308 oal-col

[308Loader]

hi again. So far in my loads I have ben using bullets with a crimp groove. Not paying attention to the over all length of the cartage, just seating the bullet to the middle of the crimp. Now that I have learned more, I see that oal is pretty important to accuracy. Setting the bullet back from the lands and such. Also I would like to load some 180 gr that don't have crimp grooves. I went out and got a oal gage and measured my chamber. I got different measurements with different projectiles, so I'm kind of confused.

180gr measured 2.992
168gr measured 2.923
150gr measured 2.898

The last batch of 150gr I loaded (they shoot well at 100-200yrds) measured at 2.740. The book says the col 2.780. Is col and oal same thing? Should I be seating closer to 2.800?

 

[F. Guffey]

I went out and got a oal gage and measured my chamber

My chambers have two different lengths, one from the shoulder to the bolt face and the other from the lands to the bolt face. When measuring from the lands to the bolt face I get one measurement because I use transfers, I transfer the dimension of the chamber to the seating die.

I am not 'all in' on that accuracy thing and off the lands. If my rifles do not shoot accurately 'off the lands' those rifle do not get shot.

I am the fan of off the lands, I want bullet jump with the running start, I want my bullets past the rifling without hesitation.

F. Guffey

 

[hartcreek]

The problem is that you are dealing with different ogives on different bullet brands. The ogive is the side of the bullet forward of the crimp to the point and there are so many different shapes that one almost has to make up a dummy cartridge for each individual bullet shape that one uses that does not have a cannalure and use this dummy and some prussian blue to estabish the length by seatin the bullet long and then shortening the OAL till it champers and then using the prussian blue to see how much clearance you have.

 

[jmr40]

If there is a cannelure, I use it. If not I load so they will fit the magazine with just a bit extra room to spare. If they chamber smoothly I'm good to go. If not I seat a little deeper until it does. I don't even know the OAL of any of my loads, and usually get MOA or better.

Some bullets, Barnes TTSX for example, shoot better seated deeper than normal. I seat those using the grove closest to the tip just like a cannelure and load there.

If you want to squeeze another .1 or .2 MOA out of a load it might be possible, but is not worth the difference to me. I'm not going to miss a deer because the load was .7 MOA instead of .6 MOA.

 

[tobnpr]

The book says the col 2.780. Is col and oal same thing? Should I be seating closer to 2.800?

Now that you have the OAL gauge, you need to do two things...

1) Forget the terms "overall length" or "cartridge overall length". As of now, they are completely irrelevant to you.

2) Get the bullet comparator. The OAL gauge depends on it's use for best accuracy, and they're designed to be used together as a system.

Look up "secant", and "tangential", ogives. Bullets like the SMK, are tangential. Those like the Berger VLD, and the Hornady Amax, are secant. Secant bullets are longer for weight- have higer BC's, and their ogive will engage the rifling at a different point than a similar weight tangential ogive bullet.

Once you have the comparator, all your measurements become relative...hence the term "comparator". You'll no longer load to an "overall" length- you will load to a comparator length.

Your OAL gauge pushed the bullet you were using into the lands- and then you measured it's overall length. What you should be measuring (and will be, with the comparator) is the length at which that particular bullet engages the rifling. From that, you can play with "jump"- how far back you want to seat the bullet from the lands.

Keep in mind, every bullet will have a different measurement, based on it's weight and ogive. Measuring to the ogive is more accurate, and preferred because bullet tips sometimes get deformed/smashed slightly and overall lengths can also vary slightly.

Rifle chambers vary somewhat from SAMMI specs. One of my rifles, is chambered in .260 Match- which is intentionally throated longer (by .04") to allow seating of longer VLD bullets.

Note that what works for your rifle, may not be suitable for someone elses- and using ammo developed for yours could develop overpressure if used in another rifle and a bullet is jammed into the rifling.

 

[AllenJ]

All the answers above are great information. Before I join in though can I ask what type/brand gauge you got and what type rifle you're measuring it with?

 

[F. Guffey]

Now that you have the OAL gauge, you need to do two things...

Seems deterring maximum overall length would be first, that would lead me to believe there is COL as in case overall length and Maximum case overall length. Then there is the O-Jive, why dies it have to be re-discovered every day? The length changes, the contact point of the ojive with the rifling does not change. Anything beyond the contact is to be considered when determining Maximum overall length.

I use transfers to transfer that dimension straight to the seating die.

F. Guffey

 

[F. Guffey]

AllenJ,

Before I join in though can I ask what type/brand gauge you got and what type rifle you're measuring it with?

I use a dowel and or cleaning rod, that would be on any chamber.

F. Guffey

 

[AllenJ]

I use a dowel and or cleaning rod, that would be on any chamber.

Sorry Guffey my question was to the OP, I should have been more specific. I've used cleaning rods also and had decent luck doing it but the OP said he went out and got one, so I was wondering what he got.

 

[tobnpr]

Seems deterring maximum overall length would be first,

Determing max overall length, I'm not sure if you're disagreeing with me- or not...

My point was that "max overall length" is entirely dependent on the bullet selected- and his rifle's chamber.

I use transfers to transfer that dimension straight to the seating die.

