Noobie question re. determining ideal Correct Overall Cartridge Length (COAL)

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woofer2609

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So I've been reloading for about a year. The load I worked up for my CZ 557 in .308 gave excellent results. (150gr Hornady 3031 over 51.0gr of H380.) Overall cartridge length was 2.750"

I used some of these rounds in a newly acquired Savage Hog Hunter, as well as some cartridges I loaded using the same powder and bullets, from 47gr up to 51 gr of powder.

For the newly loaded cartridges, I loaded to an overall length of 2.635" ( I got this measurement from some factory ammo I had around; Remington CoreLokt 150gr).

The results were pretty inconsistent at best, 3" groups at 100m.

This got me curious. I never did determine the bullet "jump" on the CZ, I guess I just got lucky with my COAL. I got many, many groups under 3/4" at 100m.

The inconsistent groups made with the Savage made me want to learn about how to determine the optimum cartridge length. I started to read about COAL.

The way I figured out my COAL on this new Savage was to crimp the neck of a shot cartridge, seat a bullet in the neck and then loaded the cartridge and bullet into the action of the gun and closed the bolt. I read about this on a few websites.

I took the cartridge out and measured it. The average over 5 samples was 2.835". This was a very consistent length.
(For what it's worth, this is less than the max. magazine COAL, so I don't need to worry about that.)

From my reading, it would appear that the ideal length to load my cartridge for this rifle is this 2.835" measurement minus .015" so the bullet is just off the lands.

So... a few questions.

Is this concept correct re. seating the ogive .010-.015" off the lands?

Am I doing this COAL measurement correctly?

Do I need to be concerned with where my ogive contacts my lands apart from having the .010-.015 "jump"? (I did the magic marker thing to find out where it makes contact.)

Is there any need to buy a Hornady Overall Length gauge? Would this help me more than measuring COAL using the crimped cartridge holding the bullet method?

Thanks a lot everybody, I'm learning as I go, but really enjoying it. Any input is appreciated.
 
Your best "gauge" is the bullet holes on your target. That means taking notes as you set up based on your chamber dimensions. Try a jump at .005"; try at .050"; and increments in between. No one can tell you for sure, and it may not especially matter, if you are checking for cartridge concentricity, neck and throat clearance. But you will only find out by sending rounds down range and by keeping notes. Lots of work - make sure you have enough components of the same lot number or you get to start over again. I never have understood how a commercially purchased "gauge" could tell me anything about the chamber and throat in my rifle, although I do believe measuring off the ogive provides a more accurate measurement to attempt to repeat, versus cartridge over all length.
 
Since you are relatively new to the game, I'm going to suggest that you be careful about loading too close to the lands. In a hunting rifle application, I limit my COAL to 30 thou off the lands for a given bullet. This accommodates the natural variation in ogives, soft bullet tips, your process, etc. Getting a jammed cartridge during a hunt can cause a lot of grief. Ask me how I know.
FWIW - I have had many rifles shoot well with over 1/4 in of bullet jump (the long freebores made it impossible to get closer.) I consider bullet jump to be a minor variable compared to bullet weight, powder type, and charge weight. In your example above, I would try another bullet weight in the Savage, or perhaps another powder if you want to stick with a particular weight.
 
SAAMI COAL for .308 is 2.800". Most bullets do well with a .040" jump to the lands. In many rifles, most Remingtons for example, loading at just off the lands will bring your COAL to over 2.950", making your rounds too long for most mags. If your new Savage is at 2.835" then loading at 2.800 would be a good start. In fact, it looks like an ideal scenario for you to experiment with reaching the lands while still being able to have your rounds fit in your mags.

I recently found out reaching the lands in my new CZ 557 Range involved having a 2.960" COAL with Berger 185 gr VLDs. Mags allow for about 2.880" max COAL. Needless to say I'm disappointed. The rifle shoots well so far, but this will limit my bullet choice to bullets that like a long jump.
 
Your technique and thoughts are correct.

I use 50 round plastic ammo boxes and mark the box with which rifle the ammo is for.

Each rifle will have its own COAL and powder preference.

I make a mark inside the lid each time i reload the brass.
 
