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Inconsistent COAL

03psd

03psd

Sergeant
Full Member
Minuteman
May 27, 2006
567
33
Oklahoma
#1
What keeps me from having consistent COAL measurements? Mine wander between .03-.05" from one to the next. I am using standard RCBS dies in a Lyman turret press with SMK bullets. I dont expect benchrest quality loads from this equipment but I dont think I am asking too much to think that 5/100 is too much variance. The dies are tight in the press and seater is snug.

thought?
 
#2
Re: Inconsistent COAL

The smk's vary a bit in oal. You'll get more consistant numbers with a comparator. They can be made more uniform with a meplat trimmer, but they shoot well enough for me without that step.
 
#3
Re: Inconsistent COAL

I guess this is dumb to ask but, are you measuring to the ogive or the tip of the bullet ?

When have the dies been cleaned last ?

What is the neck tension, and how many firings on the brass ?
 
#4
Re: Inconsistent COAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wirehand</div><div class="ubbcode-body">I guess this is dumb to ask but, are you measuring to the ogive or the tip of the bullet ?

When have the dies been cleaned last ?

What is the neck tension, and how many firings on the brass ?


</div></div>

Tip of the bullet using calipers.
Dies were cleaned 6 months ago and have less than 500 rounds loaded since
Neck tension is unknown as these are standard dies with FL sized 1x fired brass.
 
#5
Re: Inconsistent COAL

Differences in bullet shape can easily vary the lengths as much as 10 thou but changes running 30 to 50 thou is a lot of variation. That's MUCH more than can usually be attributed to bullet nose forms.

Only thing I can think of for that much OAL variability is operating the press lever too fast and, from that, inconsistantly. Slow down and hold the lever firmly in place for a full 2 seconds when seating, see if that doesn't help.
 
#6
Re: Inconsistent COAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 03psd</div><div class="ubbcode-body">What keeps me from having consistent COAL measurements? Mine wander between .03-.05" from one to the next. I am using standard RCBS dies in a Lyman turret press with SMK bullets. I dont expect benchrest quality loads from this equipment but I dont think I am asking too much to think that 5/100 is too much variance. The dies are tight in the press and seater is snug.

thought? </div></div>

03psd ......

I'm sure you mean .003" to .005"

Your bullet tips will always vary that much or more. Your actual COAL (OAL = same thing) is important to ensure reliable feeding from a magazine. However, to get a more consistent seating measurement, it's best to measure your bullets at the ogive.

- Innovative
 
#7
Re: Inconsistent COAL

If you can, purchase a comparitor that fits into your caliper. You then insert loaded rounds into the caliper and comparitor and your lengths are measured from the base of the cartridge to the ogive of the projectile.

If this measurement is consistant, than you are dealing with different lenths on the projectiles themselves (perhaps the projectile tips are whats causing varience).

Perhaps you could meplat trim, but it may not be required.

If your OAL from ogive to the base of the brass is inconsistant then perhaps it is something else other than the projectiles
 
#8
Re: Inconsistent COAL

o-give measurement is the one to use. 1+
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Innovative</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 03psd</div><div class="ubbcode-body">What keeps me from having consistent COAL measurements? Mine wander between .03-.05" from one to the next. I am using standard RCBS dies in a Lyman turret press with SMK bullets. I dont expect benchrest quality loads from this equipment but I dont think I am asking too much to think that 5/100 is too much variance. The dies are tight in the press and seater is snug.

thought? </div></div>

03psd ......

I'm sure you mean .003" to .005"

Your bullet tips will always vary that much or more. Your actual COAL (OAL = same thing) is important to ensure reliable feeding from a magazine. However, to get a more consistent seating measurement, it's best to measure your bullets at the ogive.

- Innovative
</div></div>
 
#9
Re: Inconsistent COAL

Guys-

No doubt there are subtle differences in the meplat of the bullets that are likely contributing to the variations in OAL. I am not familiar with what a "comparator" is. without one how do you measure from ogive? admittidly, I am a novice but where the ogive starts and stops seems very subjective. how do you ensure you measure from the same EXACT point on each loaded cartridge?
 
#12
Re: Inconsistent COAL

While you're rushin' about checking the pointy end, take a step back and check that you're seating your primers correctly....

That'll put you right about 2/3thou out on your C.O.A.L without you noticing.....
 
#13
Re: Inconsistent COAL

Yeh make sure ur primers arent sticking out

What the comparitor does, is clips into your digital/dial caliper. There are caliber specific inserts that then fit into the comparitor body. These inserts have a hole that would represent the lands of your rifle, or something to that degree. Basically the hole is the diameter of your ogive.

You then insert a loaded round into your comparitor and measure it in the caliper. The measurement is then take from cartridge base to the ogive.

The projectiles will not go past the ogive when inserted into the comparitor.

check this pic out... its a .50BMG comparator

Obviously if you chose you can measure either projectile base to ogive lenth, or case head to ogive length.

13684_7308_large.jpg
 
#16
Re: Inconsistent COAL

" I am a novice but where the ogive starts and stops seems very subjective. how do you ensure you measure from the same EXACT point on each loaded cartridge?"

The ogive starts where ever the body starts to curve towards the point, but we don't care about that. The only part of the ogive we are concerned with is the bore diameter, where the bullet actually contacts the rifleing. On a .308" bullet that's .300", etc. The comparator hole for a .308 bullet will be bored to .300" and that takes care of it.
 
#18
Re: Inconsistent COAL

I had the same problem but it was the turret press not giving me consistant oal. Turret was moving slightly. Went to single stage RCBS and no more problems. Plus use Stoney point gauges
 
#19
Re: Inconsistent COAL

Turret presses which hold the turret in place with a center mounted bolt do have more "spring" than any other and that does indeed often lead to variations in both FL sizing and seating.

I used to bolt my first turret head down hard to stop that but it sure made a funny looking single stage press!

Any normal single stage press will have very little springing. Used to think my Rock Chucker had none. That belief only lasted until I got a dial indicator and magnetic stand, find the RC flexes/springs about .003" FL sizing 30-06. That's not a lot but it's sure NOT rigid either.

Oddly enough, when I did the same test (same day, same dies and lot of fired cases) on my two little Lee "Reloder" C presses neither of them showed any measureable flex at all! Not saying the Lee alum alloy presses are stronger than a cast iron press but, within their limits, they ARE more rigid.

Life can be weird; facts beat opinions, every time.
 
#20
Re: Inconsistent COAL

Neck tension can play a part in this, neck is "moving" abit when you seat the bullet.
Question for the OP. How many times has this brass been loaded?
You see the "harder" the neck get(many reloads)the more spring you may see.
Oh-don't measure SMK's to the tip. It WILL drive you NUTS,BTDT.
Respectfully,
LG
 
#22
Re: Inconsistent COAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 03psd</div><div class="ubbcode-body">Neck tension is unknown as these are standard dies with FL sized 1x fired brass. </div></div>
Other people have already made some good suggestions. After you made a statement about not knowing your neck tension, I wondered whether you might have a compressed load and very low neck tension. If so, the compressed powder could be pushing your bullet out. Just a thought.
 
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