Trying to lower ES and SD no.s, I bought a sinclair primer pocket uniformer. My velocitys in a .308 win. Case with 45 gr of varget, 175 SMK, and CCI BR2 primers was 2640. But after uniforming the primer pockets my AV is 2602 Sd 9 ES 20. That's about half the ES and SD from before, but I lost 40 fps in AV. Chrono is a CED and I tried it in diffrent lighting to see if it made a difference, but got same results. Anyone else experience this?
- Thread starter Dusty
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Re: Velocity drop after primer uniforming
Dusty,
I seriously doubt that you actually "lost" 40 fps here. I suspect that it's just a case of a small sample size not really giving you the true picture of what the ammo would produce with a larger sample population. Keep shooting, and you'll probably see the variations reduce over time, and get a better picture of what the load will routinely deliver over the long haul.
Dusty,
I seriously doubt that you actually "lost" 40 fps here. I suspect that it's just a case of a small sample size not really giving you the true picture of what the ammo would produce with a larger sample population. Keep shooting, and you'll probably see the variations reduce over time, and get a better picture of what the load will routinely deliver over the long haul.
Re: Velocity drop after primer uniforming
Could be a change in environmental factors...like lower temperature of either the environment, or your ammo. If your ammo was 80 degrees the first time you checked velocity, and it is now 65 degrees out, that could easily explain the difference.
Could be a change in environmental factors...like lower temperature of either the environment, or your ammo. If your ammo was 80 degrees the first time you checked velocity, and it is now 65 degrees out, that could easily explain the difference.
Re: Velocity drop after primer uniforming
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unknown</div><div class="ubbcode-body">Could be a change in environmental factors...like lower temperature of either the environment, or your ammo. If your ammo was 80 degrees the first time you checked velocity, and it is now 65 degrees out, that could easily explain the difference. </div></div>
^This would be my guess.
However, was there a real difference at extended ranges? I don't often use a chronograph as they tend to be unreliable. I don't chase speed, I chase accuracy. What shows up on paper doesn't lie.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unknown</div><div class="ubbcode-body">Could be a change in environmental factors...like lower temperature of either the environment, or your ammo. If your ammo was 80 degrees the first time you checked velocity, and it is now 65 degrees out, that could easily explain the difference. </div></div>
^This would be my guess.
However, was there a real difference at extended ranges? I don't often use a chronograph as they tend to be unreliable. I don't chase speed, I chase accuracy. What shows up on paper doesn't lie.
Re: Velocity drop after primer uniforming
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tylerw02</div><div class="ubbcode-body">
However, was there a real difference at extended ranges? I don't often use a chronograph as they tend to be unreliable. I don't chase speed, I chase accuracy. What shows up on paper doesn't lie. </div></div>
I use the chronograph LAST, as part of my load development. First for "on paper" accuracy then over the chronograph just to determine the average speed of the load. Only want the speed so I have a ballistic's chart for intermediate or extended range changes, off those I tested at.
At that point I'll shoot from 25 to 50 rounds for "sample size" and not bother to adjust the load. I've found that the larger the sample, using my accurate loads, the less SD, EX, and MAD there is. Go figure
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tylerw02</div><div class="ubbcode-body">
However, was there a real difference at extended ranges? I don't often use a chronograph as they tend to be unreliable. I don't chase speed, I chase accuracy. What shows up on paper doesn't lie. </div></div>
I use the chronograph LAST, as part of my load development. First for "on paper" accuracy then over the chronograph just to determine the average speed of the load. Only want the speed so I have a ballistic's chart for intermediate or extended range changes, off those I tested at.
At that point I'll shoot from 25 to 50 rounds for "sample size" and not bother to adjust the load. I've found that the larger the sample, using my accurate loads, the less SD, EX, and MAD there is. Go figure
Re: Velocity drop after primer uniforming
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unknown</div><div class="ubbcode-body">Could be a change in environmental factors...like lower temperature of either the environment, or your ammo. If your ammo was 80 degrees the first time you checked velocity, and it is now 65 degrees out, that could easily explain the difference.</div></div>
This is what I was thinking also.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unknown</div><div class="ubbcode-body">Could be a change in environmental factors...like lower temperature of either the environment, or your ammo. If your ammo was 80 degrees the first time you checked velocity, and it is now 65 degrees out, that could easily explain the difference.</div></div>
This is what I was thinking also.