Lots of great info here, thanks! I really appreciate all the input. In regards to torquing the action screws, I'll do that once i start to get some better groups, as the article suggests. I may load to within .030" to begin with and work from there. I have enough of the same lot numbered supplies. Trying out a new, heavier bullet may be in the cards for this rifle, but I'll give the 150 and 147's a go first.
Again thanks for the input, much appreciated.
I'm still trying to wrap my head around why measuring the base to ogive is considered more consistent/ better for accuracy than measuring COAL if your case lengths are consistent at 2.006".
 
RangerPark said:
SAAMI COAL for .308 is 2.800". Most bullets do well with a .040" jump to the lands. In many rifles, most Remingtons for example, loading at just off the lands will bring your COAL to over 2.950", making your rounds too long for most mags. If your new Savage is at 2.835" then loading at 2.800 would be a good start. In fact, it looks like an ideal scenario for you to experiment with reaching the lands while still being able to have your rounds fit in your mags.

I recently found out reaching the lands in my new CZ 557 Range involved having a 2.960" COAL with Berger 185 gr VLDs. Mags allow for about 2.880" max COAL. Needless to say I'm disappointed. The rifle shoots well so far, but this will limit my bullet choice to bullets that like a long jump.
Click to expand...

Mine is the Ranger rifle as well with the 10rd magazine. How are you liking it so far? To me it just feels like a solid, well built rifle. The COAL on these is huge, as is the magazine oal, even if it is more than the action COAL. With the lighter bullets, as mentioned, 2.75-2.760" works great. Guess I got lucky with choising that length. Only thing Ive done to the rifle is install a limbsaver.
 
Have you tried any other powders than the H380? A slightly faster burning powder may give you the accuracy you're looking for.

If I may give one piece of advice: change one variable at a time until you see improvement. Don't change powder and C.O.A.L together, for example.
Not so much for safety reasons but it will allow you to start finding what your Savage prefers in terms of components over the CZ :)
 
woofer2609 said:
Mine is the Ranger rifle as well with the 10rd magazine. How are you liking it so far? To me it just feels like a solid, well built rifle. The COAL on these is huge, as is the magazine oal, even if it is more than the action COAL. With the lighter bullets, as mentioned, 2.75-2.760" works great. Guess I got lucky with choising that length. Only thing Ive done to the rifle is install a limbsaver.
Click to expand...

The best description for mine was a diamond in the rough. Mini review here:
https://www.canadiangunnutz.com/forum/showthread.php/1806626-CZ-Handguns?p=15490768&viewfull=1#post15490768

I just finished tuning my mags for it. I ended up opening the lips on both a bit. I found that the feeding lips were too close on both my mags, causing the bolt to ride on top of some rounds. Now it feeds perfectly.

In doing my mag feeding tests I noticed my ejected dummy rounds would hit the windage turret on my scope. The dummies are an empty case with a Sierra 175 gr TMK seated on top. Ejected empties clear the scope but barely. I'm thinking of trying to find a stronger ejector plunger spring for it.

All I've shot through it are Federal Fusion 180 grains. Very nice grouping at 200 yards. I finished my season with it and filled two tags at Camp Wainwright on the last day. I will reload for it in the Spring.
 
woofer2609 said:
I'm still trying to wrap my head around why measuring the base to ogive is considered more consistent/ better for accuracy than measuring COAL if your case lengths are consistent at 2.006".
Click to expand...

Maybe it is in the semantics? COAL is Cartridge Over All Length. Has nothing to do with the case length - COAL is the distance from cartridge base to bullet tip. Your lands engage at their diameter - nominally "bore" diameter - so measuring from cartridge base to bullet ogive is closest way to duplicate bolt face to lands distance. Bullets vary - measurement variation to their tip do not necessarily match measurement variations to their ogive. As mentioned above, this presumes that exact bullet "jump" is truly a significant factor in your reloads in your rifle.
 
Potashminer said:
Maybe it is in the semantics? COAL is Cartridge Over All Length. Has nothing to do with the case length - COAL is the distance from cartridge base to bullet tip. Your lands engage at their diameter - nominally "bore" diameter - so measuring from cartridge base to bullet ogive is closest way to duplicate bolt face to lands distance. Bullets vary - measurement variation to their tip do not necessarily match measurement variations to their ogive. As mentioned above, this presumes that exact bullet "jump" is truly a significant factor in your reloads in your rifle.
Click to expand...

