Experiment coming up

Discussion in 'General Reloading' started by DaTeacha, Aug 18, 2010.

  1. DaTeacha

    DaTeacha Things are not what they seem. Forum Contributor

    Okay, with the various opinions expressed in the thread about weight sorting, I think I have the grounds for a small experiment.

    Please let me know if you think this will give some insight. Aside from the small sample size, I don't see anything obviously wrong with it.

    I will use 60 rounds, divided into 3 groups of 20. All 60 will use Remington number 6 1/2 primers. All will use Varget for the powder, trickled and not thrown to make the exact same amount of powder in each case. All will use the 69 grain Sierra Matchking .223 bullet.

    The three groups of 20 cases each will all be the same PMC headstamp. I sorted out the ones with the large headstamp from the small, and these are all small.

    One group will be unsorted.

    The second group will be brass that weighed in at 93.2 grains +/- 0.1 grain.

    The third group will the be the brass that was on the two extremes of my recent sorting of 212 cases. There were just 3 cases that fill into the 91.8 range, 7 in the 92.0 range, 11 at 93.6, and 5 at 93.8. I'll use 10 from the light groups and 10 from the heavy groups mixed together. Of the remaining cases the biggest group was 93.2 grains, with 44 cases, so that was chosen for the second group mentioned above.

    All the cases were run through the same sizing die, all were swaged to get rid of the crimp if needed, all were trimmed, chamfered, deburred, and had the primer pockets cleaned with the same tool. I'd like to claim they were all once fired but that is not the case. Some are, some aren't, and there is likely a mix in each experimental group.

    I will put 20 rounds into each of 3 identical targets from 100 yards. The rounds will be loaded into a 20 round mag 5 at a time. I will shoot 5 from one group, then 5 from the next, and so on in rotation until all 60 rounds are fired. Any buildup of fouling or heating of the gun and so on will be distributed over all three groups. I'll take my time and use a solid front and rear rest for all shooting.

    Again, the sample size could be larger, but I hope this will give some idea if weight grouping is worth the trouble. What do you think of the protocol?
     
  2. ChaZam

    ChaZam G&G Evangelist Forum Contributor

    Its your class Teach. Sounds like it should be an enjoyable little experiment for you and provide us with some pertinent information.
     

  3. lefty o

    lefty o G&G Evangelist

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    i think your going to need a purpose built BR rifle with a proven ability of shooting tiny groups to prove if it helps or not. IMO weight sorted cases may make a .1 or .2 tenths of an inch difference at 100yds, and unless you have a rifle that will leterally put 'em in one hole i dont think you'll get anything meaningful out of your experiment. i also think you would need all once fired or all new cases with all being from the same lot.
     
  4. gandog56

    gandog56 G&G Evangelist

    I'm a hoping there is a big difference in accuracy or there's gonna be a few sad faces around here.
     
  5. 338RUM

    338RUM G&G Evangelist

    hey Teach! I hope you trimmed, de-burred, swaged, and overall case prep BEFORE you weighed them, if not your experiment will be null and void. Also I have to agree with Lefty O on this one, if your gun can't hold 1/4 inch at 100 yards you will not see the difference between the 3 groups. I also have one last question, How are you going to take the human wobble factor out of your rifle? These are just some things to consider I am in no way trying to be disrespectful, just doing some educated guessing.
     
  6. Can't wait to hear the results. I am going to start loading for a .223 bolt gun this fall.
     
  7. gandog56

    gandog56 G&G Evangelist

    Now if my .223 was a bolt instead of a semi, I might care more about careful weighing and stuff.
     
  8. I think it is a well-designed experiment. The comment by 338RUM is, obviously, critical. All the other's are best left to the interpretation phase of the test. If the results clearly show a difference in group size, you have your answer. However, if you don't get a statistically significant difference in the groups, you won't know for sure that weighing cases is not helpful -- just that for you and your rifle and for that load...it wasn't helpful.
     
  9. 338RUM

    338RUM G&G Evangelist

    How is it that asking questions is considered "critical" I have tried the same experiment he is doing now with EVERY rifle I own from my 223 WSSM up to my 416 Rigby and have yet to get ANY difference, I am sorry for trying this before and it not working. The only difference that will be found is in custom built bench guns capable of placing 5 shots in the same hole and then there is not much improvement but it is enough to lose a match, the experiment will also be kinda bumped if he is using a FL sizer die as BEST accuracy comes from neck sizing only a portion of the neck with a bushing sizing die, also if the rifle is a average production gun the chamber will not have been cut as perfect as it should have been and will be out of round resulting in a loss of accuracy. And if the action has not been trued and blueprinted there is another point of accuracy loss, and lets not get into bedding and if the crown is cut right.... This experiment is good practice for the real deal, and is like saying the reason the reason a engine broke down was because the heads were not ported and polished...

