How much to reduce powder charge when switching brass?
- Thread starter jlorenzo
- Start date
That sounds like a good plan. Tommy Mc.
I would back off 2 grains and restart testing from there.
jelenko
Gold $$ Contributor
I would first measure the fired case capacity of both types of brass. To get a few fired cases of the new brass, I'd used 10% less than the load with the LC. [24.5 of 8208 would be REALLY hot in any of my Wylde chambers].
ETA. I was typing while Walt's post was posted.
ETA II. I take it back on how hot 24.5 of 8208 would be - assuming the bullet was seated longer than mag length. Still wouldn't be mid range, but probably not over max.
ETA. I was typing while Walt's post was posted.
ETA II. I take it back on how hot 24.5 of 8208 would be - assuming the bullet was seated longer than mag length. Still wouldn't be mid range, but probably not over max.
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With 5.56/223 I’d probably drop 2 grains and work back up. If you have a chronograph you can compare speeds if your looking for the same node and velocity that you were in before. You can use water to give you the different external volume. I have actually used my powder. Pour the case completely full. No shaking or settling. Scrape it off level with a knife then pour it into pan and weigh it. Do it 5 times for each case. Then do the same procedure with the other case. That will give you your difference in your selected powder. Then back off below that and workMy Winchester 308 to LC85 Match is 1.4 grains difference. Puts me back on the node with the same speed and no pressure. Though with Lake City it tends to vary somewhat better somewhat depending on year.
jelenko
Gold $$ Contributor
Not all. The Starline I've got is ~ 2grns less capacity than the LC I've got.
ETA: Just went and checked my data. The Starline 223 is actually about 9 grains heavier than the LC I've got.
LC weighs 92 grains +/- 2 grains; the Starline is 101.5 +/- 0.5 grains. The water capacity of the Starline is 0.6 grains less than the LC [30.6 vs 31.2]
The LC brass is a mixture of 3 different years.
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I would back off 4%.
Ned Ludd
Silver $$ Contributor
Sounds like your LC brass has less internal capacity than the Winchester. This is a situation where determining average water volume from fired cases of each type of brass, then plugging the pertinent values into a reloading program such as QuickLoad or GRT will get you close in terms of identifying a slightly reduced charge weight of 8208 that will reproduce the Winchester velocity with very little effort. Some time ago, I posted on how I determine case water volume using an analytical balance that might be of interest to you (https://forum.accurateshooter.com/threads/case-volume-determination-pic-heavy.3896148/). I'd still suggest doing a complete [new] load workup in the LC brass, but this is a case where a reloading program can easily get you fairly close in silico, without even loading ammo or heading to the range.
As noted by other above, you can always drop the charge weight by a certain amount. That is the usually safest and most certain route to go. However, how do you know exactly how much to drop it to start? The exact amount of charge weight reduction necessary will depend on the difference in two brass volumes, and without the use of a reloading program with the two case volumes, it's merely a guess. If your guess is overly cautious and you drop the charge weight too much, you may end up having to test more charge weights than necessary to get back where you want to be. If you don't drop the charge weight enough, you may also end up needing more than one range trip to get it sorted out. In this day and age of hard-to-find and expensive reloading components, that is not always desirable and one good reason for having and using a reloading program.
Alternatively, you can make an educated guess from the difference in velocity of your 24.5 gr load in LC brass as compared to what the velocity at 24.5 gr 8208 was previously in the Winchester brass (same bullet, Lot# of powder, etc). 0.1 gr of powder is usually good for about 5-10 fps velocity in a typical .223 Rem load. Divide the velocity differential between the two types of brass at 24.5 gr 8208 by "5 fps" and by "10 fps", then multiply each value by 0.1 gr to identify a potential range by which you need to reduce the charge weight to get you back in the ballpark of where the load was in Winchester brass. For example, if the velocity differential between the two types of brass was 50 fps, the estimate would be that you'd need to drop the charge weight by somewhere between 0.5 to 1.0 gr. This is a very coarse estimate, but it usually works. If you think the estimated reduction in charge weight isn't enough, you can always back off a tick more for safety.
As noted by other above, you can always drop the charge weight by a certain amount. That is the usually safest and most certain route to go. However, how do you know exactly how much to drop it to start? The exact amount of charge weight reduction necessary will depend on the difference in two brass volumes, and without the use of a reloading program with the two case volumes, it's merely a guess. If your guess is overly cautious and you drop the charge weight too much, you may end up having to test more charge weights than necessary to get back where you want to be. If you don't drop the charge weight enough, you may also end up needing more than one range trip to get it sorted out. In this day and age of hard-to-find and expensive reloading components, that is not always desirable and one good reason for having and using a reloading program.
Alternatively, you can make an educated guess from the difference in velocity of your 24.5 gr load in LC brass as compared to what the velocity at 24.5 gr 8208 was previously in the Winchester brass (same bullet, Lot# of powder, etc). 0.1 gr of powder is usually good for about 5-10 fps velocity in a typical .223 Rem load. Divide the velocity differential between the two types of brass at 24.5 gr 8208 by "5 fps" and by "10 fps", then multiply each value by 0.1 gr to identify a potential range by which you need to reduce the charge weight to get you back in the ballpark of where the load was in Winchester brass. For example, if the velocity differential between the two types of brass was 50 fps, the estimate would be that you'd need to drop the charge weight by somewhere between 0.5 to 1.0 gr. This is a very coarse estimate, but it usually works. If you think the estimated reduction in charge weight isn't enough, you can always back off a tick more for safety.
