Thread: 6.5 Creedmoor load development

The final chapter in my story (not likely to be a sequel) was addressing the bullets over all length with the hope to gain back some more space in the case it was getting apparent to me that all of the tested powders were reacting badly to a full case or compressed loads.
I am running the AI style mags in my pup chassis and selected the steel Accurate-Mag brand without the front block to get a total allowable total load length of 2.965".

My loads till then however were loaded to give me a 20 thou jump to my lands which was just a starting point at the time, I was yet to revise this when I got to the fine tuning stage of the load.
However, I decided to test a few of my new pet loads of 43gr RL16 behind the 139gr Lapua with a shorter jump of 10 thou to test my powder capacity v/s high pressure issue theory.

Bingo! 40fps gain in velocity just like that with none of the pressure signs a 0.4gr powder increase would have induced at that velocity.
Now I got thinking...

I was not sure what the std measurement of the throat length is on the SAAMI specs and didnt think to look it up at the time but I now knew how to ditch a lot of pressure...
Im not sure if the Remington 700s throat is shorter than some other manufacturers throats but I didnt go searching either.. Im guessing it is a happy medium of matching with an average bullet weight and length to ogive and the M700s pathetic internal mag length.
At the time I just put it down to the fact the case was designed to run out of an AR10 upper which limits the overall bullet length to the std AR10 magazine internal dimensions. Again I still havent chased all those figures.
Without knowing all these figures I can only speculate that this is the reason for such a variation of results documented by other Creedmoor owners.

THE FIX: I seated some my rifles prefered projectiles to my max mag length of 2.965" and took some careful measurements from base to ogive and then took an average over the three 130gr TMK, 136gr Scenar L and the 139gr which gave me 100 thou to play with. This meant a minimum jump of 10 to 20 thou was possible with all three bullets loaded to full mag length.
In the lathe it went and out came 100 thou of the factory cut lands with a piloted throat reamer.

You can picture excitement as the first few test loads went over the chrono.. and yes you guessed it, another big drop in velocity but also a very low pressure load. I gained 100 thou of air space between the powder and the back of the projectile! This meant I could work my loads up further with additional powder and not see any adverse effects on the pressure until it got close to compression again.

To cut a long story short this lead me to many more load tests to find a consistent tight sub 1/2" group and eventually had me decide on the 136gr Scenar over the 139gr scenar due to ever so slightly better groups at 200y and a fraction higher speed or slightly less pressure than the 139gr bullets.
I backed my speed off to a AV of 2910fps which gives crazy little ragged hole groups at 100y and a slightly better SD than the faster loads did.

For the safety of those who will have skipped to this end of my thread to try the load at the end, I will keep my selected powder weight to myself but I will encourage you to at least try the Aliant RL16 and Peterson brass because its a big part of the battle behind you. Check your maximum load length in corolation to your lands and you magazine and find the best relation there too. Work your loads up slowly and stop at the first signs of pressure.

All the other details of my pet load are as follows:

Peterson Match brass OAL 1.916", CCI BM-4 primer, Aliant RL16 powder, Lapua 136gr Scenar L bullet, OALL 2.965", 0.015" jump to lands.