Seating depth question!

[TrentK16]

So before hunting season started this year I started working up my first load for my browning a-bolt 7mm rem mag, Using 168gr Berger vlds. I anticipated starting with the bullet touching the lands but ran into an issue. Last minute I remembered that my rifle has an internal box magazine so I had to back off the lands .069" for the bullets to fit in my magazine. So since I didn't have a whole lot of time I just started with my seating depth there and went with it. Shot my ladder test then loaded up a few rounds with the load I liked and shot those. They shot well, around 3/4 moa which I was very pleased with. My question is; is there any options for a different internal mag so I can maybe get the bullet seated closer to the lands or should I just go with what I have??? I just put a McMillan stock on it to so I'm not looking at replacing my stock any time soon.

 

[FearNoWind]

Why would you want to seat the bullet closer to the lands?
Have you tried seating it even deeper to see what those results do for your accuracy?

 

[TrentK16]

Why would you want to seat the bullet closer to the lands?
Have you tried seating it even deeper to see what those results do for your accuracy?

Well from everything I've read,watched and understood on load development is to start on the lands and shoot your ladder test from there working up the charge weight. That way when you start seeing high pressure signs you know whereas pressure is for that load, then you can work back from there whether it be seating depth, charge weight, or both. Anyways from all the info I've gathered that been my understanding. And in theory the closer to the lands the higher the accuracy potential ( I know this is not always the case.) I was just curious if I could get anymore accuracy out of it from not seating it so deep (but I have the magazine length issue.)

And to answer your question, no I have not tried that either. Once the holidays are over I'll be able to get out and shoot and start tweaking with the load.

 

[FearNoWind]

Well from everything I've read,watched and understood on load development is to start on the lands and shoot your ladder test from there working up the charge weight. That way when you start seeing high pressure signs you know whereas pressure is for that load, then you can work back from there whether it be seating depth, charge weight, or both. Anyways from all the info I've gathered that been my understanding. And in theory the closer to the lands the higher the accuracy potential ( I know this is not always the case.) I was just curious if I could get anymore accuracy out of it from not seating it so deep (but I have the magazine length issue.).

I am not a subscriber to the "start load testing at the lands" society. There are many reasons for my position on that theory but I'll offer just one point of consideration for your review.
When the bullet is seated into the lands, the case has more capacity. If we seat into the lands until we find pressure points and THEN start adjusting seating depths, the bullet moves further into the case. Because pressure in the case is a factor of case volume/powder charge (and perhaps some neck surface tension) as the free space in the case is consumed by a deeper seated bullet atop the same powder charge, the pressure in the case increases with each change in bullet seating depth so we have to constantly reduce powder charge to accommodate for increased seating depth. That, IMO, wastes bullets and powder.
If you want to start at the lands I suppose you could accomplish the tests you're seeking by simply loading rounds into the chamber in "single shot" fashion. But, IMO, it's dangerous to start high and work down - we should be starting low and working up when reloading and excellent accuracy is possible with considerable "jump" in very many good rifles.

 

[TrentK16]

I am not a subscriber to the "start load testing at the lands" society. There are many reasons for my position on that theory but I'll offer just one point of consideration for your review.
When the bullet is seated into the lands, the case has more capacity. If we seat into the lands until we find pressure points and THEN start adjusting seating depths, the bullet moves further into the case. Because pressure in the case is a factor of case volume/powder charge (and perhaps some neck surface tension) as the free space in the case is consumed by a deeper seated bullet atop the same powder charge, the pressure in the case increases with each change in bullet seating depth so we have to constantly reduce powder charge to accommodate for increased seating depth. That, IMO, wastes bullets and powder.
If you want to start at the lands I suppose you could accomplish the tests you're seeking by simply loading rounds into the chamber in "single shot" fashion. But, IMO, it's dangerous to start high and work down - we should be starting low and working up when reloading and excellent accuracy is possible with considerable "jump" in very many good rifles.

Ahhhh, that makes sense. See I guess it's true you do learn something new every day. I hadn't thought about that. Thanks for your time.

 

[C Harrison]

The bullet is pushed into the lands from the force of the primer, then stops at the lands until the charge is ignited. Seating the bullet further into the case reduces pressure in a sense. What really happens is that there are several pressure impulses throughout the firing cycle. The initial force from the primer moving the bullet into the lands before the powder charge begins to expand serves to the lengthen the pressure curve of the primer blast. As the charge ignites, the bullet is pressed forward into the barrel, etc. When we set the bullet to the lands, the primer blast combined with the charge igniting increases the pressure spike resulting in higher pressure from the resistance between the copper and the steel barrel lands.

http://www.dtic.mil/dtic/tr/fulltext/u2/462060.pdf

 

[Canadian Bushman]

The bullet is pushed into the lands from the force of the primer, then stops at the lands until the charge is ignited. Seating the bullet further into the case reduces pressure in a sense. What really happens is that there are several pressure impulses throughout the firing cycle. The initial force from the primer moving the bullet into the lands before the powder charge begins to expand serves to the lengthen the pressure curve of the primer blast. As the charge ignites, the bullet is pressed forward into the barrel, etc. When we set the bullet to the lands, the primer blast combined with the charge igniting increases the pressure spike resulting in higher pressure from the resistance between the copper and the steel barrel lands.

http://www.dtic.mil/dtic/tr/fulltext/u2/462060.pdf

+1 yup

A coarse seating depth test with a mild charge will tell you where your bullet likes to be shot from before you work up a powder charge.

