Seating Depth for reloading

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Hello all,

I was reading another thread "Ladder Test" and someone brought up trying different seating depths to get better accuracy. First I have heard of that and I am a curious guy that likes to learn. I am wondering what the execution if this method is. What does seating deeper or shallower actually accomplish?

I have been reloading for my 7mm RM and have a load that is not too bad (about a 1" group, 4 shots, 100 yards). I was told to place a bullet into an empty shell, put it into my riffle, and close the bolt slowly. Then use that empty shell with bullet in it and put it into my press and adjust the die so that it is the same.

Am I doing things okay? or should I try backing the bullet down a bit, or even leaving it out a bit just to see if the results of the group get better?

I don't have any toys for measuring pressures or speed out the barrel. I just try and find something accurate within the documented min/max for the powder and bullet choice.

[sns2]

The link below should answer all the questions you have concerning seating depth. It is straight from Nosler's manual. Enjoy.

http://www.nosler.com/news-and-artic...your-own-loads

[colroggal]

Nosler's manual is great read it. My way of understanding seating depth is this. Think about flicking a marble into a tube. The marble is the same diameter as the inside of the tube. But you have a gap between the point you launch the marble and the point it enters the tube. The marble will inevitably make contact with the entrance point of the tube somewhat unevenly. The result is friction and oscillation within the tube which will continue in waves down the length of the tube. When the marble leaves the tube it will have an inertia bias which, however minor, will be complete random.

But the closer you can get the marble to the mouth of the tube the more you can lessen that random oscillation. To a point. The same as loading a bullet closer to the lands mitigates any variance in the linear direction of the bullet. Hence the notion of only neck sizing cases because the case with stick in the chamber, centering the longitudinal axis of the round to the center of the bore.

All that aside, my understanding of RUM chambered rifles is the cartridge is that they do enjoy a little bit more free bore than most others.

There are plenty on this forum far smarter and wiser than I. Maybe they can add points to clarify

Colin

[bdub]

I don't like to reload so that my bullets are right to the lands. I was always told it can lead to pressure spikes. You want the bullet to be starting in motion before it touches the lands to avoid that is the theory.

You can get completion style seating dies that can very accurately adjust your seating depth. I just use standard RCBS dies and adjust my bullet depths by turning the seating stem down in fractions of a turn. I forget how many thousands of an inch full revolution of the seating stem is on those dies. I set up a dummy round to just touch the lands as I close my bolt and then adjust my loaded rounds in fractions of a turn of the seating stem in. Load a few at various lengths. Go shoot and see what the gun likes best.

Once I have found the distance from the lands for a particular bullet rifle combo that works I make up a dummy round labeled with the bullet type/weight and keep it with my reloading gear. When I go to reload my next batch I can set up my seating die off of it.

Hope that I explained that ok so it helps you a bit. I'm sure others will chime in with some other pointers. I'm not an accuracy buff but I do appreciate decent accuracy in my hunting rifles.

[Fredo]

You can get this tool to get a good measurement. Don't forget to buy the dummy case that match your caliber, and redo the measurement every time you change bullet grain or manufacturer or whatever change.

For a better seating, I use the RCBS Gold Medallist seating dies. They are expensive, but you can go exactly where you want, by a /1000.

[Cowtown guy]

Originally Posted by colroggal

Nosler's manual is great read it. My way of understanding seating depth is this. Think about flicking a marble into a tube. The marble is the same diameter as the inside of the tube. But you have a gap between the point you launch the marble and the point it enters the tube. The marble will inevitably make contact with the entrance point of the tube somewhat unevenly. The result is friction and oscillation within the tube which will continue in waves down the length of the tube. When the marble leaves the tube it will have an inertia bias which, however minor, will be complete random.

But the closer you can get the marble to the mouth of the tube the more you can lessen that random oscillation. To a point. The same as loading a bullet closer to the lands mitigates any variance in the linear direction of the bullet. Hence the notion of only neck sizing cases because the case with stick in the chamber, centering the longitudinal axis of the round to the center of the bore.

All that aside, my understanding of RUM chambered rifles is the cartridge is that they do enjoy a little bit more free bore than most others.

There are plenty on this forum far smarter and wiser than I. Maybe they can add points to clarify

Colin

Good way of explaining it.

VLD bullets tend to like to sit very close to, or even into the lands.

