OzFclass

bruce moulds wrote:an interestiing link pertaining to this subject.

http://yarchive.net/gun/ammo/cartridge_expansion.html

ultimately the case is the pressure vessel and must be treated as such.
whatever the case is it must be regarded accordingly.
keep safe,
bruce.

Bruce, interestingly the case is mostly a liner to the pressure vessel which is largely the rifle chamber which is reamed into the barrel. The case becomes the weakest link in the pressure vessel where it is unsupported outside the chamber with 5-10 thou of exposed case web and case head up against the bolt.

I'm sure if Lapua ran a thicker web further up the case wall then this expansion would be remedied. The compromise would be a little case capacity would be lost. The 284W (especially as Shehane) is a perfect size case for 180gr projectiles but it could do with a little 21st century tweaking.

Ian

Well put, Ian....

I think that is what Lapua did with the 338 case , modifying the african round it came from by thickening the brass inside the base. A shame they did not see fit to do that when they started making 6.5-284s ....

ian,
you are correct. it is a bit of a combined thing except where the case is unsupported.
this is where the mauser 98 breeching system is so superior to the remington system. it supports the case right back to the extractor groove, whereas the rem has some of the case head exposed behind the chamber.
a case head expansion in a rem 700 can leave the case looking like a belted case. don't ask me how i know this!
as far as primer pockets are concerned, no action supports that area, due to the extrator groove disallowing support. the flash hole area is supported.
i suppose i was trying to make the point in a simplified way that whatever brass you have, that is what allows the max pressure you can use.
i often wonder if we had larger diameter barrel shanks whether there would be any benefit due to less spring in that area when you light the flame.
the use of tempilaq 400 on case bases when annealing can eliminate case head softening.
has lapua been lax in this area with the suspect brass?
keep safe,
bruce.

Interesting about the Mauser 98, Bruce, Germans seem to excel in practical design!

I am sure Lapua could quickly fix the 284W weakness if enough of us made Lapua aware of how we now use this case in competition with 180gr+ projectiles. At the moment they probably sell every case they make and we as shooters, (customers) have not voiced our concerns in sufficient numbers to make a difference.

I am about to start a long range project using a 300WM case (belted magnum) with 230gr projectiles. I know this case does not require the belt around the web of the case that it comes with from manufacture. Winchester knew it did not require the belt when they first manufactured it back in the 1960's, but it was needed to sell as shooters expected a belt on a magnum case. The 284W does not need a belt either, just a little redesign.

Lapua can easily strengthen/redesign the web of the 284W case to eliminate case head expansion and still have a case that fits in the chamber specification. We just need to get onto customer support and demand they give us the customer support we want. Give customers what they want and you stitch up that particular market. If Lapua cant do it for us then maybe one of the other major case makers can step up to the plate.

The 180gr Hybrids really dont need a case the size of the popular RSAUM, a 284W with a solid case head would see a big swing back to this economical and efficient case.

Ian

ian,
an interesting case is the 9.3 x 64 brenneke.
the base is like a non rebated 284 win.
a set of forming dies, a boltface mod, and you could have a 284 case with the shoulder a little furthr forward and a longer neck.
rws makes this brass, and it will take pressure while being very consistent.
being smaller diameter than the saum/wsm, the barrel shank would be capable of more support.
the case itself is very similar to the 7mm rem mag without the belt.
maybe a set of forming dies and a heap of 338 lapua brass could solve it.
the wsm case is i think based on the 404 jeffery, but i could be wrong. the 338 lap is based on the 416 rigby?
does anyone know this?
then there is the good old 280 ackley.
the original 284 was meant to go head to head with the 270 win. both were loaded to quite high pressures.
this would lead one to believe that either lapua has some sus brass, or expectations of shooters are too high.
180 gn in7mm is probably a bit like 90 gn in 224. very heavy for calibre. things can peak out very suddenly here.
the 195 bergeres might be very interesting in this area if they ever materialize.
with regard the belted mags, you are correct. if it had no belt it would not sell. the belt had some phallic marketing appeal.
that is not to say that a belt is a disadvantage. it is just not necessary.
its big advantage was as a headspacing tool in dangerous game situations with primitive manufacturing standards of 1912, and allowing loose chambers for absolutely reliable feeding.
a common 1000 yd heavy gun cartridge was the 30/338 win (a clone of the 308 norma mag) using the 240 sierra. this would suggest accuracy potential.
keep safe,
bruce.
keep safe,
bruce.

As promised, I have done a test using samples from 3 other boxes of Lot 620601. And there was absolutely no problem, in fact I found a promising 2950fps load !

Here's a description of the process :

• Took 3 cases each from 3 unopened boxes of Lot620601.
• Also, took 3 new cases from Lot523501 as a reference.
• Fireformed all 12 cases with a light load.
• Fired a 2840fps load (57gn N165) with one case from each box.
• Fired a 2890fps load (58gn N165) with one case from each box.
• Fired a 2920fps load (58.5gn N165) with one case from each box.
• Fired a 2950fps load (59gn N165) with one case from each box (re-using the 2840fps cases).

