Question on cartridge length consistency

J

jamesf553

New member
Alright, so, i just fired my new lapua brass for the first time. I clean them all up nice, run them through my hornady full-resizing die, and put them on a block.

I take my digital caliper, and measure each case, end to end. According to SAAMI in my reloading book, 338 lapua max cartridge length is 2.724''. I measure each case to see if they are at or below that. They all are, but are not all the same exact length.

So, I prime them and load some n570. I adjust my bullet seating die, and place one in. Once I seat it, the COL is 3.677. I don't adjust the seating die. Next is 3.681, then 3.672, then 3.680. Is it ok to leave the seating die consistent (and then the whole catridge length will vary between each round slightly), or do you adjust the bullet seating die to adjust the COL of your case?

I found myself constantly adjusting my seating die tonight because I'd raise it a bit, then the next case would be slightly longer, so the bullet would raise the COL over the saami spec (3.681), and then I'd have to adjust it lower slightly again.

Unless I make sure every case is the same exact length before I load it, there's going to be a slight COL difference. Suggestions? What is your process?
 
Case length has nothing to do with COL.

Differences in bullet ogive is what is screwing you up.

If you have a comparator, measure bullets from base to ogive and see how much they vary.
 
Dufus said:
Case length has nothing to do with COL.

Differences in bullet ogive is what is screwing you up.

If you have a comparator, measure bullets from base to ogive and see how much they vary.
Click to expand...
Im confused. COL is the cartridge overall length, so back of case to tip of bullet correct? I am measuring that and am just saying that the col changes with each bullet I seat into the case (as I'm assuming that the cases are slightly different length after firing/resizing once).

I Can get a comparator and I imagine I have slightly messed up now because the 20 rounds I just loaded, I loaded them to get them within the saami col, not to their ogive, so some bullets I guess may be a tiny bit more pushed in then others.
 
Maybe a bit better explanation.

Bullet tips vary a bit. It does not affect accuracy but it does affect what you are seeing when you seat the bullet as the seater does not press on the tip (and not desirable that it should). So your COAL does look bad.

So when you actually measure it, you see that variation and you say, what the heck?

OGIVE is the radius of the bullet (simple, not dead tech right but good enough, its the curing part of the bullet) and is much more consistent if you are setup to set to that.

There is a tool that fits on a Micrometer with an adapter for a given Caliber Bullets that less you measure that OGIVE for seating purposes.

For the most part it does not affect bullet performance.

So its kind of a choice.

For semi serious target shooting what you can do is average the COAL and you will have a plus and minus variation that won't affect things enough to matter.

Or you can get the Horndady comparator setup and it will do it more tightly though there will be variation of .004 or so by going with the OGIVE on the bullet.

In either case you just take the average and don't chase it.

As long as your bullet is far enough out of the lands that the variation does put some bullet into the lands and stick you are good.

If it does you just move it back.

.020 off the lands is a good starting point.

some guns have shorter throats and the listed COAL may not work, you just adjust to what you have.

Trust me, if it goes into the lands you will now it, you won't be able to extract the cartridge (or at least easily)

A good sick will pull the bullet out of the case (don't ask me how I know!) and then you take your brass rod (always a good thing to have, Home Depot in a 1/8 does nicely) and tap the bullet back out.
 
Last edited:
Are you using the same grain, type, manufacturer of bullet?? Your COL should not be affected by the length of your case. The seating die should "press" the bullet into the case with the same OAL each time. On second thought even if you use different bullets for each case, your OAL should remain consistent. The only difference will be the AMOUNT of brass "gripping" the base of your bullet. I would theorize that this would disrupt your overall accuracy, since more brass would create more drag on the bullet and higher pressure prior to "release" and exit down the length of your barrel. What type of press, dies are you using? Have you ensured lock rings on your dies are tight?
 
