jam vs jump test

[Link]

Interested in 1 - 3 just talking seating depth, all being equal I'm surprised at the difference a small change in oal makes. Is this normal or am I chasing my tail? Flags were used, 70* 200 yds 6br 1=8, 108 Bergers 29.7 Varget. And look at the groups with VLDs.

 

[Bronsin]

The same powder charge won't work with both jam and jump.

 

[Link]

There was a post about finding seating depth during fireforming. Would just .005 make that much difference?

 

[Ccrider]

There was a post about finding seating depth during fireforming. Would just .005 make that much difference?

Yes.

 

[ELR LVR]

There was a post about finding seating depth during fireforming. Would just .005 make that much difference?

Yes, seating depth most often makes that much difference
So much so, that is the main tuning I do with my loads
BTW, don't use OAL, measure on the Ogive,
If you switch bullets, you can usually use the same Ogive seating depth.
it is amazingly surprising sometimes the small window in seating depth where a group start to cluster then opens back up.
.005" one way or the other is often the norm for the window when it comes to seating depth
so you want to be right in the middle of it.
sometimes less, sometimes more but most of my test groups start to close right up when I hit the mark,
then open right back up once I'm .005" out
------
Cool you tried the 108's
Somtimes one particular bullet really shines for some reason.
You might try the Berger 109's and Lapua Scenar 105 L's also
And since you're not driving them hard with a 6 BR (112 Matchburners are good too at a nice price )

 

[LCazador]

Were these fireform loads? Also you say "oal", so you measured cartridge base to bullet tip? When testing for seating depth you should measure " CBTO" or cartridge base to ogive. I'd say the variance in your groups is more pressure variation due to brass not being fireformed.

 

[Bill Norris]

Jack Neary says in this video on the Pod Cast Believe the Target .001 will make a difference in seat depth when looking for best groups.

 

[LCazador]

Jack Neary says in this video on the Pod Cast Believe the Target .001 will make a difference in seat depth when looking for best groups.

So this means you would sort bullets base to ogive. Even custom bullets could have a difference of + or minus .001". Jack is spot on!

 

[CharlieNC]

Target 3 the poi is substantially lower, more than I see at 200yd with charge weight. You have something major going on.

 

[RabbitSlayer]

I think to see .001 difference in seating depth you need to be jack neary. I probably couldn't shoot the difference using Jack's gun even if he was standing there coaching me!

 

[ELR LVR]

I think to see .001 difference in seating depth you need to be jack neary. I probably couldn't shoot the difference using Jack's gun even if he was standing there coaching me!

I haven't seen .001" do much one way or the other
.003" yes, more definitely at long distance though, more so than at 100 yds.

 

[Link]

These were not fireforming loads and I should have said ogive to head. ty guys

 

[Someone online]

3 shot groups are statistically insignificant.

 

[ShtrRdy]

A while ago I did a matrix of powder charge weight and seating depth as suggested in the book by Tony Boyer.

Charge weight is different left to right and searing depth difference is top to bottom.
Notice for a particular charge weight the group size can change a lot with a 0.003" change in length.
This was fired at a distance of 100 yards.


Click on picture to enlarge

 

[Link]

3 shot groups are statistically insignificant.

Yes , however they say if you don't make 2 shots group the 3rd one won't help. /?

 

[Link]

I guess the question is how many of you actually see a seating depth change of .005 make a 1'' change at 200Y? As seen in the picture. Is this common? ty Don

 

[mgunderson]

Lots of us. Welcome to the club.

 

[JMayo]

I got frustrated with my 6.5x47, touch - jam. I talked to others, it was suggested i try jumping them up to - 30k back from jam.
I hit a sweet spot at -8k off touch.
Difference of touch and full jam was .17 thou.
So that's 25k off jam.
Won a couple of score matches 600yrds. Can't beat the good shooters at group in IBS
But
It made a pretty good difference that i feel confident in. I'll see how i stack up at the Tack driver.....

 

[ELR LVR]

I guess the question is how many of you actually see a seating depth change of .005 make a 1'' change at 200Y? As seen in the picture. Is this common? ty Don

I'll see if I can find a pic of a seating depth ladder test
I don't usualy take pics of those since as with this one, most all groups will be crap except for 2
---------------------------------------------
But to answer your questions YES
A seating Depth ladder test will look very similar to this Powder ladder test
Groups will shrink right down immediately then open back up quickly
with only a .005" change in depth at 100 yds
So the effects will be more pronounced at 200 yds

 

[ELR LVR]

Don, I’ve posted this before but since it’s a decent example I saved it.
The first is 300 yards jumping Berger 108
The second is VT 103 jamming beyond touch at 500 yards,
Note that there isn’t a drastic change in point of impact, only the shape changes .

I see the kind of difference consistent with what this sort of test always reveals
Good Pic Example