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Why is my COAL varying so much?

I am using Redding Deluxe 223 dies. Lapua match brass all trimmed to same (+\- 0.001) length on my Forster trimmer. Flash holes deburred, which seemed pointless on this brass, champher/deburred case mouths, full length sized, etc.. Mica and case mouth brush inside all cases before sizing. All brass being used was weight sorted and found to be within 94.5-95.5 grains, heavier and lighter brass was bagged and labeled. FYI, of 100 Lapua 'match' cases, only 67 were within 94.5-95.5 grains. Press is the rock chucker. Made 25 rounds last week for my Barnes Precision AR15, my first reloading efforts. Shot them today, got 25 more cases and repeated the same recipe for retesting.

COAL on all twenty five 223 rounds are +\- 0.002 except for 6 rounds which were -0.007, -0.004, -0.003, -0.003, -0.005, and +0.006. Nineteen rounds were within 2.268 and 2.272, which I consider acceptable. I set my seating die up for a COAL of 2.270, which comfortably fits in my AR Stoner 10 round AR15 mags. Nineteen out of twenty five are acceptable, but the other six are further off than I want. How can I make all my reloads within +\- 0.002? Could the out of tolerance rounds account for flyers?

Am I overthinking things that won't matter much in reality? What bugs me is two of my 5 shot groups today with 69 SMK and Varget would have been 0.5 MOA without a flyer in each group, which opened things up to a hair over MOA. My goal for this particular weapon is 1/2 MOA, so I am eager to see what role (if any) this variance in COAL may have had. My intention is to get the load dialed in then start varying seating depth in 0.010 increments searching for a sweet spot. I just started relaoding last week, but having so much disparity from round to round just seems wrong.

Would appreciate any insight into the effects of said variances on accuracy, and of course would be interested in suggestions to remedy the issue. Case comparator needed, suggestions on which one? Saw the Sinclair and RCBS, but heard the much more expensive Accuracy One was better. Bullet comparator needed? These are things I know very little about if applicable. I have only loaded 50 rounds and appreciate any input.



Dan
 
Dan: Bullets out of the same box/ lot will vary in over-all-length, some by more than others. Hollowpoints with the sometimes jagged tips can vary as much as .020". The polymer tipped (like the Hornady A & V-Max) are usually around .003" to .005".

If you measured the length from the case head to a point on the bullet ogive, using the Hornady/ Stoney Point chamber O.A.L. gauge, they would all be the same. That's the important length, Cartridge over-all-length is important only if you are magazine feeding, and then you will have to seat to the longest length that will fit in the magazine.

If you want to get the highest degree of accuracy out of your AR you will have to try different seating depth's and single loading the rounds directly into the chamber.
 
as the man said tips of bullets vary....ONLY USE COAL FOR MAGAZINE CLEARANCE.
for all else the length to the lands or ogive length..with a stoney point type tool.
 
I have often thought when this topic comes up we need to adopt a new universal acronym. That being B.T.O. (base to ogive) This is by far the #1 measurement most of us need to know when seating bullets. I think we can blame Hornady for the confusion. Later! Frank
 
Frank Blum said:
I have often thought when this topic comes up we need to adopt a new universal acronym. That being B.T.O. (base to ogive) This is by far the #1 measurement most of us need to know when seating bullets. I think we can blame Hornady for the confusion. Later! Frank

You have my vote Frank......

Danattherock - I had some difficult with BTO consistency when I first switched from tangent ogive to secant ogive spitzer profile bullets. I found that the seater in my seating die was machined for the tangent bullet and the secant bullets didn't align well with it. My seating die supplier provided me with a secant seater - that solved my problem.
 
I wholeheartedly concur with the adoption of BTO as the more meaningful and accurate description of what we're measuring.

Now if we could only get seating stems that contact the ogive where it actually contacts the lands - we'd be comparing apples to apples instead of apples to olives.....but regardless of your datum, getting them all within .001" is the goal and the Hornady(nee StonyPoint) comparator is a good tool.
 
Dan: The Stoney Point (now Hornady) chamber O.A.L. gauge is one of my most valuable tools. In addition to taking measurements for bullet seating depth's, it can also be used for headspace control/ the amount the case shoulder is being pushed back with each FL sizing. I'd be lost without it.
 
If you would like to stop having varying seating depths I suggest you contact Bob Green and buy one of his bullet comparators. With that you can quickly measure your bullets on the same spot where your seater hits the bullet, sort them into sub lots, then Adjust your seating die and all in the same sub lot will seat the same from Base to Ogive....Easy Peasy!
 
Bobs tool looks nice, but is not offered in .224. The black granite base Sinclair bullet comparator caught my eye. Would it be as good as the Stoney Point/Hornady comparator? Any pros/cons to one or the other.
 
Danattherock said:
Bobs tool looks nice, but is not offered in .224. The black granite base Sinclair bullet comparator caught my eye. Would it be as good as the Stoney Point/Hornady comparator? Any pros/cons to one or the other.
[br]
Contact Bob. He does not offer a 7mm comparator on the web site, but I have one.
 
no...
you need a simple hornady/sinclair tool set that goes on a caliper.
a base with a caliber specific insert(22).
 
Would I need two inserts? Saw where folks put one on each caliper arm to get sidewall length?? Or do I just need one insert for each caliber, measuring ogive to base? Thanks for your time and patience. I read a lot on Alaska, fly fishing, and photography boards. I know how all the newbie questions come in. I appreciate the help, and your candor.


Dan
 
Measure the overall length of each bullet before you seat it and see if the variation in COAL is correlated to the variation in bullet length. The variation in bullet length can be at least as much as you're seeing in COAL, and if the length of the bullets varies, so does the BC of each bullet which can cause your group to open up vertically. Some people trim meplats to cure that problem.
 
it all depends on how much detail you want to get into,
the body length is what engages the rifling, and controls the drag.
so get an accurate scale and weight sort in .1 increments.
now with 2 caliber specific inserts in two holders, sort by body length.

all of this makes sense if you buy in large lots and really shoot long range.

to just seat to a known oal, a single caliber insert is all you need....
start there and work up...
are you weighing your powder to plus or minus 0.02 ??? are the cases sorted to plus or minus 0.05 ???
 
Dan....folks have already given you good info. Don't worry as long as the accuracy is there. I've had some vary as much as .015. Didn't matter because they were still dead on.
 

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