SEATING DEPTH

[RAY]

How does seating a bullet deeper effect velocity ?

What is the typical group at 100 yards
with a minimum charge using 150 gr. 3006. ( what is your experience? )
Thanks !

 

[DrMike]

There is no typical group for all rifles. Your rifle is unique with a given load. If you can shoot a load consistently to produce a two-inch group at 100 yards, that means you can deliver a twelve-inch group at 600 yards, which will deliver deer for you. Most modern rifles will deliver one MOA (effectively one inch at 100 yards) with ammunition it likes, which means that your rifle should be able to deliver the goods farther than most people can shoot. Getting accuracy requires that you seat the bullet to deliver the greatest accuracy. Again, seating depth is dictated by a number of factors. At first, you are well advised to seat to SAAMI standards. Seating depth is not a primary determinate for velocity until you begin either to intrude into the powder column and begin to generate excessive pressure by seating it too close to the lands.

 

[RAY]

My rifle likes the bullet to jump with factory loads.
I have read about the high pressure with seating too close.
Being novice , I'm thinking I want to copy factory seating .

My rifle likes the .090 " with a secant
and .048 " tangent.
These are sub moa sweet spots

 

[MrMinks2]

Hey Ray: I guess I was hoping to see more responses to your post because I have similar questions regarding seating depth. I've heard the "expert" at one of our local gun shops say to start on the lands and move back in 0.005" increments. But from what I've read on this blog over the past few months it seems that the more prudent approach is to start at 0.020" off the lands and move back in 0.005" increments. Very soon I'm going to start load development using the 0.020" plan.

 

[RAY]

Mr. Minks, I know manuals give a tested COAL , but what about factory seating depths that shoot good groups ? Is it ill-advised to copy a factory seating depth to begin load work up , this is my question on the subject.

I have some federal BTs vital shok 3006 150 gr , I measured a .023 "jump from the lands with my rifle , I haven't shot them yet.
Thanks , Ray .....

 

[tjen]

In general you work up to max load with the longest OCL you determiend you could use by the distance from your bolt fact to the lands of your rifle less .010"-.020". This could be limited by the length of your rifles magazine. So the SAAMI max OCL just may be the longest you could use.

The affect of shorting the OCL by seating the bullet deeper is less pressure and less velocity. The reason reloaders reduse the OCL or bullet seating depth on loads they have determined as safe is to fine tune the loads accuracy. Accuracy is more important than an extra 30 fps it may cost by a OCL reduction of say .015-.030".

I will add this is for bolt neck cartridges from the tiny 22 hornet and up. Pistol cartridges are the opposite do to the very fast powders they use.

 

[DrMike]

My rule of thumb is that for monolithic bullets (all metal bullets), I allow 0.100 inch jump to the lands. You will want to allow at least 0.050 inches jump to avoid pressure problems. For cup and core bullets, it is wise to allow at least 0.010 inches of jump. Some, such as AccuBonds, deliver the greatest accuracy with greater jump. Others, such as Ballistic Tips and Partitions, will give the best accuracy closer to the lands. SAAMI standards are set for each cartridge, but they don't necessarily give you the best accuracy. The reason others didn't jump in is that the true answer to the question is "depends." The bullet construction dictates in great measure the seating depth. The powder burn rate and the charge must be factored in also. The cartridge also has a role in play in determining seating depth. Then, comes the matter of whether your magazine will permit you to seat out or not. When you choose a bullet, ask what others have done and you should get an answer to permit you to begin to work from. My answer still holds. At first, seat to SAAMI standards and consider where to go from there.

 

[MrMinks2]

Dr. Mike: That's just the type of input I was seeking. Many thanks.

 

[SJB358]

My rule of thumb is that for monolithic bullets (all metal bullets), I allow 0.100 inch jump to the lands. You will want to allow at least 0.050 inches jump to avoid pressure problems. For cup and core bullets, it is wise to allow at least 0.010 inches of jump. Some, such as AccuBonds, deliver the greatest accuracy with greater jump. Others, such as Ballistic Tips and Partitions, will give the best accuracy closer to the lands. SAAMI standards are set for each cartridge, but they don't necessarily give you the best accuracy. The reason others didn't jump in is that the true answer to the question is "depends." The bullet construction dictates in great measure the seating depth. The powder burn rate and the charge must be factored in also. The cartridge also has a role in play in determining seating depth. Then, comes the matter of whether your magazine will permit you to seat out or not. When you choose a bullet, ask what others have done and you should get an answer to permit you to begin to work from. My answer still holds. At first, seat to SAAMI standards and consider where to go from there.

Mikes resoonse is how I typically go about my load work as well. Bonded and monos prefer some jump while cup and core along with PTs will usually work in the .010-.050" range in most of my rifles.

 

[RAY]

Thanks to everyone for the help.

I want to stay in the bonded line of bullets , AccuBond and swift sciroccos 150 gr.

 

[SJB358]

I would say to start at .025" and work back in .010" increments. I don't have alot of experience with the Swift's, but they seem to respond the same as AB's do.