bullet jump increments

[Texas Solo]

I'm working with a new bullet for my .308. (SMK175)
Using a fixed CBTO of .005" off the lands, I dialed the load down to the best powder charge. (42.5 Varget) (2890fps)
Now I want to play with the CBTO, hoping to get better than the .440" group I'm getting @ 100yds.
What increments of jump will give me the best results in the shortest time? (least amount of bullets)
Should I space them out at .005 increments, or maybe .010, or maybe .020 ?

The 168's I have dialed in shoot the best at .005" off the lands. If this holds true with the 175's, I'm not happy.
To limit the variables, I'm only loading Varget at this time. I know I can try other powders, but I think Varget should be capable of better groups than .440". I don't think the Varget is a limiting factor to better groups at this point.
Again, one variable at a time.

Also, If I shorten the CBTO by .020" or more, will this make a significant change in pressure, thus requiring a reduced powder charge?

Thanks for any advice.

 

[Terry]

It depends on the range of variation.
When testing +.020 to -.070 I like to jump .010 per step.

If you get a good range you might use smaller steps in between them.

 

[BoydAllen]

It has been a long time since I played with a .308 but with a good rifle, I have always been able to get slightly better accuracy loaded into the lands a bit, say .006 to .010 longer than touch. Of course this would dictate another small powder charge investigation since touching or seating into the lands will jump up your pressure some. If you are precise in your measurements, going this far into the lands, with any decent amount of neck tension, should pose no risk of pulling a bullet when unloading a live round.

 

[Erik Cortina]

.003" increments.

 

[Alex Wheeler]

I agree with whats been said so far. If you have and idea of where you want to be .003. I have been told by one of the best br shooters in the country .001 can make a big difference.

 

[Texas Solo]

Thanks so much guys.

I'm going to load at .010 increments X 4. Then pick the best one and do .003 increments.
This is exactly what I needed to know.
And yes, powder charge will be re-visited for further refinement later. Then maybe powder type....then maybe bullet choice...then maybe....crap, it never ends!!!!!!!

Now, if it will just warm up a bit, I'm GTG!

 

[TimP]

Be carefull with .010 increments you may just go right by the optimal seating depth. I would stick to increments of .003

 

[Terry]

Be carefull with .010 increments you may just go right by the optimal seating depth. I would stick to increments of .003

.003 from Jamed 20 to .070 off?

 

[Erik Cortina]

Be carefull with .010 increments you may just go right by the optimal seating depth. I would stick to increments of .003

.003 from Jamed 20 to .070 off?

You don't need to cover such a large range, he will find a good node way before he gets to .070" off.

 

[Texas Solo]

Be carefull with .010 increments you may just go right by the optimal seating depth. I would stick to increments of .003

Yeah, I see that possibility. I plan on choosing the best of 5 depths (zero jump to -.040), then going back to .003 increments, in either direction, from that figure. I would assume that if I pass the optimal depth, I will eventually get back to it this way.
Thanks again to all.

 

[spclark]

As with cartridge loads, I found there are "nodes" for seating depth as well. One bullet I like a lot (for mid- and long-range target shooting) likes jumping 0.005", 0.020" and 0.060". Equal accuracy out of two different rifles at two different velocities.

When I begin load testing I start at 0.020" off the lands, move up or down 0.005" at a time to see if there's an improvement.

Given the cost of bullets, powder and fitted barrels, I'm happy enough not looking for others in between those three.

 

[Terry]

From +10 to -10, I love .003, it works great.

My 270 Remington was best at .120 off the lands.

You don't know if you don't test.

Granted most of my guns shoot best just touching the lands.

Blonds and Redheads again!

 

[savagedasher]

I have more of a question then a answer. When a bullet is in or touching ever book say you increase pressures. So coming back you decrease pressures but gain speed from free bore. Plus your decreasing the capacity of the case. that is like adding more powder. Has anybody ever done a crony check on this. Larry

 

[Alex Wheeler]

Larry,
I was just shooting my freshly rebarreled rem 700 in 6br. I started at touch and went in the lands from there and shot through the chrono. I could not tell any speed increase. If there was one it was so small I did not detect it. I have never seen pressure increase much by jamming. I know does but, I doubt I would notice a couple thousand psi unless I was on the ragged edge.

 

[Texas Solo]

I have more of a question then a answer. When a bullet is in or touching ever book say you increase pressures. So coming back you decrease pressures but gain speed from free bore. Plus your decreasing the capacity of the case. that is like adding more powder. Has anybody ever done a crony check on this. Larry

It depends. In order to touch or jam the bullet, you have be longer than SAAMI spec. Most all load recipes in the books show an OAL of 2.800 (for .308) On one hand your increasing case capacity, thus lowering pressure. On the other hand, your jamming the bullet, causing an increase of pressure. To most of us, OAL doesn't mean squat because we all have different chambers, and bullet shapes are different from model to model. The same round will jump different amounts in different rifles (chambers)
"coming back", or decreasing the length, will only cause a pressure increase beyond the book listing when you go shorter than the 2.800" OAL that the recipe is calling for.
The simple (and safest) solution is to start low and work up.

 

[savagedasher]

Larry,
I was just shooting my freshly rebarreled rem 700 in 6br. I started at touch and went in the lands from there and shot through the chrono. I could not tell any speed increase. If there was one it was so small I did not detect it. I have never seen pressure increase much by jamming. I know does but, I doubt I would notice a couple thousand psi unless I was on the ragged edge.

What happens when you come back out. Does the free bore and the decrease of the capacity of the case. keep the speed the same? Larry

 

[Alex Wheeler]

I dont know? It shot so good in I never tried jumping.

 

[savagedasher]

Someone must sure of done a crony test from hard jam to .060 back with the same load.
Larry

 

[amlevin]

....crap, it never ends!!!!!!!

The truest statement ever posted on the internet 8)

 

[savagedasher]

....crap, it never ends!!!!!!!

It my be what you called it. I would like to know if it was tested. and what is the results and the reason why. When a bullet is in the land the pressure goes up every reloading manual warns you. When you start jumping the pressure should go down , and so should the speed that was what my question was. Larry

The truest statement ever posted on the internet 8)