Bullet seating variance


January 5, 2012, 07:05 AM
I am fairly new to reloading (.243). I have a rcbs rock chucker with rcbs full length dies. I am loading 65 grain v-max and 70 grain Berger HP. I am having problem with the cartridge overall length. With both bullets it seems to seat them differently. I am having as much as 12 thousandths variance in my overall length. I am using new wincheater brass and i noticed it wasn't perfectly the same in length to start. What could cause this much variance in overall length of my loads?

Also, i was reading about crimping. My dies can be set for crimp or no crimp, but the instructions were not very clear to me. Do I need to crimp my loads?

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January 5, 2012, 07:18 AM
Not unusual, although .012 may be a bit much.

January 5, 2012, 07:37 AM
It's the seater plug. Long pointy bullets that don't match the seater plug can't seat consistently.

January 5, 2012, 09:08 AM
With 2 different bullets I would expect 2 different lengths. The profile between the 2 are different so will require an adjustment to the seater. Any time you change bullets even if there the same weight from different mfg you will get a different length if you do not adjust your seater.

January 5, 2012, 01:48 PM
Unless by coincidence, no two bullets of different manufacturer or part #'s will seat to the same OAL. OAL really means little, it's the distance off the lands and olgive that is most important provided the rounds fit the magazine and fed reliably.

January 5, 2012, 10:07 PM
I failed to mention that I did reset the seater plug when I switched to the berger bullets. Loaded the first one to spec and the additional seats were varying as much as 12 thousandths.

I am fairly new to rifle loading so forgive me. I'm trying to learn as much as possible in a short time.

Do I need to get a different seater plug for my die to load ballistic tip V max?

As far as crimping goes? Do I need to crimp my loads?

January 5, 2012, 10:54 PM
Do I need to crimp my loads? No. I am having as much as 12 thousandths variance in my overall length. .005" variance is about normal for me. It could be how you measure it . Lee Info > There are a number of possible causes for overall length variation. One is the way it is measured. If you measure overall length from the tip of the bullet to the base of the case, remember to subtract the variation due to bullet length tolerance. The bullets will vary in length due to manufacturing tolerances (bullets with exposed lead noses are the worst in this regard) and this will add to the overall cartridge length variation. Remember that the bullet seater plug does not (or shouldn't) contact the tip of the bullet when seating, but contacts farther down the ogive. For a more accurate seating depth measurement, take the seater plug out of the bullet seating die, place it on top of the cartridge and measure from the base of the case to the top of the seater plug.

Another possible cause for bullet seating depth variation is seating and crimping at the same time when trying to apply a firm crimp to untrimmed cases. Variation in case length also causes variation in the amount of crimp applied. Long cases get a heavier crimp than short ones. When seating and crimping at the same time, the crimp is formed as the bullet is seated into the case. The crimp will form sooner on a long case, and therefore the bullet will not be seated as deeply. The solution is to seat and crimp in a separate step (the Lee Factory Crimp die is good for this) and/or trim cases to a uniform length.

The amount of force required to cycle a progressive press varies with the number of cases in the shell plate. When the shell plate is full, it is harder to lower the lever than when there are one or two cases present. This can lead to variation in cartridge overall length because there are different loads placed on the working parts of the press. When the shell plate is full, seating depth will be slightly long, because the load is higher and all of the clearances are taken up. With the shell plate nearly empty, the load is not great enough to squeeze out these clearances, and the seating depth is short.

A potential solution for this on progressive presses is to turn the sizing die in far enough so that the carrier is stopping on the bottom of the die. This removes clearance problems when no sizing but yet seating / crimping is occurring. Take special care not to turn the die in further than to just touch the shell plate and possibly just a tad more. About 1/4th of turn more is all you want to go, turning the sizing die in too far causes other problems.

January 5, 2012, 11:45 PM
I would say yes that happened to me also. I started bumping the bullet in twice so as to give the bullet a chance if it is a little crooked to straighten out. I also use a hornady comparator since polimer the tips of those specific type of bullets make your COAL measurements off round to round. With a comparator you measure the ogive of the bullet which will make your reloads more exact to what you want. That is if you ( here is where the wording gets many different opinions) ODRIV the specific rifle, for that specific bullet. Empty casing fireformed in your specific rifle. ReChamber it slowly with a fresh bullet to find where it makes contact with the lands and grooves. Back the bullet off a thousandth to start. RESEARCH THIS PROCESS BECAUSE THE WAY I HAVE EXPLAINED THIS IS VERY BRIEF AND HAS SEVERAL LONG EXPLAINATIONS ON HOW TO DO THIS. Then get a comparator reading. If you are just under COAL, and with the comparator you should be
able to get to.003 . You'll have a good controllable, consistently producible round. That's what has given me outstanding results. Of course follow reloading manuals close.

2 Wild Dueces
January 5, 2012, 11:46 PM
Measuring rounds, from the case head - to the tip of the bullet, can give significant variations. The variations are mostly due to bullet tip variations resulting from the manufacturing process. While the bullet's tip lenth may vary the rest of the bullet's shape should be quite uniform.

The best way to measure loaded rounds is to use a bullet comparator which allows the measuring off the bullets ogive. When measured in this manner variations should be less than .001".

A bullet comparator can also be used to check for variations in bullets - from the base of the bullet to a datum line on the bullet (an arbitrary circle along the bullets ogive). If you find variations (which is quite rare) I have found that it's near impossible to get those bullets to shoot accurately.

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