What are "transfers"?

By using the comparator and calipers, one gets the length from case head to ogive where it engages the lands. I then seat a bullet long, increasing seating depth gradually until the comparator length is correct- then lock down the seating die-for that bullet.

Seating dies are cheap enough (I guess it would be a different story if I used micrometer dies, I don't...) that for rifles where I have more than one bullet selection I use additional seating die(s) match to the bullet, and seating depth desired.

 

[F. Guffey]

Seating dies are cheap enough (I guess it would be a different story if I used micrometer dies,

Not fair, all of my seating dies are micro adjust, I use a micrometer height gage to measure the height of the seating stem above the die. I determine the height of the stem above the die with the transfer.

F. Guffey

 

[F. Guffey]

Tobnpr, Maximum case overall length, I was thinking if the rifle is a single shot fitting a case to fit the magazine would not be necessary. After that there is a chance a reloader will have to load one round at a time.

Then there are all those stories about reloaders that owned Weatherby rifles. They complained they could seat bullets further out but could not feed from the magazine. I thought Weatherby was making an attempt to protect the reolader from himself.

F. Guffey

 

[green_MTman]

step1 seat a bullet in a powderless,primerless dumby round so high it touches the grooves.


step 2 push round into chamber until you get resistence,then the bullet is stuck and use a cleaning rod to push out.then continue to little by little to lower the COL untill you get no resistence.at that point your just barely off the grooves.

3. measure that COL and write it down,then back off the rifling by .010.now use that as your new COL.if your accuracy is good keep it but if your accuracy i not what youwant back it off by .005 untill you like how it shoots or if you need it to be shorter to feed through the magazine

 

[F. Guffey]

Step one, two and three.

I drill the primer pocket/flash hole out to a diameter that will accommodate a cleaning rod, I also want all the bullet hold I can get, then I seat a bullet short of the lands. And? I do all of this with the bolt removed.

I chamber the test case then push the bullet out of the case until it contacts the lands. When the bullet contacts the lands I stop pushing, If I don't there is a chance the bullet will remain stuck in the rifling

The test case when removed becomes a transfer, I install the transfer in the seating die then adjust the seating die to the transfer. After adjusting the die to the transfer I have a seating die that is zero off the lands. I then adjust my dial caliper to 'ZERO' off the lands with the height of the seating stem 'above the die'.

When finished and if I want a bullet .010" off the lands I lower the seating stem .010".

Not confusing to me: Head space, I can form a case that has zero clearance between the bolt face and case head. Or I can use a full length sized case with the understanding there is a difference between the length of the case from the shoulder to the head of the case and chamber from the datum to the bolt face. I can add, if I know the difference between the case from the shoulder to the case head and chamber from the shoulder to the bolt face.

My cases do not have head space.

F. Guffey

 

[tangolima]

I use similar method. A dummy round purposely seated high.

1. Chamber the dummy round so that the rifling contacts the ogives and push the bullet into the casing. Measure the length from bullet tip to head. This is the coal (cartridge overall length) for zero bullet jump.

2. I like bullet jump of 0.03". Set up seater die to achieve final coal 0.03" shorter than the zero bullet jump coal measured in step 1.

3. Compare final coal with Max. coal for the cartridge, or check the loaded cartridges in the magazine. If they are within spec or have no issue feeding, the final coal is good, or bullet jump need to increase.

4. Repeat when I have a new bullet type.

I never need to use anything fancier than this. It works fine for me.

-TL

 

[Unclenick]

.308 Loader,

If you look at the SAAMI drawing for the .308, you see the COL is listed as 2.490"-2.810". SAAMI doesn't know what bullet is going to be used, so they give a range that will ensure the rounds fit into a magazine and are still long enough to slip up a typical feed ramp without jamming. It is not about accuracy.

If you are willing to chamber your rounds one at a time, and not use a magazine, then you can load anything from a catsneeze load with .32 wadcutter seated flush with the .308 case mouth to a bullet that kisses the lands with loads adjusted to suit in both instances.

As a general rule of thumb, I would avoid seating the bullet bearing surface (the cylindrical groove diameter portion) less than about an eighth of an inch into a case mouth for adequate grip to keep the bullet properly located. I would not seat a bullet so deep that the curvature of the ogive begins below the case mouth, though you can do that just a little in some instances, if you need it for magazine feed. Just keep in mind that high power rifle pressure typically has a minimum inbetween the extremes. When you touch the lands, it can go up 20%, which typically takes about 10% less powder than normal loads in order to compensate. When you seat very deeply you use less powder because the bullet is taking away from the powder space.

Below is an illustration that shows why the bullet design affects COL. As you can imagine, 110 grain M1 Carbine and 168 grain Match bullet will contact the lands with very different COL's because the length of the nose beyond the throat contact point is very different. Even if bullets are the same weight, the nose design will affect it.

Below that is an illustration of terminology, so you can see all the names for cartridge length.

 

[308Loader]

wow lots of good info to digest.
so to answer the question what oal gage I bought it is a hornady, I also have their bullet and head space comparator. the rounds I will be loading are for a Remington 700p with a 26in barrel.
I am going to try some of the measurement methods suggested and see how it goes. thanks every one for your comments.