COAL / Length to Ogive measurement discrepancies

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ReadyAimDuck
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COAL / Length to Ogive measurement discrepancies

Post by ReadyAimDuck »

So, I've been using a caliper with a bullet comparator on it to set my seating die for overall length. And I'm measuring each cartridge after sizing and I am getting between 1.495 and 1.500 for each seated cartridge. I'm new to reloading for the level of precision and accuracy that I am trying to obtain. Most of my reloading is for plinking loads mostly for pistol, and for 300 aac subsonic. So, I haven't really measured with a comparator previously. So I guess what I am wondering is how abnormal is it to have the variation that I am seeing? And what causes it?
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dellet
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Re: COAL / Length to Ogive measurement discrepancies

Post by dellet »

Probably the two most common reasons are
Not sorting the bullets by base to ogive first
Inconsistent pull and time at the bottom of the stroke when seating.
Neck tension.
Compressing powder that has not been dropped the same.

If you want the best chance of having your bullets seat to the same depth, they need to be the same length from the base to where the seating stem contacts them. So you would have to make that measurement using your stem. Second best is using in this case the same insert you measure assembled length with.

A faster pull with longer time at the bottom of the stroke, will generally seat a bullet deeper than a slow stroke with no hesitation at the bottom before releasing pressure and it gets worse if you are compressing powder.

Neck tension need to be the same. Seating a bullet is force overcoming resistance, if it’s not the same, the results won’t be the same.

If you sort some bullets, the inconsistency you find there will probably cut the .005” variance you have now in half
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ReadyAimDuck
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Re: COAL / Length to Ogive measurement discrepancies

Post by ReadyAimDuck »

Very good tips. I'm going to measure the bullets shortly and see how different they are. And I will work on my pull consistency.

Is the variation that I am getting so far a major issue for accuracy? I don't really have anything to compare it to. So I am wondering if I am way off or if this is somewhat "normal" for others to experience. I'm not sure if I am asking that correctly. Is it normal to have a variance for the average reloader?
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dellet
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Re: COAL / Length to Ogive measurement discrepancies

Post by dellet »

Depends on the bullet and your goals, then distance you are shooting.

I have seen a .005" change in seated depth shrink groups by 1" at 50 yards, or make no measurable change at 200.

I have culled 5 bullets in 100 Berger bullets for being outside +/- .001" and culled twice that many in a box of Hornady 150 FMJ for being outside +/- .003".

You really won't know until you try. Then move on to the next variable and tool to measure it. Small groups can get expensive.

I think I have found that good components and a good scale are the easiest way to cut group size. Then it seems that it boils down to more time and careful procedures when loading and shooting. If you are kind of a tool junkie, it gets real expensive real quick, but it does make things easier.

I never really realized how much crap is out there until I bought a comparator and started measuring brass and bullets for consistency. weighing brass and bullets is another eye opener.
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ReadyAimDuck
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Re: COAL / Length to Ogive measurement discrepancies

Post by ReadyAimDuck »

Well, I loaded up a series of these a couple weeks ago incrementing in .1 grains of powder at a time and found two really good charge weights. The groups looked great. I didn't notice the discrepancy at that point. So, I think its not making a huge difference.

That said, I just weight ten of the bullets and found that they vary +- .003 from base to ogive. The good news is if the total spread I'm seeing is .005, then my technique only accounts for .002 of that. The bad news is, the bullets vary by .003. But again, I've found two separate charges that produce groupls that I am very happy with even with the variance.
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Re: COAL / Length to Ogive measurement discrepancies

Post by ReadyAimDuck »

The second box of bullets I measured are even worse. They're varying +-.005. So I guess what I am wondering now is when I seat them, should I try to seat each to the same length off the ogive based on what the comparator is telling me? Because if the measurement from the base of the bullet to the ogive is varying, and I seat them all so that my measurement from the bottom of the brass to the ogive in the comparator is the same, wouldnt I just be seating all of those bullets to different depths in the case? Or am I thinking of that wrong. Hard to wrap my head around. I'm just wondering if the bullets vary in length to the ogive, should I seat them all so that they are the same in measurement after seated, or should I just seat them all and let them vary the way they are going to?
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dellet
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Re: COAL / Length to Ogive measurement discrepancies

Post by dellet »

It’s a pain in the butt, tho what you can do is pull the stem out of your seating die and use that as your comparator. It will hit the bullet in the spot it will seat it by, that will possibly be more consistent.

