8208xbr pressure signs with 308?

Sdupontjr · Sep 20, 2024

I was looking into a different powder for my 308 load with 155 scenars. Currently using 47.5g Varget, CCI-200, R-P Brass, CBTO 2.216" or 2.835" COAL. This gives me .050" jump on a fairly new Tikka CTR 308 20" barrel. That load is compressed pretty good and yields 2840 avg and a 10 shot moa or less groiup at 100.

When I looked on Gordons, it looks like I'm not getting 100% burn in that short of tube. So I decided to give 8208xbr a shot. Have a lb of it and its starting to show back up. Loaded 44, 44.5, 45 & 45.3 (book max) and went shoot for pressure. Saw nothing. Primer looked fine, very easy bolt lift, no swipes or ejector marks. So loaded up a few just to see. Neither were near compressed loads, so I liked that.

45g 8208, 2.216" CBTO, .050" jump
45.3g 8208, 2.216" CBTO, .050" jump

What I noticed was the SD/ES were ridiculously low and velocities were up. It was +90* when I was shooting and humidity was like breathing pea soup. When I tested for pressure, I didn't see anything to speak of, but when I shot these 3 rounds each to get some velo numbers, I noticed a few things on the case head.

Of course, only 3 shots, but 45 was .617" and 45.3 was .412" at only 100 yard (I was limited by this range)

I did notice a slight ejector mark on 1 of each set. So should I back down to 44 / 44.5 and work back up to 45? I have .050" to play with. Do I seat longer to relieve case pressure but closer to lands will build pressure back up? Any thought yall have would be greatly appreciated.

37L1 · Sep 20, 2024

I run 44.6 of 8208 in my 24" Brux 1/10, Hornady brass, .020 off. Berger 155.5

Last time I shot it at 600

Range 062824 600 yards 155 5 Berger 44 6 8208 XBR hornady brass Fed210M 2 2955 CCB.jpg

Doom · Sep 20, 2024

GRT say 43.6 gn is max @2.800" COAL. The Hodgdon data for 8208 is in Winchester brass which has greater capacity than R-P. [EDIT] Probably on the order of a grain or more of powder.

Sdupontjr · Sep 20, 2024

Yeah i saw that. On mine, 43.9g is 60,298 psi in a 20" barrel. Hell, hodgdon site has max is 45.3 at 60,900 psi. And I saw where book max (cant remember where) was also 45.3. So who knows.

I know my H1000 load in my 7 mag is 3g over book max and still not a hint of a sign of pressure. But WTH do I know, thus me asking. Ha

Evintos · Sep 20, 2024

Sdupontjr said:
Yeah i saw that. On mine, 43.9g is 60,298 psi in a 20" barrel. Hell, hodgdon site has max is 45.3 at 60,900 psi. And I saw where book max (cant remember where) was also 45.3. So who knows.

I know my H1000 load in my 7 mag is 3g over book max and still not a hint of a sign of pressure. But WTH do I know, thus me asking. Ha

Did the GRT estimated velocity match up with the real world obtained velocities? If not then the pressure simulation is very likely off as well and there's a factor in your input that needs to be changed in order to bring it more inline.

Sdupontjr · Sep 20, 2024

No it wasn't.

GRT - 45.3 was 2826
Actual - 45.3 was 2882, 2886, 2875

GRT - 45 was 2808
Actual - 45 was 2857, 2857, 2856

I'll have to play around with the factors and see where the issue is.

Evintos · Sep 20, 2024

Sdupontjr said:
No it wasn't.

GRT - 45.3 was 2826
Actual - 45.3 was 2882, 2886, 2875

GRT - 45 was 2808
Actual - 45 was 2857, 2857, 2856

I'll have to play around with the factors and see where the issue is.

Load up your GRT 308 file and click on OBT

Click "Create grtload file copy with the calibrated values" and this should then give you a new generated page with calibrated values.

GRT new calibrated value will give you 2880.6fps for 45.3gr and 2863fps for 45gr.

