6.5 PRC Load Advice

[BongEyes]

Greetings all,
This is my first post here; I have searched high and low for answers in the forum and have only partially found what I need... so my apologies if I have missed the answers for my questions... but I don't believe they exists on this forum just yet.

Behold my pride and joy. A gun I do not wish to blow up...
It is a semi-custom Tikka t3 with KRG Bravo chassis/stock and a 28" heavy profile 6.5 PRC Barrel screwed on. This action has seen 2 previous barrels (chambered in .308) so this time I have decided to go with a cartridge which can do everything the .308 could do and then a little extra as I intend to occasionally shoot long range 1000m+ (1100 yds+) at steel in windy conditions.

The primary purpose for this rifle will be vermin control on a large sheep and crop farm. Vermin include Foxes, Pigs and Kangaroos. Due to the nature of the terrain at this property shots on animals are usually fairly 'long' range (200-500 meters) so a flat trajectory (with a good MPBR) and enough energy to drop pigs cleanly at these distances is needed. I think this cartridge will do the job nicely.
Now the show and tell is done onto the load development...

The components I have chosen to test initially are;
135gr Berger Classic Hunters
H4831sc (It's called AR2213sc here but I believe they are the same powder)
Into virgin Norma brass.
Primers are surplus Indian Army LR made under contract for the US Military. They are not my first choice but I am led to believe these are good quality so I took what I could get at the time...

The best online load data I could find was from Primal Rights website. He tested this bullet/powder combo from 52-59 grains. He is using Alpha brass which I know is good stuff and can tolerate high pressures compared to Norma brass.
You can find that here

I began testing at 54 grains, bullet seated 0.020 off the lands, and increased the load by 0.5 grains to monitor pressure signs.
6 shot groups due to barrel weight and still having a good 5 shot average if there was ever a flyer...
Shooting at 100m (109yds)

The most accurate loads were at 55.5 and 57.0 grains. I pulled the last shot pretty badly on the 55.5 gr group so if you ignore that one stray it is not a bad group. Red aiming circle is 24mm or just under an inch for reference.

At 55.5 grains I recorded an average speed of 3133 FPS with an ES of 39 fps and 14 fps SD measuring in at 0.511" 5 shots
I did notice slight a "click" on bolt lift but otherwise the case extracted smoothly and had zero visual high pressure signs.

This "click" did get progressively worse at 56 and 56.5 grains, but with zero visual pressure signs on the brass still I decided to continue with testing.

57 grain was at 3223 FPS with an ES of 20 FPS and SD of 6 FPS. 6 shots came in at 0.472"
Obviously I was stoked at this group and es/sd combo... however I decided to halt further testing because the bolt click had gotten unacceptable. The brass still looked good to me, although there was very slight flattening of primer with no cratering around the firing pin mark. I did notice some marks at the web of the case, not cracks or obvious defects but more so a mirror image of the inside of the chamber? Im assuming the case is expanding excessively at the web and sticking inside the chamber? Hence the click..
However after measuring fired brass and unfired brass the expansion seems within acceptable limits?



Sorry for the abundance of information so far, but I appreciate it if you're still with me. Now onto my questions...

-Is the bolt click that I am experiencing a sign of high pressure? Considering the lack of visual pressure signs on the brass.
-Do you consider these speeds to be within safe tolerances in a 6.5 PRC given bullet weight and barrel length?
-What kind of speeds is everyone else getting if they are using a similar load?
-Is the bolt click normal? I know that some chambers are on the "tighter" end of tolerances than others and this is a known issue with some PRC cartridges, with the "solution" being a modified reamer which opens the rear most portion of the chamber up slightly.
-Does this reamer actually fix an issue or just mask bolt click as a pressure sign?
-Is 3200 Fps+ too fast for a 6.5mm barrel?

I am not trying to load for absolute speed here but I want to find a happy medium between precision, bullet energy, maintaining a high MPBR and utilising the potential of the cartridge hence the long barrel. If having that extra 100fps velocity comes at too much of a cost such as flogging the barrel out way sooner than necessary then I will settle on the slightly slower and larger group. Having said that the rifle and cartridge have proven to be high performance so far and I want to use this performance but not at the cost of safety or drastically reduced brass and barrel life. (That shits expensive and getting a new barrel here isn't that easy)

I understand there are so many variables at play so feel free to ask for any more information if you feel I have left some out. I don't have any photos of the fired brass on hand but can take some if you think that will help.

Cheers
Bongy

 

[straightshooter1]

Greetings all,
This is my first post here; I have searched high and low for answers in the forum and have only partially found what I need... so my apologies if I have missed the answers for my questions... but I don't believe they exists on this forum just yet.

