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Question on cartridge uniformity

2K views 20 replies 7 participants last post by  LDBennett 
#1 ·
Cartridge uniformity is one of my main goals when reloading, and one controllable parameter that is not discussed very much is case length. The SAAMI specifications for .223 cases (the only rifle caliber I reload) is 1.760" max and 1.740" minimum. If the cartridge overall length is constant the .020" variation in case length means that more or less of the projectile is in contact with the neck because only the neck is trimmed.

My question is does that variation in case length result in measurable accuracy variations? It seems reasonable to assume it requires more or less force (pressure) to move the bullet out of the case depending on how much of the bullet is in contact with the case and how much crimping force is applied. More contact area = more force required. If there is more pressure inside the case then is the velocity higher when the bullet exits the barrel? The next question is how much variation in velocity occurs and is it significant in terms of accuracy at 100 or 200 yds.

I'm asking this because I wonder if there is any accuracy gains to be made by sorting cases by case length. Several sources recommend sorting by head stamp, but the measurements I've made show as much variation in both weight and length within specific head stamps as there is in mixed head stamp brass.
 
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#2 ·
Trim them every time. Then they are all the same length.

See. Your problem goes away. :D
 
#3 · (Edited)
I'd suggest you do some research on ultra accurate benchrest type shooting/case preparation. Your theories seem to be plausible (neck length variations + pressure variations on the bullet affecting velocity), but in real life I doubt if they have any effect on overall accuracy. That would be a good experiment; choose some cases that have the minimum case length, and some that have the maximum. Load 50 of each identically, weighing each charge, exact same bullets +- .01 grain variation in weight (for a good test 50 of each should give adequate data), and shoot and record. But everything, all conditions like ambient temperature, sunny vs. cloudy, humidity, barrel cleanliness/fouling, shooters condition/health, would have to be exactly the same.

Or I'd look for a bench rest shooter's forum for info/research first as those guys squeeze every .01 MOA out of their guns/loads...
 
#4 ·
Trim them every time. Then they are all the same length.

See. Your problem goes away. :D
Yep.

You say you want uniformity, but then have to ask if you should make them all UNIFORM?
If you want sloppy (but safe) ammo, just keep everything inside the specs. If you want good ammo, keep every round as consistant as possible. The more consistant, the better. Ultimately, it comes down to the quality that you want to achieve.
 
#5 ·
stev32k:

The whole point of trimming cases is to keep them from jamming against the shoulder in the chamber near the throat end of the case. Get them too long and the case neck is pushed in on the bullet (a crimp like action) and the pressure zooms up to dangerous.

While bench rest competitor work to get everything perfect in order to shoot into the teens (five shot 100yd groups of less that 0.2 inches) I suspect most of us can not achieve that accuracy with any gun we have or with the skills we have at hand. Simply trimming the cases to the same length every time is about the best we can do but trim AFTER sizing.

I treat my ammo in any caliber in lots of about 100. I size five to ten randomly selected case from the lot and measure them for case length. If any are longer than the manual max length then the whole lot gets trimmed AFTER sizing the whole lot. This has worked for me for over 25 years on 30+ different calibers.

One of the manuals that shows the reloader how cartridges work and why we do particular processes, in words and pictures, is the Hornady manual.

LDBennett
 
#6 ·
Well said LD, well said indeed!
 
#7 ·
My question is does that variation in case length result in measurable accuracy variations?

Maybe, maybe not. On paper in math terms yes. In real life your probably going to have more variations caused by wind or your powder charge.

I The next question is how much variation in velocity occurs and is it significant in terms of accuracy at 100 or 200 yds.

The best way to answer this question is to buy a chrony and see for yourself what the differences are in velocity from one bullet to the next. Personally i dont think it will be much if any as long as your other items are consistent like powder charge and primer. I think the wind will be more of a factor.

I can tell you that i have found a big named company that makes so called superior bullets and there was 200fps difference in one bullet to the next in the same box. Most of the time that is not the case but it is not uncommon to have a variation of 50fps from one bullet to the next out of factory ammo.

The most uniform ammo i have ever seen was Hornady Light Magnum. They dont make that any more. Now they have the superformance line. It's ok, as good as you can get but not like the light mag was. The light mag ammo gave me rounds within 5 fps of each other. That is darn good.
 
#8 ·
The reason I'm asking the question is that that I need to load with a long OAL for both my bolt .223s. My concern is with short projectiles and short cases. If I load to 2.260 (the maximum that will fit in the mags) in cases that are the minimum case length that will crimp (1.740) the length of bullet inside the case neck is below any minimum I can find. Guess the answer is that I'll just have to try it and see what happens.

