How and why do different primers make a difference?

For pistol loads, smaller cup diameter primers like CCI/Magtech/Winchester seat easier in once-fired brass or cases with tighter primer pockets like S&B/RWS. If you are using Pro 1000, smaller diameter primers will work better with the primer attachment and essentially eliminate the "primer issue" many report.

For brass reloaded multiple times with looser primer pockets, larger cup diameter primers like Fiocchi/PMC/Tula/Wolf will extend the service life of brass but using larger diameter primers in once-fired or small primer pocket brass like S&B/RWS will not allow the primers to seat below flush and often not even to flush.

I have gotten comparable performance from Fiocchi/Magtech/Winchester SP primers and do not need to adjust powder charge when changing primers. When I use PMC non-toxic SP primers, I need to add .2-.3 gr of W231/HP-38.

I use harder cup CCI #41 military primers to reduce the chance of slam fires although Tula SR/.223 primers have worked well with my ARs.

Several years ago, benchrest shooters claimed more consistent primer flash size and duration from Wolf primers but I am not sure if this is still true. I have used Winchester/Wolf/Tula LR primers for my .308 loads but for my limited testing at 100-400, I could not tell the difference in group/pattern size as I load for minute of gong.

I think main differences in primers are cup hardness, cup diameter/height along with flash size and duration.

They also come in regular brass or nickel plated brass.

Federal primers are known to have softer cup (IME PMC also) and better suited for pistols with lighter hammer spring. CCI/Tula primers are known to have harder cup and won't consistently ignite with lighter hammer spring. When a particular batch of Tula SP primers with harder cups resulted in occasional failure to ignite in my Glocks, I found I could use them in small primer 45ACP cases and they have consistently ignited using Sig 1911/M&P45/PT145.

Winchester does not make separate "magnum" LP and the same "LP" is recommended for both regular LP and MLP loads.

Sellier & Bellot recommends use of different primers for 9mm and 40S&W. While SP primer is listed for 9mm, SPMP primer is listed for 40S&W but many reported using SP primers for both 9mm and 40S&W loads with good results - http://www.sellier-bellot.cz/en/product/components/primers/

A fella over at 300blktalk just recently did an interesting small scale test with five different small rifle primers - keeping all other aspects of the loaded ammo the same, primer being the only variable - he saw over a 100fps spread in velocity.

http://www.300blktalk.com/forum/viewtopic.php?f=141&t=97658

There is quite a bit to the little buggers, to add to what bds has mentioned:

What difference do primers make? Pistol and rifle please.

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Generally speaking rifle primers are exposed to higher pressures so they are made thicker than typical handgun primers. In some cases certain handgun cartridges call out the use of rifle primers.

Is there a marriage between certain powders, bullet and primers?

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Most important is to work from a good reloading manual and work to published data, especially when starting out. Yes, certain powders require certain primers for best performance. For example some ball or spherical powders can be more difficult to ignite. To really ensure proper and complete uniform ignition a magnum primer is suggested. When we get right down to it there are a few families of primers.

Small Pistol Standard
Small Pistol Magnum
Large Pistol Standard
Large Pistol Magnum
Small Rifle Standard
Small Rifle Magnum
Large Rifle Standard
Large Rifle Magnum

Primer dimensional data meets prescribed SAAMI specifications as do the primer cups on cases the primers fit into.
Primers are a really broad subject so this is pretty generic material. BDS pretty much covered things.

Ron

8.9gr Longshot behind a 165 MG.

When we get right down to it there are a few families of primers.

Small Pistol Standard
Small Pistol Magnum
Large Pistol Standard
Large Pistol Magnum
Small Rifle Standard
Small Rifle Magnum
Large Rifle Standard
Large Rifle Magnum

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To further complicate matters, some primer mfgs do not make both a stander and a magnum version of the same primer, so when you look at load data based on one of them, you may not be able to tell whether it's best to use a standard or magnum when using another brand.

The best primer (std or mag) for the application is dependent upon the powder used. Whether to use small rifle or small pistol primers is dependent upon the pressure being generated. Only a handful of pistol rounds call for a rifle primer.

Primers...

I think that what Cannonman is asking is something different. Obviously, you should use the correct size and type primer for the cartridge and powder you are loading.

However, the question seems to me to be, given (for example) that we are loading .38 spl cases with target loads of Win 231 pushing a 148 grain LWC, is there a difference in performance if we use Winchester Small Pistol primers, as opposed to CCI Small Pistol primers, Wolf Small Pistol primers, Magtech Small Pistol primers, or some other brand.

I use the above example specifically because IMX, there is not an observable difference on the shooting range. The POI seems to be just the same. I shoot in a league, have for years, and I use whatever primers I can get my hands on. Bullet ft/sec I have no idea of--for punching paper a steady POI is what you need.

Have had the exact same results with various brands of Large Pistol primers when loading for target shooting with the .45acp--that is, no difference in results with the various brands.

When target shooting with a pistol, there are too many other variables to consider (most being some kind of operator error) for whatever small effect the different brands of primer may have, to actually make an observable difference.

Anyhow, that is my take on the question.

For everything you wanted to know (or not) about primers.
www.sksboards.com/smf/index.php?topic=56422.0

They are just different for different applications.

Using your steak analogy you don't cook a skirt steak at the same temperature or time that you would cook a tenderloin and doing so would lead you to less than ideal results both ways.