Bullet stability

Vern

Vern

Morethan1waytoskinacat
For short range BR
There are different jacket lengths.
So when you use a longer jacket on a lighter bullet does that mean the bullets are basically the same finished length?
And the core length inside is shorter for a lighter bullet and a lighter bullet would have a balance point more toward the back end compared to a heavier bullet?
How does or can this affect the stability of the bullet.
I am mainly thinking about 68 gr vs 61 gr 6mm.
 
Bullet Lenght

Vern said:
For short range BR
There are different jacket lengths.
So when you use a longer jacket on a lighter bullet does that mean the bullets are basically the same finished length?

The finished length varies according to jacket OAL, for example the .825 jacket finishes at .850, the .790 jacket finishes at .810 and the .750 jacket finishes at .770. Now these will vary so don't take then as the absolute gossip.


And the core length inside is shorter for a lighter bullet and a lighter bullet would have a balance point more toward the back end compared to a heavier bullet?

If the finish length remained the same for all different jackets that would be a true statement, however as mentioned earlier the finish length does change. This suggests to me that the bullet manufacturers got to shorter jackets to maintain the same CG relationship for the same relative CG. Don't forget the shorter jackets weigh less therefore the core weight is going to change.


How does or can this affect the stability of the bullet.
I am mainly thinking about 68 gr vs 61 gr 6mm.
Click to expand...

For stability questions one might get in touch with Bart, Randy Robinette, Bryan Litz at Berger or established bullet maker.
 
Vern,
really not that complicated, and all BR shooters should have a handle on this ,so here goes.
Stability is primarily a bullet length--- barrel twist equation with a few other little things like velocity,weight,altitude,temp,humidity thrown in there.
For all practical purposes, a 14 twist barrel will stabilize bullets made on .825 jackets and shorter regardless of weight.But just barely,drop the velocity and you can watch a 70gr. .825 take a hike. Thats why some shooters go to a 13.5 twist. An .810 Sierra or .790 J-4 takes all the worry out of an .825 at lower velocity.
Tunability is not the same as stability and defies definition.Made on the same die and .825 jacket a bullet may be extremely tunable at 65 grains but not at 68 or vice versa. You never know till you make em and shoot em. Same with .790 jacket based bullets 'cept you cant make a 68 on a .790 without squirtin lead out the nose and ending up with a 67gr.
The whole bullet balance thing( front to back) is extremely difficult to nail down and ends up being a real crap shoot. Make an .825 jacket length bullet from 60 to 70 gr. in 1 gr. increments and it will show a preference for tunability somewhere in that weight range, never know where till you shoot 'em. Switch dies to a different profile and that tunability balance point'll be somewhere else. Again ,make 'em and shoot 'em.
This is why one die won't make great .790 jacket 65's and great .825 jacket 68's.
Some bullet makers market 65's and 68's off the same die like they are going to be equally good 'cause the die is so special ? Dosn't work that way.
Find a bullet maker that knows what bullet length / weight is workin off his dies. It will be workin for everybody.
Hope this helps the guys that don't make their own,
Joel
 
Thanks Joel that helps some, but then again it indicates what I have been wondering. It would appear that balance does make a big difference.
 
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Vern,
Yeah,
but what balance,where? Changes with different dies, jackets. No set formula for success . Gotta make em and shoot 'em. I had 6 guys shootin for me on four different dies, different bullet weights, different jacket lengths. When it worked it worked for everybody, when it didn't work,it didn't work for anybody. Again,front to back bullet balance is not definable, Agg winning results and across the board accuracy / tunability is.
Joel
 
JBM balistics.com on the web Free down loads on stability check it out Hope thats correct address.
There are windows you fill in with the proper information. change twist etc .
Usefull information and free. hope it helps'
 
Joel I guess I am going to have to plead ignorant. I take it by the comment you are a bullet maker?
Which ones worked?
I am not looking for the secret formula but you seem to be saying what I have been thinking. Maybe we dont know the balance point but its the idea behind it I am looking at and you have proven the point I am looking for.
The ones that worked worked for everyone, the ones that didnt, didnt work for anyone.
Give me an idea of what did and what didnt work please.
 
Vern,

What Joel is saying is that two exact same dies, using the exact same jackets and exact same lead, one die may make a lighter bullet that consistantly out performs other weights made on that die and the other die may make heavier bullets that out perform other bullets made on that die.

The same goes for actions, barrels, stocks, triggers, etc.... Some things with no measureable differences, rarely shoot the same.

So it goes back to what many like Joel, who have been around shooting benchrest for quite a while, they always look to the targets to judge performance.

Hovis
 
Ahh ok, so its like barrels.
2 from the same lot will not necessarily shoot the same bullets well.
Got it.
 
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