On Using Mixed Cases

H4831

H4831

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Not quite a re-run of all the posts that have been on here talking about it. Rather, this is showing some of the results of using mixed cases.
Just happened to dig a little deeper in a drawer and came up with a box of empty 270 cases, which I had shot at some time in the past. They all would have had the same charge, 60 grains of H4831, if they were 130 grain bullets and 58 grains of H4831, if they had been 150 grain bullets, and all would have the same primers. Not exactly light loads.
I noticed the box contained cases with four different head stamps. Of the four I picked out, one weighed ten grains more than the lighter ones.
One thing I think we can deduce from examining the primers in the picture, is that if you accidentally mix up your cases, you sure aint-a-gonna have your rifle blow up in your face because you mixed the cases!
So, study the primers. Can you pick out the heaviest one, the one with less capacity for powder, thus in theory, the one with the most pressure?
Well, which did you pick out?
I think the one whose primer shows the heaviest pressure would be the Winchester. And by a strange coincidence, it just happens to be the lightest weight of them all, the one that should have had the least pressure, by having more room in the case for powder!
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Bruce, I really don't trust primers to indicate pressure levels. In all honesty, I don't even trust marks from the bolt face on the face of the case.

The reason I don't trust these indicators, unless they are very pronounced of course is that you don't know the ductility of the components from one batch to another.

A few years ago, I was lucky to come across 50,000 primers on sale. A fellow had passed on and his kids were selling off everything from his reloading business at the first Chilliwack show.

I bought boxes of 5000 ea, for $65. To good a deal to pass up. Half of the primers were Winchester LR standard and half Were CCI LRM 250. Hell of a deal.

When I got them home and put them into the storage locker, I noticed the lot numbers were different on the case of 25,000 Winchester primers. All five boxes were made at different times. Not a big deal, 5000 primers of the same lot is always a bonus.

The 25,000 Federal primers were all from the same lot.

This was a good opportunity for me to play. I loaded up five rounds each of 165grain SBT Hornady bullets over 60 grains of H4831 (my favorite load). I used 5 different primers from each lot of primers. This load should be in the 45,000psi range

That gave me 30 rounds to compare. Just to be definitive, I also loaded up five extra Federal primers from another of the boxes as well, for a total of 35 rounds

The 25 rounds of Winchester all chronied at 2750fps +or- 15fps. In almost every batch of five, the primers were consitently flattened without any serious cratering. The cases were all new and this was a good opportunity to fireform them. One batch was different. It was in the middle of the lots, same load/cases/rifle. The primers were cratered much more than the other 20. Not enough to be of concern but noticeable.

Notably, none of the velocities varied from the other batches.

The Federal primers were a bit of an eye opener. All of the primeres were flattened and cratered. Much more so than the Winchester cases. Almost identical velocities though.

All of the rounds were accurate. All grouped into a nice little 1.5 inch group. Out of a sportered P17 with original bbl, I don't expect much more.

I must admit, I was concerned. I called up the people at Federal and they didn't answer but asked me to leave a message and they would get back to me. It took close to a week of telephone tag but we did get to talk.

The techie there felt that all was well and yes, some batches of primers are hotter than others. They have quality control plus or minuse tolerances that they have to work within and the particular lot number I gave him were listed as being fine. He wouldn't divulge any more info about the records than that. He also mentioned that different lots of primer metal/powder/anvils can be more or less ductile as well.

His words to me were "watch your velocities for abnormal speeds, that will always tell you the truth about excessive pressures if your're using approved powders/primers/bullets for the suggested loads."

He confirmed for me that the brass in cases varied also. Then of course so does the powder from lot to lot. If I can't buy powder in 8lb tubs, I take the 1lb containers and pour them all into a container large enough to hold them all and blend them all together. For you addicted accuracy buffs, this makes a huge difference in consistencey. Not much you can do about primers. Maybe use only Bench Rest Primers???

I agree with your consesus about safe loads. All of the components we purchase are made within a specified tolerance. Then they are tested extensively over several different lots to make up reloading manuals. They have to be extremely carefull. If anything, the manuals will err on the side of caution.
 
Here are the weights of the 4 cases in the original picture.

Winchester----188.3
Fed.---------- 188.7
Dominion-------195.5
Imperial--------200.5

Just to clarify. I, in no way said, or implied, that one could use primers to guess at pressure.
However, we all know that more pressure flattens primers more.
These primers were all the same and out of the same little box. They most likely were RWS primers, because that was what I used back then.
Therefore, if a different weight case created different pressures, we should see the primer a little flatter on the one with the smallest capacity.
This didn't happen.
It was pointed out that the extractor marks could be seen on the Dominion and the Imperial.
I had just picked those four cases at random, from the box of 20.
I have now taken the three remaining Winchester cases from the box and photographed them.
The extractor marks can plainly be seen in all of these Winchester cases, especially the one on the left, where the hole in the bolt face can be seen just before the W.
And remember, the Winchester cases are the lightest of them all, and therefore should have shown the least pressure.
The approximate 12 grains difference in weight, heaviest to lightest, only amounts to a bit over a grain of powder capacity between the lightest and the heaviest.
In my opinion, with very slow burning powder in a rifle cartridge, it makes little or no differrence, whether one case could hold one more grain of powder, than could another case.
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For the most part, cases that vary a bit in weight have little effect on the results.
However, there are notable exceptions.
For example, some R-P 7x57 cases I had were 35 grains heavier than the WW cases I had been using.
Also had a box of Imperial 7x57 cases that were an additional 5 grains heavier than the R-P stuff.
You might imagine the result if you loaded the heavy cases with a load developed in the much lighter ones.
[Yes, the primer fell out when I dropped the underlever on that #1 Ruger!!]
So many factors involved in brass showing pressure signs.
I have found that certain manufacturers' brass tends to be on the "soft" side, and shows pressure signs earlier.
Ditto lot to lot differences from an individual manufacturer.
I will not continue to shoot any load that produces marks on the headstamp area of a cartridge case. [Ejector hole, ejector slot, etc]
Regards, Eagleye.
 
I think head expansion is the most reliable. if the brass is soft and/or loading too heavy, the head expands and the primers get loose. I always consider that if the primers stay tight, the load can't be too heavy.
My brass always wears out by the necks cracking. I can't imagine how many times some of that old Norma, Dominion and CIL Imperial brass had been reloaded.
I shot a thousand rounds out of that 270, with a very small number of brass cases, before I finally had to get some more. So I bought some factory loads and realized that was the first factory loads the rifle had shot!
 
I figure that if I'm at or a little below Hodgdon's stated max load I'm safe as I think they use conservative load data.
 
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