COL and load data

[One_Duck_Limit]

Hey all,

First time poster, long time lurker. After reading all the positive reports about Burger VLD bullets I decided to give them a try. I've been realoading for 2yrs now and run in to a new situation. I shoot a Remington CDL 7mm Rem Mag. Most everything I've read suggest seating the bullet in contact with the lands. I loaded a dummy round and took some measurements. With the bullet .007 in the lands my COL is 3.468". The load data Walt Bereger emailed me uses a COL of 3.290". My question is how does this affect maximun load pressure? I would think .178" less volume taken up by the bullet would lessen the pressure. Is this correct?

 

[boomtube]

"The load data Walt Bereger emailed me uses a COL of 3.290"."

The OAL Walt used in his rifle is what he gave you. It's no more a law for you than the powder charge is.

Pick an OAL that works through your magazine and doesn't jam into the lands and develop your load normally. That will take care of any pressure differences as a matter of course.

 

[lever-hed]

I would agree with Boomtube. The load data he gave you is for his rifle, not yours.
The bullet ino the lands will be much more significant in pressure then the bullet taking up space inside the case.
If yo dont have a chronograph to chart a normally developed load, yo u will have not idea of what the pressures spikes will be except for a cracked case or worse. double check your oal to the lands (not into) and work powder charges and oal gradually and watch for signs of overpressure on the cases. For many, a standard of .010" to .020" short of the lands is where a lot of reloaders stop, but it all depends on your load testing.

 

[Ridgerunner665]

NO!

Seating the bullet longer DOES NOT reduce pressure....it increases it...alot.

When a round is fired the bullet gets pushed out of the case a bit before it engages the rifling...at that point it stops for a couple of nanoseconds while the pressure builds up enough to push it on through the barrel....that bit of movement before engaging the rifling is "the cushion".

When you seat bullets "to the lands"...you remove that cushion...meaning, when the round is fired, the peak pressure is increased and so is the muzzle velocity.

I'm not that good at explaining things, but I know what I'm talking about...I tried to find an article for you but all I came up with was "forum posts".


All Remington barrels have a REALLY long "jump" to the lands . So seating to the lands will require either feeding the rounds one at a time by hand or an after market magazine box (Midway has them), they don't cost much ($42...IIRC) but they do require some gunsmithing to install.
The Berger VLD's do shoot much better when seated "to the lands"...most of the time.

Another thing...Be very careful with using that dummy round as a measuring tool. I know...it sounds simple enough, but if the neck is left too tight on the "dummy round" it can shove the bullet into the rifling and give you a measurement that may be as much as .050 too long...that's a very bad thing that could cost you a few fingers...or worse. I'm not trying to scare you or talk you out of it...I just don't want to see you get hurt...and when you start seating bullets to the lands, pressure spikes happen fast...real fast.

Be careful...do some more research and good luck.

 

[One_Duck_Limit]

Thanks everyone.

I'll adjust my seating depth by .007" to just touch the lands.

I've got a chronograph on order, it should be here before I begin testing these loads at the range. Most of what I've ready about chronographs suggests placing them around 15 feet from the muzzle with a magnum caliber. Is there a formula to account for the distance from the muzzle to the chronograph? My buddy loads shot shells and places his chronograph 10 feet from the muzzle the adds 100 fps to the reading to account for the distance.

I measured the distance to the lands using a Hornady COL tool and bullet comparator

I used the dummy round to check magazine clearance. My box has enough clearance to load feed the loads.

So... if the load were .020 off the lands, 3.290 vs 3.441, would the difference in COL cause the pressure to be lower? Assuming the same gun and load components are used.