    Oh BTW NOW I am being critical
     
  10. samuel

    samuel G&G Newbie

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    You should call it off immediately for fear of making someones face sad. (the only reason my face would be sad is because you are doing it instead of me.) ,,, sam.
     
  11. Are you going to let the barrel cool down after each volly of shot's and do you have one of the hand held dilly whops to tell you the speed of a breeze or wind ? I would set up flag's to try to keep all things equal between groups.

    I wish you success and that you discover something note worthy. Sounds like a fun thing to do...A.H
     
  12. DaTeacha

    DaTeacha Things are not what they seem. Forum Contributor

    Okay, here are some more details:

    The rifle is my "woody" AR, built on a DPMS lower. The trigger is an RRA National Match item which breaks cleanly at about 4.5 pounds after some initial take-up. The 16" barrel is .750" diameter from end to end. It has a 1 in 7 twist and is threaded. The gas block, which I think acts as somewhat of a harmonic element on any AR, is an aluminum low rise style with an abbreviated rail on top. It is secured to the barrel with set screws, not cross screws.There is an A2 style flash hider over a crush washer on the muzzle.

    The only identifying mark on the upper is a small raised symbol that resembles either a keyhole or a chess pawn. It is located above the point where the forward assist joins the rest of the receiver. I you know what brand this is, I would appreciate knowing.

    I have a YHM free float tube covered with an octagonal elm wood sheath for looks. There is a front cap in the tube. There are 7" rails on the upper left and upper right flats of the wood, 45 degrees from the line of the bore, not that it matters since things are free floated. What does matter is that the bottom flat of the octagon (which has no rail in this particular configuration) will ride neatly and easily in the small sandbag on my Outers front rest, much in the manner of a serious bench rest rifle with it's wide, flat fore-end. I will use a matching Outers rear leather sandbag equipped with "ears" for the buttstock. There is no sling swivel on the rifle to snag or rub on the bags.

    I built the entire gun from parts, mostly from SOG, Brownell's, and Midway. I torqued the barrel to 46 pounds feet of torque using a Craftsman click style torque wrench, bringing it up in increments and backing off as Kuleck recommends in his book. I went to 46 pounds feet to align the gas tube holes.

    The gun has a fairly tight chamber, refusing to close on my Forster "NOGO" gauge that is marked 1.4666 inches while closing nicely on the "GO" marked 1.4636. When I resize the cases, there is little effort with the ones from my gun, compared to a lot from some range brass I have loaded, leading me to believe I have a tight chamber. I have not measured the leade, but working with the Hornady 80 grain A-Max bullet and trying to find a maximum length that does not touch the lands gave me a maximum working length with that bullet of 2.525 inches. I marked the bullet with magic marker and looked for marks from the lands. There are no marks on the marker ink when that bullet is seated to that depth and the bolt is allowed to slam home on the dummy round. The A-Max has a very long secant ogive and this length obviously will not work through the magazine of the AR, but this might give you some idea of the leade in my barrel/chamber.

    The BCG came from SOG. I have replaced the original gas rings with a single piece McFarland ring. The bolt is lubed with Break Free LP. I have one of those little widgets that reduce the play between the upper and lower installed. I will use the same magazine for all shooting. There is an 'ergo' style pistol grip.

    The scope is a cheapy I got at a show. It's marked B-Square, acquired NIB. The box says it was supposed to include rings, but the rings got left out, so I got the scope for $40, brand new. It's 9.5 inches long and fairly light compared to the Pentax it replaced. It has an adjustable objective set for zero parallax at 100 yards. I will use it at 9X.

    The targets are a thick black ring around a "white" center, printed on heavy yellow paper. The open center of the targets measures 1 3/4" in diameter, large enough to allow me to see the "white" in all four quadrants around the crosshairs. In addition, I have superimposed a set of vertical and horizontal lines measuring 3/32" wide on the target paper. These are visible through my scope. I will use a level when hanging the paper to make sure these lines are plumb and level. When looking at the target, by aligning these marks parallel to the crosshairs I am sure I am not canting the rifle. If in fact I am canting because my scope is slightly tilted in it's rings, it will be the same every time and will be factored out.

