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COL and Presure ??

1K views 24 replies 7 participants last post by  noylj 
#1 ·
I have a COL question. I'm reloading a Remington 700 in 308 with hornady 168BTHP
The hornady book says col max is 2.800 but my hornady gauge the me it's 2.980. To the lands. So I backed it off .020 thousands and theirs not much bullet left in the case. Just barely.308 left. Any thoughts seem way to long. Loaded to factory max of 2.800 with IMR 4895. 41.6 gr and had some flatten primers.
 
#2 ·
col max is 2.800 but my hornady gauge the me it's 2.980. To the lands.
Might just be me but this sounds a bit confusing. When you zero your gage and then measure from the base of the bullet to the tip of the bullet you get_______? The oal is cartridge only. To measure how far you are from the lands takes a different gage scenario if I am reading this correctly.

There are several of these out there and I did NOT watch this particular video but is this what you are after?
 
#4 ·
Test your gage against a standard to ensure it is reading correctly. If you don't have a standard, measure your .308 bullet at the diameter widest part and it should be .308" Common for gages to may be read .307, .308 .309.
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So you used the https://www.amazon.com/Hornady-Overall-Length-Gauge-straight/dp/B000PD01SI to measure where your bullet touches the lands. You then set your bullet to that distance minus the .020 and ended up w/ a bullet that is way shorter than the manual suggested oal for a regular loaded 308 cartridge. Is the Hornady test case you used screwed all the way into the grey plastic piece? Is the test case you are using the Hornady 308 test case and not an incorrect case?

Just and fyi before I forget: It is not uncomon that you can't get to the lands w/ certain bullets in certain chambers. You need to also leave enough bullet in the case for proper neck tension. Some times if you do this, bullets may have to be hand fed as they won't fit in a magazine.
 
#6 ·
Ideally you should have the bullet seated not less than one caliber into the case. Something sounds screwy with your numbers. I don't pay attention to the OLL listed for different cartridge's. I make sure the bullet is just off the lands but at the same time seated a min of one cartridge depth. In your case, .308. If your seated .308 min and ogive is just off the lands your good to go with what ever number's your coming up with.

Forgot, you have to seat the bullet's deep enough to fit in the magazine well.
 
#8 ·
Since you are new, for now stick to the length in the manual. Experiment with getting close to the lands later.

The measurement from the base to the tip is only relevant to magazine fit and cycling through the action. The number listed in the manual is for that purpose and has nothing to do with proximity to the lands.

As it relates to distance to the lands, you need to measure from the base to the ogive, not from the base to the tip. That's what the gauges do, if used properly.

IMO there are a bunch of things to try for accuracy improvement before messing with OAL. And if you're just starting out then a safe, functional OAL is the way to go.

Stretching that length comes at a price. They may not fit the magazine. Bullets touching the lands and not seated deep enough into the case can pull out when you try to extract them, ending your hunt or your day at the range. And bullets touching the lands can increase pressure.

Flattened primers are a bad sign, something is causing that. What is causing it is hard to say unless you're just changing one thing at a time. If this is a new load altogether, and assuming the powder charge is well in the safe area, I would seat those bullets down to that Hornaday length and try them out. I would do that anyway.

What is the load for?
I don't much mess with trying to seat bullets out closer to the lands until I've settled on the other aspects of my load and I want to fine tune. On many rifles it's a waste of time and you risk those issues I outlined above.

And I never seat the bullets out against the lands on my hunting loads. My priorities are safety, consistent function then accuracy.
 
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#9 ·
Just a commit on the loading to max. Start from start and work your way up so you can see signs before you get to the flattened state. Just because you have a great load at the manuals oal, then decide to load off the lands, start over with start. Any change to a cartridge is start over time. The problem w/ loading off the lands is the secant varies from bullet to bullet and you could end up w/ a boom condition. Unless you have various comparators, etc, stay off the lands. As a bad case example, lets say you took a random bullet from the box and made a measurement. If that bullet randomly selected was on the puny secant side and many of the other bullets were on the chunky secant side, and you are using lets say for instance, some lead tipped bullets, you can be anywhere on the lookout scale fo pressure. Using the .020 off the lands you mentioned is smart as it give your fudge room.

Not sure if you got your answer??!! Hopefully the tangents didn't contribute to derailing the question.
 
