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Puzzled. Need Explanation.

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Puzzled. Need Explanation.

Old 03-20-2015, 12:40 PM
  #1  
Typical Buck
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Default Puzzled. Need Explanation.

So I went to the range and shot some reloads. I wanted to check expansion of round but instead of expanding most of the bullets actually shrunk? I did crimp them But barely. What the heck is going on, I've never experienced this. The groups were ok.
I did some testing and non crimp bullets from magazine to chamber can add .010 to OAL. With the instructions from the crimp die it added .002 to OAL. I believe that's maximum crimp. How much is actually needed? Is maximum safe?
The best groups were at 28.5 grains of H322 with 110 Pro Hunter

6.8 AR platform

Last edited by JGFLHunter; 03-20-2015 at 02:45 PM.
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Old 03-21-2015, 06:52 AM
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Originally Posted by JGFLHunter
So I went to the range and shot some reloads. I wanted to check expansion of round but instead of expanding most of the bullets actually shrunk? I did crimp them But barely. What the heck is going on, I've never experienced this. The groups were ok.
I did some testing and non crimp bullets from magazine to chamber can add .010 to OAL. With the instructions from the crimp die it added .002 to OAL. I believe that's maximum crimp. How much is actually needed? Is maximum safe?
The best groups were at 28.5 grains of H322 with 110 Pro Hunter

6.8 AR platform
Please explain what you are talking about in what I have bolded in your post. Are you talking about how far the bullets are seated in the neck of the case? You are using the words "expansion" and "shrunk" and I don't believe anyone reading your post has any idea what you're talking about the way you have stated things and why you have had no repsonses.
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Old 03-21-2015, 07:47 AM
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I'll agree, Topgun. I've read this post several times over the last few days, but I have no idea what is happening.

When you say you "want to check expansion of the round," I think about BULLET expansion, meaning shooting bullets into gelatin or at least into water. I suppose if a guy mic'd the base of the recovered slug, it could be a bit smaller diameter than the raw bullet before reloading - but that's not what was said on the page.

Alternatively, since you've said "magazine to chamber," my mind assumes that you're talking about bullet set back, meaning you need to check your feeding, as an AR shouldn't set back your bullets if properly built.

Little more detail on what is happening would be helpful!

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Old 03-21-2015, 09:55 AM
  #4  
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Originally Posted by JGFLHunter
So I went to the range and shot some reloads. I wanted to check expansion of round but instead of expanding most of the bullets actually shrunk? I did crimp them But barely. What the heck is going on, I've never experienced this. The groups were ok.
I did some testing and non crimp bullets from magazine to chamber can add .010 to OAL. With the instructions from the crimp die it added .002 to OAL. I believe that's maximum crimp. How much is actually needed? Is maximum safe?
The best groups were at 28.5 grains of H322 with 110 Pro Hunter

6.8 AR platform
I see how it confused everyone. I meant after shooting a cartridge the case usually expands correct? I wanted to see the case expansion after firing my reloads. I shot 36 rounds. I had 12 cases that were the same or longer. The rest were actually shorter then the trim length after firing the ammo, I don't think that's common? This was crimped ammo, but very very light.

I did testing with crimp and non crimp rounds in my AR 6.8 to see how much the overall length varied(from magazine to chamber). With the FCD instuctions, the rounds still moved to add .002-.003 to total length( I belive that was maximum). Non crimped ammo added .007-.010 to overall length. How do I know how much crimp is needed and still to be used efficiently? Should crimp ammo stay the same length when it is getting feed from magazine to chamber or will it move slightly line in my testing? Any good videos on YouTube, I haven't found one yet about crimping And how to do it properly? Hopefully that cleared it up. Thanks.
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Old 03-21-2015, 12:26 PM
  #5  
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I'm sorry, but I'm just not understanding a thing that you're trying to explain the way you're wording stuff. First you talk about the case lengths varying. Were they all trimmed to the same length before they were reloaded and then fired to come up with what you stated and are now asking? Then you start talking about rounds moving in total length so I have to assume that you are talking the bullets are in or out of the cases at different depths to make a change in the OAL between them. I have three calibers that I reload for in bolt action guns and I don't crimp anything, so I can't offer anything on that process itself. However, if you're trying to say that when you feed the rounds into the chamber and then extract them without firing them and they are then different OALs it would sound like the bullets have to be too loose and are moving within the cases either during the loading or the OAL is too lengthy and are moving back into the case from being jammed into the lands. Maybe NM448 will understand what you have stated because he's a guru on here and would be the one to help along with RR if he sees this thread.

Last edited by Topgun 3006; 03-21-2015 at 12:29 PM.
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Old 03-21-2015, 02:41 PM
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So... I'll take a shot...

