Magnum Primers

[FNFbobcat]

Has anyone tried using SRMPs? May sound crazy, but maybe not.

The only SRMP that is noticeably "hotter" (greater brisance) is Rem 7 1/2. I wouldn't even think about using those.

CCI 450s have a thicker cup (+.0005in) than CCI 400s and might be worth trying, since 5.7x28 is notoriously hard on primers.

A more important reason is to create a faster pressure spike to get the bullet out of the barrel faster and drop pressures sooner.

Obviously, if one were to try these, a lower starting charge would be appropriate.

Just pondering. If I ever find dies, I'll try them and report.

[panzermk2]

You do NOT want faster pressure spike. You do want to use small rifle primers for teh thicker cup, but the last thing you need is the spike occurring sooner.

[FNFbobcat]

I'm lost Jay.

What is the negative of a quicker pressure curve, as long as peak is within SAAMI?

[panzermk2]

Well for one thing there is no SAAMI for 5.7x28mm.


Also you are missing key information.

You can have your P Max SOONER. P max is a factor of 3 things,
When it happens
How long it happens
Max pressure.

There is also a P amx for the primer ignition, Shot Start Initiation Pressure is the technical term

Primers come into play for the initial pressure spikes event time, duration and max pressure.
In such a small case as the 5.7 this will casue issues if it's too soon, too long and most importantly to hi.

You go from a nice controlled inflammation, yes inflammation is the term used, to an explosion that will damage
the case, chamber and possibly your hand. Bullet jump from the primer becomes a real issue.

The 5.7 is a very tiny pressure vessel that operates at a very hi pressure, small changes have significant ramifications.

[FNFbobcat]

Thank you Jay.

Those are the details I was looking for.

I appreciate the explanation, as always.

While you are correct about the lack of SAAMI specs for this cartridge, there are C.I.P established specs. My point was that there are generally accepted pressure limits. The name of the authority is a nuance.

[panzermk2]

Yes 50k psi, but we are talking primers not max case pressure.

And it does matter when addressing details concerning the round who provides the recognized specs.

[Saspencer64]

Can't you just use a slower powder when using the Rem 7.5 primers ? Just asking.
Been called a lot of things but sure don't want to be called "stumpy".

[panzermk2]

Has nothing to do with the powder.

[Saspencer64]

So the primer by itself causes the initial pressure spike and the powder just contributes to overall inflammation or explosion of pressure depending upon whether the primer is a magnum primer or regular small rifle primer..The speed or burn rate of the powder alone really is immaterial within reason.
So don't use a small magnum primer ?

[panzermk2]

There are 2 pressure spikes.

One is the primer that actually pushes the un ignited powder charge against the bullet and in the 5.7 can casue bullet jump.

Then there is the second spike created by the powder burning.

The powder burns/oxidises at a hi rate, it does not explode. If it did the gun would blow up in your hand.

The search for a synthetic gun powder is how we ended up with C4.

[Saspencer64]

1. So you should have a light crimp to prevent bullet jump ? 2. Can just the primer going off do that alone ? If so....
Then the primer alone pushes the Powder against the bullet forcing the ojive of the bullet into the rifling while the 2nd pressure spike is occurring just as the Powder ignites. Pressure spikes can't happen simultaneously without a magnum primer.
Got it. Just not sure of the point.
Don't use magnum primers ? Any examples please ?
Thanks

[FNFbobcat]

The idea of an INDEPENDENT pressure wave due solely to primer ignition makes an interesting theory, for which I can find no factual evidence.

Out of curiosity, I did an internet search for "Pistol chamber pressure curve" (also Rifle, with identical results). I found dozens of graphs with every imaginable combination of cartridge, primer and propellant and could find no evidence of an independent "primer spike". And it is easy to see why. The primer makes a significant contribution to total pressure, but time is CONCURRENT with the main charge IN ALL CASES. Look for yourself.

This can be deduced empirically as well. Those of us who shoot rifles appreciate the contribution to accuracy by varying bullet jump (ogive to lands). And this is with very light neck tension (.001-.002in). If an independent primer pressure wave existed, it would push the bullet into the lands and negate this variable. If you have any doubt, call tech support at any major bullet manufacturer.

If anyone has proof (a pressure transducer graphic chart) that an independent primer pressure spike exists, I would like to see it.

[Saspencer64]

Primer probably does "push" the Powder into as bullet first but I would expect the Powder would ignite dang near simultaneously. But of course I'm no expert.
Just really interested in how it changes POI.

[FNFbobcat]

That is what the available graphs show. It really doesn't matter what happens as far as powder "movement" (if such a thing exists). For the purposes of internal ballistics of small arms ammunition, existing data shows the two events are essentially simultaneous.

If this were not the case, Redding, Wilson, Forster, Whidden, RCBS and Hornady would not be selling expensive micrometer seating dies adjustable to .001in.

[Saspencer64]

And the Ruger 57 and what little I know of the FN pistol; both barrels travel With the slide linear about a 1/4 inch before being held by their recoil mechanism. This I believe delays ejection and prolongs the pressure curve.
Maybe this is what Jay is referring too as the second pressure spike.
That would explain the need for lubricate on the case, to proper powder load and primer matching, and of course precise weighing of powder.
That's what I think and don't think I'm too far off.
Still have both hands too !

[FNFbobcat]

Delayed ejection for sure, that's inherent in the design.

As far as the pressure curve, until someone presents a graph from actual transducer data, everything is conjecture.

I still have both hands too, probably because I still don't have dies. : )