Can anyone define +P?

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McCanik
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Can anyone define +P?

Post by McCanik » Fri Jun 21, 2019 4:20 pm

Is there a minimum muzzle velocity for each grain bullet that classifies the ammunition as +P?
I have been shooting Sellier & Bellot 115 grain and recently looked at the specs for it. S&B is spec'd at 1280 fps which is higher than some ammo that is spec'd at 1180 fps but rated as +P.
Same with Fiocchi 115 grain spec'd at 1200 fps but not rated +P.
I've shot many thousands of rounds of Fiocchi and S&B in the last year and I'm wondering if this higher than average muzzle velocity might have been related to the frame crack that developed in my aluminum frame Tristar T-120. Tristar's owners manual doesn't say whether their guns are rated for +P and I'm waiting for a response from them.
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jgillaspy
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Re: Can anyone define +P?

Post by jgillaspy » Fri Jun 21, 2019 4:25 pm

Although it might not be the best...

https://en.wikipedia.org/wiki/Overpressure_ammunition

At least you can see that +P means as far as SAMII cartridges are concerned.

JG
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McCanik
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Re: Can anyone define +P?

Post by McCanik » Fri Jun 21, 2019 4:49 pm

Thanks, now I just need to translate pressure into muzzle velocity.
Can any reloaders out there tell me what a 3,000 lb pressure difference between standard ammo and +P translates into in muzzle velocity?

Edit: SAAMI standards reference maximum pressures. What minimum pressures, and more importantly minimum velocities, are the threshold for +P?
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SSGNDoc
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Re: Can anyone define +P?

Post by SSGNDoc » Sun Jun 23, 2019 7:04 pm

Unfortunately it’s not that simple. The peak pressure may occurs oat different points in the bullets path down the barrel based on what powder a manufacturer is using, what overall outer diameter the bullet truly is, and how much bearing surface and friction is generated by the bullet.

Any data a manufacturer gives on velocity is based on the loads they use, and the test barrel they use. Test barrels may not be the same length as a standard service pistol barrel. So, company “Ammo X” may use a slower burning powder and a longer test barrel, and get the same velocity with lower pressure, as “Loads R Us” does, through their shorter test barrel, and faster burning powder that generates a higher pressure peak.
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higgybaby
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Re: Can anyone define +P?

Post by higgybaby » Sun Jun 23, 2019 7:56 pm

I do not know anything about reloading or loading specs-

But Remington (for instance) list the velocity of their 115 gr HTP hollow points at 1140 fps.
But for their Express +P 115 gr jhp its 1250 fps.

Fiocchi lists their 115 CMJ at 1200 fps
Fiocchi lists their 115 FMJ at 1250 fps.....??? whats the dif? I have no idea?

Seems like a lot of the ammo out of Europe runs a little hot compared to that made in the USA?
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TL1000RSquid
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Re: Can anyone define +P?

Post by TL1000RSquid » Sun Jun 23, 2019 8:08 pm

higgybaby wrote:
Sun Jun 23, 2019 7:56 pm
I do not know anything about reloading or loading specs-

Seems like a lot of the ammo out of Europe runs a little hot compared to that made in the USA?
Yes they use different specs, the majority of imported ammo will run a little hotter then U.S. made brands, SAAMI specs are U.S. only, CIP is the european version which some non euro countries use as well(IMI).
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McCanik
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Re: Can anyone define +P?

Post by McCanik » Sun Jun 23, 2019 8:09 pm

Thanks Doc.
I follow what you are saying although I'm getting to the edge of being confused.
I guess I'll quit fixating on muzzle velocity and accept that barrel pressures are what to worry about. Since neither Fiocchi or S&B rate their ammo +P I guess I won't worry about damage since their pressures must be below 35,000psi.
But I'm still going to change recoil springs twice as often.
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NWcityguy2
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Re: Can anyone define +P?

Post by NWcityguy2 » Sat Jul 20, 2019 9:21 pm

While it sounds like your gun failed faster than it should of, all aluminum framed guns day's are numbered in a way not seen in polymer or steel framed guns.

The key to remember about pressure and velocity is that they have a relationship but not an exact one. Generally speaking, a faster burning powder will develop less velocity at the same pressure than a slower burning powder. This is, of course, assuming that the person/company loading the ammunition is following safe loading procedures. This is how two rounds of 9mm can have different velocities but the same pressure. There is economy is using less of a faster powder, but factory ammunition doesn't take it to extremes because it needs to function in a wide variety of guns. My understanding of the bulk powders used in factory ammunition is that each batch is pressure/velocity tested individually, and then the loads are adjusted up and down a bit to reach the advertised velocity.
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