What could all the reason be for flatten primers?

[uncle buck]

Reloading books reference  about when you see flatten primers that it means higher pressure.. However the reloading books never spell out all the things that can cause you rifle primers to be flatten... It makes you assume that it's always using to much of a certain powder.. However it could be bullet OAL to long and they are resting on the rifling...The brass that your using...Hunting Forums posters ......will swear up or down that it's the company brass that your using..

What made me start to think about this is I have two Encore T/C Factory barrels...When I reload or even use factory ammo the primers are flatten... Now it can't be because I am using to much powder...The accuracy of these rounds even with the  flatten primers are still accurate with nice groups at 100 yards...

I have been considering purchasing the Hornady or the Sinclair measuring seating tool....This allows you to know from taking certain measurements just where your bullet should set in your chamber... Tool and all the parts for the seating depth tool to work can add up in $$$$$.  It's about $5.00 for each calbier case you want to check out..

Before I  decide to buy this measuring tool and attachments I would just like to understand more who, what, where, how, and when primers can  flatten..

Anyone have any info on flatten primers and what or all the things that can cause it?  

[Buckwheat]

uncle buck
I seen this and thought you might want to see it. Are you sure you are flatting primers? You might want to chronograph your bullets to see if they are at or even a little past what the books say. A little past or even at max speed can mean a lot in chamber pressure in some guns.

 The MYTH Of Flat Primers
Guns Magazine, Oct, 2001 by Charles E. Petty

12Next
Chamber pressure is one of many things in life that are just fine when taken in moderation but destructive when pushed to excess. The problem for the handloader is that we frequently don't know we're in trouble until it's much too late.

The use of primer appearance as an indicator of safe pressure has been thoroughly discredited. By the time primers are markedly flattened, pressures can be considerably above maximums.

As long as we stick with published data everything is fine, but suppose we want to develop a load for a new wildcat, or try a promising new powder in a standard cartridge? Published load data may not exist, but there is a way to find a sane stopping point.

We can do this by measuring the expansion at the very base of the cartridge case, just above the extractor groove. This is the thickest point on the case so expansion here is a good indicator of pressure.

A blade micrometer is the proper tool for this task. You can't make this sort of measurement with conventional calipers or even a micrometer. The anvil (contact surface) on those is much too large to make a measurement on such a small area.

It also has to be capable of measuring to four decimal places. Most calipers only read to three places, or one thousandth of an inch. In order to really get

a clue we have to be able to measure to one ten-thousandth of an inch (0.0001 "). Machinists commonly call these increments tenths.

[221 Fireball]

 You have an interesing thing going on. I reload for all my rifles and handguns. I know you said about your factory ammo having flattened primers, I noticed Federal primers have a knack for flattening quicker than most others. Have a very few rifles with custom barrels, and never really noticed bad pressure signs (primer flattening). I don't have any T/C Contender type single shot rifles, mine are variety of bolt rifles. The chamber guage from Sinclair would be a good idea. Or if you know a good gunsmith in your area that could be a good choice. Which calibers are you using? Some of the gunsmiths are really up on some of these new factory rifles and components, and they could tell you over the phone that T/C's barrels may have tight chamber's. Just an example, not saying they do. A chamber cast is a tell all, we did them quite regularly on our BPCR rifles. But if your rifles are shooting really well, and your not having casing problems, runout or seperation I wouldn't be too concerned.

[uncle buck]

One of the T/C Encore barrels is a 308 Win Prohunter 28 inch stainless barrel.. The other is a Encore 22250 24 inch blued barrel. My other Encore barrels both custom or factory T/C don't do this.. By the way it was the Federal 308 Win factory ammo that the primers did flatten. Can't remember when I did shoot factory 22250 ammo if the primers were flatten.  However both of these barrels shoot accurate.. The 22250 even with Partion 60 grain deer bullets and IMR 4350 powder is so accurate.

Buckwheat and 221 Fireball thank you for your info...Ah reloading...I do find it quite relaxing to do this when I can't get out...This year I was on light duty for 2 months after a hernia operation...It was so nice to get rid of my cabin fever by reloading shotgun shell...buckshot...and all kinds of reloads for my predator guns..

[Dale]

it could be soft primers or a headspace issue... with the factory ammo I'd think more a headspace issue... what happens is upon ignition the case is driven forward by the firing pin, pressure builds and starts to push the primer out... then you hit max pressure, the case is pushed back and it flattens the primer upon the case hitting the breech face... this can be alleviated by necksizing your cases and not setting your shoulder back to factory specs...