Oal variation

Fastestmanalive

Fastestmanalive

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Have a good Lyman T-mag turret press and AR series rcbs dies. I took my time to set up my seating die accurately (as I always do)to 2.255 (campro 55gr fmjbt) for .223. All nuts are thight, still I can't get consistency on the OAL. From 2,263 to 2,245. Seems a lot to me. Anything I should check first ? Not new in reloading but new to this caliber. I know that measuring OAL from the tip is not ideal but I am reloading for my AR and not looking for benchrest accuracy. What do you consider as a "normal" variation ?

My cases are full lenght sized with a small base die and trimmed to lenght, all tested in a go/no go tool.

Thanks.
 
Just checked my 55 gn Campro reloads with mixed brass. Across 5 cartridges I have a 0.006" extreme spread in OAL measured from tip. Measured from ogive, the extreme spread is 0.004". Not a very large sample but your spread seems large.

Is the neck tension consistent on your reloads? Any turret will have some slop which will affect seating if the slop isn't fully taken up in the process. A higher neck tension may help. Also try cleaning your seating die and shell holder - a little grit might have thrown your seating.
 
Variations in bullets account for a lot of it, but don't discount play,
slop and flex in the press itself. Just the other day I was setting up a new
Micrometer seater and the COLs were all over the place. Most sort of averaged out, but a few were way out there. Like 20 thou out there. Turns out that the link pins and links were worn right out 1/4 of the way through and it was a bloody miracle that the results weren't worse. I got an attaboy from the Hornady tech though when I ordered up the parts.;) Second press I've worn out, I've got to use the green one while they take a second crack at the right parts.
 
hometownhero said:
Measure some bullets from base to tip and you will get your answer.
Click to expand...

This is unlikely to provide meaningful data. The seating die stem should contact the bullet at the ogive so the critical dimension (that will affect OAL) is ogive-to-tip distance and the bullet-to-bullet variance thereof.
 
Pr589 said:
This is unlikely to provide meaningful data. The seating die stem should contact the bullet at the ogive so the critical dimension (that will affect OAL) is ogive-to-tip distance and the bullet-to-bullet variance thereof.
Click to expand...

Will provide good data. Base to ogive might be damn good but if the bullet themselves is different in length measuring from case head to tip will be different on every bullet. Measure some bullets some may be 20 thousandths shorter or longer then other. Cheaper bullets might have more of a difference.
 
BTW, I think you are seating a bit long. Given variations in COAL, you are risking rounds that will bind in the magazine. I set my average OAL at 2.245 to make sure all rounds will fit mag ok.
 
Buy a comparator like this: h t t p://www.sinclairintl.com/reloading-equipment/measuring-tools/bullet-comparators/sinclair-hex-style-bullet-comparators-prod83792.aspx. I'm assuming you already have reasonably accurate calipers that can measure to .001

Select 10 bullets out of a box and measure the distance from the base of the bullet to the ogive (where the diameter of the bullet becomes .224). The min/max will give you an idea of the tolerance range you should see in loaded rounds.

Then load/seat the same 10 bullets into cases as you normally would. Using the same tool measure the distance from the base of the case to the ogive of the bullet on the loaded rounds. If the variation of the base to ogive in the loaded rounds is much larger than that of the "naked" bullets there is some mechanical slop being introduced somewhere. A simple test would be to find a buddy who can loan you another seating die to try
 
Ganderite said:
BTW, I think you are seating a bit long. Given variations in COAL, you are risking rounds that will bind in the magazine. I set my average OAL at 2.245 to make sure all rounds will fit mag ok.
Click to expand...

Campro calls for 2,260. I was shooting for 2.255 because I also thought it would be tight in the mags. I am a little chicken to go shorter as I am going up close to the max load in the books. Again, pretty new in this caliber and with an AR
 
I've found Campro's to be a bit of a pain when it comes to matching COAL; Sierra's are a piece of cake by comparison - but that's the $$$ difference for ya I guess.
 
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