COAL/OAL spread greater than expected

P

packrat1969

Inactive
Greetings,

I've been reloading 9mm/.45ACP for some time now and have just entered the realm of bottleneck cartridges with my first 5.56 AR. I think I have a handle on the brass prepping situation, but I just now setting up my press for a 55gn FMJBT projectile. My reloading manuals and the internet have been great for cartridge dimensional info, as well as load data, but I haven't been able to find any statistics on COAL/OAL spread across X number of press cycles. I have a Dillon 550B with a set of Lee .223 Pacesetter dies and a Lee universal decapper die.

With the bullet-seating die firmly locked down as per Lee's instructions (screw in to touch shell-holder plus 1/4 turn), across 6 cartridges I'm getting a longest-to-shortest difference of .009 in. Is this reasonable? Even if I'm consistent on how I'm cycling the press, there seems to be more discrepancy per round than I would expect. One round will be right on, the next will be a little long, the next will be a little short, the next right on. Of course all these measurements are in the hundredths and thousandths of an inch. Even when I measure factory ammo, I'm finding some discrepancies.

What are the rest of you finding with your set-ups?

packrat
 
Try tightening up your shell plate and seating a bullet while resizing/decapping at the first station. Leave the other two stations empty. For me, on my Dillon 550B, I get far better results that way than filling every station trying for maximum output.

Also check your seating die for debris. Not likely with jacketed bullets but still a possibility. I have problems seating revolver lead alloy bullets due to lube buildup.

HTH's Rod
 
OAL will normally vary due to bullet lengths being different due to the way they are made. If they fit in the magazine, the OAL is good.

But for accuracy, you want the base-to-ogive measurement to be consistent. Which I am sure your Dillon is doing just fine.

So how to measure accurately to the ogive? Get the $20 hex nut from sinclair, that slips over the point of the bullet.
 
Well, for a rimless bottleneck case with no belt, you actually want the shoulder to ogive dimension to be consistent. It's just that your reloading press doesn't work that way. It registers on the base, and that's as close as you will get.

The way bullets are made usually involved several machines running simultaneously and whose output is combined at the end. Each machine has its own tooling, and this typically results in slight differences in the exact location of particular ogive diameters with respect to the bullet tip. Most rifle seating dies contact the bullets down on the ogive somewhere and not at the tip, so the tip can vary as much as the ogive location does. I've measured that on 30 cal match bullets to still have 0.0080" of variation of that kind, while the tips ran a whopping 0.0135" spread.

What you can do is use a bullet comparator to sort the bullets that came off the same machine by finding matching base-to-ogive lengths. You can also buy a spacer with a 3/16 inch hole in it. Set your bullet base on your caliper with the spacer resting on its nose. Measure the combination with the caliper. You might identify, say, 4 different sets of tooling by the grouping of those measurements. Usually these have a bell curve distribution, but you can still sort them fairly clearly that way. If you select one set of identical bullets from this measurement, you can then measure how consistent the lengths are. Being off the same tooling, that will be closer than for the box overall. You can select some that match at both dimensions (bullet base to tip and bullet base to ogive with the comparator or the spacer) and then try seating just these. The result will tell you how consistent your press and die are being because you matched the bullets first. There may still be a slight variation because the seater doesn't contact the bullet exactly where the spacer does, but they should be close.
 
welcome to the reloading world and you are in for a ride. I reloaded 30+ years ago and got back into the last 4.

No internet, basic loading, now I find out all sorts of stuff that I did not know I did not know. Phew. There are lots of things you can do to make them more accurate, all of them cost money! (and or time)

And wait until you trim them and find out that the trimmers vary as well!

My solution was the Little Crow Trimmer then moved to the Gerard Tri Trimmer.

Little crow is good tool if you don't do a lot (I do a 100 a week or so which is not a lot my most standards but certainly by mine)

Both index off the should which is also the places to check the set back when you re-size a bottle neck shell with the comparator (also need a .001 micrometer)

The varying in trimming is amazingly small when you use one of those two tools.
 
