Testing the Testing

Get or give advice on equipment, reloading and other technical issues.

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Gyro
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Re: Testing the Testing

#61 Postby Gyro » Wed Apr 22, 2020 7:03 am

I can’t argue with a thing u have written there Peter S. Never did actually on this ‘problem’. I’m with Albert in that there’s a bunch of other things going on that are much more worthy of attention, if only I knew what they were …

Barry Davies
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Re: Testing the Testing

#62 Postby Barry Davies » Wed Apr 22, 2020 10:30 am

All this concern about case capacity variation can be easily checked. ( 308 anyway )
Simply load some Winchester cases and check against either Lapua or ADI cases with the same load specifications.
The difference between these cases is around 1.5 grains powder weight /capacity. Lapua is about 1.5 larger than ADI and Winchester is about 1.5 larger than Lapua.
Trying to measure differences between cases that vary a few tenths of a grain in capacity is rather hit and miss.
Weighing cases is just as hit and miss.

williada
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Re: Testing the Testing

#63 Postby williada » Wed Apr 22, 2020 1:16 pm

The rifle will tell you what it likes to eat. Fresh cases seem to shoot well at times if they are weight sorted but it depends on the luck of the draw with your chamber and general setup. It is not always the case. The new cases can be .005" or a tad more less than minimum head space so what is going on?

The analogy I give is related to issued ammunition of the past. You could use crush head space as we did in Oz with issued ammo; but in testing Blue or Brown box for Bisley, you would be in shitter's ditch because not only did their powder vary, the case specs were shabby at times and unsuitable for small crush. The variable ignition problem was bigger. A solution was to uses a bigger pressure vessel which could absorb the impacts of small variables to obtain more consistent pressures. This might be counter intuitive, but a maximum head space amounted to a bigger pressure vessel, much the same way increasing the seating depth does. Some used combinations of both for issued ammo. That means a small variable has less effect in a big hole. But if you decrease the size of the pressure vessel it raises pressures and little variations have a bigger impact. Playing with head space does have an effect on pressure and has to be understood for safe operation. Bear in mind in those days the .004 max head space for target rifles could be increased again to field head space measurements and was legal and still is under our rules in Oz. Omark rifles in the day enabled the head space to be varied with their interchangeable bolt heads. This could explain why new cases shoot well at times even though they have to stretch so far to reach minimum head space. The chamber has to be suitable too. Firing pin protrusion maybe an issue. Modern, new case base measurement in a suitable chamber may cater for sufficient firing pin protrusion to give consistent ignition. Mind you I would not advocate playing with this except for armorers and would keep within the maximum and minimum head space configuration. Issued ammo was only fired once and further stretching to extreme is problematic for reloads with regards to cases failing near the web. Not a good idea.

The second firing should not be used for testing. The second firing consolidates case dimensions and in the process tightens the junction of the shoulder neck area. This is because metal is used elsewhere to fill the chamber. That has to be expanded out to size with an expander iron then the case can be full length re-sized. Cases are now suitable for the third firing at a critical distance of 140 yards to detect outliers which get piffed. Group size is less important here because that can be adjusted in development suited to a chamber with higher pressures now new cases have been expanded. It is critical thereafter, to keep head space tolerance within .001" for further firings to maintain chamber volume. That's where setting up your dies for each reloading session is important, rather than set and forget because the brass keeps moving with each firing. By culling cases at a critical time and keeping head space under control, the case is always centered in the chamber and volume variation is minimised. It will not develop into a banana case where the top thins and the bottom thickens from sitting loosely at the bottom of the chamber or add to run out problems.

For further firings, and in the day when I could be bothered, I would volume sort with metho/water etc. I would do it once at the third firing. With the primer pocket plugged I would weigh the case empty. Then fill it with water/alcohol and squeeze off the excess by sitting the bottom of a penlight battery on top of the case. Then wipe off excess droplets and then weigh. It was in the ball park seeing I had piffed outliers. If I have any shot that is unexplained in general club shooting, I cull the case.

Any variations are sorted by the tune I desire from the rifle.

ps Take case head space measurement after the third firing.
Last edited by williada on Wed Apr 22, 2020 1:46 pm, edited 1 time in total.

pjifl
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Re: Testing the Testing

#64 Postby pjifl » Wed Apr 22, 2020 1:36 pm

If you are going to use a fluid, then weigh the cases containing the fluid at some stage, it is almost mandatory that you use a removable platform on your scales. It is inevitable that some fluid will spill onto the scale pan or plate so you need to be prepared to clean the plate bone dry quite often without loading the scales. Also to make sure the exterior of the cases is bone dry. I know this is obvious but don't get caught part way through the experiment.


