Thread: Primer question

Originally Posted by Micky Duck

I really want to know why would you?????

if you need to re-resize the case.....if its a big long case you can left primer rod up so it doesnt touch or remove it completely.

many on here will suggest you dont need expander ball at all...

too easy to fire them off in empty case now we have suppressors..but dont try and muffle the hole in end with your new polarfleece coat it will burn wee holes like ciggy burns.

How do you know :-)

lets just say I have a polarfleece vest that looks like it was owned by a smoker.....

Originally Posted by zimmer

Primer pockets like the cases themselves (well USA ones) are governed by SAAMI specs ie a maximum and a minimum value provided for primer pocket depths for manufacturers to work to. Primers vary between brands in over all length. Maybe even between batches. You could have a primer pocket at the deepest end of the SAAMI spec (still within spec) and a primer that is shortish. Outcome if seating flush is the bottom of the primer may not be correctly in contact with the bottom of the primer pocket which can lead to erraric ignition or no ignition.

I'd have to rechech SAAMI but I think these are the specs/tolerances -
Large Rifle PP specs 125 thou to 132 thou.
Large Rifle Primer specs 123 thou to 136 thou
So a 123 thou primer seated in a 132 thou pocket, flush, will not be a good combination.

The other thing that happens is if you uniform your primer pockets with for example a Sinclair tool, which is non adjustable, you may cut your pockets too deep. I had that happen with a Sinclair tool which before I realised it was cutting my pockets to 132 thou whereas I wanted 128 thou. IIRC 132 thou is still within SAAMI spec or right on it. They refunded me for that tool.

I have always believed that to be the most important objective of seating primers ( i.e. seating to the bottom of the cup ), for certain and consistent ignition. To me, secondary and almost as important is to have primers flush with or just under the case head surface. Just so if cartridges are moving under recoil in the magazine there is no chance of the primer being contacted by any surface or projection.

Originally Posted by zimmer

Primer pockets like the cases themselves (well USA ones) are governed by SAAMI specs ie a maximum and a minimum value provided for primer pocket depths for manufacturers to work to. Primers vary between brands in over all length. Maybe even between batches. You could have a primer pocket at the deepest end of the SAAMI spec (still within spec) and a primer that is shortish. Outcome if seating flush is the bottom of the primer may not be correctly in contact with the bottom of the primer pocket which can lead to erraric ignition or no ignition.

I'd have to rechech SAAMI but I think these are the specs/tolerances -
Large Rifle PP specs 125 thou to 132 thou.
Large Rifle Primer specs 123 thou to 136 thou
So a 123 thou primer seated in a 132 thou pocket, flush, will not be a good combination.

The other thing that happens is if you uniform your primer pockets with for example a Sinclair tool, which is non adjustable, you may cut your pockets too deep. I had that happen with a Sinclair tool which before I realised it was cutting my pockets to 132 thou whereas I wanted 128 thou. IIRC 132 thou is still within SAAMI spec or right on it. They refunded me for that tool.

Thanks for getting back to me on that one, a good example for me of you don’t know what you don’t know.

Originally Posted by zimmer

Ah, almost right. CCI for example have the anvil petals sticking out. With RWS the anvil is flush with the bottom edge of the cup so you cannot preload them or push the anvil back in. With early Murom it was essential to drive the anvil in against the compound. If you didn't there was chances of erratic ignition or no bang at all. Don't know if Murom are still like that.
My practice for target ammo is to preload my BR4s by 1 1/2 thou and BR2s 2 thou preload. You cannot do that with normal priming tools. I currently use a Primal Rights tool. For sporting ammo I just seat by feel with a hand tool.

There is always the risk of overdoing it and crushing the primer material.

Before I started taking care priming I measured some of my early efforts done with an RCBS tool, carefully I thought. All primers were over seated and crushed.

One of the biggest priming issues, and I see the advise on the net, is to seat primers flush with the case base.

OK - RWS shipped sensitized. Nice to know! Presses are a known cause of erratic primer ignition if you are having issues - with a lot of the press designs the primer arm contacts right on the point the lever connections cam 'over center' which gives you very little mechanical feel of what is going on and as noted it's actually really easy to crush the primer. Hand primer devices where your hand is directly connected to the pushy bit without much in the way of linkages give you more feel, and you can usually feel the primer sliding in and the primer cup bottoming into the cases pocket. I'm not too sure for the record that exact primer crush figures make too much of a difference or even a measurable difference for the average shooter - might be something that you can quantify and measure in extreme precision competitions but on the other hand if it makes you happy and improves your confidence in your gear mean. My less than scientific testing, measuring Federal GMM primers in Lapua cases is that the hand primer tools generally get less than a thou of variation in seating depth so a well enough accurate for most purposes. If you have to uniform primer pockets you are likely to end up with greater variation in primer pocket depths depending on how repeatable you are with the uniforming tool!

Seating primers flush I think came out with the US shooters who were having issues in Russian semi's with slam fire. The cause was said to be primers not being seated flush with the bottom of the case and getting set of by the bolt face slamming the case home, which wasn't correct on a few different counts.