Behold my pride and joy. A gun I do not wish to blow up...
It is a semi-custom Tikka t3 with KRG Bravo chassis/stock and a 28" heavy profile 6.5 PRC Barrel screwed on. This action has seen 2 previous barrels (chambered in .308) so this time I have decided to go with a cartridge which can do everything the .308 could do and then a little extra as I intend to occasionally shoot long range 1000m+ (1100 yds+) at steel in windy conditions.
View attachment 8539417View attachment 8539919

The primary purpose for this rifle will be vermin control on a large sheep and crop farm. Vermin include Foxes, Pigs and Kangaroos. Due to the nature of the terrain at this property shots on animals are usually fairly 'long' range (200-500 meters) so a flat trajectory (with a good MPBR) and enough energy to drop pigs cleanly at these distances is needed. I think this cartridge will do the job nicely.
Now the show and tell is done onto the load development...

The components I have chosen to test initially are;
135gr Berger Classic Hunters
H4831sc (It's called AR2213sc here but I believe they are the same powder)
Into virgin Norma brass.
Primers are surplus Indian Army LR made under contract for the US Military. They are not my first choice but I am led to believe these are good quality so I took what I could get at the time...

The best online load data I could find was from Primal Rights website. He tested this bullet/powder combo from 52-59 grains. He is using Alpha brass which I know is good stuff and can tolerate high pressures compared to Norma brass.
You can find that here

I began testing at 54 grains, bullet seated 0.020 off the lands, and increased the load by 0.5 grains to monitor pressure signs.
6 shot groups due to barrel weight and still having a good 5 shot average if there was ever a flyer...
Shooting at 100m (109yds)

The most accurate loads were at 55.5 and 57.0 grains. I pulled the last shot pretty badly on the 55.5 gr group so if you ignore that one stray it is not a bad group. Red aiming circle is 24mm or just under an inch for reference.

At 55.5 grains I recorded an average speed of 3133 FPS with an ES of 39 fps and 14 fps SD measuring in at 0.511" 5 shots
I did notice slight a "click" on bolt lift but otherwise the case extracted smoothly and had zero visual high pressure signs.
View attachment 8539975

This "click" did get progressively worse at 56 and 56.5 grains, but with zero visual pressure signs on the brass still I decided to continue with testing.

57 grain was at 3223 FPS with an ES of 20 FPS and SD of 6 FPS. 6 shots came in at 0.472"
Obviously I was stoked at this group and es/sd combo... however I decided to halt further testing because the bolt click had gotten unacceptable. The brass still looked good to me, although there was very slight flattening of primer with no cratering around the firing pin mark. I did notice some marks at the web of the case, not cracks or obvious defects but more so a mirror image of the inside of the chamber? Im assuming the case is expanding excessively at the web and sticking inside the chamber? Hence the click..
However after measuring fired brass and unfired brass the expansion seems within acceptable limits?
View attachment 8539976


Sorry for the abundance of information so far, but I appreciate it if you're still with me. Now onto my questions...

-Is the bolt click that I am experiencing a sign of high pressure? Considering the lack of visual pressure signs on the brass.
-Do you consider these speeds to be within safe tolerances in a 6.5 PRC given bullet weight and barrel length?
-What kind of speeds is everyone else getting if they are using a similar load?
-Is the bolt click normal? I know that some chambers are on the "tighter" end of tolerances than others and this is a known issue with some PRC cartridges, with the "solution" being a modified reamer which opens the rear most portion of the chamber up slightly.
-Does this reamer actually fix an issue or just mask bolt click as a pressure sign?
-Is 3200 Fps+ too fast for a 6.5mm barrel?

I am not trying to load for absolute speed here but I want to find a happy medium between precision, bullet energy, maintaining a high MPBR and utilising the potential of the cartridge hence the long barrel. If having that extra 100fps velocity comes at too much of a cost such as flogging the barrel out way sooner than necessary then I will settle on the slightly slower and larger group. Having said that the rifle and cartridge have proven to be high performance so far and I want to use this performance but not at the cost of safety or drastically reduced brass and barrel life. (That shits expensive and getting a new barrel here isn't that easy)

I understand there are so many variables at play so feel free to ask for any more information if you feel I have left some out. I don't have any photos of the fired brass on hand but can take some if you think that will help.

Cheers
Bongy

You've given how far you are off your lands, but that doesn't tell anyone your seating depth as .020 off can mean a very different seating depth from any other chamber. It's better if you state your cartridges average COAL that the seating depth can better be determine by us.

Have you measure the case volume of your Norma brass? The last I heard, it was at 71.4 grs of H2O, which seems pretty high to me.

Am not sure that AR2213sc is really the same as H4831sc as you velocity number of 3133 fps for 55.5 grs out of 28" is 100 fps faster that what H4831sc tends to produce. . . even when figuring for high ambient temperatures.

The clickers you're experiencing could simply be the how this particular brand of brass works in your chamber or that the brass just isn't getting sized down enough. The only chambers I read where there was often this issue with a manufacturer and the best solution was a "modified reamer". That might be the place to go after you check out whether a sizing die solution can't be found.

