Reloading long C.O.A.L

[stevemiller]

How much would you increase in powder when working up a load that you are seating the bullet longer than sammi C.O.A.L.?I am working on accuracy with my rifles,Some are as much as .150 away from the lands.I realize that as I load longer I am increasing the volume of the casing,and lowering cup pressure and losing velocity.I would like to get back the lost velocity.Is there a formula that a re loader could look at to know how much pressure would be there to start,So they new that the bullet would in fact come out of the barrel?

Example:180 grain Nosler ballistic tip,IMR 4350 powder 70.grains. .300 Weatherby 26 in. barrel. Sammi seating depth is 3.533 or so,Im wanting to load out to 3.700 leaving .012 to the lands.

[bobcat]

I don't think the seating depth makes that much difference in pressure/velocity. I wouldn't adjust the powder charge at all. But if you want more velocity go ahead and increase the powder until you get pressure signs. The best tool to have is a chronograph if you want the maximum velocity possible out of that cartridge. I normally just load to the max charge in my book. But with a chronograph you would know how much you're losing with the longer seating depth. I doubt it's very much, probably less than 25 fps.

[b23]

Keep in mind, when you start getting close to the lands, the closer you get the faster the pressure curve spikes up so you can have a load that doesn't show pressure when it's loaded 30 thou off but has heavy bolt lift or ejector marks when it's 0-10 thou off.  Pressure starts ramping up pretty quickly when you get within 10 thou and less.  Just something to keep in mind.

[BULLBLASTER]

Seating depth absolutely has a pretty good impact on pressure and velocity. It does decrease as you go longer until you get right up to the lands if you are very close or touching the lands it can cause pressure to spike.
It is always important to be very careful when deviating from published load data. And a chronograph and ability to identify pressure signs is very important.
Also be careful if you are right on the edge pressure wise because changes in weather can put you over pressure very quickly including moisture in the chamber.

[BNAElkhntr]

No Need to increase COAL in a Weatherby   they are free bore     This technique works best in other guns

[MuleySniper]

I was loading for my .257 wby for the first time last night. I was trying to determine the lands on my 700. I gently seated a bullet shallow into a new formed brass and carefully chambered it into the rifle. I felt zero resistance from what at least I could feel. Measured the COL and was around .25 longer than the max COL in my speer book. I tool black marker and covered the bullet and re chambered not noticing any markings.  The books call for 3.24 and some 3.25 and I was 3.5 something. I looked online and saw some custom non book loads guys had that were measuring that long. Im still unsure if I touched the lands or not but it made me a little concerned. I haven't charged any rounds yet because I am still a little confused on how long I can get away with and still be safe.

[b23]

Loading manuals COAL is mostly based off what they know will cycle through the magazine of all guns and less about anything else. 

[Curly]

How much would you increase in powder when working up a load that you are seating the bullet longer than sammi C.O.A.L.?I am working on accuracy with my rifles,Some are as much as .150 away from the lands.I realize that as I load longer I am increasing the volume of the casing,and lowering cup pressure and losing velocity.I would like to get back the lost velocity.Is there a formula that a re loader could look at to know how much pressure would be there to start,So they new that the bullet would in fact come out of the barrel?

Example:180 grain Nosler ballistic tip,IMR 4350 powder 70.grains. .300 Weatherby 26 in. barrel. Sammi seating depth is 3.533 or so,Im wanting to load out to 3.700 leaving .012 to the lands.

The best answer to your question is to run the scenario thru a reloading program like quickload and it will tell you the max powder you can use. Or you can do what most people do and just look for pressure signs and then back off.  Pressure signs sometimes only occur well over max pressure though, so maybe you could find a nice guy with quickload to run your scenario.

[Kittman]

I would be more concerned about loss of accuracy from adding more powder rather than pressure spike concerns.  When seating longer, make sure each case is miked out properly and/or properly trimmed each time for your safety.  You don't want a pressure double whammy to occur.  There are other powders that will work for that combo as well. 

[Stein]

I don't think the seating depth makes that much difference in pressure/velocity. I wouldn't adjust the powder charge at all. But if you want more velocity go ahead and increase the powder until you get pressure signs. The best tool to have is a chronograph if you want the maximum velocity possible out of that cartridge. I normally just load to the max charge in my book. But with a chronograph you would know how much you're losing with the longer seating depth. I doubt it's very much, probably less than 25 fps.

Just what I was going to say.  If you are going for accuracy, you likely won't be at max velocity anyway.  I don't even know what the sammi is for the cartridges I load.  For my rifle, I load max that will work in the magazine and for my daughter's I load to 0.01-0.02 off the rifling.

[stevemiller]

Thanks for all the replies,Now am I trying to do something that wont make any diff. in accuracy or what.It was posted that with the Weatherby it wont but I thought and I'm no pro by any means,That when you get closer to the lands it gets more accurate and when rifles get older the rifling can extend out even further from the heat and pressure so moving forward would bring an older rifle new life.  Am I way out in left field here?

[jasnt]

Do you seating depth testing first. Then work up your powder charge. Then fine tune seating depth if needed.

[stevemiller]

Ok  .Thanks.I am under the max load by a couple grains so should be fine. 

[xXLojackXx]

What bullet are you shooting? its common for VLD bullets to jump .020" to .100" in order to get bughole groups. My 7mm happens to like a .030" jump. The close I get to the rifling, the bigger the groups.

[JackOfAllTrades]

Do your seating depth testing first. Then work up your powder charge. Then fine tune seating depth if needed.

That's your best advice!  Get accurate loads (and that's why you're seating long anyway), then fine tune charge/seating within your defined accuracy range. Is another 100fps at 100yds really worth the hassle? It's a 300wym, Not a 300Rum.  Make sure that what you're loading will reliably cycle through your action. You may not want to build a single shot.. But could end up with one.

I seat out to .010" off the lands with my 30-338, for accuracy. I'm lucky to get another 100fps with the load I've worked up,  but only with certain bullets. Some bullets I've tried, I lose the accuracy when I use an identical powder/charge for the same weight, Ogive seated at the same distance from the lands. -even with a bullet that has a near same base shape and total bullet length.  So I stick to what works.  (66.5gns of IMR4350, Hornady 180gn Interlock BTSP (because they don't make the 190 any more) 3,100fps)  Yes, four - six loads on fire-formed 338win cases and I split the cases at the belt. -even with neck sizing only. So, hone your skills at recognizing pressure signs when you're max loading or extending the OACL for anything, and especially the belted magnums.

-Steve