I've found that if I load to the OAL in the manuals and do not crimp my groups look like a shotgun pattern. If I load long and don't crimp the groups get better, but not the best they can be. If I load long and crimp I can shoot sub MOA groups at 100 yds every time.

I trim every case that is over the trim to length of 1.750, but a lot of cases - maybe 50% - are below that. So trimming them more is not the answer. Guess I need to find out how much the cases will grow after being shot and re-sized.
 
#9 ·
stev32k:

You either have crummy cases or you are not re-sizing the cases BEFORE you trim. With all the cartridges I reload for (remember 30+ different cartridges) none ever are less than the trim to length unless someone else made them that way. I start (usually) with new cases (Remington or Winchester).

I'll say this one more time: YOU MUST SIZE BEFORE YOU TRIM.

If your chamber is such that when you put the bullet just off the rifling or out much father that the recommended OAL for that bullet/cartridge and you get less than one caliber of bullet still in the case, you are asking for trouble, especially if it is in a lever, pump, or magazine feed semi-auto gun. If your rifling twist allows then go for a heavier (longer ) bullet. Use the Greenhill formula to determine what the longest bullet is that you can use.

Reliability of ammo is much more important than velocity you gain with light bullets.

Now, if it is a bolt gun and your ammo is handled extremely easily, those short bullets barely pushed into cases can be OK. I think if you use the LEE Rifle Factory Crimp Die the bullet might be secure enough for normal handling (??). Only testing will prove it one way or another.

LDBennett
 
#10 · (Edited)
I've found that if I load to the OAL in the manuals and do not crimp my groups look like a shotgun pattern. If I load long and don't crimp the groups get better, but not the best they can be. If I load long and crimp I can shoot sub MOA groups at 100 yds every time.

I am gona throw some other factors out there so i make darn sure i get a headache now. :D:D:D:D:D:D:D

Ok What gr and type of bullet are you using? FMJ, V max, 55 gr 62 gr, and finally what is the twist rate of your bbl and the length of your bbl. The reason i ask is that (and here comes the headache) longer or shorter, crimp, non crimp may be assisting your launch in one way or another. The real reason may be a bad combination of bullet type, gr and bbl. For example i have a 1in7 rifle that shoots fmj like crud but in the same wt will shoot a vmax like a tac driver. Vmax bullets change the center of gravity because of design. All the variations your making may be causing the same effect. So whata shooting? While your answering that i am going to get some tylenol. :D:D:D:D:D:D
 
#11 ·
LD, I have never, ever, ever, trimmed a case before it was re-sized. I received 350 fired .223 cases last week and separated them by size as received. 192 (55%) were below trim to length size, 48 of the 192 were below minimum case length (1.739" or less). I don't know if they are bad cases or someone trimmed them too short, but since I started measuring every case I receive those are about the same numbers I always get.

I will put every one of them in the trimmer AFTER re-sizing and if they all average gaining .006" in length more than 50% will trim. After trimming I will still be left with some large percentage of brass that is below trim to length size.
 
#12 ·
LD, I have never, ever, ever, trimmed a case before it was re-sized. I received 350 fired .223 cases last week and separated them by size as received. 192 (55%) were below trim to length size,
Lake city FC brass?


48 of the 192 were below minimum case length (1.739" or less). I don't know if they are bad cases or someone trimmed them too short, but since I started measuring every case I receive those are about the same numbers I always get.

You sure your yard stick is measuring correctly?
 
#13 ·
stev32k:

Maybe and maybe not??? To be truthful I never measure new brass. I size them, load them up, and shoot them once then do my test to see if the lot needs trimming. When I do trim, every case shows signs that the cutter touched them and I set up the cutter to the exact trim-to length probably plus or minus a thousandth. Its not that I want them that accurate but my setup just allows that, so why not.

Also I don't trim unless one of the 5 to 10 random sample cases is beyond the max case length. Trimming before that I believe gains nothing if all you are trying to do is keep the case length below the max for the sake of the gun's chamber.

The point was made we don't know all the facts. How about you tell us what gun, what barrel twist, what bullet, whose brass, and what you are doing with the ammo after it is loaded. Benchrest competition is different requirements for reloads than plinking at tin cans.

By the way I did not mean to imply you did not size but wanted to make the point to others "size first, trim second". I searched all over manuals to dig that info out when I started reloading and there was no internet at that time. In fact wide spread TV was only about 10 years old at that time and it was B&W! :) :)

LDBennett
 
#14 · (Edited)
I have a bolt action Mossberg MVP chambered in 5.56 NATO. It has a 20" barrel with a 1:9 twist. I also have a Remington 700 BDL chambered in .223 Remington. It has a 24" heavy barrel with a 1:12 twist.

