C.O.L. and powder charges

[Gtimothy]

I need some advice...


I'm just starting to reload for a Rem Model 700 in .308 and have really started to pay close attention to what is going on in each step of the reloading process. Before, all I was concerned about was keeping my wife and kids in ammo that would be reasonable for punching paper. Now I want to take it up a notch.

I made a "dummy" case so I could check my rifle for C.O.L with different bullets. According to the dummy test, using a Hornady 168gr BTHP, I have an C.O.L. of 2.945". If I back it off .02" to get it off the rifling, I come up with 2.925".

According to the reloading manuals I'm using, (Hornady 4th edition) shows MAX C.O.L. of 2.800" and (Lyman 49th edition) a MAX OAL of 2.775". I know the round can be longer to better fit my gun but how will this affect the powder load? I read somewhere that a rifle bullet that is seated longer than the OAL in the manual creates a higher pressure. My question is how do I work up a load using the data in the manual and how do I determine a safe load to start? Reduce by how much, 10-20%? I appreciate your help on this matter and look forward to useful replies.

 

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Unless I have missed somthing a col longer than what is listed will have less pressure. Start at the starting charge listed and you will be ok. You are more likely to run into problems using a manual that is out of date, than having too much pressure from seating the bullet longer than what was tested in that manual. Unless you ram it into the rifleing.

 

[918v]

I read somewhere that a rifle bullet that is seated longer than the OAL in the manual creates a higher pressure. My question is how do I work up a load using the data in the manual and how do I determine a safe load to start? Reduce by how much, 10-20%?

Yes, it raises pressures but only under certain conditions: You don't wanna load into the lands with solid copper or heavy jacketed bullets. Those need a fair amount of jump to stay inside a safe pressure range. With normal bullets, just rework the load like before. Start low and work up. 20% is too low. 10% is fine.

 

[NeuseRvrRat]

you could have pressure spikes if you seat the bullet too long and jam it into the lands. sounds like you're staying out of the lands, so pressure shouldn't be an issue.

remember, book COAL is simply SAAMI's spec. they give a max COAL so gun manufacturers know how long to make the magazine to hold any factory ammo. book COAL just puts everyone on the same page.

 

[Gtimothy]

Thanks for the help guys. I'll start with a 10% reduced load and see how my gun likes it.
Won't be able to get to the range til next week.....

 

[steve4102]

10% below MAX is we're you start! Not 10% below Min. Going below a min charge can be dangerous .

 

[ranger335v]

Book OAL is the length the book makers used to develop the listed data; it's no more a law than the powder charges they show.

Seating deeper in small capacity, high pressure cartridges when using fast burning pistol powders will raise pressure due to a reduction in powder space. In practice that mostly means 9mm and .40 cal handgun ammo.

With larger capacity and/or lower pressure handgun cartridges - especially revolver cartridges - with slower powders, and with virtually all rifle cases, seating deeper within reason reduces peak pressures because the jump to the lands allows bullets to have speed to engrave the lands more easily.

 

[Gtimothy]

10% below MAX is we're you start! Not 10% below Min. Going below a min charge can be dangerous .

Yup, I know that. Thanks for replying! My biggest concern is the powder I'm using. Right now I only have IMR 4064 for rifles (gun show this weekend though) so I have to be concerned with compressed loads. Reducing the MAX load (compressed) by 10% puts me smack in the middle of the load table for this powder so I'm safe there.

 

[steve4102]

Compressing powder, if there is load data to support it, is not a bad thing. Most if not all of my rifle loads are compressed. Some extremely heavy compression. I find them more consistent and accurate than non-compressed loads.