primer seating depth
- Thread starter cptjack
- Start date
Aguila Blanca
Staff
Duplicate threads merged.
I'm a benchrest shooter , I try my best to make every round measurements as exact as possible , using a uniformer on the primers pockets making all the depths the same . Only has to be used once so no big deal . Does it help in group size , if I could shoot a one hole 10 shot group then maybe I could answer that . It cuts down on the excuses , thank God for wind.
No, seating to same depth is no guarantee they'll all fire uniformly.
Even with the primer cup, anvil pellet and seal are all uniform in their thickness and composition, seating all to a given depth below the case head is no guarantee they'll all fire uniformly.
Anyone ever notice that striker springs weaken with age and shots at longer ranges start stringing more vertically plus group center is lower requiring more sight elevation?
Even with the primer cup, anvil pellet and seal are all uniform in their thickness and composition, seating all to a given depth below the case head is no guarantee they'll all fire uniformly.
Anyone ever notice that striker springs weaken with age and shots at longer ranges start stringing more vertically plus group center is lower requiring more sight elevation?
Last edited:
at the risk of derailing the thread I tried the primer seaters which allow the depth to be dialed in. I found them to be unsatisfactory because cup depth tends to vary .001 or so. Therefore to be effective each primer needed to be measured and sorted. I went back to my RCBS bench primer, I find it gives me the best "feel" of any primer seating device I have used, plus it easiest on the hands which have more than a tad of arthritis setting in. Just my opinion
edit- the purpose of uniform seating is to provide uniform lock time which is the time from when the sear breaks to when the firing pin (or striker) hits the primer. It is actually more important to a three position shooter than a benchrest shooter. Lock time is measured in milliseconds but during that time a shooters position can vary resulting in a pulled shot or flyer so the faster the better if you are shooting unsupported. Bart pointed out a strong firing pin spring is an important factor in a fast lock time. I change my firing pin springs every 2000 rounds or so, they are cheap and easy to replace.
edit- the purpose of uniform seating is to provide uniform lock time which is the time from when the sear breaks to when the firing pin (or striker) hits the primer. It is actually more important to a three position shooter than a benchrest shooter. Lock time is measured in milliseconds but during that time a shooters position can vary resulting in a pulled shot or flyer so the faster the better if you are shooting unsupported. Bart pointed out a strong firing pin spring is an important factor in a fast lock time. I change my firing pin springs every 2000 rounds or so, they are cheap and easy to replace.
Last edited:
Competative and benchrest shooters have their own reasons for obsessing over primer seating.
Us recreational, hunting, and paper punchers only need to make sure the bottom of the primer pocket is free of debris that would keep the primer from seating below the case head by .001 or so. Your finger can easily feel if the primer is hi or flush (not desirable) or below the head (safer and desireable).
Us recreational, hunting, and paper punchers only need to make sure the bottom of the primer pocket is free of debris that would keep the primer from seating below the case head by .001 or so. Your finger can easily feel if the primer is hi or flush (not desirable) or below the head (safer and desireable).
oldmanFCSA
New member
As a 50BMG Target shooter, my primer seating methods vary from my other priming techniques.
Using the CCI#35 Arsenal primers, I do several steps to ensure consistent ignition of primers. The Arsenal primer is quite domed and RCBS provides a concave primer seater stem that fits this primer.
First I use my Primer Pocket Swaging tool to push the military crimp out of pocket, a slight taper is all that's required to permit easy entry of primer.
Second, because I use various military lots of brass, I uniform the primer pocket with the K&M Uniforming tool to clean primer pocket to a consistent depth cleaning corners to permit proper seating of primers.
Third, using the RCBS seating stem, I seat the CCI#35 primers until anvil and cup press firmly into bottom of pocket.
Then Fourth, I add a step that only applies to target shooters using the CCI#35 primers previously seated to depth, I slowly flatten the dome of the rounded top of primer using a flat pin (I reuse my Swage Tool for this purpose) resulting in 70-80% flattened primer face, and 0.002-0.010" below base face
WHY do we (FCSA Members) "ARM" CCI#35 primers using this method, because some target rifles have a soft spring on firing pin that does not hit with force required to uniformly set off the military styled primer. By slightly crushing the primer mix to a uniform thickness, Ignition of these CCI#35 primers is enhanced.
To avoid the CCI#35 Arsenal primer issue, use RWS primers IF you can find them.
YMMV.
Using the CCI#35 Arsenal primers, I do several steps to ensure consistent ignition of primers. The Arsenal primer is quite domed and RCBS provides a concave primer seater stem that fits this primer.
First I use my Primer Pocket Swaging tool to push the military crimp out of pocket, a slight taper is all that's required to permit easy entry of primer.
Second, because I use various military lots of brass, I uniform the primer pocket with the K&M Uniforming tool to clean primer pocket to a consistent depth cleaning corners to permit proper seating of primers.
Third, using the RCBS seating stem, I seat the CCI#35 primers until anvil and cup press firmly into bottom of pocket.
Then Fourth, I add a step that only applies to target shooters using the CCI#35 primers previously seated to depth, I slowly flatten the dome of the rounded top of primer using a flat pin (I reuse my Swage Tool for this purpose) resulting in 70-80% flattened primer face, and 0.002-0.010" below base face
WHY do we (FCSA Members) "ARM" CCI#35 primers using this method, because some target rifles have a soft spring on firing pin that does not hit with force required to uniformly set off the military styled primer. By slightly crushing the primer mix to a uniform thickness, Ignition of these CCI#35 primers is enhanced.
To avoid the CCI#35 Arsenal primer issue, use RWS primers IF you can find them.
YMMV.
Seat the primer til it is bottomed out in the primer cup. Actual distance below the bottom of the case is not the most important thing. You can feel with your finger if the primer is actually high. If it is high your gonna have some problems. I clean the cups on rifle ammo but not on handgun ammo, it's not necessary, it may not be necessary for rifle but I do it anyway.
OldmanFSCA is echoing the principles worked out for maximum consistency and reliability by NOIH (Naval Ordnance at Indian Head) in the early '80s. They found for the standard small arms primers that they all needed to be "reconsolidated" for best performance. "Reconsolidation" means the primer and anvil are "consolidated" into an assembly by the primer maker, and seating pushes the anvil in deeper, thus reconsolidating it. Allan Jones refers to this as "setting the bridge", which is apparently an industry term. I don't know the standard NOIH used to measure the effect other than the standard H test, but I have seen a description of the primer test apparatus McDonnell-Douglas used in assessing primers as including UV and flame temperature and explosive impulse measurements, so it may have been something fancy llike that.
The bottom line was that while Olin and Remington had recommended reconsolidation of 0.002"-0.006" for all small arms primers up until 1981 (IIRC), NOIH recommendations were narrower and called for 0.002" to 0.004" of reconsolidation with both sizes. The only thing I've seen different from that is specific to Federal primers, which we all know use a slightly different form of lead styphnate in its standard primers. In Precision Shooting magazine in the mid-'90s Federal was quoted as having recommended 0.002" of reconsolidation for small rifle primers and 0.003" for large rifle primers.
The only commercial tool I am aware of that lets you control reconsolidation directly is the K&M primer gauge tool, but it is slow to use as it requires both a measuring step to allow for the depth of the individual primer pocket and the height of the individual primer going into it, and then the actual seating step. It is slow going, and I vaguely recall one of the benchrest shooters writing around then (Dick Wright, maybe) mentioning that he had given that up because of the tedium involved, but that his wife had continued the practice and seemed to be beating him at all the matches they'd recently shot in.
The first person I am aware of to bring the idea reconsolidating could have a significant effect to the public was the late Creighton Audette, whose last three articles for PS Magazine were about the "analog" nature of primers. By that he meant how much they were reconsolidated affected how hot and consistently they performed. Resulting velocity SD was one metric used to validate this. Up until then, many benchrest shooters favored seating primers only until you could just feel the feet of the anvil kissing the bottom of the primer pocket. Audette's experiments showed you need more pressure than that, and he proposed a primer seating tool design that later was realized by Sinclair as their hand priming tool. It was to give better feel to primer seating, though the later-developed K&M tool I mentioned lets you read consolidation directly on a dial indicator so you don't have to guess by the feel.
However, putting special tools aside for a moment, it seems just knowing you need some degree of reconsolidation puts you ahead on the subject. In the 1995 Precision Shooting Reloading Guide, Dan Hackett wrote:
So that gives you some idea about what you are looking for when you experiment with priming. Whether getting your velocity SD down from 20 fps to 10 fps is something that matters in and of itself depends on the range you shoot at, but keep in mind that here a low SD is being used to indicate consistent ignition. At 100 yards, velocity SD doesn't contribute much vertical stringing, but getting barrel time and pressure waves consistent still may shrink your groups. Unfortunately, you have to try it to find out.
As to how far below the back end of the case you should seat a primer, Hounddawg is correct that there is enough variation in primer pocket depth and anvil height after initial consolidation to cause that indicator to be too imprecise to be relied on to produce the most exact possible effects.
The bottom line was that while Olin and Remington had recommended reconsolidation of 0.002"-0.006" for all small arms primers up until 1981 (IIRC), NOIH recommendations were narrower and called for 0.002" to 0.004" of reconsolidation with both sizes. The only thing I've seen different from that is specific to Federal primers, which we all know use a slightly different form of lead styphnate in its standard primers. In Precision Shooting magazine in the mid-'90s Federal was quoted as having recommended 0.002" of reconsolidation for small rifle primers and 0.003" for large rifle primers.
The only commercial tool I am aware of that lets you control reconsolidation directly is the K&M primer gauge tool, but it is slow to use as it requires both a measuring step to allow for the depth of the individual primer pocket and the height of the individual primer going into it, and then the actual seating step. It is slow going, and I vaguely recall one of the benchrest shooters writing around then (Dick Wright, maybe) mentioning that he had given that up because of the tedium involved, but that his wife had continued the practice and seemed to be beating him at all the matches they'd recently shot in.
The first person I am aware of to bring the idea reconsolidating could have a significant effect to the public was the late Creighton Audette, whose last three articles for PS Magazine were about the "analog" nature of primers. By that he meant how much they were reconsolidated affected how hot and consistently they performed. Resulting velocity SD was one metric used to validate this. Up until then, many benchrest shooters favored seating primers only until you could just feel the feet of the anvil kissing the bottom of the primer pocket. Audette's experiments showed you need more pressure than that, and he proposed a primer seating tool design that later was realized by Sinclair as their hand priming tool. It was to give better feel to primer seating, though the later-developed K&M tool I mentioned lets you read consolidation directly on a dial indicator so you don't have to guess by the feel.
However, putting special tools aside for a moment, it seems just knowing you need some degree of reconsolidation puts you ahead on the subject. In the 1995 Precision Shooting Reloading Guide, Dan Hackett wrote:
"There is some debate about how deeply primers should be seated. I don’t pretend to have all the answers about this, but I have experimented with seating primers to different depths and seeing what happens on the chronograph and target paper, and so far I’ve obtained my best results seating them hard, pushing them in past the point where the anvil can be felt hitting the bottom of the pocket. Doing this, I can almost always get velocity standard deviations of less than 10 feet per second, even with magnum cartridges and long-bodied standards on the ’06 case, and I haven’t been able to accomplish that seating primers to lesser depths."
Dan Hackett
Precision Shooting Reloading Guide, Precision Shooting Inc., Pub. (R.I.P.), Manchester, CT, 1995, p. 271.
Dan Hackett
Precision Shooting Reloading Guide, Precision Shooting Inc., Pub. (R.I.P.), Manchester, CT, 1995, p. 271.
So that gives you some idea about what you are looking for when you experiment with priming. Whether getting your velocity SD down from 20 fps to 10 fps is something that matters in and of itself depends on the range you shoot at, but keep in mind that here a low SD is being used to indicate consistent ignition. At 100 yards, velocity SD doesn't contribute much vertical stringing, but getting barrel time and pressure waves consistent still may shrink your groups. Unfortunately, you have to try it to find out.
As to how far below the back end of the case you should seat a primer, Hounddawg is correct that there is enough variation in primer pocket depth and anvil height after initial consolidation to cause that indicator to be too imprecise to be relied on to produce the most exact possible effects.
scatterbrain
New member
To remove 'me" from the equation of feeling the primer bottom out, I started using a K&M depth cutter to uniform my depth of pocket, .131" for large and .121" for small. This measures from the base of the case. I then use a K&M primer setter to get each to the same depth, this measures from the inside edge of the case rim. That's when I learned that rims aren't the same thickness at all! Now I have made a gauge using a dial indicator that measures from the top of the case to the top of the primer that tells me they are set the same, to the nearest .0005". I also get SD's below 10 just about every time out. Does this make me shoot better, there's still "me" at the trigger.
In my view, overthinking has to be tested rather than assumed. It's only sure to be true after the fact, unfortunately. I say that because sometimes you surprise yourself by finding something that makes a significant improvement when it makes little abstract sense to believe it would do so. I had flash hole deburring reduce group size 40% with one powder (2520) in .308 after everyone told me even considering taking that sort of benchrest competitor's step was overthinking and a waste of time, and that was in an M1A, which is not exactly a benchrest gun. It made no difference with any other powder I tried, but that one needed it in that gun. One of the Precision Shooting authors reported outside neck turning took a 300 WM of his from a 2 moa gun to a 1 moa gun after he had tried every other reloading trick he could think of to get it to shoot. It's another a time-consuming benchrest competitor's step that most folks see as overthinking to contemplate, but in that instance, it wasn't.
Perfect primer seating seems likely to like those examples. I imagine following Dan Hackett's admonition simply to seat primers hard will usually get you all the help you can expect, and doing that doesn't take any special tools or extra time. But somewhere will be a gun and powder and bullet combination that just has to have the primers seated perfectly to minimize its groups, and I only know one way to find out if that is the gun I happen to have.
Scatterbrain,
I don't know which K&M tool you got, but the primer/gauge tool does not register from the inside edge of the rim. It drives the seating ram up until it stops against the bottom of the primer pocket, locating that as its reference point regardless of how low or high rim thickness has positioned it. It subtracts the height of the primer you placed on the platform from that location at the same time. At that point, the dial needle stops moving even if you push harder, so you can turn the indicator's dial bezel to put its zero at the needle location. Then you remove the case and take the primer from the platform and put it into the primer guide sleeve on top of the ram, put the case back in, and run the ram back up. As the primer pushes in, the needle returns to the zero you set exactly when the primer anvil feet are even with the location of the bottom of the primer pocket. That is where further seating becomes harder. At that point, every thousandth the needle shows you have seated the primer past zero is a thousandth of reconsolidation. You can push until the needle is just three thousandths beyond zero to achieve what NOIH considered ideal reconsolidation.
Perfect primer seating seems likely to like those examples. I imagine following Dan Hackett's admonition simply to seat primers hard will usually get you all the help you can expect, and doing that doesn't take any special tools or extra time. But somewhere will be a gun and powder and bullet combination that just has to have the primers seated perfectly to minimize its groups, and I only know one way to find out if that is the gun I happen to have.
Scatterbrain,
I don't know which K&M tool you got, but the primer/gauge tool does not register from the inside edge of the rim. It drives the seating ram up until it stops against the bottom of the primer pocket, locating that as its reference point regardless of how low or high rim thickness has positioned it. It subtracts the height of the primer you placed on the platform from that location at the same time. At that point, the dial needle stops moving even if you push harder, so you can turn the indicator's dial bezel to put its zero at the needle location. Then you remove the case and take the primer from the platform and put it into the primer guide sleeve on top of the ram, put the case back in, and run the ram back up. As the primer pushes in, the needle returns to the zero you set exactly when the primer anvil feet are even with the location of the bottom of the primer pocket. That is where further seating becomes harder. At that point, every thousandth the needle shows you have seated the primer past zero is a thousandth of reconsolidation. You can push until the needle is just three thousandths beyond zero to achieve what NOIH considered ideal reconsolidation.
The only possible benefit I can see of having primers seated perfectly would be consistent lock times. Bear in mind here we are dealing in milliseconds when discussing lock times. A millisecond could affect of difference could affect the POA in a minor way on a unsupported rifle. When using a bipod or front rest I seriously doubt there would be any effect at all since the rifle is being held perfectly steady.
Also remember that even in the same card of primers cup thickness can vary slightly so you will need to check each primer even if using a primer seating tool this allows adjustment. I have the Darrel Holland mod for my RCBS bench tool that allows adjustment but after experimenting a bit I simply set it to seat the primers to the bottom and go by feel. After a few hundred primers you can tell when the primer hits bottom and preload.
I do uniform my cases pockets before the first firing and use wet/pin cleaning for to keep them clean. I also check the depth to ensure it is between .003 and .006 below the case head just as the USAMU recommends. That may be overthinking but I am the odd bird that enjoys case prep
Also remember that even in the same card of primers cup thickness can vary slightly so you will need to check each primer even if using a primer seating tool this allows adjustment. I have the Darrel Holland mod for my RCBS bench tool that allows adjustment but after experimenting a bit I simply set it to seat the primers to the bottom and go by feel. After a few hundred primers you can tell when the primer hits bottom and preload.
I do uniform my cases pockets before the first firing and use wet/pin cleaning for to keep them clean. I also check the depth to ensure it is between .003 and .006 below the case head just as the USAMU recommends. That may be overthinking but I am the odd bird that enjoys case prep
scatterbrain
New member
UNCLENICK, i didn't blow the budget on the best one K&M made with the gage. The one I have lets you set the depth of the primer by limiting the movement of the ram. A Lee case holder is used and that indexes off the inside of the case rim. The rims vary in thickness, causing the difference is depth of the primer. Now, I have no idea what the ideal depth is, but I do know they are the same depth.
I have both K&M tools. They are operated differently. If you are interested, check with K&M to see if the one you have can be converted (the original versions could be, but they changed the Primer Gauge tool so it couldn't be done to the original version of the simple tool that I have, but I don't know if that applies to one purchased more recently or not).
Assuming you are not interested in doing in that, you can use the tool you have by turning the ram out so that you are seating by feel before the end of the paddle stroke. It is pretty hard not to notice when the primer touches bottom as its slide into the pocket stops and you feel the added resistance. Different makes and lots of brass and brass with different load histories can feel different, so you want to keep your brass segregated by having those factors in common. One thing to do about the feel difference, as long as your chamber's excess headspace isn't too big, is you can wet the primer pockets using a cotton swab dipped into a thin mix of alcohol and graphite and allow the alcohol to dry off before seating. This increases the feel of the difference between the primer sliding in and stopping on the bottom by minimizing the effect of friction between the pocket and primer cup.
Once your primer touches down, you can simply press hard, as Hackett did. But you can also calibrate your actions. Use a depth mic to measure how far below flush with the case head the primer is when it has just touched down. Then pop the case back into the tool and push a little harder and take it back out and measure the effect. Keep repeating until you find what it feels like to compress the primer 0.002"–0.004" past the touchdown point.
You could set the tool on a bathroom scale to measure your pressing effort, I suppose, but I don't think you'll need to go that far.
Assuming you are not interested in doing in that, you can use the tool you have by turning the ram out so that you are seating by feel before the end of the paddle stroke. It is pretty hard not to notice when the primer touches bottom as its slide into the pocket stops and you feel the added resistance. Different makes and lots of brass and brass with different load histories can feel different, so you want to keep your brass segregated by having those factors in common. One thing to do about the feel difference, as long as your chamber's excess headspace isn't too big, is you can wet the primer pockets using a cotton swab dipped into a thin mix of alcohol and graphite and allow the alcohol to dry off before seating. This increases the feel of the difference between the primer sliding in and stopping on the bottom by minimizing the effect of friction between the pocket and primer cup.
Once your primer touches down, you can simply press hard, as Hackett did. But you can also calibrate your actions. Use a depth mic to measure how far below flush with the case head the primer is when it has just touched down. Then pop the case back into the tool and push a little harder and take it back out and measure the effect. Keep repeating until you find what it feels like to compress the primer 0.002"–0.004" past the touchdown point.
You could set the tool on a bathroom scale to measure your pressing effort, I suppose, but I don't think you'll need to go that far.