Correct me if I'm wrong - it SOUNDS LIKE you are measuring your cases after trimming, then again after firing. Is that correct?

Are you trimming then sizing, or sizing before trimming? If you're sizing AFTER trimming, then not all cases will be the same resultant length before firing.

To be honest, I'd really say that this is largely irrelevant. I'm a numbers guy if there ever was one, and I really can't say that I'd put any value in measuring my cases after firing, other than to confirm my chamber dimensions to know how far I need to bump the shoulder and prevent over-working or stretching at the shoulder. I suppose if you're bumping your shoulder too much, as the case obturates, it either has to draw the case neck shorter as it fills the shoulder, or it has to thin the wall at the shoulder.

It also sounds like you're measuring COAL, then chambering and NOT firing rounds, and experiencing either bullets getting pulled, or getting set back. Set back is pretty common in AR's, but also pretty simple to fix. I'd be surprised if they're getting pulled, since the 6.8 SPC mag length COAL really shouldn't let you get into the lands to pull the bullets at all. Bullet set-back is a big issue.

For factory chambers that don't have tight throats, I generally figure around 3-4 thou for neck tension. So bullet diameter plus twice the neck thickness, minus 3 or 4 thou.
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Old 03-21-2015, 05:49 PM
  #7  
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Ok I'll try to explain better in different way in different sections.
All cases were trimmed the same length and made to same overall length
example - trimmed to 1.672" total length - 2.260"

1. Whenever you shoot ammo, shouldn't the case expand and become longer then previously before firing? But to answer your question, after firing my ammo I wanted to see if the cases were longer in length. Most cases were actually shorter than what they were before being shot. I hope that's clear. Are cases supposed to be shorter after they have been shot? So like in example, the case length before was 1.672" and after being fired was 1.670". Shouldn't the case be longer?
Different subject
2. I was testing crimp and non crimp bullets from magazine to chamber, without firing to see what actually happens to the total overall length of the ammo. I found that without a crimp on the ammo, in my AR, the total overall length increases between .007-.010". So like example the 2.260" would actually end up being 2.267" etc.
The ammo that had a crimp using the FCD instructions (maximum crimp I believe) the total overall length of ammo was .002" longer. Are there any good videos to actually see how to crimp and how to do it properly? Is that heavy a crimp safe to use?
3. The bullets do not get set back but actually are being pushed forward (even with heavy crimp as stated above) Is that a huge deal in terms of accuracy and performance in general?
Different subject
4. How do I set the die to the deminsions from a fired cartridge? I did measure inside the mouth(fired cartridge) and after running through the FL die to compare the to, the mouth or neck (where you seat bullet) was actually smaller (.007") than the fired case.

I really hope this makes sense, I'm trying to explain it best I can. Thanks for the patience

Last edited by JGFLHunter; 03-21-2015 at 05:53 PM.
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Old 03-21-2015, 06:43 PM
  #8  
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Flying at 30,000ft here, it sounds like you need to look at your die set up.

It sounds like your full-length sizing die is set too deep, and your bullet seating die and FCD are not set deep enough. Sounds like you might be bumping the shoulder too far and expanding the neck too much, and not putting enough taper crimp back on the neck.

The die set-up instructions provided with dies tend to give good ballpark case dimensions that will be functional and safe, but not necessarily ideal dimensions to match up to pure SAAMI specs, let alone with your individual firearm's chamber.

Originally Posted by JGFLHunter
1. Whenever you shoot ammo, shouldn't the case expand and become longer then previously before firing? But to answer your question, after firing my ammo I wanted to see if the cases were longer in length. Most cases were actually shorter than what they were before being shot. I hope that's clear. Are cases supposed to be shorter after they have been shot? So like in example, the case length before was 1.672" and after being fired was 1.670". Shouldn't the case be longer?
Not necessarily. The case expands like a balloon due to the internal pressure, however, that doesn't necessarily mean it will 'extrude' more length into the neck, lengthening the case, especially after just one firing.

Alternatively, if your case shoulder is a bumped back too short for your chamber (i.e. your FL resizing die is bumping too much), when the shoulder fire-forms to the chamber, it will have to "suck" brass out of the neck, shortening your case. That might be what's happening for you.