Massage case volume slightly to 56.5gr H2O (up from 56.3) and you'll get new calibrated values of FPS at

45.3 gr - 2875.4fps, 69780 psi
45gr - 2857.9fps, 68321 psi

If your actual measured velocity for 44.5gr was 2827.7fps average and 44gr was 2797.8fps (velocities predicted by GRT), then the simulation calibration is completed and matches real world (ideally within 10fps). You can use the simulated pressure values as reference compared to max SAAMI or CIP pressures with the new calibrated values. If not, more inputs need to be modified.

Sdupontjr · Sep 20, 2024

Oh man. Thanks a lot for the info. I'll try that out.

Sdupontjr · Sep 20, 2024

Also I noticed that the load ratio was 102.7% in GRT. 45.3 sloshed around in my loads seated where I was. Wonder if that has something to do with it?

Doom · Sep 20, 2024

Did you enter the correct COAL?

wvfarrier · Sep 20, 2024

Why not back off .02 grains and see where yer at?

spife7980 · Sep 20, 2024

wvfarrier said:
Why not back off .02 grains and see where yer at?

I imagine pretty much exactly the same with a one kernel difference

XLR308 · Sep 20, 2024

From your pics it looks like you starting get the slightest amount of primer cratering and you have a very faint ejector mark on a couple like you mentioned so yes your on the edge of seeing pressure signs.
The cratering could just be a dimensional issue with the bolt face firing pin path.
It looks like the lower charge group was a considerably tighter grouping but just three rounds isn't enough to be definitive.
I personally would back off the charge a bit to give yourself some cushion should you end up shooting in wet conditions and also see if it tightens up a bit more.
Then screw around with seating depth to fine tune.
I have chased velocity before and came to the realization that the last 50-60 fps realy doesn't mean much compared to pure accuracy and component longevity.

Edit: Sorry I read that backwards your higher charge was the tighter grouping but I would still back off a bit and then screw around with s3ating depth.

Sdupontjr · Sep 20, 2024

Doom said:
Did you enter the correct COAL?

Yes and jump.

wvfarrier said:
Why not back off .02 grains and see where yer at?

Yeah i plan on loading from 44 on up just to see. But i do like the potential of this powder compared to Varget in a 20" tube.

XLR308 · Sep 20, 2024

Before I sold my last 308win I was exclusively using AR-COMP as it surprisingly outperformed all other powders including Varget.
Another option if you are the experimenting type.

wvfarrier · Sep 21, 2024

Sdupontjr said:
Yes and jump.

Yeah i plan on loading from 44 on up just to see. But i do like the potential of this powder compared to Varget in a 20" tube.

It is one I have been wanting to tey but have never seen for sale locally

Barelstroker · Sep 21, 2024

Sdupontjr said:
I was looking into a different powder for my 308 load with 155 scenars. Currently using 47.5g Varget, CCI-200, R-P Brass, CBTO 2.216" or 2.835" COAL. This gives me .050" jump on a fairly new Tikka CTR 308 20" barrel. That load is compressed pretty good and yields 2840 avg and a 10 shot moa or less groiup at 100.

When I looked on Gordons, it looks like I'm not getting 100% burn in that short of tube. So I decided to give 8208xbr a shot. Have a lb of it and its starting to show back up. Loaded 44, 44.5, 45 & 45.3 (book max) and went shoot for pressure. Saw nothing. Primer looked fine, very easy bolt lift, no swipes or ejector marks. So loaded up a few just to see. Neither were near compressed loads, so I liked that.

45g 8208, 2.216" CBTO, .050" jump
45.3g 8208, 2.216" CBTO, .050" jump

What I noticed was the SD/ES were ridiculously low and velocities were up. It was +90* when I was shooting and humidity was like breathing pea soup. When I tested for pressure, I didn't see anything to speak of, but when I shot these 3 rounds each to get some velo numbers, I noticed a few things on the case head.

