Number 34 Primer with .303 British

[Bruce_in_Oz]

I guess it also depends on your chosen propellant..

US powders like 3031 and 4895 are excellent for driving 150gn bullets from a .303. You can happily ignite those powders with ANY "standard" Large Rifle primer.

I stared reloading Boxer-primed .303 with Remington 9 1/2 primers fifty years ago. Later, I moved to CCI standard Large Rifle primers , partly because, in these parts, they became easier to find than the Remingtons and they seemed to be a little "tougher" in "stiff" hunting loads in .30-06. Thicker cups?

Regardless of the cartridge, the usual caveats apply:

HEADSPACE, Max load warnings, triim length, flash-hole diameter, striker protrusion and radius, striker /striker hole "fit". etc.

If you are loading heavier bullets , eg. 180gn and above, a slower powder is advised. Endless good data in print and on line out there, Powders, primers and bullets come and go over time, so you need to keep current with data..

[AD-4NA]

Beware of internet assertions that the CCI #34 is a "hard" primer. There is credible evidence that the cup is the same as other CCI primers but that the anvil is in fact shorter.
https://www.milsurps.com/attachment....50&cid=1&stc=1

Your pic makes your point well. I'll bet this would pretty well absorb the forward inertia of a free floating firing pin, preventing a slam fire. Thanks for illustrating how this primer actually performs this function.

Interesting, that would explain how it could survive dimpled primers in M1 Rifles all the time.
Sounds like no one has tried it in .303 though.

[Bruce_in_Oz]

There are "limits" on primer protrusion because too much WILL pierce the primer cup. EVERY time a primer is struck, the brass is stretched and "work-hardened". Too much stretch and it will fracture. The high-pressure and temperature gases that leak backwards through such cracks act like tiny plasma cutters and "eat" the tip of the striker. The not-so-smooth striker tip will then be even more effective at puncturing the primer cup. and the consequent gas escapes will attack not just the striker tip, but the circumference of the striker hole. This is why "serious" small arms inspections include close visual examination of these features and careful gauging thereof.. "Burned" strikers are relatively cheap and easy to replace; bolts / breech blocks much less so. Arisaka shooters will probably have noticed the rather "casual" relationship between the diameters of striker tips and striker holes, especially in some later-production Type 99s.

Headspace is important, but so are the limits for striker and striker hole dimensions. Primer SEATING DEPTH is also important; check you loading manual. Take care and do not get "adventurous" or "distracted" at the loading bench.

[Bruce McAskill]

The dimpled primer happens with not much force. As a round is loaded in an M1 chamber, the primer hits the firing pin forcing it back into the bolt. The primer gets a little bit of a dent but nowhere enough force to cause the primer to detonate.

[Daan Kemp]

Semantics. The primer detonates=explodes? My understanding it provides the flame to ignite the propellent, don't have a correct word for that. Ignites? Just like the propellent burns/flames/etc and doesn't explode.