I loaded up some 7mm ultra mag bullets earlier, and out of the four they all have different COAL. One thing i did not do is trim all the cases, i already had them primed before i learned to trim every case even if under case length max specs. These cases DID fall within specs, they just didnt get trimmed to the EXACT length. Could that be causing the diff. COAL? Im using the lee breech lock, the seating die isnt moved or tampered with in between each bullet.

One more thing, for you guys with the lee case trimmer. The guide only allows you to trim if the case if over COAL specs. Do you still trim every case so they will all be exact? You can trim shorter when not using the shell holder. Would this be ok? Its not a problem to turn with my hand, just takes a second longer. Thanks.

what type of bullets? if they are soft lead tips then they will be off. Hornady has the supplies to measure off the ogive which is better to do. I shoot alot of Nosler ballistic tips and accubonds so measuring overall length is usually consistant. Always trim brass.

Overall length won't change to to case length change...some bullets would be a bit farther past the neck, some a bit less, but if the bullets were all the same length the loaded ammo would be the same length. Case length is important for other reasons, but over all loaded round length isn't one of them.


Most overall length variations can be explained by the bullets.

A poor fit between the seating stem and the bullet will cause variation..

I wouldn't seat minor variations....so far as the rifle is concerned, it's the length to the first part of the bullet's bearing surface that counts....a hard thing to measure without the right tool.

bottom line: if they shoot well, it's no issue at all.

When measuring C.O.A.L it is hard to get consistant measurements if measuring to the tip of the bullet .I use a hornady bullet comperator it measures from the ogive (the point were the bullet starts its curve to the tip) this gives much more consistant readings.

ok, so say you guys load up about 25 rounds. You wouldnt worry with going back and making sure they are all the exact or very close to the same overall length? The bullet im using for this batch is the combined technology ballistic silvertip.

Well, how far off are they? Your bullet seater doesn't go off of the tip of the bullet so a little variation in c.o.l. would not be unheard of.

That could actually make the ammunition worse. The tips of match hollow point that I use will vary around 0.010" in how far forward they stick out. Some are square to the axis, some are at a slight angle. It just doesn't matter much to ballistics, so the manufacturers don't fuss with making the tip length especially tight. Knowing the tips can vary that much, if you seat all the bullets to the exact same length, you will probably find the bases of the bullets are no longer seated to the same depth.

Measure your bullets before seating. Find a dozen of them that match and seat them and see how closely the resulting COL's turn out? That will be more representative of what your loading procedure is turning out by way of consistency with those bullets. Note, however, that at the factory the bullet ogives don't always spring back out from the bullet forming dies with the exact same form. Again, with accuracy being far less sensitive to bullet nose form than it is to bullet base consistency, it's not really a flight problem. It can still cause a few thousandths of COL variation due to variation in where the seater touches down on it with respect to the distance from the bullet base.

Achieving 0.005" variation or less with your selected bullets should be possible. If you can't get there, you might call your seating die maker and ask what it would take to get a seating stem better matched to your bullet choice? Some will help with that. Otherwise, you need to get an ogive type comparator and sort the bullets by ogive location. You can try that and see if rounds loaded with those bullets actually shoot with measurable improvement or not?

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thanks unclenick. I just want the loads to be as accurate and reliable as possible, thats why i was asking this. Ill load some more up and ill measure the bullets before seating them. thanks alot.

The ones 've reloaded so far have varied by about .003 between batches of bullets. I was aiming for 3.250 with some 150gr Sierra spitzers and I think they measure between 3.249 and 3.252.... about .003.

Another batch I was loading Nosler Ballistic tips and they only varied probably less than .001 either side of my target OAL, if that much even.

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Yes. The plastic tip requires the manufacturer to uniform the meplats so they can be inserted. Great for bullet length regularity.

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Nick

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CMP Certified GSM Master Instructor
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"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley