Primer pocket dimension

[Jtate]

If a small rifle primer is .175 how many thousand smaller is the primer pocket on let's say a new Laupa 6mm br case, and how consistent is that dimension lot to lot of brass?

 

[Chiquita]

I don't have a new 6mm Lapua. But FWIW, my Lapua .308 SRP is. 0.1725 and my primer pocket checking tool is 0.1725.

 

[RegionRat]

That answer varies over time by the batch lot, but it is basically controlled by specification that allows the following spec and it shows SRP should be within a range of 0.0015" dia.

I recall a few batch lot measurements where the best I had as little as 0.0002" spreads, and other times when I had something like 0.0007" spreads, but mostly in between there someplace depending on the source.

Some of this was due to the tool maintenance and some of it was just the nature of the brass.

 

[Nick Caprinolo]

When I get new brass, I always uniform the pockets.

 

[Jtate]

I want to order some pin gauges to check the pockets, they are only 2.50 each, so if I use a 1.73 as go and a 1.74 as a no go, does that sound right for a good pocket?

 

[RegionRat]

I want to order some pin gauges to check the pockets, they are only 2.50 each, so if I use a 1.73 as go and a 1.74 as a no go, does that sound right for a good pocket?

No, you slipped a decimal for starters.

When you look for pin gages, you will find they tend to come in sets when they go in steps of 0.0001". For example a Deltronic brand set contains a center value plus ten steps above and ten steps below in 0.0001" steps. We used a set made up with steps well above and well below the tolerance range to be able to report things that went out of spec.

Some companies offer pins in bigger increments that would be "good enough" for home use. There are also tools that are a simple Go-No-Go that also work, but won't gage the hole. For a Go-no-go set, I would just grab the Ballistic Tools and be done with it.

Try Vermont gage if you want to fill out a set that spans from 0.1730" to 0.1745" and just decide how many steps in between you want. Or, you can watch surplus sites and be ready when gages come up second hand.

https://vermontgage.com/

https://deltronic.com/class-x-pin-gages/

https://ballistictools.com/store/small-and-large-primer-pocket-gauges

 

[Chiquita]

This is what I have.

Small and Large Primer Pocket Swage Gage ® Set

Swage Gage Small Primer Pocket Gauge

ballistictools.com

 

[Webster]

I want to order some pin gauges to check the pockets, they are only 2.50 each, so if I use a 1.73 as go and a 1.74 as a no go, does that sound right for a good pocket?

If it takes resistance to push a primer in and you feel resistance pushing out a fired primer why would you have to measure anything?

 

[RegionRat]

why would you have to measure anything?

You don't "have to" if you don't want to.... Heck, you don't have to get out of bed in the morning either... but many of us do it anyway.... (Just kidding)

Why invest in gaging primer pockets?
There are more than a few optional reasons to want to know. Since we are just passing time here I will give you an optional view. You can opt to have a go-no-go gage, or even pins to be able to actually measure pocket diameters, but you don't have to.

Some of us are not BR shooters and can prep or fully load in advance for large batches.

Knowing the dimensions of a batch of brass pockets and primers is not necessarily for the present loading, some of us use it for planning purposes to know if the next time will mean that batch goes in the trash and we had better either have the next batch in hand or know where it will come from. Pushing your luck with loose primer pockets generally ends with erosion on the bolt face.

If you think about traveling with a few thousand rounds of 223 or 204R loads that might get used in an AR platform, it makes sense to gage primer pockets. When you learn how an AR works in terms of pressure and brass, you can tell when the brass will start to give you trouble in advance. It really helps with planning for the next year when discussing PD shooting or Service Rifle competition. AR platforms are notoriously hard on primer pockets and generally that issue drives the brass life if you do everything else right.

You can absolutely get away with feel. But keep in mind, the "feel" depends on both sides of the relationship, the primer batch and the brass batch.

Is that feel soft because the pockets are getting loose, or is it just these primers in this brass? Will this be the last cycle on the brass? But you could just go by feel if you had to. I just never want to see bolt face erosion on my rigs and getting large batches of brass is getting more and more difficult these days.

I choose to have the gage pins around in order to know how the pocket diameters are running. It isn't expensive or difficult if you are the sort that is okay with spending on gage pins. I also have them in 0.0001" steps for the necks, not just the primer holes. But to each their own... YMMV

 

[Ned Ludd]

I also use the Ballistic Tools primer pocket gauges: https://ballistictools.com/store/small-and-large-primer-pocket-gauges. They work.

I use .308 Win "Palma" brass (SRP) for the most part in .308 F-TR loads, and I have not felt the need to use the tool with that brass very often. The "extra" metal around the primer pocket renders Palma brass much more resistant to pressure. However, I also load .223 Rem for F-TR and the loads are fairly stout. As a result, brass life isn't the greatest and the Ballistic Tools gauge makes it very easy to cull cases where the pocket will no longer hold a primer. It is not easy to tell by force/pressure when removing the previous spent primer whether the pocket is good. Doing so requires a certain amount of force even if the pocket is trashed. I can't explain why the last spent primer doesn't just easily fall out once the pocket has enlarged beyond the usable range, but it doesn't. The gauge makes it very easy to check cases once they have been cleaned, so you aren't wasting time processing cases with trashed primer pockets any further.

 

[Webster]

You don't "have to" if you don't want to.... Heck, you don't have to get out of bed in the morning either... but many of us do it anyway.... (Just kidding)

Why invest in gaging primer pockets?
There are more than a few optional reasons to want to know. Since we are just passing time here I will give you an optional view. You can opt to have a go-no-go gage, or even pins to be able to actually measure pocket diameters, but you don't have to.

Some of us are not BR shooters and can prep or fully load in advance for large batches.

Knowing the dimensions of a batch of brass pockets and primers is not necessarily for the present loading, some of us use it for planning purposes to know if the next time will mean that batch goes in the trash and we had better either have the next batch in hand or know where it will come from. Pushing your luck with loose primer pockets generally ends with erosion on the bolt face.

If you think about traveling with a few thousand rounds of 223 or 204R loads that might get used in an AR platform, it makes sense to gage primer pockets. When you learn how an AR works in terms of pressure and brass, you can tell when the brass will start to give you trouble in advance. It really helps with planning for the next year when discussing PD shooting or Service Rifle competition. AR platforms are notoriously hard on primer pockets and generally that issue drives the brass life if you do everything else right.

You can absolutely get away with feel. But keep in mind, the "feel" depends on both sides of the relationship, the primer batch and the brass batch.

Is that feel soft because the pockets are getting loose, or is it just these primers in this brass? Will this be the last cycle on the brass? But you could just go by feel if you had to. I just never want to see bolt face erosion on my rigs and getting large batches of brass is getting more and more difficult these days.

I choose to have the gage pins around in order to know how the pocket diameters are running. It isn't expensive or difficult if you are the sort that is okay with spending on gage pins. I also have them in 0.0001" steps for the necks, not just the primer holes. But to each their own... YMMV

Cannot disagree with your point of view. 52 years of non-competitive BR shooting and GH hunting. Never had a bad primer pocket.

 

[Walt Krafft]

Gaging the primer pockets is only half of the system. You will need to gage the primers too. And they will both have a range of sizes. A better option IMO is to monitor the resistance felt when seating a primer in the case. If there is no resistance there is a problem.

 

[Jtate]

If it takes resistance to push a primer in and you feel resistance pushing out a fired primer why would you have to measure anything?

All the reasons RegionRat said. Plus I am going to try to tighten up some loose pockets, So I needed to know the "spec".

 

[Doom]

All the reasons RegionRat said. Plus I am going to try to tighten up some loose pockets, So I needed to know the "spec".

How do plan on doing that?

 

[Jtate]

I got a plan, if it works I will PM you