Jamesf553,

Here are some measurements I took of some hollow point match bullets. You can see the lengths varied 13.5 thousands. Even the length from the bullet base to the ogive varied 0.008". This is an artifact of several different sets of tooling being used to make the bullets and the resulting output of the machinery being mixed together before boxing them.

attachment.php


The SAAMI maximum COL is designed to make ammunition and magazines universally compatible. SAAMI is a manufacturing standards organization first and foremost, and that length standard, like other SAAMI standards, exists so a manufacturer can make ammo he knows will fit and function in guns he will never see and never be able to test it with. Handloaders are loading for their own guns, so they can ignore it. All you need to do is make sure that what you load fits and functions in your gun properly. The only safety concern is that bullets seated out so far that they get close to or actually touch or jam into the rifling of the barrel throat will raise pressure to near proof load levels. Seating that long requires dropping the powder charge around 10%, typically, to avoid the excess pressure.

attachment.php
 

Attachments

  • 150 grain SMK variance.gif
    150 grain SMK variance.gif
    13 KB · Views: 493
  • Distance off lands.gif
    Distance off lands.gif
    56.3 KB · Views: 664
"...Next is..." You're probably not operating the ram exactly the same amount every time. SAAMI cartridge Max OAL is 3.6811 - .120. That's 3.6811 minus 120 thou. Makes the minimum COAL 3.561". Anything between those numbers is fine. No ogives involved.
"...are not all the same exact length..." SAAMI Max case length is 2.7244 - .020. That's 2.724 minus 20 thou. So 2.704" is the absolute minimum case length. The Trim-to is 2.714". Any case that's between the 2.724" and 2.704" is ok.
However, it's best to have 'em all the same length. Easiest to find the shortest case that's in spec and trim to that length. Use your calipres as a case length gauge to find the cases that require trimming and trim 'em. Don't forget to chamfer and deburr.
And remember that trimming is not an every time thing. Checking lengths is, but trimming is not. Only trim the cases that get longer than the 2.724".
 
I'll probably confuse the issue but, the only control you have is base to ogive. The seater presses on that to seat the bullet. So this is what you should measure. The ram is flush with the base and the ogive is controlled at top by the seater. Bullets vary and brass varies. Get the hornady tool to measure (it looks like you already have something similar) and the measurement with this tool base to ogive should be within +-.002.

The dark path would be to start sorting bullets, but you would have to decide OAL, base to oogive, tip to ogive or weight.
 
consistancy

What a great topic and such great responses.

I always loaded a dummy rifle round with the bullet I plan to use and seated same quite a bit out of the case and then chambered it.

I then would measure how far the bullet was pushed back into the case and adjusted my seating die 0.02" less.

Failed to consider the primer push.
 
Ok, i'm to disagree with Unclenick here.

"Firing pin jump" would push the case the distance from the case shoulder datum point to the actual chamber of the barrel. Theoretically 0.002-0.003".

Now then after the firing pin strike on the primer it has been theorized that there is enough pressure build up to unseat the bullet and shove it into the lands of the barrel before the powder actually ignites to the point of building it's pressure.

Please feel free to correct me if i'm wrong.
 
James, what type of rifle are you reloading for? If it is a clip-fed rifle, your final measurement just became very simple...your coal has to be short enough to fit in your clip and feed consistently. I went through all the work of measuring all of my rifles with a seating depth gauge, both my bolt actions, semi-autos and pump Remingtons. For the bolts, I seated the bullets .002 off the lands and they fit in the blind magazines just fine (ADL). As for the semis and pump, I learned that they wouldn't fit in the clips if seated .002 off the lands. I had to seat them so that they fit in the clips. Lesson learned.
 
Last edited:
blackwidowp61 said:
James, what type of rifle are you reloading for? If it is a clip-fed rifle, your final measurement just became very simple...your coal has to be short enough to fit in your clip and feed consistently. I went through all the work of measuring all of my rifles with a seating depth gauge, both my bolt actions, semi-autos and pump Remingtons. For the bolts, I seated the bullets .002 off the lands and they fit in the blind magazines just fine (ADL). As for the semis and pump, I learned that they wouldn't fit in the clips if seated .002 off the lands. I had to seat them so that they fit in the clips. Lesson learned.
Click to expand...
First-off thanks for the replies guys! I appreciate it.

blackwidowp61, I am reloading for a savage 110 BA stealth. I just did 20 reloads of berger 300 gn otm hybrid bullets with 82 and 84 gn of N570 powder. Worked well.