I don't even look at COAL anymore unless I'm loading the 77gr smk for my Service rifle . I use a comparator and measure to the ogive . It is incredibly frustrating with those 77gr bullets . The 77gr smk's I've used lately ( about 500) in the last year . Most from different lots and they all have a HUGE difference in bullet lengths from bullet to bullet . To the point I'm not going to use them any more . The 75gr Hornady bullet is MUCH more consistent . I'm going to try custom competitions next as well .

The AR is limited to a COAL of 2.260 . My issue is I can seat these bullets to where they measure to the ogive +/- .001 but my COAL will swings as much as .012 . That's unacceptable for a top match bullet . I often have to seat the 77's .009 deeper then I want . Meaning some will have a COAL of 2.251 while others will be 2.261 and everything in between . Now the head to ogive measurement will be consistent so my jump should be to . I often wonder if the difference is just in the tips or the whole bullet . If it's the whole bullet that would mean some of the bases are seated deeper then others . But when you must load to a specific length do to mag restrictions and loading a very long bullet for the caliber . I'd like the bullet length to be a little more consistent .

End rant :) I got a little worked up right there :rolleyes:
 
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Thank you for all the replies. I learn more every time I come here.

The shellplate is as tight as I can get it and still be able to rotate the cartridges from station to station. I still have the stock setup, so there will always be some play here, though I've got it tight enough that it doesn't wobble. I've seen bearing kits online that allow one to fully tighten the shellplate bolt, but I'm not sure if they are really worth the $$ or if they can cause other issues. Any feedback on this topic would be appreciated.

The bullet seating die in my setup has a moving plug below the O-ringed adjustment cap. This plug has a tapered end and a flat end. I've been using the tapered end, as it will self-align the bullet. It is, however, resting on the ogive, and if the curve of the ogive varies from projectile to projectile like UncleNick says, then I will never get a consistent COAL. Is it reasonable then, to flip the plug so it always seats the bullet via the tip of the projectile? The FMJ and the lead core would seem hard enough to allow for this without deforming. Is it worth the $15 to have a custom-shaped plug?

I also wonder about the O-ring in the adjustment cap. It seems like it's just there to prevent the threads from backing out, but it does have a certain amount of "springyness" to it. It is rubber, nitrile, or somesuch material after all. Maybe it allows the threads to move up and down slightly?

packrat
 
The o-rings force the threads to be pushed or held in the upward position . Which is the same direction the cap would be pushed when seating a bullet . This means there should be no movement in the direction you don't want movement .

I would use the ogive as my baring surface when seating the bullets . It should give you a more consistent seating depth and jump to the lands . As for the actual seating depth for the 55gr FMJ-BT for the AR . I don't crimp so I seat them right to the bottom of the bullet cannelure or 2.240
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What I have done was buy the Redding standard seating die http://www.midwayusa.com/product/376014/redding-seater-die-223-remington

Then the micrometer plug separate http://www.midwayusa.com/product/71...9083-223-remington-22-250-remington-220-swift

For a total of about $71 rather then the $109 comp seating die . I like the results and it really helps when you load for multiple rifle using many different bullets . You just note what the micrometer setting is for each . Then dial to the correct setting each time you change loads .

I'll add that combo is pretty accurate as far as how much the bullet is moved when you adjust the micrometer . If you seat the bullet long then measure with the bullet comparator http://www.midwayusa.com/product/23...ad-bullet-comparator-basic-set-with-6-inserts
If you need to seat it .043 deeper . Just turn down the micrometer that much and it's just about right on . +/- .001 which in pretty good really IMO .

I'll also add all those fancy doohickeys are not needed but I do enjoy using them.
 