Originally Posted by JGFLHunter
2. I was testing crimp and non crimp bullets from magazine to chamber, without firing to see what actually happens to the total overall length of the ammo. I found that without a crimp on the ammo, in my AR, the total overall length increases between .007-.010". So like example the 2.260" would actually end up being 2.267" etc.
The ammo that had a crimp using the FCD instructions (maximum crimp I believe) the total overall length of ammo was .002" longer. Are there any good videos to actually see how to crimp and how to do it properly? Is that heavy a crimp safe to use?
It's not surprising that you're getting less "crimp jump" for the rounds ran through the FCD - you don't have enough neck tension, nor enough crimp, but the FCD is adding grip that the taper crimped rounds didn't have, so they slip less. I think of the "grip" that the neck has on the bullet like this - neck tension holds onto the bullet at the shoulder/neck junction, then crimp holds the bullet at the case mouth. This could easily go hand in hand with your die being set up too deep - if your FL sizing die is set too deep, the decapping pin and expander will run too deep and open your necks too much, killing your neck tension (base of the bullet isn't held tightly). Then if your seating die is set too shallow, it won't replace enough taper crimp to properly hold the bullet. Equally, if the FCD isn't seated deep enough, it also will not add enough crimp to make up for the lack of tension.

Is it easy to set the bullets into the case before seating? How far does the bullet tail slide freely into the case by hand?

As I mentioned before - I start out setting my neck tension by measuring the diameter of the bullet and the thickness of the case neck, bullet dia + 2 x neck thickness - 0.004 = neck diameter of loaded round. (0.003 to 0.004). That generally holds just fine.

You shouldn't need the FCD to hold 6.8 bullets in place, a taper crimp in your seating die should treat you just fine. The FCD is simply a "feel good" extra measure. You do not have enough crimp or neck tension right now.

Originally Posted by JGFLHunter
3. The bullets do not get set back but actually are being pushed forward (even with heavy crimp as stated above) Is that a huge deal in terms of accuracy and performance in general?
The bullets are most likely getting pulled by recoil. You can confirm this by this process: Load a full magazine, shoot all but the last 2 rounds. Drop the magazine (should have ONE round left) and eject the round from the chamber and mic them both. If the one in the mag is longer than when you put it in the mag, then it got pulled by recoil. If the one in the mag is NOT longer, but the one in the chamber is, then it will likely have been pulled by the rifling, so you're seating to jam length, which isn't advisable for AR's, or even really hunting rifles. I HIGHLY doubt that's your problem - more likely that it's the recoil pulling them.

Originally Posted by JGFLHunter
4. How do I set the die to the deminsions from a fired cartridge? I did measure inside the mouth(fired cartridge) and after running through the FL die to compare the to, the mouth or neck (where you seat bullet) was actually smaller (.007") than the fired case.
The case mouth SHOULD shrink when you size it. It had to expand to release the bullet, and the chamber has to be larger than the loaded round to let it fit to feed, so yes, that's normal that the FL die shrank the case mouth.

With a careful hand and eye, you can measure your fired brass to determine the length from the base to the 'corner' where the shoulder meets the tapered body, but that's not a perfect system. There are headspace gauges, precision mic's, and other kits out there that will let you measure your fired cases to help you set your dies appropriately. The idea here is that you want to minimize how much you're working your cases, and minimize how much obturation (stretching) your cases have to do to fill the chamber when fired. Too much of this and you'll get premature case splits at the shoulder. You should be setting your FL sizing die just deep enough to bump the shoulder so the rounds will chamber easily and your bolt with close without resistance. If you run your chambers clean, you can usually get away with a 2-3 thousandths bump, but a good rule of thumb for AR's is 3-5thou.

So with NO other tools, you measure the distance with calipers from the base to the corner of the shoulder and the case body. Twist your sizing die out so it won't touch, and run your ram all the way up. Spin the die back down to make contact, and lock it down. When you cam over the handle, it usually gives a very slight bump. Measure the case again. With a 7/8-14 die (standard), 1/16 of 1 turn is a touch over 4 thou, so you can't turn them much otherwise you'll bump it a LONG way.

You can use the depth spindle on your caliper/mic to determine how far to turn the die to gain your desired bump. I've done this in the past, add a washer or a quarter on top of the shell holder to let you press the die up against the press as if it were sizing a case as you measure.

A good investment is an RCBS precision mic, or at least a hornady headspace gauge. This will give you very repeatable results and eliminate the guess work in the measurement method I described above. You'll be able to VERY precisely set your dies to your desired shoulder bump.

So again, I'd start looking at your once fired brass and your die set up on your press and make sure everything is ticked and tied appropriately.
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Old 03-22-2015, 03:50 PM
  #9  
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OK I will check that out and see what happens. When I did those reloads, seating the bullet was not difficult. I used the recommendation in my reloading manual. But with brass being short maybe I should seat deeper?

I did a trim length like the example 1.672
overall length of the round was 2.260

I'm not sure how long the Sierra PH 110s are, maybe that will help also
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Old 03-28-2015, 08:35 AM
  #10  
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How much bearing surface do you have when seated? A good rule of thumb is to have 1 bullet diameter in the case - so 0.277" for your 6.8spc. Boat-tails and secant ogives can bump that around one way or another, but that's a good starting point.

Book numbers don't matter much. Mag length, bullet jump, and neck bearing length is what matters.
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