Peter Smith.
Last edited by pjifl on Wed Apr 22, 2020 3:32 pm, edited 1 time in total.

ajvanwyk
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Re: Testing the Testing

#65 Postby ajvanwyk » Wed Apr 22, 2020 1:46 pm

Brad, thank you for the kind words. The west was certainly an experience I will never forget, not only for the competition but even more so the company and friendly environment. One of the toughest ranges by some margin, cant wait to shoot and be tested there again...

Back to the topic, allow me to try and broaden my explanations with some practical examples and observations.

Approximately 12 months ago, I purchased and weight sorted 3,550 RSAUM cases. They were all from the same batch. The cases were weighed on an A&D scale and batched into 0.01 gram lots. I used the third decimal to round up or down. You could argue that sorting in grains would have offered even tighter lots but I took the decision that between the time to sort and the benefits gained (remembering that I still had to do a lot of case prep that would see parts of the brass removed) grams would batch the cases appropriately in my situation. Out of interest, the total spread of the sorted cases was 15.21 - 15.54 g

ccaes.jpg


From this, I sold off the majority of cases in tightly sorted lots and kept about 1,000 cases for myself that was in two lots 15.36g and 15.37gn. As aside, those sorted but unfired cases is what I used in WA.... looking at over 6thou shoulder bump compared to a fireformed case :shock: :shock: but as a well-regarded smith said ... "when you blow 60,000 psi up your Ar$e....you would blow out too.... :lol: :lol: :lol: " SD and ES measurements with a LabRadar showed minimal improvements compared to fireformed cases (New Cases: 15/4.8 FireFormed: 12/3.7) Admittedly this measurement was only a small sample of 2x 15 shot strings to compare. On target the groups were marginally better with fireformed brass, but at 1,000yd this might also have been conditions that influenced that. Although all care was taken to produce perfectly loaded rounds for this test, it does stand to reason that not all variables would have been accounted for. I guess this is the purpose of testing the test.....

So back on topic.... after case prep, (tasks that would have an effect on weight and dimensions, primer pocket and flash hole uniforming, sizing down from 30cal to 7mm, full-length trim, neck turn from 0.017 to 0.014, Chamfer & Debur) I proceeded to fire these new rounds twice. As mentioned earlier, I used the cases in every situation, be it a competition or a weekend shoot. After completing this process (2,000 firings) I decided to clean and sort these cases, ready for the FCWC in South Africa.

Now, this is where the story takes a terrible turn.... My once small lot of sorted brass (to 0.01g) now showed variations as wide as 0.21g #-o #-o so somewhere I have increased the lot size by working the cases.... I had not noticed any poor performance on target and when doing the general ES/SD/V checks were still within spec. So, with that, I proceeded to check internal volume.... It was a task that I had on my list as something to do across all the cases in an attempt to "silence the squirrels"

So, following some internet wisdom with a 90% Isopropyl mix, I proceeded to volume sort/weigh cases. After 150, which took a lifetime and thought me how to curse silently.... I had seen a spread of 0.4gn (0.02g) My next step was to try and test the sorted vs unsorted cases at the next 1,000yd shoot but unfortunately Corona put a hold on that activity. So maybe there will be a follow-up post.....

When I do however consider the effect that case volume might have on velocity, as I mentioned in a previous post, it might actually be accounted for within the natural spread of your loaded ammunition... If 0.5gn variation of case volume produce a 7fps variation in velocity (as calculated with Qucikloads) does that mean that 0.0gn variation reduce your ES by 7fps ? Likely not.... certainly not in my mind.....

I do think though that if you "believe" that one of those tasks that no one else is performing is giving you the edge, it probably is.... if only to silence those voices or squirrels between the ears.....
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Last edited by ajvanwyk on Wed Apr 22, 2020 4:39 pm, edited 1 time in total.
Albert
Rosedale Rifle Club
Australian Points Series

Gyro
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Re: Testing the Testing

#66 Postby Gyro » Wed Apr 22, 2020 2:23 pm

Albert if u take the relative density of the iso solution to be around 0.8 then your case volume variance is nearer 0.3gn ?

Gyro
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Re: Testing the Testing

#67 Postby Gyro » Wed Apr 22, 2020 3:47 pm

Maybe not ? 1/0.8 x .4 = 0.5gn ? Help.

