Accuracy=seating depth or tenths of powder

[Kevin87]

As I understand it, seating the bullet deeper into the case will reduce case volume and increase pressure for a given powder charge.

 

[SidecarFlip]

Phil....

What works for me is those 3 x 5 'Post It Notes' with the sticky edge on the backside and Frankfort Arsenal ammo boxes (flip top type) for every caliber,,, I use 308 boxes, sometimes the rounds fit, sometimes they go in upside down, but they go ...

That way I can access the previous loads and compare jumps, propellant load, basically everything from one session to the next and everything is attached to the inside lid of the respective ammo box. I actually leave all the notes inside a small plastic zip bag that stays with the rifle so I have everything 'at hand' all the time.

I've also found (from trial and error) that there are no shortcuts to achieving accuracy and consistency. Everything from the initial case prep to the actual sizing and bumping of the shoulders to the seating and neck tension to the concentricity of the pill in the case neck, all impact grouping and accuracy and especially consistency....

From my hands on experience, being consistent and meticulous in the way you load and adhering to your (Berger) regimen, yields the best performance and best groups.

I built loads for 3 rifles this summer, 2 custom builds and one off the shelf and all are shooting sub moa at 200 yards very consistently,,, and none of the 3 rifles jump even close to each other (something I would have never found out without using the Berger regimen)... Heck, I'd still be fiddling around with less that desireable results.

IMO, chambers are like fingerprints, no 2 are the same.

 

[SidecarFlip]

As I understand it, seating the bullet deeper into the case will reduce case volume and increase pressure for a given powder charge.

.......deeper than what? If you look in any loading manual, the pressure will be listed at Sammi seating depth (which most times is a helluva lot deeper than yopu would be seating anyway....)

 

[Pdvdh]

As I understand it, seating the bullet deeper into the case will reduce case volume and increase pressure for a given powder charge.

Test your theory while recording MV. Start with the bullet near the lands with a normal pressure rifle cartridge. Then increase jump to the lands with identical powder charges. Velocity will go down with increasing bullet jump (seating the bullet deeper in the casing). Or simple research further. It shouldn't be difficult to confirm this with the Google search tool.

I hear your thought process. It seems logical. But it neglects to include the pressure spike that occurs as the bullet enters the rifling. Muzzle velocity and pressure will be largest with the bullets jammed into the lands, because the additional friction required to start the jammed bullet will increase pressure substantially, compared to giving the bullet a friction free jump into motion before it enters the rifling. Higher pressure = higher MV.

 

[Kevin87]

Sidecarflip, I understand what you are saying. Let's say I work up a load to max and the bullet is seated at .020, then I decide to try .060 off the lands with that same powder charge. Are you saying that the pressure would not increase?

 

[Mikecr]

The deeper seated(given normal adjustments) pressure will not increase until affecting bullet grip (tension). This occurs as you near any sized donut with the bullet bearing. And you'd have to FL size necks or seat bullet bearing into neck-shoulder junction to see it.

 

[NATE40]

In the situation you posted, the pressure would increase because your load showed pressure signs at at a longer seating depth and then you reduced your case capacity by seating deeper. That said if the COAL was changed to .015 your pressure would decrease and would keep decreasing until the bullet contacted the resistance of the lands and the pressure would increase due to resistance.
SAMMI OAL specs in factory ammunition and many reloading books are printed for deeper to accommodate all types of firearms old ,new,auto loaders ,magazine length and so on . The reason for seating longer is to increase powder capacity in a case for increased MV and reduced pressure It's commonly called caliber up.
A 30.06 shoots the same bullet as a 308 win but the case capacity is much larger increasing MV. There are limits in caliber upping and those start when the lands are touched and even brass thickness neck tension and so on but with work the safety,muzzle velocity and accuracy can be obtained with this method. Berger bullet website has really good reading on this subject

 

[Kevin87]

Ok. I appreciate the clarification from everyone.

 

[Pdvdh]

In the situation you posted, the pressure would increase because your load showed pressure signs at at a longer seating depth and then you reduced your case capacity by seating deeper. That said if the COAL was changed to .015 your pressure would decrease and would keep decreasing until the bullet contacted the resistance of the lands and the pressure would increase due to resistance.

Nope. MV will decrease as you seat the bullet deeper in the case - farther off the lands. At least within the seating depth ranges almost anyone would every employ. I've read about this countless times. I've chronographed MV while varying seating depths, holding the powder charge constant, as have many others. The results are always the same. Pressure and MV will be highest with the bullet jammed into the lands, and then pressure and MV will continue to decrease as the bullet is seated deeper into the case, at least within reason - like for the first .150" off the lands there will be a steady and consistent reduction in MV.

If you set the bullet WAY into the case, then I suppose you could see increasing pressure. But you won't see that until you take seating depth to the extreme.

As stated earlier, you could demonstrate this to yourself if you have a quality chronograph. Or you can research this further and end at the correct understanding.

 

[Pdvdh]

Ok. I appreciate the clarification from everyone.