Barnes bullets tend to like a little jump. Typically 50 to 70 thousandths of an inch to the lands.

I have found the best results with cup and core bullets in my rifles to be achieved when I can have a jump of 15 to 25 thousandths of an inch to the lands.

[Cowtown guy]

Originally Posted by Fredo

You can get this tool to get a good measurement. Don't forget to buy the dummy case that match your caliber, and redo the measurement every time you change bullet grain or manufacturer or whatever change.

For a better seating, I use the RCBS Gold Medallist seating dies. They are expensive, but you can go exactly where you want, by a /1000.

I love my Hornady OAL tool. The first thing I do when I get a new rifle is get dies, brass, and a modified case for the tool.

[Icon]

Wow, I came to the right place I think!

Great stuff guys. I have the regular RCBS full length dies. I will try to adjust with that to start. 100 bucks is a bit much for dies as I don't shoot that much.

[Sabre tip]

I use the RCBS Precision Mic for this purpose. It is calibre specific so if you have a lot of calibers it gets costly at about $65 per set. Maybe more nowadays as I haven't had to buy one in years. They are fun to work with and deadly accurate measurements are made. They may be a bit more finicky to work with than Hornadys system but I've never used Hornadys.

[meatball]

My experience (which is limited) on this topic is Barnes TSX seem to like being set off the lands by quite a bit in my opinion.

When trying to find a load and COAL for my 270wsm I did the measurement with Hornady's gauge and came up with a 2.83 COAL so I started to load at 2.80. After playing with charges from 59 up to 63 (0.5 gr incriments of IMR 4350) I found decent grouping but not great.. A fellow Barnes fan told me to back off the COAL and see how it shot. As I backed the depth off ( down to 2.75) I found noticeably better groups, however on average, the groups were about 1 inch higher at 100yds. With further playing I found my best group is at a 2.70 COAL.

Comparing my original 2.80 depth to my most recent 2.70 depth I noticed about 1.5 to 2 inch difference of height at 100 yds. My muzzle velocity should be higher ( I think) based on the height but I have not chronographed the load yet.

By no means am I a reloading expert, just giving my 2 cents towards the topic. Hope it helps a little.

One last note, I had an old box of factory loaded ammo and measured the COAL on the shells. I found COAL ranging from 2.67 up to about 2.73.

[ramonmark]

Originally Posted by Cowtown guy

I love my Hornady OAL tool. The first thing I do when I get a new rifle is get dies, brass, and a modified case for the tool.

Thanks for the reminder. I picked up a tap and die on ebay so I can make my own modified brass but haven't done that yet.

[58thecat]

Remember COL is going to be slightly different but it is a starting point for all cartridges, You need to find out what your rifle likes with all things put into perspective which may take sometime, that's why we reload to have a pet recipe for our rifles. Some rifles/bullets like the bullet into the rifling, some like a jump, watch pressures, start at the low end work up, just find what the gun likes and go from there.

[1899b]

Originally Posted by 58thecat

Remember COL is going to be slightly different but it is a starting point for all cartridges, You need to find out what your rifle likes with all things put into perspective which may take sometime, that's why we reload to have a pet recipe for our rifles. Some rifles/bullets like the bullet into the rifling, some like a jump, watch pressures, start at the low end work up, just find what the gun likes and go from there.

If the handloader is loading for a levergun with tube magazine however, you are relegated to utilizing the bullets' cannelure and a heavy crimp for correct and safe functioning in a tube magazine.

[colroggal]

Originally Posted by 1899b

If the handloader is loading for a levergun with tube magazine however, you are relegated to utilizing the bullets' cannelure and a heavy crimp for correct and safe functioning in a tube magazine.

That's when you get to play with case trim length instead.

[1899b]

Originally Posted by colroggal

That's when you get to play with case trim length instead.

Yup but really sucks when you experiment with brass and sacrifice it when said brass is rare.....

[xxclaro]

I've used a Lee Factory Crimp die to seat the bullet wherever I want regardless of cannelure, and its worked quite well. Usually I just use the groove, but if I feel like messing around, its an option.

[elkhunter11]

Originally Posted by xxclaro

I've used a Lee Factory Crimp die to seat the bullet wherever I want regardless of cannelure, and its worked quite well. Usually I just use the groove, but if I feel like messing around, its an option.

The OP mentions the 7mmremmag,so a tubular magazine is unlikely, so with proper neck tension,crimping shouldn't be required.