Cartridge OAL testing, what are good increments to test?

Evil_Dark

Evil_Dark

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Hi all,
After having found the proper powder charge for my .308 with Hornady Match 168gr HPBT, I want to fine tune that load with playing with the OAL. I've started at 2.775" as the standard stated in my manual, but what would be goods increments to tests?
Five rounds of 2.785, then 2.795 (0.010" incréments) ? Or more? Less? Never played with that before...

Does this play with the pressure and the FPS?

Thanks

Dark
 
Measuring OAL is an uncertain way to keep "x" distance off the lands. A comparator is the way to measure case head to land engagement length. Bullet tips are not as uniform as the diameter that engages the lands.
 
My 223 and 6mmBR like either a 10 jam or 10 jump - but my very very accurate 308 seems to like the bottom of the bullet (175 TMK) bearing surface right in line with the bottom of the case neck - which results in a huge jump...coincidentally, its the same OAL length as some manuals suggest...go figure!
 
So, if I have understand correctly, i've should have played with the COAL before playing around with powder charge??

Dark
 
My gig is to find the best powder charge, i.e., best groups, then play with seat depth and see if it tightens things up - as mentioned above, 5 thou increments from jam outward.
 
Evil_Dark said:
So, if I have understand correctly, i've should have played with the COAL before playing around with powder charge??

Dark
Click to expand...

You can do it either way. I started a thread on this a while ago and most guys said they find the load first but I read something by Bryan Litz (Chief ballistician with Berger) and he said find the best COL first.

I start 20 thou off the lands and go out further from there, Around 80 thou seems good in a couple Model 70s I have, but change bullets and you have to start over. For hunting the advice seems to be 'no closer than 20' since you don't want to get the bullet jammed and pull out a case and have a stuck bullet in the barrel out in the field somewhere.
 
Varmit said:
You can do it either way. I started a thread on this a while ago and most guys said they find the load first but I read something by Bryan Litz (Chief ballistician with Berger) and he said find the best COL first.

I start 20 thou off the lands and go out further from there, Around 80 thou seems good in a couple Model 70s I have, but change bullets and you have to start over. For hunting the advice seems to be 'no closer than 20' since you don't want to get the bullet jammed and pull out a case and have a stuck bullet in the barrel out in the field somewhere.
Click to expand...

yes coal and jump are important but the determining factor to what that group will look like at distance is ES what you think may be a great group at 100 yards may be very different at 1000 if your extreme spread of speed of the bullets is large. the amount of spread will determine group size the lower the better. also after you get the load down use a concentricity gauge to measure bullet run out.
 
I start with bullets at jam. Then I look for the best powder charge and lowest ES at the range. Once optimal charge is found I start loading 5 rds starting with increments of .003 jump up to .015. My testing is done at 300m anything closer is a waste of time.
 
PitBull1973 said:
I start with bullets at jam. Then I look for the best powder charge and lowest ES at the range. Once optimal charge is found I start loading 5 rds starting with increments of .003 jump up to .015. My testing is done at 300m anything closer is a waste of time.
Click to expand...

then once you have found the best load for that bullet and powder combination you try a different primer and things change once you work there that adjustment you find you are out of that lot of powder you were using! then you OCD starts all over again good luck have fun and em braise it Enjoy!!
 
I'm waiting for my Hornady Ogive comparator set for my calipers. Up til now I've measured base to bullet tip, but I've learned that base to ogive is a better way to do it. The comparators are not terribly expensive.

WTF is the ogive, you ask? I asked the same thing not long ago. It's where the taper of the bullet stops being a taper and it starts being the actual diameter of the caliber. At least that's how I think of it.

I've been taught to choose the charge first, then vary the seating.

Some say seating doesn't matter, but it sure did in my 6.5.
 
yes it sure does can change greatly and jump for one charge may be different than another, some weight their brass and load different for a set weight of brass but to me weight does not work volume is the variable that can change pressure.
 
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Gunneegoogoo said:
I'm waiting for my Hornady Ogive comparator set for my calipers. Up til now I've measured base to bullet tip, but I've learned that base to ogive is a better way to do it. The comparators are not terribly expensive.

WTF is the ogive, you ask? I asked the same thing not long ago. It's where the taper of the bullet stops being a taper and it starts being the actual diameter of the caliber. At least that's how I think of it.

I've been taught to choose the charge first, then vary the seating.

