COL for .308 Match

[speedtriple]

Good Day,

I have been working up loads for my Remington 700 .308 Varmint SPS. Got my bullet, my powder, and the amount of powder working quite well. Next I wanted to start working on the seating depth on the bullet. The "book" length for the .308 with a 168 GN BTHP match bullet is 2.800. I find that on my rifle, the COL putting the bullets against the lands is 2.858". So if I wanted to have the bullet jump .020", the overall length would be 2.838".

How much extra length do others find they need to set the bullets close to the lands? That seems like a lot to me.

Thanks in advance for your help.

Gregg

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[2506]

Every rifle is different and every rifle is particular about cartridge AOL for optimal accuracy.

 

[deadshot2]

Many of the record holders for .308 cal competitions use a "jump" of .018"-.020" before the bullet hits the lands.

as 2506 stated, every rifle is different but these numbers keep popping up among the "big guns" that have rooms full of trophy's. My rifle shoots great at 2.800"-2.810" COAL and these rounds will also feed from the magazine. That's another consideration. Rounds jamb in my mag at 2.820" and I don't want to "customize" the box yet.

 

[speedtriple]

Thanks for the replies so far. I may not have stated my question well enough. I am not looking for a number, either the overall length of the cartridge , or the length of jump to copy for my rifle. What I am asking is what is the range of extra length people find they need to put the bullet close to the lands. Or in other words, is the chamber of my particular rifle machined extra deep? Setting the bullet out nearly a MM from the "normal" 2.800" COL seemed like a lot to me. This is the first rifle I have tried to tune the COL on.

Gregg

 

[deadshot2]

You need to invest in a Hornady Lock-N-Load Overal Length Gauge and determine the actual effective length of the chamber in YOUR rifle. Then play with the OAL which will determine the amount of "jump". It may be necessary to set the bullet out until it is barely held in the case if that's what your rifle wants.

Some find that the resultant OAL is longer than what will actually feed from the magazine box of the rifle and they have to shoot it as a "single shot".

If you want to see the extreme of this, go to the range sometime and watch the shooter that is loading bullet and cartridge separately. First he seats a bullet into the rifling and then chambers a cartridge that is filled with powder only. To keep the powder from spilling out they plug the case mouth with the green foam that florists use to hold flowers upright in a vase. The bullet never is inserted in the case mouth. They can achieve accuracy that some of us can only dream of.

 

[saxon]

COL for .308 Match
well a lot more goes into that then you think really
for a true 308 match primer case bullet etc etc and then the COL
all of that make up a true match grade round.
as far as jump or distence from the sholder of the 168 BTHP to the start of the lands
i would start a .010 from the lands and see where i am at As far as COL
and start there
and check your group.
i would do this after i had the case's and powders and bullets all weighed out
and have it as accurate as i can
and then play with the "jump"

 

[speedtriple]

Thanks for all the input. I have the measurement tools, and feel very comfortable making accurate measurements. I am comfortable doing statistical measurements of my group sizes.

What I have been trying to ask is.... Does 2.038" COL (which will give me a .020" jump) seem like a lot of extra length over the 2.800" published COL? If I seat my bullets to the 2.800" standard COL, or use factory ammo, the jump is .058" I would have thought the chamber would have been machined to tighter specs than that from Remington.

 

[Crispy]

Fool around with the C.O.L. till you found what works for your rifle or you. The O.A.L will very from rifle to rifle, play with it till you have the max accuracy load from your rifle, or accept what you have been able to find thus far.

 

[deadshot2]

Thanks for all the input. I have the measurement tools, and feel very comfortable making accurate measurements. I am comfortable doing statistical measurements of my group sizes.

What I have been trying to ask is.... Does 2.038" COL (which will give me a .020" jump) seem like a lot of extra length over the 2.800" published COL? If I seat my bullets to the 2.800" standard COL, or use factory ammo, the jump is .058" I would have thought the chamber would have been machined to tighter specs than that from Remington.

You are not allowing for several other factors in the chamber. A factory chamber is machined to allow for a wide range of ammunition to be utilized and it allows for the extremes of tolerances. First there is the free-bore which begins immediately after the case mouth. It can be short or very long, as much as .250", depending on the bullets expected to be used in the rifle. Then there is the leade which is usually a 1-1/2 degree taper which "starts" the bullet into the rifling.

You appear to be hung up on what's "too much" extra length. The answer is very simple. Unless the bullet falls out of the case while handling/loading the cartridge, and you can chamber the round and lock the bolt, the round is not too long. Unless the chamber is a Match Chamber that was cut to be used with a particular bullet, then you will always find extra room for the variety of bullets that COULD be loaded into that firearm. Would make no sense for Remington to cut their chamber for a .308 round using a 155 Lapua Scenar and not have it fit a cartridge loaded with a 170 Grain Nosler Round Nosed Partition. That's what free-bore is all about.

Just for grins, read the information that some of the champ shooters have provided on their .308 loads here:

.308 Winchester Cartridge Guide

Take a look at the second to the last load where the individual loads his to 2.845". Also note load #4 at 2.850".

 

[speedtriple]

Thanks Deadshot. That is the info I was looking for. As you say, I was hung up on thinking the bullet was going to be set out too far after taking my chamber measurements.

 

[SnapShot]

What I have been trying to ask is.... Does 2.038" COL (which will give me a .020" jump) seem like a lot of extra length over the 2.800" published COL?

my remmy 700 i bought this last winter is about 2.93x to the lands

the thing to remember is the COL is not anything other than the "standard" so that rounds will fit into magazines and so forth. and thats uasually where they do their ballistic tests. also concider, as you seat the bullet out further, the bullet will now be slower, as there is more room inside the case for expansion, this is how people put in way more powder than recommended by factory books, and have no pressure signs. i do not bother seating to the lands, as my internal magazine only allows for a coal of about 2.84 if i want to pack it full. i have found that i have been seating to a depth of 2.810 recently and had great results, 1/2 inch grps, good enough for me.