It probably is semantics. To me, if all my cases are measured to the same spec (2.005-2.006") and my seating die is a constant, I would think that after loading numerous rounds BOTH my COAL and my shell base to ogive length (and therefore my bullet jump/distance from lands), would remain consistent.
As mentioned by you and others however, there are a number of other factors. Having worked up a load for my 223, I do understand how different powders affect accuracy.
That being said, if this Savage doesn't like H380, I should have enough (13lbs) to keep the CZ in loaded cartridges for the foreseeable future. ;)
 
RangerPark said:
The best description for mine was a diamond in the rough. Mini review here:
https://www.canadiangunnutz.com/forum/showthread.php/1806626-CZ-Handguns?p=15490768&viewfull=1#post15490768

I just finished tuning my mags for it. I ended up opening the lips on both a bit. I found that the feeding lips were too close on both my mags, causing the bolt to ride on top of some rounds. Now it feeds perfectly.

In doing my mag feeding tests I noticed my ejected dummy rounds would hit the windage turret on my scope. The dummies are an empty case with a Sierra 175 gr TMK seated on top. Ejected empties clear the scope but barely. I'm thinking of trying to find a stronger ejector plunger spring for it.

All I've shot through it are Federal Fusion 180 grains. Very nice grouping at 200 yards. I finished my season with it and filled two tags at Camp Wainwright on the last day. I will reload for it in the Spring.
Click to expand...

Congrats on the hunt. Your observations on the rifle are similar to mine, except I didn't have issues with the lips on the mag, just having it drop free. I used some parafin wax on the mag body and bolt and it is now smooth as butter. Empty cases hitting the windage knob are a pain in the butt, especially as I have a tactical style Nikon P-308 scope on the rifle (big knobs). They almost want to bounce back into the rifle.
 
woofer2609 said:
It probably is semantics. To me, if all my cases are measured to the same spec (2.005-2.006") and my seating die is a constant, I would think that after loading numerous rounds BOTH my COAL and my shell base to ogive length (and therefore my bullet jump/distance from lands), would remain consistent.
As mentioned by you and others however, there are a number of other factors. Having worked up a load for my 223, I do understand how different powders affect accuracy.
That being said, if this Savage doesn't like H380, I should have enough (13lbs) to keep the CZ in loaded cartridges for the foreseeable future. ;)
Click to expand...

The issue is that soft tipped bullets don't display a constant base to tip measurement. So if you go to duplicate a previous batches COAL by measuring to the tip, the bullet jump may be off. To avoid this, and avoid expensive ogive measuring gimmicks, just measure the actual bullet length and ensure that the same length is used in successive efforts.
 
woofer2609 said:
It probably is semantics. To me, if all my cases are measured to the same spec (2.005-2.006") and my seating die is a constant, I would think that after loading numerous rounds BOTH my COAL and my shell base to ogive length (and therefore my bullet jump/distance from lands), would remain consistent.;)
Click to expand...

If you use the exact same make, type, and weight of bullet this will likely be true. If you change one or more of those items, then it will probably not be true. Simple as that.
 
I usually start cup and core bullets at .010", off of the lands, and monometals at .050", as long as this functions in the magazine. I use the lock ring on my seating die and once I find the optimum COL, I record the micrometer setting, so I never have to adjust the seating die again. I use a fired case with a small flat spot on the neck to maintain tension, to find the distance to the lands.
 
stubblejumper said:
I usually start cup and core bullets at .010", off of the lands, and monometals at .050", as long as this functions in the magazine. I use the lock ring on my seating die and once I find the optimum COL, I record the micrometer setting, so I never have to adjust the seating die again. I use a fired case with a small flat spot on the neck to maintain tension, to find the distance to the lands.
Click to expand...

This is exactky what i plan to do and have dine in the past. I love your signture. Totally agree.
 
rick357 said:
If you use the exact same make, type, and weight of bullet this will likely be true. If you change one or more of those items, then it will probably not be true. Simple as that.
Click to expand...

I am using the same weight, make and lot of bullets. i buy in lots of 500 to utilize the exact same bullets for the life of 100 cartridges.
 
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