Thread: Practice make perfect 300prc load development

The big day has come and passed and my semi custom Bergara 300PRC arrived this week after a very patient 3 week wait
I'll run through the set up then I'll get into the load development
24" Bergara Wilderness barrel and action
Timney Elite trigger
Precision Platforms picatinny rail
Precision Platforms carbon stock
DPT MK2 suppressor with braked cap
Wheeler 2 piece cant bubble rings
Athlon Midas BTR gen 2 4.5-27x50 scope
Total package weighs 4.3kg including the DPT

This rifle came with a partially developed load with Hornady brass, 225gn eldm's over adi 2217 seated at 20thou off the lands.
The loads were substantially longer than SAAMI but still easily mag fed...happy days.
Took said hand loads to the range today to get acquainted with the rifle and also validate the speed as the previous owner had only used drop at 500y to calculate the velocity.
The claimed velocity was 2840fps the magnetospeed confirmed velocity was a anemic 2700fps.....
So whilst it was super accurate shooting a .6" 6 shot group, I find myself just wanting a little bit more as the cartridge is capable of pushing them to 2850fps at book max.
I'll be happy if I can get 2750-2800fps with the same accuracy.
I knew I'd be tweaking the load as I'm switching to virgin Lapua brass, keeping the powder and projectiles the same.

Now the Hornady brass hand loads were loaded with 77gn of 2217 (remember that the C.O.A.L is substantially longer than SAAMI so will require more powder to reach the book quoted velocity) as stated above these hand loads achieved 2700fps.
The load seated at 20thou off the lands seems accurate so I'll stick with that seating depth for now.
I have loaded a charge ladder to see where I need to be for the velocity I want, and check for pressure.
Unsure how the Lapua brass will compare as far as velocity goes I have loaded my charge ladder as below:

77gn (same as Hornady hand loads that came with the rifle)
78gn
78.5gn
79gn
79.5gn
80gn

The book data shows a fairly linear increase over the entire data set for this powder and projectile choice of approximately 3gn for 100fps increase in velocity hence my charge ladder is over 3 gn, I'm expecting the Lapua may have less internal volume as it's heavier so I may actually see an increase even with the same load, I won't get a chance to shoot the ladder till next weekend now but it's loaded ready to go.

Factory C.O.A.L is 3.680"

My hand loads are at 3.731"

That thing is hanging waaaaay out there. Where is the start of the boat tail relative to shoulder/neck junction?

Set a round count your happy with and if you don't have a decent load by then ditch the eldm.

This is coming from a eldm fan boy.

Originally Posted by chainsaw

That thing is hanging waaaaay out there. Where is the start of the boat tail relative to shoulder/neck junction?

Crude but effective comparison, they are very long pills

Originally Posted by SPEARONZ

Set a round count your happy with and if you don't have a decent load by then ditch the eldm.

This is coming from a eldm fan boy.

If they shoot at 2700fps they will shoot at 2750-2800fps, I'm not expecting to burn through a heap of components to find a load.
If I can't get velocity and acceptable accuracy have a few other options I'm considering but in no rush to discount the ELDM's yet.
Time will tell.

I also found I have to increase powder charge by .5gr to match the velocity of the hornady brass, when I swapped to Lapua.
I'm throwing the 230gr Atip at 2850fps out past a mile

Originally Posted by lau lau

I also found I have to increase powder charge by .5gr to match the velocity of the hornady brass, when I swapped to Lapua.
I'm throwing the 230gr Atip at 2850fps out past a mile

yup will see what the charge ladder throws....hopefully this weekend.
what powder are you using with the 230gn A tips ?

Originally Posted by dannyb

yup will see what the charge ladder throws....hopefully this weekend.
what powder are you using with the 230gn A tips ?

I using 2217 in mine.

So finally got to the range this weekend to shoot my pressure/velocity ladder....
Results as follows:

*77gn 2761 fps

*78gn 2797 fps

78.5gn 2818 fps

79gn 2836 fps (slightly heavy bolt lift so didn't shoot the higher çharges)

There's the charge ladder pic, 77gn center, 78 and 78.5gn touching, then 79gn further right.....
What I didn't realize was this ladder was warning me of pending trouble......more on that soon.

I went home and loaded up 2 lots of test loads 8 rounds each....
78gn and 78.5gn
Then went back to the range.
Shot 7 of the 8 78gn loads (I had 1 primer fail to fire) accuracy was not stellar but not rubbish no pic but explanation coming.....
Shot 3 rounds of the 78.5gn load and was looking through the scope decidedly unimpressed, between the 2 groups I corrected the scope left 2" and down 3" however my poi had only shifted down 3" and despite the change in poi the group was shit house
Then I cycled the bolt to eject the spent case and that's when a small stainless screw fell from the rifle onto my shooting mat
Hadn't noticed any stainless screws when I stripped the rifle a week earlier, immediately began investigating where it had come from....nope all 12 scope ring screws present and correct (also not stainless), screws holding cant bubble all present and correct (not stainless either), even though I new there was no stainless screws in the saftey and trigger system I gave them both a good wiggle and tested function (nope no issue there either), finally a gave the scope a bit of a wiggle holding the front objective bell (seems ok there) then went to wiggle the rear occular bell when it became obvious where the screw Had left the chat from
Yup the rear most rail screw was missing and the second rear rail screw was only held in by the fact the ring was clamped over it.....mutter mutter expletive etc.....pack my shit up knowing full well the first ladder was likely a wasted exercise due to loose rail.
Thankfully I only shot 3 of the second charge weight.
Got home stripped the scope and rail off, threw the stainless screws away, replaced with some base screws I pinched off a set of talleys, there was no loctite or epoxy used when this rail was fitted by the previous owner so was a recipe for failure
I refitted using red loctite and torqued everything back up. Then went and loaded up enough rounds to re do my 2 test load charge weights 8 shots each, packed my shit back into the car and returned to the range.....tbc

is this the replacement for your 7mmRM ?

Returned to the range, got everything set up again got behind the rifle and sent the 8x 78gn rounds down range without issue and unsurprisingly quite a large poi shift. Group was around 1" I didn't measure it but for 8 rounds it was not to shabby.
Velocity E.S and SD were acceptable.



My poi was now 3" low and 3" left so I corrected that then made a phone call whilst I let the barrel cool down.
8 rounds at 78.5gn sent down range no fuss no drama, through the scope it looked like a pretty decent group so I was quietly optimistic.
The velocity ES and SD were not bad either, in fact the velocity was right in the gravy zone for where I wanted to be


I suppose you all wanna see the group ? ........