustment, fired the factory Win 300gr at 1880fps and it strikes the target 12 inches below the slower 405gr. Repeated from a rest, same result.  Used sighting vise, same result.

Then at 200 yards, sighted for 100, the 405gr strikes low 24 inches, about what the charts call for.  Then the 300gr strikes 30 inches low.

Seems like I knew the answer to this question once, but refresh me, why does the faster round strike lower again?

Thanks.

[SHOOTALL]

because the gun rises with recoil and the faster bullet gets out the bbl faster.

[PawPaw]

Yep!  Barrel time.  The slower 405 grain bullet is in the barrel longer.  The muzzle starts to rise before the bullet leaves the barrel, hence, it seems to shoot higher than the faster bullet.

[tacotime]

Well, that sounds like the answer I used to know...  but what didn't make any sense about it was that it seems then if the barrel rise was affecting the point of impact, that the gun would shoot differently each time, even with the same load, depending on how firmly one gripped the forearm.  Like a resting shot with no grip would be very different on the target than a shot made with a very firm grip on the forearm, or as some folks do, with a hand over the barrel holding the forearm down firmly on the rest.  Why wouldn't this be the case?

Thanks!

[SHOOTALL]

It is and its what makes a good shot vs. a great shot. The shooter that can duplicate his hold and sight picture the best will shoot the best. As an example i have neck trouble so to sight in hard kicking guns i have a lead sled. I sighted in my encore 50 cal. with it and went hunting . had a good hold and sight picture. I missed big time . Went back to the range with the sled and was perfect. Then tried with out the sled and missed . point is anything can effect the shot as a shooter its our job to control of all the things that effect a shot. If you want a lesson in gripping a gun and its effect try shooting a slug gun grip is a big deal there.

[necchi]

You have the scope set for the rainbow trajectory of the 405,
the 300 is faster and flater,,it's gonna hit lower,
Zero for the 300 and see what happens with the 405's 

[tacotime]

By no means intuitive though - with the barrel pointed in exactly the same place, I would have expected the flatter round to hit above the slower, lower powered round, because if the barrel is pointed upward to arc the big bullet into place, it would seem that the flatter round would fly well high, more closely following the direct line of the bore, pointed high, well above the target.

[kynardsj]

I agree with what SHOOTALL said. Have the same situation with my 500 S&W mag Encore. 367 gr lead moving 1250 fps will shoot higher than the 350 gr JHP's I have that are 1697 fps. This is at closer ranges, 50 yards and such. After some distance the faster bullet will shoot higher as the slower bullet drops.

[PawPaw]

It's odd the way that works.  When I'm benchresting a gun to find the best load, I'll normally get a close zero too keep the bullets on paper, but when I've settled on a load and get away from the bench to sight in for hunting, I normally have to make a sight change.  The rifle simply recoils differently when I'm settled into a shooting position than it does when it's resting on sandbags.

My .30-30 Handi shows as much as 8" difference at 100 yards between the bench and a hunting position.

[SHOOTALL]

By no means intuitive though - with the barrel pointed in exactly the same place, I would have expected the flatter round to hit above the slower, lower powered round, because if the barrel is pointed upward to arc the big bullet into place, it would seem that the flatter round would fly well high, more closely following the direct line of the bore, pointed high, well above the target.

Keep in mind that the arc in the slower bullet is also part of the rise from recoil . If you zeroed a rifle at the bench then locked into a fixture that would not allow it to rise with recoil it would shoot low. Why ? because when you zero you aim where the bullet will be after all the influnces have had their way with the bullet . The faster bullet still leaves faster leaving less time for the bullet to be influnced or corrupted .

[tacotime]

That does add clarity...  since I plink and hunt with the 405gr but may need to hunt with the 300gr if the big hogs are around, I'll probably just learn the hold-high allowance for the 300gr.  The plinking is a good 99%+ of the shooting.  Love the 45-70.  Glad I found it again after a 32 year absence.

[Range Rider]

Lots of good advise. The later 86' Winchesters and the much later 86' Brownings were sighted for the 300 gr. bullets.  It seems Winchester was pushing the 45-70 Express loads in the later years. These loads were fast 300 grs. loads.  I have found these later rifles have to have the front sights changed if you want to use the heavier slugs.

[Darrell Davis]

Yep, has to be "barrel time."

I have seen and or heard of this with a handgun, but this year, working up cast boolit loads for my RUGER #1-s 45/70 was the first tme I had seen the situation with a rifle.

Started with the 405 RCBS, and the faster the load, the lower the impact point.

Sure made for lots of scope setting, back and forth/forth and back, when I started.

Now with my 350gr LBT, running in the 2100 - 2200fps range, things are still moving around a bit, but nothing like when I started up from the 1300/1400fps range.

Keep em coming!

CDOC