Re: Velocity drop after primer uniforming
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dusty</div><div class="ubbcode-body">Trying to lower ES and SD no.s, I bought a sinclair primer pocket uniformer. My velocitys in a .308 win. Case with 45 gr of varget, 175 SMK, and CCI BR2 primers was 2640. But after uniforming the primer pockets my AV is 2602 Sd 9 ES 20. That's about half the ES and SD from before, but I lost 40 fps in AV. Chrono is a CED and I tried it in diffrent lighting to see if it made a difference, but got same results. Anyone else experience this?</div></div>
Was the 2640 fps from new brass and the 2602 fps from once fired brass?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dusty</div><div class="ubbcode-body">Trying to lower ES and SD no.s, I bought a sinclair primer pocket uniformer. My velocitys in a .308 win. Case with 45 gr of varget, 175 SMK, and CCI BR2 primers was 2640. But after uniforming the primer pockets my AV is 2602 Sd 9 ES 20. That's about half the ES and SD from before, but I lost 40 fps in AV. Chrono is a CED and I tried it in diffrent lighting to see if it made a difference, but got same results. Anyone else experience this?</div></div>
Was the 2640 fps from new brass and the 2602 fps from once fired brass?
Re: Velocity drop after primer uniforming
Same time of day, same clouds, sun direction? Chrono's are inconsistent due I light variations on the sensors.
Same time of day, same clouds, sun direction? Chrono's are inconsistent due I light variations on the sensors.
Re: Velocity drop after primer uniforming
I don't now the answer. I think this is one of the 'tail chasers' folks get themselves into by trying to process too much information.
My experience with chronos and chrono data (and I have put them through the rigors plenty seriously) has led me to conclude that the information they provide is more disruptive than constructive, and that there is very little real relationship between chrono readings and what we see on the target.
To me, a chrono is helpful for getting very rudimentary baseline MV data so a POI can be plotted at various distances.
Beyond that, I take the manufacturers' cautionary instruction that numbers can be off by +/- one percent of the numbers being displayed (and that's with a perfect setup) and recognize that for 2600fps, true velocity can be anywhere between 2574 and 2626fps for each and every reading of 2600fps. In such a circumstance, a variation of 40fps, and SD/ES numbers under 50fps are unreliable and inconclusive.
Stop chasing your tail, and concentrate on the target. That's where the real data lives.
Greg
I don't now the answer. I think this is one of the 'tail chasers' folks get themselves into by trying to process too much information.
My experience with chronos and chrono data (and I have put them through the rigors plenty seriously) has led me to conclude that the information they provide is more disruptive than constructive, and that there is very little real relationship between chrono readings and what we see on the target.
To me, a chrono is helpful for getting very rudimentary baseline MV data so a POI can be plotted at various distances.
Beyond that, I take the manufacturers' cautionary instruction that numbers can be off by +/- one percent of the numbers being displayed (and that's with a perfect setup) and recognize that for 2600fps, true velocity can be anywhere between 2574 and 2626fps for each and every reading of 2600fps. In such a circumstance, a variation of 40fps, and SD/ES numbers under 50fps are unreliable and inconclusive.
Stop chasing your tail, and concentrate on the target. That's where the real data lives.
Greg
Re: Velocity drop after primer uniforming
I too have pulled my hair out over using a chrono!!!! The way I figured my MV was to shoot at a 6" shoot-n-see at 900 yards. Once I got my elevation turret set so that I was hitting consistently, I just changed to MV entry in my ballistics calculator until it matched what my scope said at that yardage.
I too have pulled my hair out over using a chrono!!!! The way I figured my MV was to shoot at a 6" shoot-n-see at 900 yards. Once I got my elevation turret set so that I was hitting consistently, I just changed to MV entry in my ballistics calculator until it matched what my scope said at that yardage.
Re: Velocity drop after primer uniforming
Problem with that method is the BC of bullets is almost never match what the manufactures say it is, a chronograph even with it's inherent built in errors is still a better tool, I use what my chrono reads and adjust BC to match my actuals.
Problem with that method is the BC of bullets is almost never match what the manufactures say it is, a chronograph even with it's inherent built in errors is still a better tool, I use what my chrono reads and adjust BC to match my actuals.
