Rim Thickness

[Bench Addict]

Has anyone here ever tried sorting brass by rim thickness to gain more round-to-round primer seating depth consistency for improved ignition consistency (MV ES)?

 

[Fast14riot]

Just get a priming system that isn't rim thickness dependant.

 

[Bench Addict]

Just get a priming system that isn't rim thickness dependant.

That is the easy answer although very limiting: Lee APP (yuck) or Sinclair. No "good" bench priming tool that isn't rim thickness dependant to choose from. The Sinclair is a very nice hand tool and I do have one, but is not very fun to get dialed into a specific optimal seating depth. Once it is set, I leave it set for that cartridge and pretty much buy another one for every different cartridge.

 

[Fast14riot]

Whats wrong with the Lee? Easy to modify so it's adjustable for primer depth.

 

[Bench Addict]

I've just never been happy with the quality of their products. My solution to rim thickness dependancy is the RPG tool. Allows me to use any primer seater I want (Primal Rights CPS in my case) and I can eliminate the whole issue down to +/-0.0005" seated primer variation with minimal effort. Can get even less than that but I don't believe there is much benefit in trying for less than +/-0.0005".

 

[Fast14riot]

When are you going to have them in production or how long is your pre-order?

 

[Bench Addict]

First run of them is done, a little over half of them are gone. Website shows pre-order only but I still have some in stock. Stock will get updated once the waitlist and new pre-orders have been fulfilled. If you want one then place a pre-order and it will ship out later this month.

Rabbit Hole Precision, LLC

 

[ebb]

Is there any data that suggest primer seating depth has an effect on accuracy? I read all about it here but have never seen it mentioned on any of the other gun sites. Yes, I think rim fire rim thickness has an effect on consistency, and would have an accuracy effect, but maybe not that the actual thickness has any effect. I am not trying to rain on anyone's parade just seeking accuracy, and trying to not do stuff that may not matter. I've seated to the bottom of the pocket from day one, and had 300 RUM with single digit ES. Then on some others not so much.

 

[Bench Addict]

Is there any data that suggest primer seating depth has an effect on accuracy? I read all about it here but have never seen it mentioned on any of the other gun sites. Yes, I think rim fire rim thickness has an effect on consistency, and would have an accuracy effect, but maybe not that the actual thickness has any effect. I am not trying to rain on anyone's parade just seeking accuracy, and trying to not do stuff that may not matter. I've seated to the bottom of the pocket from day one, and had 300 RUM with single digit ES. Then on some others not so much.

There is data supporting it but it's useless to share because everyone's level of benefit varies by lot to lot, brand to brand, or priming tool to priming tool. I'm a nutshell, the more variation you have in your rims - the greater the benefit of sorting them by rim thickness.

 

[ebb]

I certainly get that.

 

[Webster]

Is there any data that suggest primer seating depth has an effect on accuracy? I read all about it here but have never seen it mentioned on any of the other gun sites. Yes, I think rim fire rim thickness has an effect on consistency, and would have an accuracy effect, but maybe not that the actual thickness has any effect. I am not trying to rain on anyone's parade just seeking accuracy, and trying to not do stuff that may not matter. I've seated to the bottom of the pocket from day one, and had 300 RUM with single digit ES. Then on some others not so much.

Right on. Seat to the bottom of the pocket by feel. Nothing to measure. The ultimate consistency.

 

[Bench Addict]

Right on. Seat to the bottom of the pocket by feel. Nothing to measure. The ultimate consistency.

Hard to make that claim until you've tested both ways, although you'd need a rim thickness gauge in order to seat with the most consistency by measurement. Perhaps you are able to "feel" to the precision of +/-0.0005" but I personally do not know anyone who can (let alone repeatably). Not trying to be snarky, just being straight forward and honest.

 

[Webster]

Hard to make that claim until you've tested both ways, although you'd need a rim thickness gauge in order to seat with the most consistency by measurement. Perhaps you are able to "feel" to the precision of +/-0.0005" but I personally do not know anyone who can (let alone repeatably). Not trying to be snarky, just being straight forward and honest.

Seating a certain distance from the case head should have nothing to do ignition consistency? If the firing pin pushes the primer cup forward you have a problem. Every case and primer has its own dimensions which will determine the resistance to the cup getting pushed forward. if a primer gets pushed forward by the FP firing pin energy is lost. You probably cannot test primers unless you have a rifle that can shoot groups close to 1's. and you shoot in a tunnel. If you don't seat to the bottom of the pocket, you don't know how much FP energy is being used to set the primer charge off. Even if you don't have failure to fire you have inconsistency in energy setting the charge off. I would think seating to the bottom of the pocket would give you the most consistency possible. The cup rim edges contact the bottom of the pocket and the anvils are always pushed the same amount since the cup cannot go any farther than the bottom of the pocket. I don't need to test. I am happy with my results.

 

[Fast14riot]

Primers seated to high can cause fliers, primers crushed can cause poor ES/SD. Primers seated to bottom of pocket give the most consistent ignition.

 

[Bench Addict]

I'm not going to debate with anyone that seating by measurement (given you know the pocket depth and primer height) is better than seating by feel. As a matter of fact: these two different styles create quite a rivalry amongst shooters. What i will say is that my testing as well as many others that have the mentioned method have found lower ES over seating by feel. I do not believe there is anyway to convince a "feel" guy otherwise unless there were a whole crew of guys gathered at the same place doing the testing. And even then (in my experience) they always have some comment to throw to make all testing null and their method correct; or they'll just say seating by feel is "good enough" and can't shoot the difference anyways.