That speed you're getting with 55.5 grs does seem plenty safe with some room to spare. Just keep an eye out for pressure signs when increasing that is you choose to.

With 54.3 grs of H4831sc pushing Berger 140 Hybrids being out of my 26" barrel (COAL at 3.093 in Lapua brass with case volume of 68.8 grs of H2O) I get 2903 fps with excellent results.

 

[BongEyes]

You've given how far you are off your lands, but that doesn't tell anyone your seating depth as .020 off can mean a very different seating depth from any other chamber. It's better if you state your cartridges average COAL that the seating depth can better be determine by us.

Have you measure the case volume of your Norma brass? The last I heard, it was at 71.4 grs of H2O, which seems pretty high to me.

Am not sure that AR2213sc is really the same as H4831sc as you velocity number of 3133 fps for 55.5 grs out of 28" is 100 fps faster that what H4831sc tends to produce. . . even when figuring for high ambient temperatures.

The clickers you're experiencing could simply be the how this particular brand of brass works in your chamber or that the brass just isn't getting sized down enough. The only chambers I read where there was often this issue with a manufacturer and the best solution was a "modified reamer". That might be the place to go after you check out whether a sizing die solution can't be found.

That speed you're getting with 55.5 grs does seem plenty safe with some room to spare. Just keep an eye out for pressure signs when increasing that is you choose to.

With 54.3 grs of H4831sc pushing Berger 140 Hybrids being out of my 26" barrel (COAL at 3.093 in Lapua brass with case volume of 68.8 grs of H2O) I get 2903 fps with excellent results.

Thanks sharpshooter,

Seating depth averages around 2.895" meplats aren't very consistent shapes so the COAL varies quite a bit.

I have not measured the case volume of my brass however so I couldn't tell you that right now. In theory what effect would having ~2 grains of case capacity over your Lapua brass have in the process of firing?

You very well may be right about the powder, however I have looked to multiple sources which state the two powders are equivalent and have burn rates within 5% of each other. So this is the first I have heard for the contrary.
ADI Powder Equivalents
By many accounts AR2213sc is sent to the US where it is repackaged and labelled as H4831sc, however as you've said there is about 100fps discrepancy between the two so that is some interesting information... I have heard some barrels just shoot faster than others but 100fps seems a bit much? I know 2 extra inches can be considered a lot to some people but in the world of rifle shooting does it really matter that much

The brass I was using was unfired, and I never ran it through a sizing die before shooting it. Unfired web diameter is a consistent 0.528"
Fired cases at the web measured 0.532 - 0.533" which is 0.005 stretch is that normal?

 

[straightshooter1]

Thanks sharpshooter,

Seating depth averages around 2.895" meplats aren't very consistent shapes so the COAL varies quite a bit.

That's close enough and understood about meplats variations. It's better than .020" off chambers where there's something like .060 off. After all, throats do erode too.

I have not measured the case volume of my brass however so I couldn't tell you that right now. In theory what effect would having ~2 grains of case capacity over your Lapua brass have in the process of firing?

2 grs could make a difference of something like 40 fps.

You very well may be right about the powder, however I have looked to multiple sources which state the two powders are equivalent and have burn rates within 5% of each other. So this is the first I have heard for the contrary.
ADI Powder Equivalents

Burn rates alone don't help compare powders very well as it's only one factor of the equation. Like energy content per unit mass is another factor. I think burn rates are helpful to know in terms of when is completely burnt before leaving the muzzle.

By many accounts AR2213sc is sent to the US where it is repackaged and labelled as H4831sc, however as you've said there is about 100fps discrepancy between the two so that is some interesting information... I have heard some barrels just shoot faster than others but 100fps seems a bit much? I know 2 extra inches can be considered a lot to some people but in the world of rifle shooting does it really matter that much

Note, I did take into account the 2 extra inches for that 100 fps. And yes, that extra 2 inches makes a good difference that need to be considered when comparing velocities.

The brass I was using was unfired, and I never ran it through a sizing die before shooting it. Unfired web diameter is a consistent 0.528"
Fired cases at the web measured 0.532 - 0.533" which is 0.005 stretch is that normal?

.005" is a LOT of stretch for the web. I've not used Norma brass before, so am not really familiar with it. But I have read many reports of its short lifespan. This could, in big part, be a good explanation for that. For my 6.5 PRC, my virgin Lapua brass starts out at .5295 and my virgin Peterson brass starts out at .530. After firing all my brass ends up at .532. My sizing die reduces that web area down to .5315. I would not like to see .005 movement in that web area, even if its only for the first firing.

 

[db2000]

I like 156 Bergers for longer range

24” Christensen Arms
Magnetospeed V3
53F 44% 30.23in

Berger 156 gr Elite Hunter HPBT
H4831 54.8
Hornady brass x 6
Fed 210M
COL 2.035
COAL 2.940
2852, 2866, 2852, 2870, 2859
2865, 2875, 2877, 2868, 2877 SD 7.5