Re: Velocity drop after primer uniforming
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PCR</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dusty</div><div class="ubbcode-body">Trying to lower ES and SD no.s, I bought a sinclair primer pocket uniformer. My velocitys in a .308 win. Case with 45 gr of varget, 175 SMK, and CCI BR2 primers was 2640. But after uniforming the primer pockets my AV is 2602 Sd 9 ES 20. That's about half the ES and SD from before, but I lost 40 fps in AV. Chrono is a CED and I tried it in diffrent lighting to see if it made a difference, but got same results. Anyone else experience this?</div></div>
Was the 2640 fps from new brass and the 2602 fps from once fired brass? </div></div>
This was my first thought, also. Once fired brass is "bigger on the inside"
{like may time lord technologies.}
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PCR</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dusty</div><div class="ubbcode-body">Trying to lower ES and SD no.s, I bought a sinclair primer pocket uniformer. My velocitys in a .308 win. Case with 45 gr of varget, 175 SMK, and CCI BR2 primers was 2640. But after uniforming the primer pockets my AV is 2602 Sd 9 ES 20. That's about half the ES and SD from before, but I lost 40 fps in AV. Chrono is a CED and I tried it in diffrent lighting to see if it made a difference, but got same results. Anyone else experience this?</div></div>
Was the 2640 fps from new brass and the 2602 fps from once fired brass? </div></div>
This was my first thought, also. Once fired brass is "bigger on the inside"
{like may time lord technologies.}
Re: Velocity drop after primer uniforming
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tylerw02</div><div class="ubbcode-body">I don't chase speed, I chase accuracy. What shows up on paper doesn't lie. </div></div>
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 427Cobra</div><div class="ubbcode-body">Problem with that method is the BC of bullets is almost never match what the manufactures say it is, a chronograph even with it's inherent built in errors is still a better tool, I use what my chrono reads and adjust BC to match my actuals. </div></div>
+1
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tylerw02</div><div class="ubbcode-body">I don't chase speed, I chase accuracy. What shows up on paper doesn't lie. </div></div>
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 427Cobra</div><div class="ubbcode-body">Problem with that method is the BC of bullets is almost never match what the manufactures say it is, a chronograph even with it's inherent built in errors is still a better tool, I use what my chrono reads and adjust BC to match my actuals. </div></div>
+1
Re: Velocity drop after primer uniforming
When I first started loading for this rifle, with this bullet and powder combo, I loaded up OWC weight charges all the way up to 45.8 before I started to getting extractors ekes on my case heads. I saw best groupings around 45.4. I backed off to 45 grains to more of a safety margin.
I went back out today and loaded some up at 45.3 and 45.5. Let the ammo sit in the sun till it was almost too hot to touch and then fired 5 shot groups at 230yds. 45.5 was the best with 1/3 Moa vertical and .2moa horizontal spread. No sticky bolt or extractor marks. Primers where starting to show some flattening. Oal is 2.860. Temps are high 90's. You reckon this load is too hot?
When I first started loading for this rifle, with this bullet and powder combo, I loaded up OWC weight charges all the way up to 45.8 before I started to getting extractors ekes on my case heads. I saw best groupings around 45.4. I backed off to 45 grains to more of a safety margin.
I went back out today and loaded some up at 45.3 and 45.5. Let the ammo sit in the sun till it was almost too hot to touch and then fired 5 shot groups at 230yds. 45.5 was the best with 1/3 Moa vertical and .2moa horizontal spread. No sticky bolt or extractor marks. Primers where starting to show some flattening. Oal is 2.860. Temps are high 90's. You reckon this load is too hot?
Re: Velocity drop after primer uniforming
I would strongly suggest that you refrain from letting your ammo bake in the sun, that's a nonstarter.
But, back to the question. Some factors might have changed between sessions but the idea that uniforming the primer pockets might be responsible is very unlikely.
Also, these machines are informative but not absolutely bet your life reliable, as far as accuracy. One day you set it at 9.5' and the next day maybe 12' and at a slight angle. I can't think of a bunch of scenarios, but yeah, weather and ambient temperature, including humidity "could" affect your readings. This is an optical instrument, not like a speedometer, the fact that we can use one for this purpose, at all, is pretty awesome!
BB
I would strongly suggest that you refrain from letting your ammo bake in the sun, that's a nonstarter.
But, back to the question. Some factors might have changed between sessions but the idea that uniforming the primer pockets might be responsible is very unlikely.
Also, these machines are informative but not absolutely bet your life reliable, as far as accuracy. One day you set it at 9.5' and the next day maybe 12' and at a slight angle. I can't think of a bunch of scenarios, but yeah, weather and ambient temperature, including humidity "could" affect your readings. This is an optical instrument, not like a speedometer, the fact that we can use one for this purpose, at all, is pretty awesome!
BB