View attachment 8506203 View attachment 8506204

Of course, only 3 shots, but 45 was .617" and 45.3 was .412" at only 100 yard (I was limited by this range)

I did notice a slight ejector mark on 1 of each set. So should I back down to 44 / 44.5 and work back up to 45? I have .050" to play with. Do I seat longer to relieve case pressure but closer to lands will build pressure back up? Any thought yall have would be greatly appreciated.

Just did your load on GRT & although it's way over budget on pressure & load ratio, it's not as bad as the other GRT load shows.

Barelstroker · Sep 21, 2024

Provided the case volume is accurate, a truer representation of pressure is achieved by inputting your bullet jump. If you leave "Bullet Jump" without changing it, GRT assumes JAM which, always pushes pressure up. How much depends on the cartridge, powder & projectile but, it can be quite significant at times.
Note on the screen shot I've highlighted the powder load which I would call max. It's up to you but, there's no prizes for getting every Ft/sec out of your rifle. If'n you need more horse power, ramp up to a 300 Win Mag or some such. 8208 is one of the most forgiving powders I know of but, it can't compensate for complete stupidity.

918v · Sep 21, 2024

Doom said:
GRT say 43.6 gn is max @2.800" COAL. The Hodgdon data for 8208 is in Winchester brass which has greater capacity than R-P. [EDIT] Probably on the order of a grain or more of powder.

^^^ This, but given the environmental factors and that you’re not running heavy bullets and have plenty of jump you should be ok. Just don’t let them get hot out in the sun. Also, remember that RP brass is soft so primer pockets will loosen pretty quickly.

Barelstroker · Sep 21, 2024

918v said:
^^^ This, but given the environmental factors and that you’re not running heavy bullets and have plenty of jump you should be ok. Just don’t let them get hot out in the sun. Also, remember that RP brass is soft so primer pockets will loosen pretty quickly.

Yeah, but he's at 2.835"

Barelstroker · Sep 21, 2024

This is where you are now by GRT.
You could also be close to loosing an eye, half your face, or maybe just a couple fingers. Impossible to know when running supposed pressures like this. The pressure curve would be starting or well into the knee region which is the transition from deflagration to detonation. The knee region is horribly unpredictable & very non linear.
You have been warned.

Sdupontjr · Sep 21, 2024

Barelstroker said:
Just did your load on GRT & although it's way over budget on pressure & load ratio, it's not as bad as the other GRT load shows.
View attachment 8506764

I played with it this morning and got close.

I'll have to check case volume of my brass because clearly this program thinks its a compressed load. And also as you mentioned, jam, which it isn't either.

Anyway, I'm headed to the range to shoot my buddies 7 SAUM so I decided to load up a few at 44.8 and 44.6 (just under those that I shot) and see how they do pressure wise.

Barelstroker · Sep 21, 2024

Sdupontjr said:
I played with it this morning and got close.

I'll have to check case volume of my brass because clearly this program thinks its a compressed load. And also as you mentioned, jam, which it isn't either.

Anyway, I'm headed to the range to shoot my buddies 7 SAUM so I decided to load up a few at 44.8 and 44.6 (just under those that I shot) and see how they do pressure wise.

Just a few questions if you've time.
Is the load compressed?
What is the base to datum of the cases?
Have you full length sized?

918v · Sep 21, 2024

Barelstroker said:
Yeah, but he's at 2.835"

With .050” jump

Why is 2.835” significant?

Barelstroker · Sep 21, 2024

918v said:
With .050” jump

Why is 2.835” significant?

Well it's 2.835" +0.050". that's a further reduction in pressure according to GRT.
Most SAAMI or CIP chambers can be loaded longer than spec COAL due to the lead length. I think the 300 Win Mag is one of the worst chambers for lead length.
It's the case volume at the specified seating depth. The less volume the higher the pressures.
I know you're familiar with all this although it's not something that's regarded in the loading manuals.
I know some caution has to be taken when using the ADI loading manual because they use mostly Winchester brass which, is generally thinner & has higher case volumes than R-P, Federal, ADI & Rem cases. Most of their load data seems fine but, I have come across a couple loads that are quite bit higher when case volume is taken into consideration in GRT & in my testing. I have 2 loads to date which exhibited blown & very flattened primers with Federal brass which is very similar in volume to Lapua cases at 53.7 grns compared to Winchester 308 cases at 56.6 grns.

