Bullet jumping question...

[Judd]

Today I shot some test loads loading in .020 increments out to .110...starting at .010 jammed. The weird (to me) part is .050 and .110 shot the best of the group. I never hear of anyone jumping bullets this much but it was recommended on Berger's site so I thought I'd try it.

My question is why do guys typically not jump this much? Is there a downside? Does it hurt the barrel throat?

Thanks.

 

[Nomad47]

Beats me, Judd. I know Weatherby jumps a bunch and that is how they get their velocity so high. I would guess most guys either jam or look for a sweet spot in the first .050" of jump. The further you jump the more case capacity is reduced. But Walt Berger says it is a wash - ie, more jump reduces case capacity but the bullet gets a head start when it jumps more.

 

[BlackKnight755]

Judd,

The reason I don't jump Bergers is that I usually can't get the accuracy that I want out of them if I jump them. This has just been my experience with the Bergers, some other bullets will take the jumping and some a lot more than others. I see that you referenced the Berger site suggestion so I assume that you are shooting Berger bullets. I usually have to seat a VLD either very close to the lands or touching and or jamming in the lands all together to get the long range accuracy out of my rifles. I know you said that you were shooting test rounds but you didn't state the range. I have tested and found some loads that were great @ 100 or 200 yards but just wouldn't fly at 1000 yards, had to work on seating depth.

Your other question "will it hurt the throat", I don't think so. I base this on the fact that the same charge weight builds more pressure when seated into the lands than if you back it off and have it jump.

These are just my personal experiences and opinions, have fun and good luck in your testing... BK

 

[lpreddick]

i have no choice in one of my 22-250s built in the early 1970s. for some reason the freebore was built in as a very long jump and if i seat to touch the lands, the bullet falls out of the case. i get good groups with jumps like .150 and more. i have always been a jumper as i feared a jam might cause me and my gun harm. if you start at slight jam and seat deeper by .005, you'll find several "sweet spots" where groups get tight. it's neat if you shoot a series of 10 groups, 3 shots each at .005 deeper, leaving powder charge the same and watch as the three holes move around the point of aim and eventually start to get closer, then move apart again. "barrel harmonics" is at play here. jumping seems to get a bit more speed also. i am currently trying seating bullets into the lands and see the same group movement by adjusting the powder charge, leaving the "jam" the same. i believe you can get into trouble jamming quicker than if you jump. there is a bit of danger seating bullets deeper while leaving powder charge the same as you reduce case volume with the bullet and might get pressure problems. some feel a long jump could allow the bullet to "yaw" before engaging the lands and become deformed leaving the barrel as such and accuracy is lost...don't know about this one. try both ways and select the one that works for you.

 

[mikecr]

why do guys typically not jump this much? Is there a downside? Does it hurt the barrel throat?

-Because most never did the test you just did
-Won't hurt the throat, and no downside provided you're not seating bullet bearing into neck-shoulder junction

 

[Judd]

Okay...you guys make me feel better and I get what you are saying about further distances. I'll check it out.

Again, thanks...now I have some further tweeking to do.

Judd

 

[Skeeter]

I shoot lots of Berger Bullets (20 cal, 22 cal, 6mm, 6.5mm) and all of them like something a little different. On the 20 cal (40 gr BTHP) they like jumped about 16 thous off the lands. My 220 Swift (52 gr BTHP) like then 10 thous off the lands. The 22BR (55 gr BTHP) and 6mm Dasher (87gr VLD & 95 VLD) 15 thous off the lands and a 260 Remington (130 VLD & 140 VLD) hard jam into the lands (between 5-20 thous into).

Its all about what your barrel likes and the Berger BTHP's seem to like the jump while the VLD's perform better in the lands.

Skeet