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MG,

Have you ever tried out one of the Redding Competition Seating Dies? When I switched from the Redding standard seater to the Competition die in 30-06 (my first one) back about 1990, the total indicated runout of my finished cartridges was reduced by a factor of four.


packrat1969 said:
and if the curve of the ogive varies from projectile to projectile like UncleNick says, then I will never get a consistent COAL. Is it reasonable then, to flip the plug so it always seats the bullet via the tip of the projectile?
Click to expand...

No. It's not meant to be flipped. The flat surface slides against the aluminum plug to float the seating ram for self-alignment. If you run it backward, the smaller area of the bottom side can mark the aluminum and interfere with that sliding motion when you reverse it again.

Second, with just a flat surface, your bullets will go into the case less straight. That will open groups up on target, especially at longer ranges.

Third, if you make all the tips meet exactly the same COL, then the ogives will be jumping an inconsistent distance to the lands and the bullet bases will be a less consistent seating depth into the case. Both of these factors will tend to reduce accuracy. For best accuracy, you want the ogive in the same place from one bullet to the next, and not the tip.

Over a century ago, Harry Pope said, "the base steers the bullet". Ninety years later, Harold Vaughn demonstrated that filing a 45° slant on a bullet nose affected accuracy less than half as much as a 1.5° slant filed onto the base does. So Pope, who built many highly accurate cast bullet rifles, had it right. The exact shape and position of the nose is far less important than other bullet shape and positioning factors.
 
Have you ever tried out one of the Redding Competition Seating Dies?
Click to expand...

No ,and the only reason is I don't own a concentricity gauge . If I did I'd know if I should switch seating dies or not . I figure with in the next year or so I'll own one . Likely the Sinclair model .

I just ran some measurement tests/comparisons using the 77gr SMK .

Bullet only

Comp------OAL
.6060-----.9850
.6055-----.9875
.6055-----.9865
.6055-----.9840
.6055-----.9850
.6060-----.9855
.6050-----.9835
.6055-----.9860
.6050-----.9830
.6050-----.9840
+/-.001--+/-.0045

Bullet seated in case Random seating depth and the above numbers were NOT measured in the same order as the numbers below

Comp-------COAL
1.8565----2.2355
1.8565----2.2360
1.8570----2.2360
1.8555----2.2335
1.8560----2.2365
1.8560----2.2340
1.8550----2.2340
1.8565----2.2350
1.8560----2.2350
1.8560----2.2310
+/-.002--+/-.0055

So although not to bad it appears my seating stem is not dead on . After the test I checked where the seating stem engages the bullet in comparison to where my comparator engages the bullet .

comparator = .220 in diameter

seating stem = .1995 in diameter

or .1190 higher on the bullet

It's likely this discrepancy that gives me the .002 swing .
 
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A less expensive approach than the competition seater that some folks use is to get a Lyman M die and run their cases in just far enough so it forms the step for the bullet, but not the flare above the stem that you use with cast bullets. This lets you seat the bullet straight up and down for entry into the seater, and that straight start goes a long way toward eliminating runout. The crimp should in the die can be set to just barely remove that step.

You can make a perfectly good runout gauge of your own. I should make one and take some pictures just for educational purposes.
 
So, after reading the last few posts, it seems the COAL is not the end-all, be-all measurement I thought it was supposed to be. Inconsistencies found in any given batch of projectiles can throw it up or down, and, I imagine, this gets worse if the bullets are made on different machines. I can see how keeping a specific diameter of the ogive the same distance from the lands and grooves can maintain shot consistency, but it is up to me to find THE position that provides the best shot accuracy.

So, I see COAL is there to:
1) Prevent the cartridge from being too long to fit in the magazine
-This is pretty self-explanatory.

2) Prevent the bullet from being seated too deeply
-I see bullet depth being more critical in handgun loads, as the volume of the cartridge is much less. In the .223 cartridge is projectile depth a major factor for keeping pressures manageable? As I have yet to drop any powder in these loads, I don't know what kind of volume 24-27 grains of CFE223 will occupy.

packrat
 
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