918v · Sep 21, 2024

I was saying he’s ok because I know RP brass in a SAKO chamber has more than 57 grains of h2o capacity. And the slight pressure sign is not significant to me given the environmentals.

Barelstroker · Sep 21, 2024

918v said:
I was saying he’s ok because I know RP brass in a SAKO chamber has more than 57 grains of h2o capacity. And the slight pressure sign is not significant to me given the environmentals.

Yes, I agree however, he may still have a significant issue. I'm beginning to think he may have a headspace issue, albeit intermediate.
I know everybody says swipes display overpressure but, not in any of my testing &, I've had some fairly grossly overloaded loads.
Swipes in my experience are a symptom of a long chamber or or oversizing the case during FLS.
Although I can't see any sooting around the primers, both the cratering & swipe are definite symptoms I've seen when I've accidentally oversized the cases.
I was hoping to get a few answers from him one of which is an average length measurement of the projectiles. GRT can be off by quite a bit sometimes which effects the COAL vs calculated case volume remaining although, I've never seen the differential large enough to account for a 2.7% error in load ratio.
Depending on the number of reloads those cases have had, I was going to ask him to check for insipient case head separation with a sharp piece of wire. That'll tell us if there's anything bad enough to be concerned with.

918v · Sep 21, 2024

Could be too much too much shoulder bump. I agree. But I’ve gotten case head swipe with RP brass and that’s with .002” shoulder bump and mild-warm loads. The brass is decent but not for hot loads.

Sdupontjr · Sep 21, 2024

Ok guys, sorry for the late response to everyone. Just got back from the range. I decided to shoot 44.6 and surprisingly, the velo was only 50fps slower than the 45.3 and ES/SD was similar.

918v said:
^^^ This, but given the environmental factors and that you’re not running heavy bullets and have plenty of jump you should be ok. Just don’t let them get hot out in the sun. Also, remember that RP brass is soft so primer pockets will loosen pretty quickly.

Barelstroker said:
Just a few questions if you've time.
Is the load compressed?
What is the base to datum of the cases?
Have you full length sized?

- Not compressed by a good bit. Can clearly hear powder shaking around.
- not sure, never measured it before.
- yes, FL size every time and anneal everytime. I could possibly space out the annealing, but it works and doesn't take long to do with my machine.

I have about 100 R-P brass. I usually run through them all, them punch primers, tumble, anneal, trim if needed (sometimes they do need a little, sometimes no), FL size, prime with hand tool. I go off of feel for setting primers. If they give me little to no resistance, I set aside. Usually get some resistance when setting them. Out of 100 or so, I may have 4 that are loose, and this set of brass is on its 7 reload.

918v said:
With .050” jump

Why is 2.835” significant?

It was brought up that GRT sets at jam thus higher pressures. I had .050" at 2.835" so the program wasn't set correctly or I have a setting wrong.

Barelstroker said:
Well it's 2.835" +0.050". that's a further reduction in pressure according to GRT.
Most SAAMI or CIP chambers can be loaded longer than spec COAL due to the lead length. I think the 300 Win Mag is one of the worst chambers for lead length.
It's the case volume at the specified seating depth. The less volume the higher the pressures.
I know you're familiar with all this although it's not something that's regarded in the loading manuals.
I know some caution has to be taken when using the ADI loading manual because they use mostly Winchester brass which, is generally thinner & has higher case volumes than R-P, Federal, ADI & Rem cases. Most of their load data seems fine but, I have come across a couple loads that are quite bit higher when case volume is taken into consideration in GRT & in my testing. I have 2 loads to date which exhibited blown & very flattened primers with Federal brass which is very similar in volume to Lapua cases at 53.7 grns compared to Winchester 308 cases at 56.6 grns.