I'm not going to be offended one way or the other as to your conclusion. MV and pressure will either increase with increased bullet seating depth, or MV and pressure will decrease with increased bullet seating depth. It's a one or the other. So one position / understanding is correct. The other is wrong.

And my position on this is the correct one. I've got a quality triplicate chronograph setup. I obtain 3 recorded velocities for each bullet fired. I've recorded MV versus seating depth myself, more than once. My experiences were identical to others that have done this during load development, or just of the 4ell of it.

Misunderstanding this concept can lead to rude surprises. You work up a maximum load 0.125" off the lands, and then seat a bullet 0.010" off the lands under the mistaken belief that pressure will decrease, and you could learn the fallacy of your misunderstanding the hard way. So I'll end with this: I tried to steer you to the correct understanding...

 

[SidecarFlip]

Sidecarflip, I understand what you are saying. Let's say I work up a load to max and the bullet is seated at .020, then I decide to try .060 off the lands with that same powder charge. Are you saying that the pressure would not increase?

The next two posts after yours sums it up pretty well.

I became a believer after I bought the Berger reloading manual and carefully read the chapters on jump and how it impacts pressure versus powder charges.

I think it's also online in the Berger website...

I even apply the philsophy to Sierra's too. Little fatter ogive than a Berger VLD but it works just as well.

The one rifle I load laddered would not shoot Bergers for crap no matter what I tried, so I switched to Sierra's in the same caliber / weight and viola, sub-moa at 200. That just proved to me that Bergers are not a fit all pill. Not every stick will shoot them, I have one that refuses to...

What I often wonder is how many reloaders use the base to tip measurement for determining COAL as it pertains to jump.... I bet quite a few and thats an erroneous measurement.... Even though SAMMI specification as it pertains to COAL is exactly that.....

I guess if you pointed every pill and checked every one for tip consistency, it might work, but then, it might not.

I uniform all my meplats prior to loading in one of the shop lathes with an end mill chucked in the tailstock and the pills in a high precision collet. Every little bit helps...

I looked at the Whidden pointing die but I can achieve the same thing without it. I do use John Whidden reloading (bushing) dies however and I machine my own bushings from drill rod.

I have to say that Berger bullets are very consistent diametrically. I've gaged them and at no time have any runout more than 0.0002. Can't say that for the meplats however. The latest box of 500 I bought have improved, but, the meplats are still slightly inconsistent (VLD Hunting).

I might be a bit anal but I have the tools to 'adjust' stuff so why not.

My reward is that sub moa downrange consistently at 200 yards with a respectible velocity, maybe I should say really sub moa, more like sub 1" groups at 200.

 

[SidecarFlip]

Furthermore, discussing charges, I still abide by an exacting charge. If I'm running the tightest group at say 0.016 off the lands with say 43 grains of Varget in a 308 Lapua case with Fed LR primers, I want to maintain that charge exactly at 43 grains, no matter how many I load. (thats an actual load for one of the rifles...)

Guess I'm anal about that too.

I didn't buy an Omega Auto trickler for nothing..... ........and I liike it alot.

 

[NATE40]

I'm a reloader of course I chronograph my loads over and over with I reload Tuesday Thursday and Saturday I shoot Monday Wednesday and Sunday all year round religiously. Being retired Army at a young age and living in Wyoming gives me that opportunity. I will agree that a bullet seated too far into the lands will increase pressure even with light loads but once the resistance of the lands is removed muzzle velocity and powder capacity will safety increase. Working loads above book max and reducing pressure is the goal in tuning my rifles. A book maximum load is set to the book minimum seating depth increasing the seating depth reduces pressure just like seating a bullet deeper with the maximum load will increase pressure that's why the book seating oal is set to minimum seating not maximum seating depth. This is my opinion and by no means will dismiss your recommendation and will openly test what you are saying as I'm loading for my 6.5 creedmoor tonight I'll let you know what I find if you want. I'm not trying to belittle anything your saying and I will always be willing to learn new things about reloading as I'm not quitting soon and I'll admit I am always learning.and appreciate any tips

 

[Mozella]

Nope. MV will decrease as you seat the bullet deeper in the case - farther off the lands. At least within the seating depth ranges almost anyone would every employ. I've read about this countless times. I've chronographed MV while varying seating depths, holding the powder charge constant, as have many others. The results are always the same. Pressure and MV will be highest with the bullet jammed into the lands, and then pressure and MV will continue to decrease as the bullet is seated deeper into the case, at least within reason - like for the first .150" off the lands there will be a steady and consistent reduction in MV.

If you set the bullet WAY into the case, then I suppose you could see increasing pressure. But you won't see that until you take seating depth to the extreme.

As stated earlier, you could demonstrate this to yourself if you have a quality chronograph. Or you can research this further and end at the correct understanding.

I have to chuckle when someone lays down the law on the Internet. What you say may be true in your experience, but that doesn't make it a universal truth. Measuring MV vs Seating depth doesn't produce results which are "always the same" as you contend. Here is a chart of three 6mm BR bullets I tested not long ago. The muzzle velocity is the average of 10 identical rounds at each of the listed seating depths.
MV vs Seating Depth