Bullet seating depth vs increased pressure

[Guest]

Seating bullets deeper would I be correct in thinking it will elevate the pressure?

Currently my COL with my 300 RUM is 4.030 and looking to seat deeper to 3.992 with 180 AB.

Don

 

[woods]

No, seating bullets deeper will decrease pressure

up to a certain point then it will start back up again

 

[nvbroncrider]

It takes more energy to release a bullet touching the lands than if the only thing holding it is the neck. But you will see increased accuracy and increased velocity if your bullet is touching the lands.

 

[Elkman]

I don't believe that increased accuracy is a given, many bullets recommend seating off of the lands for the best accuracy. Also as most of you probably know it is impracticle to seat the bullets against the lands in many rifles because of the magazine length. Start with the longest length that will function in the rifle then work shorter from there.

 

[nvbroncrider]

Your right on that elkman I forgot to mention the whole magazine thing. Ran into that the other day on the .243.

 

[Guest]

Here's what I observed yesterday at the range. I was shooting the 300 Ultra Mag. Remington 700 gun. Load was 96.1-RL25 with 180 AB, 215 primer, new REM. cases. Seated at 4.030 COL, enables the shell to just fit in the Magazine and feed well working the action etc. The velocity at this seating depth was 3289-3300 fps. Last year shooting this same load seated at 3.992 COL was producing 3372 fps. I lost about 80 fps.

Is it possible seating it deeper causes increased velocity? Maybe it was just my Chronograph too. Maybe the lot of Powder I have as well. I do want to add here at 3372 fps the temp. was 82F,
yesterday it was 70F.

I'm just curious to know. The gun shot well. But I'm going to adjust the seat depth to 3.992 anyway as it generally shoots a little better.

Don

 

[rick smith]

There is no magic being close to the lands. Just a place to measure from. Rounds should fit/function from the mag box and not be jammed into the lands. Does Barnes still recommend 50 off the lands for their bullets? WBY Mags, bullets usually can't touch the lands and still be in the case. That creates freebore which drops pressure but increases velocity.
For fellow loaders who are looking for every fps they can get, look at a drop chart for that round to see how many fps is necessary to make a realistic difference at 500 yds. If you are shooting whitetails can you really aim 1" different at 500yds. Most are kidding themselves about their abilities. Plus you can't control deer movement nor the wind differences. I know there are shooters that can make unbeliveable shots but they aren't average shooters and they probably practice at those distances. I shoot at a private range that has 100/200/300 yd benches. Have shot with a friend that has benches to 400yds and a tower where one can shoot to 1000yds. He practices before hunting season at the various ranges and regularly shoots deer at 600yds, shot a coyote at 800yds. But I digress from the topic.
You don't have to be at/into the lands for accuracy. Rifles normally have more than one accuracy node.Rick.

 

[velvetant]

Was the load last year also in new brass?
In my experience you loose a little velocity when using virgin brass.
In my 25-284 I lost an average of 40 fps using virgin brass vs once fired.
I've also found that RE25 is not temperature sensitive so I doubt the small drop in temp made a difference.
Could be the different lot.

Randy

 

[Guest]

Yes the comparison is with new brass in both instances. I'm thinking it is just the lot of powder.
I'm not real concerned about the velocity loss long as the groups stay some what consistent.

Don

 

[jmad_81]

I found somthing out about this the other day. I had been loading the 140 Bt at the same lenght as the 160 AB in my 280 AI. The 160 Ab was .010" off and as it turns out the 140 BT was .30 into the lands . It shot lights out, but I could never get above 3150 without PSI issues. I seated the deeper to the point that they were .010" off the lands. I got the same groups, and fps went to 3220! I have reloaded that brass again and it still help primmers just fine, and didn't have any sign of increased pressure.

 

[bullet]

Woods has it right, pressures increase when bullets are seated against the lands as opposed to giving them a jump. What a lot of people don't understand is that when a bullet is given a jump or is seated against the lands and enters the bore it actually for a very brief moment STOPS and at that point the pressure increases enough to start the bullet moving again and pushes the bullet on down the bore and out the barrel. When you seat a bullet on the lands it also stops for that brief moment, but with much less momentum to start with than the bullet that has a jump. So, it takes more pressure to build up to get it started moving again down the bore and out the barrel, than does a bullet that was NOT seated against the lands. You should always reduce any book max or near max load by 2% or 3% and work back up when seating bullets on the lands.