Reloading: I don't want you to get all excited yet...interesting update POST 88 - Page 5

Reloading: I don't want you to get all excited yet...interesting update POST 88

This is a discussion on Reloading: I don't want you to get all excited yet...interesting update POST 88 within the General Firearm Discussion forums, part of the Related Topics category; Originally Posted by OldVet Be prepared for what happens when you catch that dragon! ............

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Thread: Reloading: I don't want you to get all excited yet...interesting update POST 88

  1. #61
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    Quote Originally Posted by OldVet View Post
    Be prepared for what happens when you catch that dragon!
    .........
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

  2. #62
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    It's amazing how these 60+ fps spreads gnaw at me! As much as anything, it perplexes me that I/we can't figure out what causes this.

    I've been looking at my data and sometimes it's just that one aberrant bullet that's either much faster or slower than the others. But the real brain strainer are the ones where I get a aberrant high AND an aberrant low velocity in one group. Here's an example taken from yesterday's velocity data.



    Notice the spread is essentially two low and two high. Where do those come from!

    It's not the bullet - there's nowhere near enough bullet variation in weight or shape to cause a 65 fps spread

    It's likely not the Federal GM205M match grade primers, surely match grade primers aren't that bad.

    It's not the powder charge, even straight out of the +/-0.1 gr dispenser, that's not anywhere near what it would take to cause the random high spread I'm seeing

    And, it would be very hard to believe there is such a difference in powder burn rate from one dispensed powder charge to the next to make such a spread.

    It's not bullet seating depth - they're all measured and set to within +/-0.001". Even if they were off 4 times that it wouldn't cause a 65 fps variation

    It's not neck tension. According to QuickLoad widely varying neck tensions won't cause these kinds of velocity spreads.

    So what is it??? An occasional accumulative build up of variations???

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  3. #63
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    Tangle, bmcgilvray and airslot like this.
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  5. #64
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    Quote Originally Posted by OldVet View Post
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    Man, ain't that the truth!

    I did a shoot today, same charges, but Sierra 77 TMKs (Tipped Match Kings) and got a spread of 70 fps on one group; the other were decent to good, one was real good.

    I can buy premium factory ammo that's produced by the millions that don't have spreads anywhere near 70 fps. And I'm pretty sure they don't sort cases by weight or measure the seating depth of every bullet; not sure if they even measure powder as closely as I do.

    What am I doing or not doing that generates these random high spreads?

    How do I test for something to identify the problem???
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
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  6. #65
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    How much jump do you have, ogive to lands? I'm guessing you're seating out far enough that you may not have much. If so, you might try seating deep enough to give 0.020" to see what happens.
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  7. #66
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    I'll give it a try. I've been seating to mag length, 2.260". I can probably go to 2.250". I'll measure the chamber and see what kind of room I have. It's a Wylde chamber,
    We don't have a gun problem in the US, We have a people problem.
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  8. #67
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    The more I think about this, the less it seems likely to be a bullet issue, a powder or powder charge issue, primer inconsistencies, I mean we're talking about what seems to be random, sporadic, velocity variations - I've seen them as high 108 fps.

    This week, in all my shoots, I've used an adaptor in a magazine that lets the cartridge just lay in the receiver. I lower the bolt slowly with the charging handle through 2/3s of it's travel before I release it. The purpose is to avoid the nose of the bullet contacting the loading ramps and to prevent a bullet pulling inertia effect when the cartridge stops suddenly in the chamber.

    That should eliminate bullet movement and tip distortion. So what else would cause up to a 108 fps change in velocity???

    A thought about the sizing die came up; I cleaned it and the neck sizing bushing and then got the 70 fps variation today after the cleaning. Case lengths vary from 1.750" to 1.755". and I always crimp for an AR. Hmmm....

    Tomorrow I'm going to run the same components and charges without the crimping. I suppose it is possible that there is a difference in tension on a shorter case and a longer one. Pretty much shooting at anything that moves at this point.

    I have checked runout, it's not bad at all.
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  9. #68
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    Id stop crimping. I must have missed this in your previous posts. I never crimp for my AR.

    Its close to impossible to measure neck tension so Id venture a guess is your crimp pressure may not be consistent (but theres not really a way to prove it beyond measuring the OD of the neck after bullet is loaded). Brass holding onto the bullet inconsistently will mess with velocity.
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  10. #69
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    No crimp would be a good check. If you're not trimming every time around, you're probably not getting uniform crimps.
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  11. #70
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    I'll go without the crimp today on a full set.

    I have been checking the length of every case I load, I trim any that are too long and ditch any that are too short. All cases the fall within 1.750" to 1.755".

    Honestly, I don't think the problem is due to case length or the crimp, but we have to do something and that's as good as anything I can think of.

    Of course when you don't crimp you're at the mercy of the neck tension itself which can vary due to wall thickness, neck thickness uniformity, and nature of the brass itself, i.e. soft, brittle, whatever.

    But, you guys do have me thinking about some things - maybe we're on to something here...

    According to QuickLoad, neck tension could be a viable suspect. Of course QL is theoretical but it has proven to be pretty reliable and usefully accurate. I tested the effect of neck tension this by changing what QL labels Shot Start (initiation) Pressure. That's probably not quite the same as crimp pressure, but it should be close. The default value is 3626 psi and with 24.2 gr of A2520 the predicted velocity is 2678 fps. If I double the Shot Start Pressure to 7252 psi, the velocity changes to 2728 fps. That's a change in velocity of 58 fps.