I favor the bullet close to the lands, ive always found better accuracy and e.s. with the bullet somewhere between .03 jump and -.01 jam. I always shoot vld bullets with secant ogives as well.

When im working with a rifle thats like the bullet close to the lands i usually start .01 off ( or wherever my initial seating test suggested) and find a powder charge, then move the bullet around .005-.010 to shape the grouping. Typically moving into the lands at this point will raise pressure and moving away will reduce it. Never have conducting seating test with these small increments shown unpredictably high pressure. If you pay attention to your brass and speeds its very easy and safe conducting seating test in this manner.

If you are using a load on the upper end and conducting seating test with large increments you are asking for trouble. If you have to change your seating by more than +/- .02 - .03 you are no longer shaping your grouping, you are changing the load and need to reconsider the decisions that lead you to this point.

 

[dkhunt14]

In 1000 yard match rifles I have seen very few that shot a Berger VLD off the lands. I am talking over a hundred different rifles. These were shot at 1000 and not 100 yards and were 10 shot groups so it is not a luck thing. The Berger VLD just loves it in the rifling. I did see one or two that liked it 100 off. I am a believer that shooting at 100 yards with a long bullet like a Berger VLD will not show the best accuracy. I have seen groups shoot way smaller MOA at 300 or 400 yards. Most of my good heavy guns (80 pounds) will only shoot 3/4 inch at 100 but will shot an inch at 400. My 17 pound light guns are the same way. Matt

 

[4xforfun]

I am not a subscriber to the "start load testing at the lands" society. There are many reasons for my position on that theory but I'll offer just one point of consideration for your review.
When the bullet is seated into the lands, the case has more capacity. If we seat into the lands until we find pressure points and THEN start adjusting seating depths, the bullet moves further into the case. Because pressure in the case is a factor of case volume/powder charge (and perhaps some neck surface tension) as the free space in the case is consumed by a deeper seated bullet atop the same powder charge, the pressure in the case increases with each change in bullet seating depth so we have to constantly reduce powder charge to accommodate for increased seating depth. That, IMO, wastes bullets and powder.
If you want to start at the lands I suppose you could accomplish the tests you're seeking by simply loading rounds into the chamber in "single shot" fashion. But, IMO, it's dangerous to start high and work down - we should be starting low and working up when reloading and excellent accuracy is possible with considerable "jump" in very many good rifles.

While your general premiss is true..... seating the bullet deeper in the case reduces case volume and thus, increases PSI, it realy is a moot point here.

First off, you need to move the bullet a hell of a long way in to make any meaningfull difference in PSI. BUT....move the same bullet out the other way, say .020 .....from say at the lands to a twenty thou jam, and you could see a HUGE spike in PSI.

If you start your load development at 10 thou or so INTO the lands and work SHORTER (if needed) you will NEVER have to worry about a PSI spike. You may see a very small and gentle PSI increase once you move a full 100 thou, you will NEVER be in danger.

The ONLY problem I ever see or hear about with a jam is the occasional time where the bullet gets stuck in the lands. I rarely see that in HUNTING CHAMBERS..the brass in the necks are usually pretty thick and the neck tension is usually substantial. You need to have a hell of a jam to cause problems. Of course, there are guys (like me) who run competition spec chambers in thier hunting guns. I have to neck turn for lots of my guns and run very little neck tension, and , yes, I have stuck bullets. But I have never had a problem with stuck bullets in my more "factory" type chambers.

And, in my case, anyway, the fact is that EVERY gun that I have ever done load development for has shot best with a SLIGHT to hard jam. Most of the loads are VLD's or Hybrids, but not all. Amax, Vmax, Balistic tips, X bullets...ect are also in the mix.

To the OP.....start your load development with a slight jam (as long as you are not running very thin necks with little neck tension) and work up in powder charge till you hit max (with the jam). You may well have seen at least two "sweet spots". Once you find "the load", simply do a group comparo at longer ranges with your current jam and maybe a .010 and .030 jump and let your groups decide the load. NEVER try and load to a .000 jam..or "just kissing". General bullet run out mixed with loading run out will give you a plus or minus .002 in ojive length....that means a small jump MIXED in with a small jam. And that very small difference ....002 jam vs jump will be HUGE on target.

Just my .02
Tod

 

[TrentK16]

This was my understanding and that's what I was planning on doing. I know I wasn't planning on having my final load jammed (just my personal preference for reliability). But I was gonna start there like you said find my nodes then compare those nodes and work the depth backwards from there. But I still have the magazine length issue. Thanks for your input.