Some say seating doesn't matter, but it sure did in my 6.5.
Click to expand...

....and those that say this have no idea. It can make a considerable amount of difference with pressures.
 
You can burn out a barrel trying different powders, loads, and OAL's.

Each gun is unique, but for the 308 with that bullet, I'd go with a max load of Varget and work back from "at the lands" in 10 Thou increments.
 
.....then, once you find the happiest .010", depending how type A you are, and what your goals are, you can go up and down .005 to see if it helps.
 
WTF is the ogive, you ask? I asked the same thing not long ago. It's where the taper of the bullet stops being a taper and it starts being the actual diameter of the caliber. At least that's how I think of it.
Click to expand...

You're concern is over the proper place where the curve transitions to the straight portion. But technically "ogive" is the shape of the curve on the nose of the bullet. It's much like "parabolic" or "hyperbolic" in that it describes a certain shape of curve.

The point at the end would be the "transition from the ogive (nose)". Or perhaps calling it the "shoulder" might not be too far amiss? Or perhaps the "ogive base" or "base of the ogive"? Or maybe (likely) the bullet makers have a name for this point where the straight side transitions to the curve.

Kudos to those of you writing about how the bullet meets the leade. I'm picking up some good information that I'd not seen before.

Is it fair to say that some barrels will like the bullet to be lightly pushed into the rifling and others set back a hair from it? And maybe some others that do best when either just in contact or just a whisp away from contact?

And if this point of contact or relief is quite critical would the same barrel and brass react differently to different bullets in this relationship of the ogive to the leade?

This all pre-supposes we're shooting critical ammo from a bench rest. But for more casual use or those of us that enjoy free standing or shooting from prone using our own arms to test ourselves more than the ammo is it just splitting hairs for the most part?
 
BCRider said:
You're concern is over the proper place where the curve transitions to the straight portion. But technically "ogive" is the shape of the curve on the nose of the bullet. It's much like "parabolic" or "hyperbolic" in that it describes a certain shape of curve.

The point at the end would be the "transition from the ogive (nose)". Or perhaps calling it the "shoulder" might not be too far amiss? Or perhaps the "ogive base" or "base of the ogive"? Or maybe (likely) the bullet makers have a name for this point where the straight side transitions to the curve.

Kudos to those of you writing about how the bullet meets the leade. I'm picking up some good information that I'd not seen before.

Is it fair to say that some barrels will like the bullet to be lightly pushed into the rifling and others set back a hair from it? And maybe some others that do best when either just in contact or just a whisp away from contact?

And if this point of contact or relief is quite critical would the same barrel and brass react differently to different bullets in this relationship of the ogive to the leade?

This all pre-supposes we're shooting critical ammo from a bench rest. But for more casual use or those of us that enjoy free standing or shooting from prone using our own arms to test ourselves more than the ammo is it just splitting hairs for the most part?
Click to expand...

Ya - unless you're a super human if you're shooting standing or off your arms, this is splitting hairs. If you throw a bipod on though, you'll see benefit. I shoot sub .25MOA with my 6.5 prone off a bipod. Not always, but I've done it.

You're dissertation about the term ogive is probably right. They talk about secant and tangent ogives - rocket science that I haven't got into yet. I think we're on the same page though about taking about measuring from the "shoulder" to the case's base vs. the tip to the base. There's an acronym for it - BTOL I think - "Base to Ogive Length" vs. COAL "Combined OverAll Length".

I'm learning as I talk, so if someone can correct me, do.....
 
the style of curve affects the bullet for the designers in terms of Ballistics Coefficient and the like. And it's good to realize that the nature of this curve can affect how the bullet chambers in relation to the rifling leade.

I'm learning with you. That BTOL isn't a term I'd run across. But I'm only getting into rifle loading seriously. And there's lots of holes in the process due to reading a bit here and a bit there on different accuracy rifle loading information. Up to now it's all been about handgun loading which is so much less critical for the styles of shooting I do.

Overall a superb thread. I'll be watching from the wings unless I have another question.
 
I looked it up - it's CBTO - Cartridge Base To Ogive

YoDave tells me is a way better way to gauge seating depth as some tips can be .02-.03 off, hence my comparator purchase.

Very very good thread.

"Clearly you can see all of my knowledge of missiles comes from watching cartoons....."

1337192734_Dictator.jpg
 

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