UL1700
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Re: Testing the Testing

#68 Postby UL1700 » Wed Apr 22, 2020 5:02 pm

Yep I think that getting past our own intrinsic biases (yes all 10 of them) when we develop and run our own testing is possibly the biggest hurdle that many of us face. It's almost impossible to double blind yourself which means we have to become very self-aware to get meaningful results. Time and round count helps but it's still too easy to excuse the anomalies. At the end of the day I suspect that saving a couple of FPS of extreme spread is of far less value then "knowing" that you kit will perform at the top level. Will reaming and internally chamfering your flash holes win you your next OPM, I very much doubt it. But will having the confidence that when you get onto the mound all you have to do is worry about is where to point the barrel and when pull the trigger, well I suspect that, that will put you in pretty good stead.

pjifl
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Re: Testing the Testing

#69 Postby pjifl » Wed Apr 22, 2020 5:57 pm

On eliminating bias - has anyone done this very simple but telling experiment.

1/ Deliberately load a dummy cartridge which has no primer and powder. Or use an old primer.

2/ Arrange for another person to insert the cartridges into you chamber while you shoot. This is deliberately done so the shooter cannot see the cartridge in detail.

3/ At some random point introduce the dummy round.

4/ Watch the shooter (maybe yourself) flinch or not.


It can be almost devastating even to an experienced shooter to see how much flinch is present. VERY well worth doing with fairly new shooters but it can also be very interesting with seasoned shooters. It is a different type of bias but very relevant when testing on paper.

Gyro
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Re: Testing the Testing

#70 Postby Gyro » Wed Apr 22, 2020 6:44 pm

Yep been thru the flinch stage and came out the other side. I started flinching about 6 years back and knew I was and knew it was no good for good shooting so I got thru it by saying to myself "hold sqeeze", I think it was as I let each shot go. Didn't take too long and I got rid of it.

Brad Y
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Re: Testing the Testing

#71 Postby Brad Y » Wed Apr 22, 2020 9:23 pm

Try going from a front rest to shooting off a bipod. Flinches are magnified like crazy

UL1700
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Re: Testing the Testing

#72 Postby UL1700 » Wed Apr 22, 2020 9:39 pm

Nothing like a duff primer to suddenly find that you still have a flinch :oops:

Gyro
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Re: Testing the Testing

#73 Postby Gyro » Thu Apr 23, 2020 7:19 am

Anyone tested the effects on the target of runout ? Not me. I’ve always had a fairly cynical view on runout because to me if u have run out ( and how much ? ) then you’re better off looking into why u have it in the first place. Then get rid of the cause. Then go shooting and worry about all the other stuff.

There’s lots of dodgy measuring tools for shooters on sale and one I’ve seen to check for runout did not look like it would give meaningful readings. I believe it was red ?

Re what’s happening at ignition it makes sense to me that a boolit slammed into the rifling “cocked” will not get a good start on its journey.

While I remember there's a book, " The Benchrest Shooting Primer " that has a LOT of info and interesting reading. In that book is a lot of stories about BR shooters testing all kinds of stuff.

pjifl
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Re: Testing the Testing

#74 Postby pjifl » Thu Apr 23, 2020 9:54 am

Out of curiosity, I searched for material being promoted on the web for using a fluid to measure internal case volume. I am not sure why Isopropanol is being used as the liquid. There are problems which seems especially prevalent in the US about the simple use of the word 'Alcohol' indiscriminately and often it is poorly defined. Ethanol and Isopropanol (often referred to as IPA) are often confused. Both are available in different concentrations and one often needs to search for the fine print to unravel confusion.

Both form constant boiling point mixtures (fancy name - Azeotropes) with water and it is understandable why commercial suppliers often favor handling this over 100% pure Anhydrous Alcohols. Thus 91% IPA is cheaper and more readily available.

Just because a product is a Constant Boiling Point mixture does not mean that it retains that concentration when it is stored. Differential evaporation or absorption of water from the atmosphere will change its composition depending on how it is stored.

The bottom line is that one seldom knows exactly the composition - hence the Density - of purchased IPA. And there is no guarantee your sample will retain its density during storage. Added to that, a temperature change of from 20 degree C to 30 degree C will result in a density change of about 1 to 2 %. Since a SAUM case will hold a little under 100 grains of IPA, that could translate to over 1 grain discrepancy if measurements were taken at different times of the day.

Added to this, the main web material I found was in reality an advertisement for a device to plug the primer hole and it seems to me that little thought had been given to the validity of the whole process.

I really do not know enough to come to any firm conclusion. Nor do I have a lot of experience in using a fluid since I went the other route and used a fine powder on the basis that, while it may not be as precise, it was more convenient. Perhaps more thought - even some experiments - need to be done to reassess the process.

Peter Smith.

AlanF
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Re: Testing the Testing

#75 Postby AlanF » Thu Apr 23, 2020 10:30 am

It could be preferred because of its low surface tension properties?

http://www.surface-tension.de/


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