In the Mossberg I shoot 55 gr V-max, 55 gr, BTHP, 55 gr FMJ-BT, 60 gr V-max, and 60 gr SP, and 69 gr HPBT. In the Remington I shoot 40 gr V-Max, and 50 gr V-Max. The Remington likes the 40 gr V-Max best. The Mossberg shoots everything well except the 69 gr. The Mossberg likes at or near max velocity at any range, the Remington a little less at 100 yds and near max at 200 yds.

Surprisingly the Mossberg is every bit as accurate at 100 yds as the Remington. At 200 yds the Remington is better.

Oops, the Remington has a 26", 1:12 twist barrel.
 
#15 ·
You'll have to lookup the Greenhill formula but based on my experience your guns are doing what you'd expect for the twist rates in them. Greenhill twist rates are a guide. The actual bullet construction can effect accuracy too.

The Mossberg must get less accurate results from the 69 grainer, I would think. One in 9 is slow by today AR standards and they normally shoot 69 grainers. The Military AR's are typical one in 8 or 7.5 or even 7 inches.

The one in 12 inch Remington is strictly for light varmint bullets. It should barely shoot the 55 grainers. One in 12 was the first twist rate of AR, I believe, quickly replaced with faster twists. Back then 55 grain bullet were the AR bullet later changed to 69, was it?

To be clear, it is not he weight but the bullet length that dictates the twist rates minimum rate.

Since these are bolt guns you can be a bit less worried about seating the bullet way out. I try to set up bolt gun cartridges so that the bullet is just a few thousandth off the rifling. But it has been proven that might not get the best accuracy. Only experimentation with seating depth tells you what the gun likes. Some guns like multiple tens of thousandths off the rifling. Weatherby's have a pretty good reputation for accuracy and they are set up with lots of travel before the rifling (like more than 0.060 inches in some cases).

LDBennett
 
#16 · (Edited)
cycloneman
I had big problems with my earlier yardstick. It was a Starrett digital caliper I had used for over ten years. It was the most accurate and dependable caliper I have ever owned. The electronics started getting flaky and I didn't catch it until I had trimmed almost 200 cases that were too short.

Since then I purchased a set of gage blocks that are certified accurate to .000008" (that's 8 millionths of an inch and those are grade 3 blocks). I have calibrated two micrometers and a new set of calipers using the blocks. So now I feel pretty confident in my measurements.
 
#17 ·
cycloneman
I had big problems with my earlier yardstick. It was a Starrett digital caliper I had used for over ten years. It was the most accurate and dependable caliper I have ever owned. The electronics started getting flaky and I didn't catch it until I had trimmed almost 200 cases that were too short.

Since then I purchased a set gage blocks that are certified accurate to .000008" (that's 8 millionths of an inch and those are grade 3 blocks). I have calibrated two micrometers and a new set of calipers using the blocks. So now I feel pretty confident in my measurements.
Thats good. Sometimes you have to ask or go back to the stupid stuff before you can move on to other things to blame.

I am curious about your brass that was short. I have bought some in the past and found LC FC to be short. Just wondering.
 
#18 ·
Thats good. Sometimes you have to ask or go back to the stupid stuff before you can move on to other things to blame.

I am curious about your brass that was short. I have bought some in the past and found LC FC to be short. Just wondering.
Something I have not done is check head stamps of the short brass. I'll look at that. I have not bought any LC (military) brass on purpose but I know some has been mixed in with the commercial stuff. I'll start keeping track when I get a new batch after the first of the year.
 
#19 ·
Something I have not done is check head stamps of the short brass. I'll look at that. I have not bought any LC (military) brass on purpose but I know some has been mixed in with the commercial stuff. I'll start keeping track when I get a new batch after the first of the year.
I have a thought for you. If you know of a range that does not allow FMJ ammo, that is the range you want to buy brass from. I have one close to me and of course he gets all kinds of brass. All i have to tell him is what i want and he will pick it out and call me. That why you will get commercial brass for 223 and 308 which makes it easier to prime.

Just a thought im passing on to you.
 
#21 ·
I USE TO belong to one that would not allow steel cored ammo. They got religion after I had been a member for over five years and drug out an old by-law and started enforcing it. When they kicked me off the range for some Military Surplus ammo that was steel cord (or so they said ?) I quit the club and demanded my dues back (got them too).

The indoor pistol range I used when I lived in the LA area did not allow bare or exposed lead bullets (lead vapors on an indoors range). I just shot plated pistol bullets. I too have never heard of no FMJ bullets. Are they trying to protect their back stop? or metal targets?

LDBennett
 
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