When you increase your COL on your cartridge, do you see the velocity go up or down or no change. I figured it would go down. Cause area would open up alot

I just fired several different COL in my 22/250 over my chronograph. There was only a 10-15 fps difference going from the shortest round to the longest round. Length changed by 0.04" in 0.01" increments for four different lengths. This may differ depending on the cartridge. I know that in my 7mm Rem Mag the velocity does change more with seating depth. In this instance I was seeing only around 30-40 fps difference going from shortest to longest COL.

The pressure very marginally goes down as you increase the OAL until you reach the point where the bullet touches the lands. At that point the pressure spikes up by several thousand PSI. This is from playing with a strain based pressure rig.

I've seen an increase in fps with an increase in col(aol). I can speak in relation to a 14" .41 magnum I've been working with. With the col(aol) set at 1.612", H110 powder, and 210 grn JHC the velocities were in the 1600's. When the col(aol) was reduced to 1.585", velocities dropped into the 1510's to 1520's. Accuracy also greatly improved with the slower velocities.

[ 05-28-2003, 23:43: Message edited by: T/C nimrod ]

Quickload makes some worst case assumptions about decreasing OAL and pressure. In some cases that is not at all valid:

1) The change in pressure with change in OAL is not always very big. In 9mm with Power Pistol and 124 gr bullets 11 gr will pierce the primer at 1.169", but 10.5 gr at 1.000" will not. Quickload thinks the later is over 1,000,000 psi.

2) Sometimes the change in pressure with change in OAL is quick and nasty, like in 38 sp with 15 gr 2400 1.590" flat primer, easy extraction, 1.465" top hat primer, S&W 60 cylinder loose in lock up.

Chris F,

Using the Oehler 43, I've noticed pressure drop with increasing OAL, and in most cases it doesn't go up when hitting the lands either. It has shown it can and does happen though. Most always, it slowely and steadily drops, or stays almost the same in some cases. Decreasing OAL by around .100" will almost always jump pressure and velocity. I've found the pressure rise to be much more substantial with going from say .100" off the lands to .150" off, rather than .100" off down to .50" off.

When you get close to the lands I think it starts to flatten out the noticable "drop" in pressure because the sooner resistance. On the other hand, psi ramps up faster if moving the bullet deeper by the same amount. Just an observation, and no way indicative of every situation, interesting none the less...

So for my case where I could never hit the lands, the pressure goes down with increasing COL? Right? So for my 308Win, lets say at 2.785" COL, I get 2800fps with 46gr of Varget for a 150gr Bullistic Tip. But if I moved down to 2.685", how much would expect the velocity to go down? For some reason, my Medallion likes deeper seating. Thanks for all the comments

So for my 308Win, lets say at 2.785" COL, I get 2800fps with 46gr of Varget for a 150gr Bullistic Tip. But if I moved down to 2.685", how much would expect the velocity to go down?

In your example, you are likely going to "increase" pressure and MV when you seat them deeper, it will not likely go "down". I would bet a 40-60 fps and 2-4k psi increase when going that much deeper, maybe even 75 fps and 3-5k psi more. My recommendation is to start a grain or two lower than your max load when seating them that much deeper, chrono that load, seat deeper and then chrono at the new depth to compare.

I'm much more leary of altering seating depth to a "shorter" OAL on a max load than seating them out farther and increasing it.

Just one of the latest examples; My 300 Ultra with a 178 A-Max seated at 3.710" OAL (.050 off the lands) is running 68-69k psi (M43) and seated at 3.760" (on the lands) is running 65-66k psi (M43).

I haven't run the 150BT through any of the 308win's but the 155 S.Palma was real accurate at 46gr and 2.8" OAL, 150 Scirocco at 47gr and 2.845" OAL was too, probably even better overall. Both were about 2800 fps and 60k psi (M43) in the 20" bbl M70 Compact.

I loaded up some .375H&H with 210gn X bullets, some of which I seated all the way to the "shoulder" of the bullet, I noticed that these loasdss kicked a lot harder than others with the same charge and different COL.

Wasn't shooting over a chrony so I can�t say any more.

the other loads were longer, as the ones I mentioned were seated as far as you really can seat.

The barnes X in 210gn for .375 does not have a conical shape to it, just a straight shank, then it drops to a point.