#21 ·
Maybe we need to know what you consider a pressure sign with the primer. There's flat and then there's flat. A primer flattened by pressure become's immediately recognizable. Check for an extractor mark on the face of the cartridge and don't ignore a sticky bolt. Some people think measuring the head of the case works, I don't use that anymore. I have never seen a new case not get a bit bigger with firing.
 
#13 ·
What do you think is a flattened overpressure primer? Can you show us a pic of yours?

I would be really surprised if 41.6gn behind a 168 give you overpressure signs, the load is just above starting load.
Judging primers for pressure signs is very hard and unscientific, flat primers can also be caused by other things like headspace.
 
#18 ·
I would have no problem shooting either, although the right one is more what I would expect from a starter load.

You have 50K to 60K PSI of pressure trying to push a primer out of the pocket which is only stopped by the bolt face. You can't expect them not to show anything :)

But what Jwdurf said, what changed?
 
#19 ·
Red Carmine Paint Coquelicot Tool
Seated bullets down a little. Guess I need a ogive gauge instead I've the OAL gauge. Been using this. The videos on YouTube are a little miss leading when
trying to reach the lands. Understand that bullet lenght is not consistent. Been measuring and some are way longer and some short.
 
#22 ·
Ok. That gauge is a good tool, and it is part of the puzzle. It is a very good way to find the measurement from the bolt face to the lands in a given rifle. As you have learned, it isn't the best way to find OAL for a given case/bullet combination. For that you need a bullet comparator, which allows you to measure to the ogive. Then you can mathematically adjust your OAL to your individual firearm.

For now I would suggest you stick to the recommendations in the manual. In my experience, getting the bullet close to the lands is over rated as an accuracy tool, unless you're precision target or bench rest shooting. For the average shooter, bullets, powders, velocity and primers all have a much greater impact on accuracy than seating that bullet out to the lands. Furthermore, many factory rifles have very long throats, making it difficult to impossible to seat bullets close to the lands anyway.

Spend some time prioritizing why you handload and what you use the ammo for. Hunting? Plinking? Serious target shooting? Each use creates different priorities. I like to think I load custom premium hunting ammo for my rifles. These get a lot more care and development than the plinking ammo I load for my handguns.

My priorities for my hunting ammo are, in order, safety, reliability, function (feeding through the rifle) terminal ballistic performance, then accuracy. And they all shoot MOA or better, and none of them are seated out near the lands.
 
#24 ·
Flattened primers along with being a sign of a grossly overloaded cartridge, is also a sign of excessive headspace or more likely than that, a cartridge with the shoulders pushed back too far. This happens in the milliseconds of the firing sequence when the case gets pushed forward in the chamber by the firing pin strike. Pressure starts pushing both the bullet and the primer, the unsupported primer smacks the bolt face with enough force to flatten it, then pressure pushes the case back against the bolt face and re-seats the now flattened primer into the primer pocket.
I had this very same problem with my own Remington 700, also chambered for .308. I got in a hurry to get my first set of dies set up for use, and ran the die down to touch the shell holder when the press ram was at it's highest, and pushed the shoulders back about .008" too far. These cases had the flattened primers at less than max loads. I re-adjusted the dies with a Wilson case gauge and a depth micrometer. To salvage the cases, I expanded the necks up to .33 caliber to create a false shoulder to "headspace on" and re-sized back to .30 caliber in the now re-set die.
 
#25 ·
I don't follow the question.
You start at the start load and work up. No matter what COL you use, you start at the start load and work up.
You find the COL that works in your gun (in your case, that probably means a COL that fits the magazine) first, and then you work up the load from start.
You might play with COL after, but if COL really effected pressure much, then NO BODY could have done this without having to totally re-work the load from start load for every COL change.
Now, I have been told that, unlike straightwall pistol cases, bottleneck cases actually can LOWER pressure as COL goes down (since case volume is so great that the loss in volume is very small compared to the additional length of bullet travel before hitting the lede that drops pressure).
All I know is that when I can, best accuracy has been with the bullet just on the lede and I have never seen any pressure signs starting at the start load and working up at max working COL. I generally find that the COL that just fits the magazine works for all the bullets I have ever used and they have always been well short of the lede and, for off-the-shelf rifles, a change of +/- 0.010" COL doesn't have much effect.
 
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