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Old July 30, 2021, 08:07 AM   #1
alanwk
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Small Pistol MAGNUM primers

The only sp primers I could get were the magnums. I have read to lower the load a smidge. Would that be below the starting load? I will be loading 9mm, 40S&W, and 45acp. What say you? Thanks
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Old July 30, 2021, 08:30 AM   #2
Jim Watson
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9mm + HP38 in my guns, the type of primer made NO difference in velocity. Well, RP SP was a smidge faster than even magnums but not much. Is there Secret Pressure in there somewhere? I doubt it, but I am not loading to the maximum anyhow.
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Old July 30, 2021, 08:55 AM   #3
BillM
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Unless you are loading max loads, you probably don't need
to do anything. I've chronographed SP vs SPM in several
calibers and loads---the most I saw was an increase of 10 FPS.
If you are loading hot, reduce 10% and work back up.

Load a few and try for function. Some striker fired guns have
problems with the slightly harder SPM.
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Old July 30, 2021, 02:28 PM   #4
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Western Powders used to hold that handgun ammo should start at max minus 15%, and that 10% was for rifles. I'm not sure of their reasoning, other than tolerances for smaller charges, but following that advice doesn't hurt anything. Load one round a 0.85×Max and work up from there.
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Old July 30, 2021, 06:26 PM   #5
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https://www.youtube.com/watch?v=NGVRGsoOr6k

This video concluded no discernable difference if I remember correctly.
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Old July 31, 2021, 07:50 AM   #6
sevt_chevelle
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In 9mm with sport pistol powder, using regular, mag and Remington 6.5 rifle primers I found no difference.
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Old July 31, 2021, 08:17 AM   #7
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I have found zero difference between small pistol primers and small pistol magnum primers in any of my 9mm, 38 special or 357 magnum loads. I ran them all through my chronograph and found no spiked velocities or evidence of over pressures. I don’t load any maximum loads but mine are all mid to upper loads. I even tested them in some small primer .45 acp cases I have and once again there was no difference in performance.
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Old August 1, 2021, 03:14 PM   #8
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I have used SMP in 9mm for the last year. They worked fine with Unique, Universal and CFE Pistol. With Titegroup I dropped my load .2 gn as I was getting residue from the coated lead bullets in my barrels, but I have heard some say that is a Titegroup issue.
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Old August 1, 2021, 04:06 PM   #9
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Quote:
Originally Posted by cavediver27
I ran them all through my chronograph and found no spiked velocities or evidence of over pressures.
Just to be clear, a chronograph doesn't measure pressure. Matching velocity (actually, matching muzzle energy, but the two coincide) proves the average force due to pressure on the bullet over its whole trip down the barrel (less that needed to overcome friction) was the same, so average pressure was the same. But it doesn't tell you what the peak and muzzle pressure values that made up most of that average pressure were.

Nonetheless, as long as you are using the same charge of the same powder, it is unlikely the same average velocity would be produced if the peak wasn't averaging very close to the same value. There are some odd situations where it could happen, but they are mostly applicable to rifles shooting bullets too light for the burn rate of the powder used with them. I am just posting this detail so that someone reading the thread doesn't take the notion into their head that they can get peak pressure values directly from chronograph readings regardless of powder type. The relationship between peak pressure and velocity varies by powder, sometimes quite a bit.
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Old August 1, 2021, 05:52 PM   #10
cavediver27
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Quote:
Originally Posted by Unclenick View Post
Just to be clear, a chronograph doesn't measure pressure. Matching velocity (actually, matching muzzle energy, but the two coincide) proves the average force due to pressure on the bullet over its whole trip down the barrel (less that needed to overcome friction) was the same, so average pressure was the same. But it doesn't tell you what the peak and muzzle pressure values that made up most of that average pressure were.

Nonetheless, as long as you are using the same charge of the same powder, it is unlikely the same average velocity would be produced if the peak wasn't averaging very close to the same value. There are some odd situations where it could happen, but they are mostly applicable to rifles shooting bullets too light for the burn rate of the powder used with them. I am just posting this detail so that someone reading the thread doesn't take the notion into their head that they can get peak pressure values directly from chronograph readings regardless of powder type. The relationship between peak pressure and velocity varies by powder, sometimes quite a bit.
To expand even more, there was zero evidence of anything associated with over/excessive pressures. No extractor marks…no flattened, cratered or pushed primers…..no case separation or splits. The rounds ran exactly the same as with standard primers. Winchester pistol primers even state on the box that they are for “standard or magnum” loads. How can that be???? Over 45 years of reloading I have had to adjust components based on availability with primers usually the issue. I have ZERO hesitation in using magnum primers in starting to mid range loads. Of course that is what “I” choose to do and absolutely NOT what I recommend anyone else to do. Anyone else should adjust their loads based on their own experience and judgement. I do not endorse using magnum primers, I just described what I choose to do.
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Old August 2, 2021, 09:45 AM   #11
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Yep. I think Winchester figured out the difference tended to be minimal in large primers, so they combined them. When German Salazar still maintained his Rifleman's Journal, he had a lot of information on different large rifle primers in the 30-06, and the effect on pressure was very limited.

Small primers are a bit different. In 2006, Charles Petty documented a 223 Rem 55-grain bullet load over 24 grains of RL10X could see its velocity increase from 3150 fps to 3300 fps by changing primers. That likely represented about a 16% difference in peak pressure. Something similar may occur with a small pistol primer, as you will note Winchester still has separate standard and magnum primers for that size, however, it is going to be cartridge and load-dependent. I've actually seen magnum primers reduce velocity in a .380 ACP. As near as I could tell by the accompanying increase in velocity SD, the magnum primer's larger gas quantity was unseating the bullet ahead of the powder burn getting underway.

So it's a funny business. Allan Jones's primer on primers is worth reading.

This paper is interesting because of the high standard deviation in primer blast waves it reveals, suggesting that differences in primers might be masked by variation in some instances.
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Old December 4, 2021, 02:17 PM   #12
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Thanks so much for posting this video--excellent content!
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