Bullet Seating Depth

Foxamaphone

Foxamaphone

Member
EE Expired
Rating - 0%
0   0   0
Location
Lower Mainland
Hey Guys!

Just wondering on how to detemine your proper seating depth, right now, I'm just going off the manuals depth, but would like to do it properly. What are some ways of figuering out that perfect depth?

Cheers!

Dan
 
Perfect from what standpoint?
Feeding from the magazine?
Optimizing accuracy? This can be determined by experimentation. Be careful if you are jamming the bullet into the rifling; there can be issues with pressure and unloading.
 
Stick with the manuals COAL. The seating depth directly relates to the pressure inside the case. Deeper into the case, less case space, more pressure and vica versa. Start with manual COAL. you can move out slightly, but with a jacketed bullet you do not want it to touch the rifleing. If you are trying different lengths, do not change anything else (bullet weight, powder or powder weight, primer etc.) Only change one variable at a time and move slowly, looking for over pressure signs. My 2 cents anyways. Matt
 
Foxamaphone said:
Hey Guys!

Just wondering on how to detemine your proper seating depth, right now, I'm just going off the manuals depth, but would like to do it properly. What are some ways of figuering out that perfect depth?

Cheers!

Dan
Click to expand...

The only way to determine perfect depth requires you to load bullets at varing lengths and shoot them for group. FS
 
sisiphunter said:
Stick with the manuals COAL. The seating depth directly relates to the pressure inside the case. Deeper into the case, less case space, more pressure and vica versa. Start with manual COAL. you can move out slightly, but with a jacketed bullet you do not want it to touch the rifleing. If you are trying different lengths, do not change anything else (bullet weight, powder or powder weight, primer etc.) Only change one variable at a time and move slowly, looking for over pressure signs. My 2 cents anyways. Matt
Click to expand...

Well Matt, what about the theory that Berger bullets shoot best when jammed into the lands? FS
 
Stick with the manuals COAL. The seating depth directly relates to the pressure inside the case. Deeper into the case, less case space, more pressure and vica versa.
Click to expand...

Your theory is in error,at least when dealing with rifle cartridges,in reality,the deeper the bullet is seated,the greater the jump to the lands,the lower the pressure.

As for the manuals COL,they mean very little in regard to your rifle.
 
Last edited:
Are you taling pistol calibers? If so here is a method that works for all pistol bullets.

a) Remove your barrel from your gun.
b) Drop a bullet into the chamber and using your calipers measure from the base of the bullet to the barrel hood where the case rim would normally sit flush
c) Measure the length of the bullet you are going to use.
d) Add the two measurements and you have the maximum length of your cartridge for that bullet.
e) Back, off a few thousands to allow for variance in your presses seating die and check to see if a loaded bullet will fit in your mags.

Seating depth for pistols is determined in part by the bullet olgive. This is one reason why truncated cone bullets will often allow for longer OAL than fatter round nose bullets.

The problem with most manuals for pistol cartridges is they usually refer to one type and make of bullet. You may have a 125 gr RN bullet but with a different olgive than the one quoted in your manual.

Hope this helps.

Take Care

Bob

 
OK, i was misinterpreted. Start off with the manual COAL. Then you can change from there, but beware of overpressure signs. As for berger I have never used them, but generally you want a slight jump intot he lands, by slight I meana couple thousands of an inch. The Manual COAL is a general guidline, a starting point to work from, it usually is good in pretty much any rifle.

As for the deeper the bullet the greater the pressure, that is correct. The same powder in a smaller space creates a greater pressure at ignition.

Matt
 
"As for the deeper the bullet the greater the pressure, that is correct. The same powder in a smaller space creates a greater pressure at ignition."

Matt, where did you get this information from? As has been pointed out, that theory doesn't apply to the slower burning powders used in bottle neck rifle cases.
 
ok, I see my error here. I am right, but also wrong. If we didnt take into account the rifle, the greater seating depth creates a greater pressure. Now what I do know is that Speer manual says that you try to get that bullet seated just a few thousands short of the rifling. As a general rule, especially if new to loading, start with your manual data, change things slowly, and watch for pressure signs. I am no physics professor, but I know that if you go with the manual and change one variable at a time, looking for pressure signs, you will find the correct load.
 
As for the deeper the bullet the greater the pressure, that is correct. The same powder in a smaller space creates a greater pressure at ignition.
Click to expand...


Actual pressure readings prove your theory wrong.

sampleseatingtrace.gif


Here's a classic good load for 6PPC. The only difference between all these traces is the first 3 were seated right on the lands. The last 4 were 30 thousands of an inch off the lands. Note the substantially reduced pressure and overall reduction in energy.

As the bullet broke its neck tension and jumped to the lands it provides more expansion room for the gases reducing both the energy and velocity.
Click to expand...


ok, I see my error here. I am right, but also wrong.
Click to expand...

Mostly wrong,since the increased jump to the lands results in a much greater reduction in pressure while the lands engrave the bullet, than the theoretical slight reduction in case volume,before the bullet starts to move in the case.
 
ok, now I remember why I dont comment often on this site, the thread gets off subject so quickly.

Read your manual Fox, and as I said start with manual COAL and try different things from there. Make sure to change one variable at a time. Maybe some others could actually answer your question instead of arguning over my statement haha.
 
Make a dummy round for your rifle by just slightly resizing the neck of the case. Just insert the bullet into the case. Insert into your rifle and close the action, The bullet will back into the case as you close the action. Remove the dummy slowly and measure overall length. This is the max length with bullet touching the rifling. Most likely this round won't fit in your mag, but you now know the max with THAT BULLET. The shape of another bullet may let it go farther into the bore before the wider part of the bullet hits the rifling. Adjust your depth from this reference point. Hope a little clearer than mud now.
 
For rifle ammunition,ignore the COL printed in the manuals,instead actually measure the distance to the lands for a given bullet in your rifle.

There are several ways to do this,but an easy way is to seat a bullet in the case very shallow so that you can't quite close the bolt.Then seat the bullet deeper .005" at a time until you can just close the bolt with no more resistance that closing it on an empty cartridge case.That is the approximate distance to the lands for that particular bullet in your rifle.

If you are using an all copper bullet such as Barnes TTSX,seat the bullet .050" deeper,and use this as a starting point.For a cup and core bullet,start around .015" off of the lands,and go from there.

If the gun is a repeater using a box magazine,make sure that the loaded cartridge will fit in the magazine,if not,seat it deeper until it does.

When selecting a bullet to use as your dummy round,measure the length of several bullets out of the box,and use a bullet that is approximately the average length.
 
You must log in or register to reply here.
Back
Top Bottom