Just started working on loads for my new 6mm/284. I've noticed about .002" expantion no matter how hot/mild the load is. 52 grains of H414 is the same as 57. Where do I stop. I guess a Chrony would answer this question real easy. But, access is slim. Any thoughts? ~lokey

A chronograph could be of tremendous help. Look at your primers. If they are flattened and cratered, then you are probably well over maximum. If extraction of spent shells is difficult, then you are probably well over maximum.

I tend to stick to standard calibers and compare my reloads to factory ammunition. This helps keep me out of the danger zone.

Lokey, if this occurs with mild loads, something is wrong, loose chamber, excess head space, micrometer lacks accuracy, something. Max expansion should be in the .0004-.0005 range (ten-thousandths). good shooting.

There is no noticable defference in primers either, that's why I'm trying to base things on case head expantion. I'm looking for advice from people who know what they're talking about, but thanks anyway. ~lokey

these loads are from a Layne simpson article on the 6mm-284.
55 gr Nosler BT-49 gr RL15 @ 4082 fps
70 gr Nosler BT-56 gr RL19 @ 3772 fps
80 gr Nosler BT-56 gr RL22 @ 3433 fps
85 gr Nosler Part-55 gr RL22 @ 3419 fps
95 gr Nosler Part-53 gr RL22 @ 3344 fps
100 gr Nosler Part-52 gr RL22 @ 3256 fps

He also suggets using 240 Weatherby data as the case capacity is very similar. I have to agree with the other posters, .002" is way too much case expansion. Now, other things can cause this besides excessive pressure. I would suggest reviewing your case resizing procedures and perhaps picking a slower powder. Also, in the Sierra manuals they list H414 as a powder for the 240 Weatherby, but only with 60 gr bullets, and the max charge is 53.7 grains. Considering that Weatherby's have a fair amount of freebore 9unless your rifle was chambered with freebore), I think you are probably pushing the envelope by a fair amount. FWIW - Dan

lokey,

It sounds like your measurement is picking up some of the case body in front of the solid head.

.002" case head expansion would be a lot. Loose primer pocket area of pressure and ejector marks on the case head.

Mike

As Mike said you must be measuring ahead of the solid head of the case. Also at the transition point there is some displacement of brass into the solid head area. I think you get your most reliable readings from neck sized brass that is fire formed. My personal felling is that any expansion is excessive. Usually by the time it shows up it is already at .0005 at which point I think you should back off a bit. Generally speaking if a case expands by .0005 on one firing it will expand another .0005 with the next etc. So after 5 loadings you will have .0025 expansion and, probably, loose primer pockets. Regards, Bill.

I follow Bill L,s rule of thumb and it has worked for 50 years, well 40 anyway..

I couldn't read a mic until I was twenty some odd. Still see folks read them backwards. I always get a chuckle out of that. But they have dummy mics now, call'em digital.

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

Ya'll were right on the money. Those loads were all, well, WARM. After resizing they fit very snug, although, there seemed to be no effect on the primer pockets. I threw all the brass out, and I'm starting over with RE19. Thanks to all for your advice. ~lokey

I'm not a follower of the expansion measurements, but I would like to point out that the cases must be full to partial length resized. Neck sizing wont do it (or at least that's what I'm told by ardent followers).

If the primer seats easily, or is loose, the pressure was too much. If the primer seating stayes the same, your pressures are fine FOR THAT case. Pretty simple, and you don't have to fart around with, or spend shooting money on mic's.

Turok

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Make it idiot proof, and some one will make a better idiot

Turok,
That is the case if you are going by the so called expansion ring but not if you are looking for the amount of expansion on the solid head. Actually even if using the expansion ring method one might be best served by using new brass to check pressure since with each sizing the structure of the brass is altered. New brass can be used when checking the solid head as long as one is sure to be measuring behind any possible distortion which would arise from normal expansion of the case ahead of the solid portion. The thing is that once the solid head starts to expand the load is too hot. If a case is developing loose primer pockets then you may be quite certain that expansion of the case is significant.
Measuring the expansion ring is a way to compare against a baseline for instance factory ammo. In order for the comparisons to be valid brass must be at least of the same manufacture as the baseline ammo and it should be in the same condition. That is new. The chief difference in the two methods is the measuring of the solid head is used to establish the absolute max for the brass and the rifle (much like the "load til the primer gets loose" system!) whereas the expansion ring method is used to estimate related to a base. This is useful perhaps when working with rifles which are not necessarily stronger than the brass like a win 94 or a Krag. As many have pointed out the ready availability of chronographs has added another dimension to load development. Regards, Bill.

Bill,

I don't really want to get into an expansion debate, but I would like all to note that Speer claims (as pertaining to Case head expansion):

"New cases can give deceptive readings. The first firing of any case will usually cause more deflection of the brass than subsequent firings. At Seer we start with once-fired brass so the initial deflection is already accomplished." (Speer #12 p 55)

"Once fired cases are loaded and each one is carefully measured. After firing, each case is measured again at the same point and the difference in diameter is calculated. We look for an average expansion of .0003 with no individual reading over .0005 ... Case head expansion measuring .0003 to .0005 is generally accepted as representing pressures in the 50,000 CUP range with typical cases"
(Speer #12 p56). So obviously SOME case head expansion is Ok.

I am in no dissagreement with you on the similarities between case head expansion and load until you get loose primer pockets statement made earlier.

Primer pockets expand due to the fact that the case head has expanded. That is the point. It is the same thing and it is easier. Why? Because you don't have to buy separate tools and learn to read them.

I do, however, find it curious that many people have different versions of how the actual measuring should be done and exactly where it should take place. The numerous variations in the whole method really do (in my mind at least) detract from its credability. Lab tests are standardized. This should be no different.

Turok

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Make it idiot proof, and some one will make a better idiot

Turok,
You will note that the Speer manual mentions that new brass may give erroneous readings due to deflection which is as I said. This is the same reason that neck sized brass is best when using this method. The deflection has taken place and won't influence subsequent tests. If the case is full length sized then such deflection can occur again. As I said new brass is advised only when going with the expansion ring method where one actually measures the amount of expansion at the juncture of the solid head and the body of the case.
You are absolutely right when you say that a loose primer is an indicator of head expansion and a mike is unnecessary to verify this. The problem is that a loose primer pocket may not show up until expansion of .001 or even more is reached which means that you are well beyond the limits. The fact remains that Rocky Gibbs' statement that "good case life with repeated reloading" was the determining factor as to load suitability was a good one. If the primers get loose after 5 firings the load is still too hot and measurment may have determined this before the brass was ruined.
Anyway there is nothing really wrong with your contention that measurment is unnecessary just as chronographing is unnecessary both are just means of having a more thorough understanding of what's going on in the rifle. Regards, Bill