Yes to all.
Was using Fed brass because I had a ton of it. I found it much softer even with reduced loads. Could hardly get within 1.5g of boox max. So had 100 or so R-P lying around and have been using them with no issues for the last 4 years.

918v said:
I was saying he’s ok because I know RP brass in a SAKO chamber has more than 57 grains of h2o capacity. And the slight pressure sign is not significant to me given the environmentals.

Thats what I really need to do is measure the H2O of my cases. I did weight each of them and they are pretty dame close considering I weighed them all.

Sdupontjr · Sep 21, 2024

918v said:
Could be too much too much shoulder bump. I agree. But I’ve gotten case head swipe with RP brass and that’s with .002” shoulder bump and mild-warm loads. The brass is decent but not for hot loads.

Using RCBS FL die, usually FL resize all my brass because my son's also have 308's. That way there is no chambering issues across the board. But like I said, I run through the all (about 100) before i start any brass prep. Do that so I don't just keep reloading the same 20 or so .

Barelstroker · Sep 21, 2024

Sdupontjr said:
Using RCBS FL die, usually FL resize all my brass because my son's also have 308's. That way there is no chambering issues across the board. But like I said, I run through the all (about 100) before i start any brass prep. Do that so I don't just keep reloading the same 20 or so .

Well, if you've FLS them a bunch they're probably ok for insipient head separation. Might as well check them though. You can grab a torch & look into the case & see if there is a crack running around the circumference just above the solid web of the case.
I didn't think you'd seat with 102.7% over load ratio but, I've yet to measure 308 case volume greater than Winchester brass so I'm a little concerned with what's going there. The only way I can think of to have a COAL greater than Winchester cases is if the projectiles are shorter in length than the GRT listed length.
We'll get to the bottom of it, no doubt.
Note for clarity;- By this statement ......."The only way I can think of to have a COAL greater than Winchester cases is if the projectiles are shorter in length than the GRT listed length."
The COAL vs volume remaining. The actual COAL is the same no matter the case brand.

Barelstroker · Sep 21, 2024

918v said:
Could be too much too much shoulder bump. I agree. But I’ve gotten case head swipe with RP brass and that’s with .002” shoulder bump and mild-warm loads. The brass is decent but not for hot loads.

Was just looking through my brass & I realized I don't have any R-P 308 brass. I confused it with my 243 menagerie of brass.
Looking at my notes, 243 R-P brass still has considerably less case vol than Winchester cases.
Bit of a head scratcher this one.
I hope he has a Hornady headspace gauge so we can see what that comes out at. Unless those R-P cases are wafer thin, I can only assume that the chamber is long & the cases have been stretched. Then again, if that were the case, with repeated FLS, I'd imagine he would've seen case ruptures by now. Hmmmm.

Barelstroker · Sep 21, 2024

Barelstroker said:
This is where you are now by GRT.
You could also be close to loosing an eye, half your face, or maybe just a couple fingers. Impossible to know when running supposed pressures like this. The pressure curve would be starting or well into the knee region which is the transition from deflagration to detonation. The knee region is horribly unpredictable & very non linear.
You have been warned.

View attachment 8506773

To all those who are getting started with GRT.
GRT is an exceptional program in my experience. Provided all the data is correct & all the relevant inputs adjusted, I'm yet to see a GRT load far off my measured velocities prior to adjusting (K) & (Ba).
The trap with any of these programs is the tendency to take the pressure calcs with a grain of sugar rather than the obligatory grain of salt.
We all MUST keep in mind that the calculated pressures are just & only that. They are not measured & thus, should never be assumed to be "JUST A LITTLE OVER or NOT TOO BAD.
Use this program wisely & you'll probably never have an issue. Start using it to see how far you can push your luck &, well....................
Start imagining your life with one eye or a couple less fingers or a thumb. It could very easily get to this if you don't respect the warnings stated in GRT & load manuals.