    I realize I can't rule the human factor, my bad eyes, and a couple of other things, but I hope to find out if a set of cases that I know exhibit a wide variation in weight (2 grains, about 2%) will give different results than a set that has a minimal (.2 grains, about .2%) variation. The unsorted set is going to act as a control, representing a normal mix of brass.

    The probable makeup of that normal mix can be ascertained by looking at the distribution of weights in the sample population. The sample from which the cases to be used were chosen consisted of 212 PMC cases, all with the small headstamp. Some are once fired, some twice fired, some with an unknown number of firings behind them. There was no effort to sort them based on number of firings.

    The flash holes have not been uniformed. All have been deprimed and resized on the same press with the same die at the same setting. The die was not removed from the press during the deprime/resize operation. All have had the primer pockets swaged, were trimmed to the same length with a Forster Classic trimmer with a .223 pilot, were chamfered and deburred with an RCBS tool, and had their primer pockets cleaned, also with an RCBS tool.

    During the trimming operation, I did notice an apparent difference in neck thickness evidenced by differences in the amount of effort needed to put the trimmer pilot into the case neck. The cases did not have the necks inside or outside reamed, nor was neck thickness measured. This could mean a difference in effort to remove the bullet from the case and thus could affect overall pressure, possibly producing pressure spikes early in the combustion process of those cases with thicker necks and adversely affecting case to case repeatability.

    They were weighed after treating on an Ohaus 505 beam balance. I placed a case on the pan, and moved the poise(s) until the pointer was within +/- 2 graduations of the zero mark on the scale. If a case was close the +/- 2 graduations, the poise was moved to the next setting to see if it was a better fit. The poise settings were arbitrarily chosen in .2 grain increments. I feel the cases were weighed to within +/- .1 grain of the nomimal weight of their group.

    I graphed the distribution of the case weights and found a basic normal curve that is skewed to the heavier case weight. With a maximum of 93.8 and a minimum 91.8, the median weight of the sample is 92.8 grains. That interval had 27 cases. Going down in weight from there, I found 23, 20, and 20, then a drop in population size to 7 and 3, which groups were include in my extreme weight dispersion experimental set. Going up in weight from the median, I found 39, 44, then 23 cases, followed by a drop to 11 and 5. I dumped the last two sets together and picked 10 to go with the light cases. I chose the modal group of 44 cases at 93.2 grains to represent sorted cases, operating on the baseless presumption that there would likely be less sub-incremental variation within that group than the others. I picked the 20 cases from this group at random.

    The range is in a ravine at my club. Wind is essentially removed from the equation since the ravine is approximately 40 or 50 feet deep and 50 yards wide at the location of the range. The ravine is located in about 135 acres of mature deciduous forest with most trees in the 100 foot or taller size. I will be shooting from the east to the west, about 20 degrees south of due west, just in case someone wants to be concerned about Coriolis Force. Shooting will be from a heavy bench located under a roof. There will be no sun glare on the scope, and the target butts are in the shade also. I will do my personal best to press the gun to my shoulder with the same amount of force for each shot, but will have no way to measure the pressure other than the somewhat unscientific "how it feels".

    By shooting in 5 shot samples and rotating from one set to another, I hope to minimize any effect of dirt in the barrel, gun temperature, shooter eye fatigue and so on. I will fire a couple of fouling shots before starting the experiment to eliminate the possibility that the first shot from a cold, clean barrel might behave differently than those that follow.

    Past experience with this gun and similar loads has shown minimal accumulation of dirt in the barrel, chamber, or BCG from firing approximately 100 rounds in a session. An impromptu session with my 2 sons-in-law and myself each dumping a 30 round magazine of factory loads through the gun quickly on the 4th of July followed by some more shooting did not leave the gun very dirty, so I don't think dirt will be a factor.

    Following each group of 5, I will pick up the brass and return it to the proper box, then load the magazine with 5 from the next box. The action will be open during this time to allow the barrel to cool from air circulation. I will not time the intervals between 5 shot sets, nor will I time the act of shooting each set. I will not take the temperature of the barrel to make sure it is the same for each set.