Most of the inserts are designed to touch the bullet where it hits the lands, to control jump. This assumes the Bullets are consistent from base to ogive. You might also be able to find an insert that is the same diameter as your seater.

The problem is that the more you learn, the more you question how you were ever able to hit the target without having all these gadgets. Don’t get hung up in that unless you really want 1/4 MOA groups. Take it a little bit at a time and see what difference it makes in your groups and consistency.

For now group your bullets by size, maybe into five groups. Shoot groups from each set of bullets and a 6th group that is one from. In theory, the mixed group should be worse than the others. Might be an indicator of if it’s worth your time.

It might not really make much difference at 100 yards. At 300 yards it might shrink groups by 1/2.

Every new tool you buy will teach you something, it’s worth it to take the time find learn that lesson before moving on to the next. At least that’s how it works for me.

By some match grade bullets to see how consistent they are. What the premium components should do is keep you from sorting. The flip side is you might be able to get close to match quality bullets from cheap stuff. It will cost your time.

Sit back, enjoy ride and watch your targets. One other problem is that all the improvements to your ammo won’t do you any good if you can’t outshoot the ammo. So every time you up the quality of your ammo, if it’s not showing in your groups, you have to decide if it’s you or the ammo causing the problem. Endless circle.

You have a good handle on the measurement and what you’re doing. Just need to apply it
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ReadyAimDuck
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Re: COAL / Length to Ogive measurement discrepancies

Post by ReadyAimDuck »

Well, thank you for all of that info. I think I'm in for a lot more trial and error and spending money, the deeper down the rabbit hole I want to go. I think I might go further with it when I finally get around to loading for the 308 bolt gun. For the 300, I'd like to be able to make shots out to 300 once my shooting is capable at that distance. For the gun, I had two different charge weights that were sub MOA. Probably about 3/4. I was very pleased with that.

I did have a flyer every now and again and I was starting to obsess over whether that was due to the seating discrepancies. One group put 4 shots in 0.7" at 100 yards, with the 5th shot to the right of that group and slightly higher. I'm using a caldwell lead sled so the rifle is pretty steady. But my scope is a 1 MOA red dot at 6 power, so I'm not sure if the flyer was my eyes or the seating, or some other variable. I'll have to get out and shoot it more to find out. Either way, it exceeded my expectations for accuracy so I am pleased. But as you know, its very hard to stop at being pleased. Its very easy to become obsessed with tweaking things even further.
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Gallo Pazzesco
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Re: COAL / Length to Ogive measurement discrepancies

Post by Gallo Pazzesco »

dellet wrote: Wed Sep 08, 2021 9:32 am Probably the two most common reasons are
Not sorting the bullets by base to ogive first
Inconsistent pull and time at the bottom of the stroke when seating.
Neck tension.
Compressing powder that has not been dropped the same.

If you want the best chance of having your bullets seat to the same depth, they need to be the same length from the base to where the seating stem contacts them. So you would have to make that measurement using your stem. Second best is using in this case the same insert you measure assembled length with.

A faster pull with longer time at the bottom of the stroke, will generally seat a bullet deeper than a slow stroke with no hesitation at the bottom before releasing pressure and it gets worse if you are compressing powder.

Neck tension need to be the same. Seating a bullet is force overcoming resistance, if it’s not the same, the results won’t be the same.

If you sort some bullets, the inconsistency you find there will probably cut the .005” variance you have now in half
That was really very well stated.
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ReadyAimDuck
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Re: COAL / Length to Ogive measurement discrepancies

Post by ReadyAimDuck »

I took the seater stem out of the seating die today and sure enough the polymer tips of the Tac TX and VMAX bullets are hitting the top of the stem before where the stem is supposed to contact the bullet to seat it. I'm thinking this has a lot to do with the discrepancies I am seeing. I noticed that Lee advertising that they will make you a custom stem for 8 bucks if you send them an example of the bullet. So, I am going to send them both bullets and see what they can do.
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