Doom · Sep 21, 2024

HERE IS SOME DATA WE PULLED TOGETHER ON PRACTICAL RIFLERY FORUM A FEW YEARS BACK. THE DATA IS FOR FULL LENGTH SIZED 308 BRASS FROM SAME GUN.

Barelstroker · Sep 21, 2024

Doom said:
HERE IS SOME DATA WE PULLED TOGETHER ON PRACTICAL RIFLERY FORUM A FEW YEARS BACK. THE DATA IS FOR FULL LENGTH SIZED 308 BRASS FROM SAME GUN.

View attachment 8507270

View attachment 8507269

Very interesting.
I think my case volumes are a little lower because I have a tight match chamber & measure volumes from FLS cases which I try hard to keep 0.002" under. The general trend is the same as I look down the list of cases that I've measured though.

918v · Sep 21, 2024

When I measured Remington cases they weighed around 165 grains and held 57.5 grains of water as opposed to Winchester which were 58grs plus. Looking at the chart above, I dunno where he found 172gr RP brass. I have never seen them that heavy unless he’s weighing them with the primer in place.

Barelstroker · Sep 21, 2024

918v said:
When I measured Remington cases they weighed around 165 grains and held 57.5 grains of water as opposed to Winchester which were 58grs plus. Looking at the chart above, I dunno where he found 172gr RP brass. I have never seen them that heavy unless he’s weighing them with the primer in place.

I don't bother weighing cases unless measuring for volume. I never bother to record the case weight although, maybe I should. Better to have a little more info than not enough.
It took me a while to realize the case volume could make such a difference so, I just regard volume measurements as part & parcel, tedious as it is.
I've been using GRT for about 4 years or thereabouts & use it to concoct many iterations of each load. I couldn't go back to load manuals now. For those that don't use GRT, I can highly recommend it. By far the most benefit using GRT is the considerably larger & vastly more truthful your loading knowledge becomes. Although there is a learning curve at the start & it seems far more cumbersome than just choosing a load from a manual & "have at it" (as you yanks say) & ofcourse, you have to put the time & effort in but, the rewards are many & proficiency with the program comes relatively quickly if the time is assigned.

straightshooter1 · Sep 21, 2024

918v said:
When I measured Remington cases they weighed around 165 grains and held 57.5 grains of water as opposed to Winchester which were 58grs plus. Looking at the chart above, I dunno where he found 172gr RP brass. I have never seen them that heavy unless he’s weighing them with the primer in place.

The weight of my RP brass is very close to what you've got there. My Winchester brass is a little less. . . like at 57.7 grs H2O. Based on what I see in Peterson's chart, their case weight can certainly be that much different. So, 172 gr PR brass seems very plausible to me; even without a primer.

Barelstroker · Sep 21, 2024

straightshooter1 said:
The weight of my RP brass is very close to what you've got there. My Winchester brass is a little less. . . like at 57.7 grs H2O. Based on what I see in Peterson's chart, their case weight can certainly be that much different. So, 172 gr PR brass seems very plausible to me; even without a primer.
View attachment 8507339

I notice some strange numbers in the "loaded neck dia" column. The bullet diameters must have far more varied than I've ever thought possible.
What say ye Straightshooter?
Although a few seem a little off, I'm referring to 4th & 7th row in particular.

straightshooter1 · Sep 22, 2024

Barelstroker said:
I notice some strange numbers in the "loaded neck dia" column. The bullet diameters must have far more varied than I've ever thought possible.
What say ye Straightshooter?
Although a few seem a little off, I'm referring to 4th & 7th row in particular.

Yeah, that's interesting alright. Given that they stated "neck thickness is calculated by subtracting the actual measured bullet diameter from the actual measured loaded neck diameter, then dividing that number by 2", it must have something to do with their measurement of the bullet diameters.

