Prequel to ELR with a 50bmg

[big5ifty]

In the months while this remained a thought experiment, I had decided to use the locally produced Peregrine Glider Rangemaster bullet, in 750 grains. I use Glidemaster bullets in my 375     RUM for one mile shoots, with good results. Availability is at the moment more reliable than with imported products.
 
 While I was waiting for the license, I tried to find information on 50 bmg reloads, and there is nothing useful to me outside of the official manuals.
 
 There is a dedicated 50 caliber shooters forum, but it's a paid subscription, and I refuse to pay money to eventually contribute my intellectual property obtained at my cost.
 
 The reason for that is the load data specifies a 45 inch barrel. GRT seems to think that powder burn is not complete with the normal powders in my barrel length, such as 869, the two VV BMG powders, and H50BMG.
 
 I particularly wanted data for a shorter barrel, because I know that when powder doesn't manage to burn in the barrel, it just produces muzzle flash and a concussive blast when the bullet exits.  That's a lot of excess powder to experience the effects of in this rifle.
 
 I know from experience with my other target rifles, that best accuracy and consistency follows complete powder burn in the barrel.
 
 I found data for N570 and the AMAX 750, and I had some N570 left over.
 
 I had used N570 in my 375 RUM, and it gave great velocity, but powder burn was too slow for my 30 inch barrel, which showed in the lack of consistency. There was half a container left,  and GRT showed it would give 100% burn in the BMG barrel length, so I decided I would try it first.
 
 Co-incidentally, the day I was prepping the brass, I found that Vihtavuori had updated their load data with Cutting Edge 720 grainers and N570. This was closer to what I was trying, so I used that data as a start. There are faster powders listed, but this gives the highest velocity for that bullet, even more than the actual BMG powder, 24N41. That data is also for a 45 inch barrel, but GRT is confident that the burn of N570 in my barrel is 100%.
 
 I started at 5% below the minimum, 206 grains, and went to 228 grains, two grains over maximum.
 
 The 206 grain charge gave 2588 fps, and the 228 grain 2930 fps. I moly coat my bullets. Over time, as the barrel gets coated, I expect velocity to drop off slightly.
 
 To compare pressures of the reloads, I used a 1/10,000 micrometer, measuring the base of the case just above the extractor groove, before and after firing at the range. I measured the initial size on the range on the day, in case the temperature difference between the reloading room and the range had effect.
 
 I did not use virgin brass, which makes the measurements slightly less indicative. I assumed that whatever the previous firing had expanded the brass to, it would ether not expand or expand a bit more if the pressure was higher. I was more interested in the final size, which I compared to the size of the virgin brass I have. In fact, the initial lower charges produced no additional expansion on the brass.
 
 The max load tested of 228 grains produced acceptable to me relative expansion, and should give good case life.
 
 First shot was the sighter, scope adjustment of 2 mils if I remember correctly, then second shot was top right, scope adjusted 2 tenths of a mil down, then the rest.
 
This is at 148 meters, and shows some promise as far as accuracy potential is concerned.

My biggest concern was the recoil, which is why I opted for the bench first. It's easier to manage the recoil at the bench than prone. It proved not as much as a 500 Jeffery or 450 Watts in a hunting rifle, neither of which I can safely shoot from the bench. Seems more than my braked 375 RUM, but not as vicious. My RUM cheek-piece used to slap the side of my face blue,     I have to shoot it with a padded foam cover on the cheek-piece. It does move me back a bit further than the RUM shooting from the bench. No bruising the next day, but I expect with a higher round count, it will leave a mark.
 
I will repeat this test, increasing the AOL by 0.1 inches and 2 grains charge at the same time, per increment. GRT seems to think that the max pressure remains the same as my 228 grain load up to 232 grains and 0.2 inch greater AOL.
 
And shoot it prone.

[Treeman]

That's how I lost my immunity to the flinch, I could shoot anything once twice. When we started load development and experiments with the .458 x 2", we would shoot 50 rounds in a day, often really hot stuff and or very heavy bullets. One day thereafter I had a miss-fire and boy did I notice a beeeeeg flinch.
Took a lot of work to rid myself of that reflex.