The first sign of any primer pocket expansion came with the last of the 2920fps shots. And this was actually the case from the reference Lot (523501). With the hottest (2950fps) load, all 4 cases showed some expansion, about 0.001 in the extractor groove, and a definite, albeit slight, reduction in primer seating effort required. I also noticed a slightly increased resistance on the bolt lift, and the first signs of cratering on the primers. My guess is the cases would do at least another firing without any problem. A bonus was that the SD for these four 2950fps shots was quite good at 5.5 fps, so I'll investigate this further as a "thumper" load for when conditions get rough, or very switchy at the longs. I don't mind sacrificing a few older cases for a big event.

Now the question is, why are some others having serious problems with the same Lot of brass???

Here's my list of possible reasons :-

• I use a slow powder (N165) (less pressure).
• Mine is a Shehane with about 2gn extra capacity over the standard 284 (less pressure)
• I moly all projectiles (less pressure)
• The barrel I used was 32" (longer barrel = less pressure for a given velocity)
• My chronos may read faster than average
• Others' chronos may read slower than average (are they using chonos?)
• Powder batches used by others may be hotter than they previously used
• Others may not be cleaning all lube off cases (increasing force on boltface)
• Others may have over-polished chambers (increasing force on boltface)

IMHO it will probably be the combined effect of several of the above. Comments welcome.

Alan

Hi All,

I emailed Lapua again asking for an update on their findings. If you remember my earlier post, they had allocated a case number to it.

Its not a very positive response, but its something:-

Hello Denis,

I checked the status of this claim. Claim is closed in our database and you should have got the final answer letter from Mr. Melcher. Have you got it? We also agreed to send you few new boxes of similar cases for testing – have you got these?

We look through all test results from the time of manufacturing of these cases (hardness, reloading tests etc. which could have something to do with this kind of a problem), but we didn´t find any good reason why these two case lots are not working as they should.

BR,
NOTE: I haven't recieved a final letter or any cases, though I'll be happy to take them if they want to send them

On another note;
Heres a REALLY rough sketch of a collett die idea I've been churning in my head. Only to crimp the web and rim (not the head) back to SAAMI specs which would no doubt spring back to some degree.
The bottom pic of the double tapered collet's is an second idea to the first..



Things I'm not sure of:
a. Are the collets easily made? What material? The die body and base would be easy to turn.
b. Will a regular single stage reloading press have enough oomf to squeeze everything back .002"?
c. How realistic is an idea like this?

What do y'all think of the idea, not the artwork or handwriting?

Denis,

I think the weak point in the case is the thin wall between primer pocket and extractor groove. Can you come up with a collet die that "throttles" the extractor groove? (probably would need to be a separate operation)

Alan

AlanF wrote:Denis,

I think the weak point in the case is the thin wall between primer pocket and extractor groove. Can you come up with a collet die that "throttles" the extractor groove? (probably would need to be a separate operation)

Alan

I think thats the idea of this collet system. The resized area would be the extractor groove (which I may have wrongly labelled the web) and the rim.

My idea to the collet was inspired by the collets of a kinetic bullet puller. They have a jaw that sits inside the extractor groove.

For example, In a completely closed position the inner collet dimension would match SAAMI specs. That is the extractor groove and and rim diameters (and rim thickness to stop it flaring rather than reducing O.D)
The collets would be opened over the shell base and be held together via the o'ring. Then placed on the ram seat.
As the tapered collets were driven up into the tapered die via the tapered ram seat, the tapers would force the collets to close, inturn re-sizing the extractor groove and rim. The bottom part of the pocket inside the head should be untouched.
Double tapered collets would keep the squeezing pressure even at the top and bottom.

It may not make the pockets as tight as new, but if it were to close the pocket by .oo1" after spring back, that may be all that is needed.

Okay. Now I get it. The whole of that bottom assembly is in 4 quarters held together by the O-ring. Hmmm. My immediate thought is that it'd need a powerful press. Maybe if the "squeeze angle" was changed to less than 45 deg, it would increase the compression force?

That's a poor reply from Lapua, this wasn't an issue with previous lot's, something has to have changed !!!!

Matt,

I reckon it must be a general reduction in hardness across all their brass, which is particularly noticeable with this case design. My testing has shown no difference between the 3 identified blue box lots. We'd need some virgin brass from well before the blue boxes to be able to prove anything.

Alan

I know Lapua's brass composition has changed with the blue box brass.
I just can't find the chart that showed the comparison.

Cam

Uploaded with ImageShack.us

Found one chart

Matt P wrote:That's a poor reply from Lapua, this wasn't an issue with previous lot's, something has to have changed !!!!

I agree Matt. I'm just one squeaky wheel though. Maybe if everyone on this forum thats experienced this problem with .284 brass sent Lapua an email quoting "C2013-0005" as the case number, they may be inclined to take the matter more seriously.

Although I wouldn't knock back free brass, it seems like quick'n easy solution "grease me".