For some of those I looked at, when you reverse their measurement process, you do get a bullet diameter of .308. But those two you mention come out to be .309 plus a little. There was no mention of who's bullets were being use. But looking for SAAMI specs, that's within tolerance (see pic below). They don't say who's bullets they're using, but I'd sure want more consistency than that, assuming they're using the same bullet manufacturer.

Barelstroker · Sep 22, 2024

straightshooter1 said:
Yeah, that's interesting alright. Given that they stated "neck thickness is calculated by subtracting the actual measured bullet diameter from the actual measured loaded neck diameter, then dividing that number by 2", it must have something to do with their measurement of the bullet diameters.

For some of those I looked at, when you reverse their measurement process, you do get a bullet diameter of .308. But those two you mention come out to be .309 plus a little. There was no mention of who's bullets were being use. But looking for SAAMI specs, that's within tolerance (see pic below). They don't say who's bullets they're using, but I'd sure want more consistency than that, assuming they're using the same bullet manufacturer.

View attachment 8507379

Bit of head scratcher. Thanks for posting the chart anyway. Interesting figures in that chart.

Barelstroker · Sep 22, 2024

Straightshooter, what's your take on what's going on with Sdupontjr loads?
Doom asked if he had the correct COAL. That could definitely cause this mix up.

Doom · Sep 22, 2024

918v said:
When I measured Remington cases they weighed around 165 grains and held 57.5 grains of water as opposed to Winchester which were 58grs plus. Looking at the chart above, I dunno where he found 172gr RP brass. I have never seen them that heavy unless he’s weighing them with the primer in place.

Was your measurement on fired or resized case?

NOTE: The measurement in the above post were all FLS in the same die. Also the test was run to get approximate differences in different manufacturers cases, not to justify measuring weight to determine volume. Obviously weight and volume work together but it would not be a good means to sort brass within a specific lot in most cases. With older Winchester cases maybe? As for Hornady and BHA cases in those days it appeared that they were using Winchester manufactured brass.

918v · Sep 22, 2024

It was in fired brass. You should use fired brass out your rifle for the calculation otherwise it will be off.

Sdupontjr · Sep 22, 2024

I personally think it's something I may or may not have inputted into GRT. I have 4 different sets of brass but use the R-P mostly.
All of these cases have been de-primed, tumbled, annealed, FL sized, trimmed, the whole nine yards.

RP brass Win Fed Win (dots on headstamp)
165.6 176.6 176.6 155.8
166.1 178.1 175.4 155.8
166.0 176.8 175.6 156.5
165.9 177.6 175.7 156.3
166.7 176.9 175.7 155.2

The gun is a stock Tikka CTR 20" 308 that all I have done to it was change the stock, trigger spring, and added an APA little bastard.

The data I input definately isn't jiving with the program. And Like I mentioned, I probably have less than 2 months of playing with this program. I've always used a manual, data from the bullet manufacturer or powder manufacturer. So I'm sure I don't have the data input correctly. But the one thing I can say it that at 45.3g of 8208, it's not 102.7% load fill.

RP case both filled to max load from my testing.
45.3g 8208 is at the case / shoulder junction

47.5g Varget is at the base of the neck, thus lots of crunch when I seat to 2.216" CBTO or 2.835" COAL

And seated as such, the base of the bullet isn't even to the case/shoulder. When seated I can shake it and hear the powder moving back and forth. So far from compressed like Varget.

That bring me back to the GRT program. I think my data that I input is wrong OR my inexperience with GRT is the issue.

918v · Sep 22, 2024

The 176gr Win case is not what Hodgdon’s data is based on. They used a 155gr case. I dunno where those heavy cases came from. I find them on the ground occasionally but toss them because they cause problems. Winchester commercial brass has weighed 155grs for decades. Their military brass weighs 176grs. Putting that commercial head stamp on a heavy case is idiotic.

37L1 · Sep 22, 2024

Your results with 44.6 looked good and the cases appear to be fine.

I wouldn't worry about your program, you found out what you need to know by actually shooting. Imagine that?