    To me, it seems reasonable that neck tension can and does vary. Of course we have no way to know if it could double, but if one case had a slightly thinner wall, and was a little more supple, and another case had a slightly thicker wall and was stiffer maybe the doubled neck tension would be reasonable. Even if it doesn't double, lesser variations coupled with other issues could have an adding/subtracting effect and generate wide variances. Sounds good anyway!

    Also, remember I refer to my reloading very similar to my PRSB? Well there is one thing he does do that I don't - he anneals his brass. As a matter of fact, I talked to another reloader, precision I presume, and he anneals every time he reloads. His reason was to restore neck tension. I don't know that every time is necessary, still the thought that he believes neck tension is critical to precision...

    Another thing that makes neck tension suspect is the random nature of the spreads. Notice in the table above, the spreads greater than 50 fps are all over the place. And they are unpredictable, i.e. random in nature. I would think varying neck properties would show up as random, i.e. there is certainly no reason to believe the neck tensions would be in a predictable order.

    It's certainly worth trying without the crimp. I'll do everything else the same.

    Here's a table of extreme spreads generated by 10 sets of 5x5 all loaded the same way but with different cases. Cases were new Lapua (3 sets), Lapua reloads (1 set) new Hornady (2 sets), Sig reloads (1 set), the rest Hornady reloads (3 sets). The same 77 gr SMKs were used in all but the last set and those were 77 gr TMKs - I ran out of SMKs.

    The table looks funny because I used a hotter load in the very first set and felt like the highest load was a little too hot so I back subsequent sets down by 0.2 gr. The charge increments are 0.4 gr and that makes that first set fit right between the charges of subsequent sets, hence the funny look.

    I had Excel highlight any ES that was greater than 49, or said another way, any SD of 50 or more is highlighted in red.

    There were 52 sets in all, two sets were 5x6 instead of 5x5 and they are the "2" of 52. I had Excel calculate the percentage of sets that had an ES of 50 or higher - 38.5%! I didn't realize it was that much!

    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

  12. #71
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    'Scuse the interruption - had to go eat breakfast.

    I think we've got this!!!

    Consider neck tension variations coupled with case volume variations. We've just seen (my previous post), that doubling neck tension can cause a 58 fps change in velocity. I will now change the case volume and see what happens.

    I have weighed cases previously and for 100 Hornady cases, the weight varied from 89.7 to 99.1, that's 9.4 grains, or a percentage variation of 10.4%. While I think that's awful, I have seen Lapua cases vary by similar amounts. So based on 10% weight variation, I'll change the case capacity by 10% and see how that affects velocity.

    case vol.......vel
    30.0 gr.....2738 fps

    and 10% more volume
    33.0 gr......2605 fps

    That's a change in velocity of 133 fps. The highest velocity variation I've seen with my reloads is 108 fps.

    So now let's combine the neck tension and case volume and see what possibilities we get. I'll let the neck tension vary by 50% instead of doubling and a case volume change of 1 gr instead of 10%. That's about a 3% change in case volume. We could have velocity variations as shown in the table below - and everything in between!



    I believe we've solved the mystery! Notice the ES of 78 fps and minimal changes of 22 fps. So the best I could hope for given these variations is 22 fps and the worst is 78 fps. Of course there could easily be lesser variations of both parameters that would give even lower ESs, and I have seen them,

    This also accounts for the randomness I see in velocity variations.

    Thanks to the inspiration and thoughts from you guys, I believe we've found the answer - the answer - not the solution.
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

  13. #72
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    A 50% change in neck tension seemed a bit high to me, and 1 gr change in case volume seemed a bit small. So I changed the neck tension to a 20% change and the case volume to a 2 gr change. Here's the numbers:



    Notice again, this accounts for the randomness and the max spread is 109 fps, remember me saying I had seen velocity variation as high as 108 fps? The low has also changed to 11 fps.

    If we look at the entries in the table where one parameter changes and the other doesn't, for example row 1 and 2, we see there's a 98 fps change due to case volume change alone.

    If we look at rows 1 and 3 where the case volume remains the same but the neck tension changes by 20%, we only get a change of 11 fps.

    So a case volume change of 6.7% generates a velocity change of 3.7%. OTOH, a neck tension change of 20% only causes a velocity change of 0.4% (less than 1%).

    I'm not sure any of this will hold up in court, but unless you've got a better idea that explains the velocity variation and randomness, this is my story and I'm stickin' to it!
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

  14. #73
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    That sounds like a story worth sticking too.

    No need for golf now.
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  15. #74
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    Quote Originally Posted by Rock and Glock View Post
    That sounds like a story worth sticking too.

    No need for golf now.
    Yeah, you can keep those clubs I was asking about.

    Although, I think, as in "think", we've identified the problem, there's not a whole lot that can be done to correct it Hmmm, don't get rid of those golf clubs.
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

  16. #75
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    And, FWIW, if anything....

    Here's the sensitivity of velocity to neck tension,



    and the sensitivity to case volume,



    And, keep in mind, all this is calculated using QuickLoad.
    We don't have a gun problem in the US, We have a people problem.
    The problem we have is people that want to kill large numbers innocent people
    in Gun Free Zones.

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