Does velocity change the optimal seating depth??

[M60A3TTS]

Lets say my .239 Super Mario was dialed in at .029 jump, at 2550fps, for no particular reason other than the 42 gr of Speed Dust, was what I chose. It is in the middle of the recommended range of charge weight. If I decide to try for 2700 fps, does my leade depth then possibly change?

 

[Straightshooter1]

Lets say my .239 Super Mario was dialed in at .029 jump, at 2550fps, for no particular reason other than the 42 gr of Speed Dust, was what I chose. It is in the middle of the recommended range of charge weight. If I decide to try for 2700 fps, does my leade depth then possibly change?

Hmmmm??? The question isn't quite making sense to me. Maybe I'm a just little thick-headed. But, I'll try to make sense of it anyway.

The "leade depth" isn't much of a factor at all. If you're going to 2700 fps from 2550, you're changing the amount of time the "freedom seed" will exit the muzzle, which will most likely not match your harmonics that the 2500 fps was exiting at a good time. So, you'll need to find the right amount of pressure that gets your "freedom seed" out of the muzzle at the right time. That involves the right amount of powder and seating depth (very little to do with leade depth).

 

[Hoot]

Now if you're asking (in a convoluted way) whether changing your seating depth (jump) in order to reduce group dispersion, effects the velocity for the came charge weight, then Yes. Deeper seating into the case raises pressure and almost always equates to slightly higher velocity. I'll qualify one exception. Seating the bullet so long that it jams into the rifling can also raise the pressure and with it, slightly increase velocity. That being said, the biggest factor in velocity is obviously charge weight.

Hoot

 

[M60A3TTS]

Actually Hoot my question is the reverse. Does the velocity change also affect the seating depth? If a certain bullet likes .029 jump, does it change at a higher velocity?

 

[Straightshooter1]

Does the velocity change also affect the seating depth?

No.

If a certain bullet likes .029 jump, does it change at a higher velocity?

No.

 

[CharlieNC]

Maybe!

 

[Coyotefurharvester]

No

 

[jelenko]

I think you need to add what you're wanting to do with the rifle and what role you want accuracy/group size to play.
When you say 'recommended charge' and 'go for 2700 fps' it sounds like you aren't testing for accuracy/group size, yes?

 

[M60A3TTS]

Well everything goes hand in hand. It might very well be more accurate at 2700, or maybe at 2300, It's like the one powder is more accurate question. Is it really that the powder or velocity or bullet etc, are really better than any other or did you just stumble on the combo that worked. The amount of force jamming the bullet through the barrel will change going from X velocity to Y velocity. It would seem that this might change the amount of jump to the lands a bullet might like, or the bullet/gun combo will be fine, at Z jump regardless of velocity. It would appear , you are more likely to wear out a barrel, before you can find the optimal load. You can probably find an accurate enough load, depending, but in the really high velocity barrel killers, optimal might be out of reach. Just my ponderings, as I get into the LRT game.

 

[Jeff Porter]

That is a definite maybe. When I have done that I have had mixed results. Some times the accuracy was the same other times I needed to tweak the jump to match the other velocity.

 

[284winner]

That's kinda what I thought you meant in the initial post. Does seating depth effect velocity. My answer is no from my experience also

 

[Ned Ludd]

I think the more important question here is exactly what does seating depth due to affect precision? I've heard explanations that include tuning muzzle exit to the barrel harmonics, bullet alignment/entry into the lands, neck release, and a few others that I can't even recall at the moment. My point is that knowing exactly what seating depth does to tune group size should allow someone to better predict whether changing velocity should affect optimal seating depth. Unfortunately, I am not convinced that any of the explanations I've heard over the years for what seating depth actually does to optimize precision are correct, or at least the "whole" story, so I don't have the answer. I've often wished I did.

In my hands, large changes in velocity do seem to require different seating depths for a given bullet on occasion. By "large", I mean velocity changes well outside the ES/SD for a given tuned load, such as when adjusting charge weight to hit the next higher or lower node, which might be as much as a 60-100 fps velocity change (or more). Much smaller velocity changes such as are typically observed when changing the charge weight by a few tenths of a grain (i.e. perhaps 10-20, or even 30 fps) do not seem require any change in seating depth.

At the end of the day, simply conducting a seating depth test when some other parameter of a load has been changed is simple and straightforward enough that it is possible for anyone to empirically determine where the optimal seating depth for a specific bullet/load should be. In contrast, the experiments and/or equipment necessary to rigorously define exactly how seating depth affects precision likely preclude many of us from going down that road when we can simply carry out a seating depth test to answer the question. Nonetheless, understanding the specific mechanism(s) by which seating depth can facilitate very significant and obvious changes in group size/shape would be useful, if only for answering questions such as the OP posed in a predictive manner.

 

[Northridge]

yes, even though it may just be slight it likely can be adjusted to realign your tune, sometimes it may need more adjustment to clean it up let your ladders tell you what to do.

Shawn Williams

 

[CharlieNC]

I think the more important question here is exactly what does seating depth due to affect precision? I've heard explanations that include tuning muzzle exit to the barrel harmonics, bullet alignment/entry into the lands, neck release, and a few others that I can't even recall at the moment. My point is that knowing exactly what seating depth does to tune group size should allow someone to better predict whether changing velocity should affect optimal seating depth definitively. Unfortunately, I am not convinced that any of the explanations I've heard over the years for what seating depth actually does to optimize precision are correct, or at least the whole story, so I don't have the answer. I've often wished I did.

In my hands, large changes in velocity do seem to require different seating depths for a given bullet on occasion. By "large", I mean velocity changes well outside the ES/SD for a given tuned load, such as when adjusting charge weight to hit the next higher or lower node, which might be as much as a 60-100 fps velocity change (or more). Much smaller velocity changes such as are typically observed when changing the charge weight by a few tenths of a grain (i.e. perhaps 10-20, or even 30 fps) do not seem require any change in seating depth.

At the end of the day, simply conducting a seating depth test when some other parameter of a load has been changed is simple and straightforward enough that it is possible for anyone to empirically determine where the optimal seating depth for a specific bullet/load should be. In contrast, the experiments and/or equipment necessary to rigorously define exactly how seating depth affects precision likely preclude many of us from going down that road when we can simply carry out a seating depth test to answer the question. Nonetheless, understanding the specific mechanism(s) by which seating depth can facilitate very significant and obvious changes in group size/shape would be useful, if only for answering questions such as the OP posed in a predictive manner.

It is indeed strange that we understand charge weight tuning via positive compensation, but no definitive clue how seating depth works!

 

[CNC-Dude]

It probably somehow affects the pressure of the explosion and then the resulting frequency of the barrel vibration follows.....just guessing!

 

[M60A3TTS]

I would think this^^^^^