Sdupontjr · Sep 22, 2024

37L1 said:
Your results with 44.6 looked good and the cases appear to be fine.

I wouldn't worry about your program, you found out what you need to know by actually shooting. Imagine that?

Thats actually what I intend to do. Brass life will be better, appears to have same if not better accuracy and SD/ES is very similar. For 50fps less, I can shoot this load now in 95* down to whatever I want without any worries.

Sdupontjr · Sep 22, 2024

918v said:
The 176gr Win case is not what Hodgdon’s data is based on. They used a 155gr case. I dunno where those heavy cases came from. I find them on the ground occasionally but toss them because they cause problems. Winchester commercial brass has weighed 155grs for decades. Their military brass weighs 176grs. Putting that commercial head stamp on a heavy case is idiotic.

Didn't know that. They are tossed. The range officer gave them too me because he knows I shoot 308. The 155 makes sense being I've read alot of info online talking about win cases have more capacity. Makes perfect sense.

Doom · Sep 22, 2024

Looking back on this post it seems that the initial question concerned the cases and primer. With a load of 45.3 gn it looks like there is the beginning of some signs of pressure. Any of the signs that are seen mean the load is over the maximum pressure accepted for the round (with maybe the issue of some primer flattening). Hodgdon list 45.3 as a maximum load in a 24" test barrel with a velocity of 2854 fps. This is with a 155 SMK which is a much shorter bullet than the Scenar. The case used by H is Winchester which has a case volume greater than R-P.

Looking at only the Hodgdon data it would imply that the load is probably overpressure. Case volume is less to raise pressure. Bullet is longer so may be seated deeper which would raise pressure. Measured velocity is ~2880 fps in a 20"barrel. The 20" barrel should lose about 100 fps (4x25). So it implies the load is approximately equivalent to 2980 fps in a 24" barrel which is about 130 fps over the Hodgdon velocity. The things that would tend to lower pressure from tested are chamber volume (case related portion of the chamber) and freebore. The case volume region is likely larger than the SAAMI/CIP minimum due to the reamer being oversized to reduce retooling frequency and the freebore is likely longer. The bottom line is that based on the velocity alone the 45.3 load is over the rated pressure. Looking at the cases I personally think this is the case.

With regard to GRT things are more complicated. The fundemental design of both Quickload and GRT is that they are simulation programs of a highly complex and to some extent only marginally understood combination of processes. As such there certain combination of estimations and physics that come together to simulate a final results. In the case of both QL and GRT that result is to correlate powder charge, chamber pressure, and velocity. When digging down into the other results of the simulation and trying to compare the results to real world things begin to deviate. Some more than others. In particular the case fill is one that is subject to gross differences. The calculation is based on the use of a bulk (density of a large volume/number of particles) density of a granular material. Bulk density of extruded powder can very quite a bit based simply on how the material is loaded into case or how it was tested in a lab (think long drop tubes for Varget and electronic tooth brushes for 4350). it is at best an approximation.

The OP mentioned when asked about COAL "Yes and jump." As far as I know the only way to play with jump is to modify the "G" chamber dimension which I would be reluctant to do on any commercial chamber even though I would speculate it is actually greater than the CIP specified value.

So there is a test @45.3gn that shows the load is overpressure. So there is a program than predicts the load is overpressure. You have a velocity that indicates you are over pressure.

The 44.6 gn load using the 2.835" COAL is only slightly overpressure and being temp stable powder it is not going to go crazy high as long as the cartridge does get too hot as in leaving it in the sun.

Sdupontjr said:
Didn't know that. They are tossed. The range officer gave them too me because he knows I shoot 308. The 155 makes sense being I've read alot of info online talking about win cases have more capacity. Makes perfect sense.

The light brass was developed somewhere in the 90's for Palma competition and Win stayed with it. That 176 Win Brass is either old or Winchester is running it on the Lake City equipment if it's new. If its new then it's going to really confuse a lot of reloaders.

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