I understand now what you are saying about the bullet seater and it not changing the OAL. I guess what I must have been seeing was the difference in the bullet tips. This makes sense because not every bullet tip was completely flat across the top. They were imperfect, sometimes slanted, if that makes sense. I would measure by just putting my caliper end on the back of the case, and then the other end onto the tip of the bullet.
 
I seat rifle rounds by measuring OAL from the base to the ogive. Even at that, I see an inconsistency in OAL which, for some time, I considered a difference in bullet ogive position in the same box and lot number, as described by UncleNick. Then I happened to put a charged and primed case on the bench rather than in the die until I reached for a bullet to seat and noticed the case rocked a bit. I reseated the primer a bit more and that completely eliminated the discrepancy I have been seeing. Check your primers.
 
Not to be a doubter, but is it at all possible that the small difference in length you are seeing is caused by your method of measurement??

There are times when the trouble taken to ensure as much uniformity as possible is simply wasted effort.

Look at it this way, if you, and your rifle can't tell the difference, except with a caliper, is it really something to worry about??
 
I understand now what you are saying about the bullet seater and it not changing the OAL. I guess what I must have been seeing was the difference in the bullet tips.
Click to expand...

Yes.

You can see the range of possible bullet lengths from Unclenkicks chart.

You are just shooting (pun) for an Average and the set back from engaging the lands needs to be less.

If you want to get into more advanced let us know, but that covers the basic part.

The easiest way to find the lands ala maximum COAL is to seat a bullet in a case without powder or primer (its safer as its going to be in and out a lot though Savage has a nice in between safety that allows operation of the bolt and still won't let the firing pin go)

You just seat the bullet about .050 further out than the recommended.

Then very gently you try to close the bolt.

It likely will come to a stop, you don't want to push past that as it just forces the bullet into the lands and likely will stick.

It likely will stick a bit but a tap on the bolt handle will pop it loose (plastic tool only, screwdriver handle works nicely)

If it sticks, move the bullet in deeper .010 and repeat.

When it goes full forward and closes (again gently on the close and stop, seat deeper if any resistant on the bolt handle going down) you have very close to the true COAL maxim for that rifle and that bullet (other bullets have different shapes so each one has to be tested if you use different ones)

You then adjust your seating COAL for that bullet another .015 to .020 (as a start) deeper.

The bullet OGIVE method is more accurate but the above is more than good enough until you feel ready to get the other OGIVE and or case shoulder tool setup.

The OGIVE adapter and setup also had advantage as it gets you most of ht way to minimum shoulder bump back which will save on those expensive cases.

Hornady has inserts to fit the adapter for both bullet and cartridge shoulder.
 
Last edited:
Not to be a doubter, but is it at all possible that the small difference in length you are seeing is caused by your method of measurement??

There are times when the trouble taken to ensure as much uniformity as possible is simply wasted effort.

Look at it this way, if you, and your rifle can't tell the difference, except with a caliper, is it really something to worry about??
Click to expand...

Bullet do vary so its a very legitimate question.

If you are new to reloading then you don't know all the nuances and I was bothered by the same issues when I got back into it seriously.

We tell people to pay attention to details then tell them some of those are not safety related.

So until you get comfortable with the process and understand all those funky relationships, you want to do it as right as you can.

I had loaded for hunting and when I got back into it all that stuff started popping up and I wanted answers. Data is presented down to .001, obliviously that is important.

I can relax now and understand far more but that sure was not going to suffice when I started seeing this stuff pop up.

Frankly I continue to be annoyed at the top slathering over of the tech aspects only to find those hidden gotcha parts (minimum shoulder bump back)

It got to the point that it was, what next and how much do I have to spend?

I am happy to answer the question in the moment and then have the OP come back with more questions as he gets comfortable with the process.
 
If I am trimming cases for length it is important to match the length if I am going to crimp and it is important to trim the case to prevent the neck of the case from getting into the throat of the chamber.

A case that requires trimming does not add to the Overall length of the case. SO? If you have a problem with consistency, you could have two problems; the case length would be one problem and the COL could be the other.

When it comes to case length consistency there is nothing that works better than a trim die. My trim dies are also forming dies When forming I use a hack saw, when trimming I use a file.

F. Guffey
 
You must log in or register to reply here.
Back
Top