Thanks guys. I am going to try Neds way. The LC brass I have coming is once fired, same headstamp bought of gun broker. The seller has done the following.
- Initial wash
- Deprime
- Primer Pocket Swage
- Full Length Resize
- This process uses a carbide small base die
- Trim OAL
- All brass is trimmed per SAAMI specifications: 1.760 -.020 OAL. This is the same tolerance that factory ammo is manufactured to. The OAL for most of our cases will be 1.750 +/- .005.
- Tumble with stainless steel pins
- Multi-step QA inspection:
- Primer Pocket Swage
- Inspected with primer pocket go / no-go gauge
- OAL after trim
- Case Gauge
- Final inspection on full case body to ensure that case will chamber properly.
My experience with tumbling with steel pins, has been badly peened case mouths that required an inside and outside chamfer before loading. Something you should check.
Just weigh it for pete's sake. The outside dimensions won't vary, so any weight variance is all internal. Dropping a full 2 grains is overkill. There was a chart here which showed that most .223 is pretty much the same. Recent Norma brass and MEN 223 brass is thicker, but most major flavors don't vary much.
If it were 308 brass I could get you pretty close. But I haven’t messed with 5.56 as much as I rarely use the cartridge. If you have access to a chronograph you can drop 2 grains and load a couple, then a couple of 1.5, then 1.25, etc. grains and look for pressure. Compare Velocity then work in the area that gave speed matching the Winchester load. Be careful with 8208 as it tends to be fine but then cross the line quickly. At least with the Grendel it does. It’s probably going to take more than one trip. I’m lucky, the range is my yard.
There is really no way to get an exact grain difference without shooting. There are too many variables. Even between years of LC things change. But you can get close. I do seem to remember when I was messing with 223 and LC brass years ago that there is not quite as large a difference between the brass as there is with 308. A percentage may get closer. But water or powder will get you in the ballpark. I should have taken better notes.
There is really no way to get an exact grain difference without shooting. There are too many variables. Even between years of LC things change. But you can get close. I do seem to remember when I was messing with 223 and LC brass years ago that there is not quite as large a difference between the brass as there is with 308. A percentage may get closer. But water or powder will get you in the ballpark. I should have taken better notes.
The good news is that most headstamps, most of the time, are reasonably close to each other with respect to their volume capacity.
That bad news is that they aren't always.
A few years ago when I first started shooting and loading the .300 AAC Blackout, I was stunned to find that the X-TREME headstamp (from Freedom Munitions factory ammo) came in at 21.7 gr when Barnes, Winchester, and R-P were all around 24.3 gr.
Take a perfectly fine SAAMI max load of, say, 19.6/W296 in Barnes brass, behind a 115gr Berger... and throw that load in an X-TREME cartridge and you're going to suddenly have chamber pressures north of 80K psi.
Dropping two full grains when you've got a critical unknown variable (case volume) and a baseline load already known to be "hot"... is hardly overkill.
@jlorenzo you're smart for both asking the question; and taking Ned's advice.
That bad news is that they aren't always.
A few years ago when I first started shooting and loading the .300 AAC Blackout, I was stunned to find that the X-TREME headstamp (from Freedom Munitions factory ammo) came in at 21.7 gr when Barnes, Winchester, and R-P were all around 24.3 gr.
Take a perfectly fine SAAMI max load of, say, 19.6/W296 in Barnes brass, behind a 115gr Berger... and throw that load in an X-TREME cartridge and you're going to suddenly have chamber pressures north of 80K psi.
Dropping two full grains when you've got a critical unknown variable (case volume) and a baseline load already known to be "hot"... is hardly overkill.
@jlorenzo you're smart for both asking the question; and taking Ned's advice.
Agree on 8208. I shoot it in 223, and it will turn on you. Nothing catastrophic, but you'll start ruining brass and popping primers.
Also agree on "too many variables"... just go shoot it. 308 does indeed have much larger brass variances than most common 223/5.56
I recently was working on a 308 load for deer hunting in a new rifle using 150gr Lapua Mega bullets. Only load data was in the VV manual and I had it in my head that an 18” bbl should use 4895. Loads for that mega were as much as 4-5 gr less than other 150 and their 155gr bullets with the VV powders. I used what I THOUGHT would be a safe starting point using other 150 bullet data out of MULTIPLE manuals and the first shot blew a primer and had significant protrusion into the ejector hole…oops. Switched to a different powder and reduced even more than my edjumicated guess and finally arrived at a respectable load at 2730 FPS….you never know, safer to back down a couple more and start right off the bad shooting through a chrony so you know you’re in the ballpark. Just a recent and surprising experience I had…actually don’t remember doing anything close to that excess in the past!
Reduce your load by 10% and back your COAL off by .020". Fireform your brass and then start your load process from that same point. So many reloaders stand on their brass to fireform. A process that makes money for the brass manufacturers!!
Good advice , I don't normally make it to full house loads so I just load and shoot over a crono and check for any signs of pressure...
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