Bryan Zolnikov just took 1st place last year in 600yd benchrest nationals using this very method and my RPG tool to sort rims. Take it for what it's worth.

 

[Webster]

Primers seated to high can cause fliers, primers crushed can cause poor ES/SD. Primers seated to bottom of pocket give the most consistent ignition.

I'm not going to debate with anyone that seating by measurement (given you know the pocket depth and primer height) is better than seating by feel. As a matter of fact: these two different styles create quite a rivalry amongst shooters. What i will say is that my testing as well as many others that have the mentioned method have found lower ES over seating by feel. I do not believe there is anyway to convince a "feel" guy otherwise unless there were a whole crew of guys gathered at the same place doing the testing. And even then (in my experience) they always have some comment to throw to make all testing null and their method correct; or they'll just say seating by feel is "good enough" and can't shoot the difference anyways.

Bryan Zolnikov just took 1st place last year in 600yd benchrest nationals using this very method and my RPG tool to sort rims. Take it for what it's worth.

It's been a while since I reloaded due to surgery. Some brands of primers the anvils don't protrude outside the cup. If I remember correctly one of the brands I use the anvil legs are only about 5 thou outside the cup. That means the anvil legs can only be pushed into the cup to the height of the cup edge. The legs may get bent inward without the center of the anvil moving very little. It’s the pointed center of the anvil that sets the charge off. The legs support the center of the anvil so it has resistant to movement. The FP dents the cup and pushes the charge into the anvil center, The anvil doesn’t move into the charge. If the legs don't support the anvil some FP energy must get lost. If you seat to a certain ht. the anvil legs are kind of floating in open space. We cannot measure good ignition we can only look at the target. I guess ES is an indicator of good ignition mixed in with the effects of powder type and weight. I know the FP where it goes thru my bolt shroud has a lot of rubbing but I don't want to spend the money to fix it. It's a big contributor to bad ignition.

Don't understand rim thickness.

 

[Bench Addict]

It's been a while since I reloaded due to surgery. Some brands of primers the anvils don't protrude outside the cup. If I remember correctly one of the brands I use the anvil legs are only about 5 thou outside the cup. That means the anvil legs can only be pushed into the cup to the height of the cup edge. The legs may get bent inward without the center of the anvil moving very little. It’s the pointed center of the anvil that sets the charge off. The legs support the center of the anvil so it has resistant to movement. The FP dents the cup and pushes the charge into the anvil center, The anvil doesn’t move into the charge. If the legs don't support the anvil some FP energy must get lost. If you seat to a certain ht. the anvil legs are kind of floating in open space. We cannot measure good ignition we can only look at the target. I guess ES is an indicator of good ignition mixed in with the effects of powder type and weight. I know the FP where it goes thru my bolt shroud has a lot of rubbing but I don't want to spend the money to fix it. It's a big contributor to bad ignition.

Don't understand rim thickness.

This is good and glad to see the subject staying on track. In hindsight, perhaps I should have been more clear on exactly what is measured and what grounds these measurements are based upon.

With a fresh box of virgin brass and my primer of choice, I will sit and measure at least 25 primers out of a sleeve from a brick of all same lot number. Overall primer height gets measured, cup height gets measured, and it is all charted into Microsoft excel spreadsheet to calculate anvil protrusion for each primer, average overall height, average cup height and average anvil protrusion. With Fed GM210M primers, I generally find around 0.008-0.010" anvil protrusion. If I can cut/uniform my primer pockets to average overall primer height, then that is most ideal and makes for easy math on anvil preload. With the pockets uniformed, the relationship between the case head surface and bottom of the pocket is consistent from casing to casing within +/-0.0005" (or less). This gives me a reliable reference point for measuring seated primers which generally are getting 0.008" anvil preload (aka: "crush" for lack of good terms).

My findings on lapua brass rim thickness variation is +/-0.0015" at best which translates into 0.003" extreme spread on thickness which puts me outside of my window for optimal ignition which is 0.007-0.009" anvil preload. I'm not sure how to paint the picture in text to explain the correlation between rim thickness and seated primer depth but it is in fact 100% tried and true (no b.s.).

I generally like to stick with my Fed GM primers but will switch them up for CCI BR's if needed. I don't really use anything else.

 

[Bench Addict]

Best way I can describe rim thickness subject in as few words as possible is:
Due to the nature of where a shell holder holds the casing in a micrometer adjustable priming tool - a thicker rim will give deeper seated primers while thinner rims will give shallower seated primers. That is unless you are using a priming tool that is not rim thickness dependant such as the Lee APP or the Sinclair hand priming tool.

 

[Fast14riot]

Rim thickness is a factor in floating shell holders that index off the extractor groove side of the rim. Priming tools that lock the case head down to a reference surface do not exhibit a correlation of variation of primer depth to rim thickness. I do agree that too much or too little is bad, however the window for just right I have found to be rather wide in my case. I do uniform pockets, but do not clean them and I seat by feel to bottom of pocket.

Either way, I'm happy to see new products for the precision loading scene and wish you the best.

 

[ShtrRdy]

@Bench Addict -- how do you go about measuring the height of primers?