    By doing this bit of experimentation, I hope to provide some evidence to help reloaders decide whether or not to invest the time and effort in sorting cases by weight when preparing for precision shooting activities with a semi-automatic non target grade rifle. If the theory that weight sorting increases precision is true, the set of 20 weight matched cases should give the smallest group size and that with the intentionally mismatched cases should give the largest. If it is not true, there should be no discernable difference in group size among the three targets.

    Again, I realize a sample of 20 cases in each category is far from definitive. I realize the human fatigue factor (eyes in particular) and simple shooter ability will inevitably be part of the results. I realize the fact that I will know which set I am shooting from may subconsciously affect how hard I try with each group, but I will certainly do my best to eliminate that factor.

    Above all, I hope my results, whatever they may be, don't turn this thread into a heated argument. I am open to criticism, and I hope the rest of you are too, in the name of improving our shooting and loading skills and habits.

    If this shows there is a useful increase in precision to be gained from weight grouping cases, you are free to do so or not after deciding if the improvement is worth the time and effort. If it shows there isn't a useful increase and you think that's because I was using a field grade gun, please repeat the exercise with a target grade bolt gun and let us know how it turns out.

    I'm just trying to get my self built gun to shoot as well as I can in the hopes that any groundhog I can see can be killed with one precisely placed shot.
     
    Last edited: Aug 19, 2010

  13. OMG! You misunderstood! I meant critical as in significant, decisive, vital, important, essential, crucial, key!
    I can see why, if you interpreted my comment to mean that you were just being picky, you were offended. I assure you, that was not my meaning. In fact, I was pointing out that your comment was, in my opinion, the "key" observation!
     
  14. samuel

    samuel G&G Newbie

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    COMON!Lets quit writing and get to shooting and then write and tell me how you did!!! ,,,sam.
     
  15. lefty o

    lefty o G&G Evangelist

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    how does the rifle shoot normally/ i dont honestly think you have a rifle capable of performing this test. secondly you havent deburred flashholes, thats a bigger variable than weighing cases which is goign to nullify anything your experiment discovers. go shoot and have fun.
     
  16. FortyXDM

    FortyXDM G&G Evangelist Staff Member

    A couple of things. I am posting as this was from experience in doing a very similar project.
    First. You are including several variables that could be eliminated... (once fired brass, de-burring, etc.) You are clearly on the right track, but need to make 'everything' as uniform as possible. As to needing a bench rifle......perhaps not so much as at first glance. Reason - You are trying to find out what you can do with YOUR rifle.
    I would approach the same way, except.......After determining what seems to be the best powder weight of varget...I would work on bullet seating depth. Not as hard to do as some think. Start at nearly touching (ogive to lands) Ogive is pronounced OH Jive. And work back in increments of 5 to 7 thousandths. You SHOULD see the groups shrink as you hit the sweet spot, then begin to open up again. Once you find that seating depth, then begin your test as mentioned in your first post. Be sure to de burr all the brass and it should be once fired and neck sized only, trimmed and deburred....then weighed back in.

    Tom
     
  17. DaTeacha

    DaTeacha Things are not what they seem. Forum Contributor

    Man, you guys sure want me to do a lot of work! Lefty, have you tested to see about the flash hole uniformity? I mean it makes sense, but how much variation is there in the factory product?

    Forty, I have the bullets seated to the maximum length that fits in my magazine. For practical purposes, anything longer kind of negates the whole point of the AR. I think from what I found out with the 80 grain A-Max bullets that I have a pretty long leade.

    If I get into messing with seating depth, it will be to shorten the round from where it is now, pushing the bullet deeper into the powder. At this depth, the point where the boattail ends is just about even with the base of the neck.

    Okay, I have to go before I find I've been here an hour. :)
     
  18. 338RUM

    338RUM G&G Evangelist

    I apologize for snapping on you, it was a long day at work and the "tone" seemed negative, once again I am sorry Pilgrim and will try to refrain from doing that again. I did not take into account that there is more than one definition of a word and hope you can forgive me...

    Joshua

    And Teach,
    I think your experiment is going good and you are on your way to having lots of fun if anything! I hope it turns out for you and you find results!
     
  19. 338RUM, let's just chalk it up to the limitations of typed media, where facial expression and other forms of non-verbal communication are lacking, and misinterpretations are possible. No offense intended, nor taken.
     
  20. samuel

    samuel G&G Newbie

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    ^^ Darn,now I am dissapointed! ,,,sam.