The max will depend on your rifle and is around 2.38". Yamaraja recommends 2.36" fpr 100% functioning. However, check your rifle's distance to the lands with the SST. In my 18" ARP, the SST touches the lands at 2.35".
BTW, the Powder Charge vs Velocity Ladder I showed above was when I first started using 1200R (purple). You can see how much velocity variation it has after 5 range sessions - almost 200 fps. Over a year that grew to 300 fps with the 100 AB. Maybe I should just use it for fertilizer.
In all 3 of my lowers I have found that loading over 2.36 the tip of the bullet can drag against the front of the magwell causing the top bullet to pop out of the mag.
Its happened at 2.365. I have never had a ftf once the mag is inserted all the way at any oal that fit in the magwell.
That is why in my lowers I am only loading to 2.36 as I want it to be 100% reliable for hunting purposes.
Now as Xman has said if you follow his fantastic work he adjusts his feed ramps to point the tip of the bullet up slightly to help with feeding.
I have not done that so my bullets sit lower than his do. I have not adjusted the feed ramps because I have not had feed issues.
This would actually allow a slightly longer loading as the change in angle also changes the available length slightly.
With only 2 or 3 in the mag to run testing this may allow 2.37 or 2.38 due to the change in angle and associated available length.
As more are loaded into the mag this would change back as the angle of the cartridge would come back down.
So it may work with the first few but not if you say load 10 in the mag.
That would be something you would have to test yourself in your weapon.
With a modified lower I may need to adjust the feed ramps, this I don't know yet.
As to 1200R.
I have used it in even the 90gr Gold Dots and 2200 as well.
I found RL7 gives me better accuracy at .5 MOA. With 1200R and 2200 I got .9 MOA
Now I use the 1200R in the 115gr Custom Comps.
In this load I have not seen a shift in speeds over the last 1.5 years.
This makes me wonder if this only happens with lighter projectiles and if you make the powder "work" harder its not as susceptible to the variations.
At 28.8gr 1200R @ 2.29 OAL in Fed brass I am .4 MOA
At 28.8gr 1200R @ 2.28 OAL in Fed Brass I am .6 MOA
Both of these run right at 2600 FPS and have maintained that.
At 28.8gr 1200R @ 2.28 OAL in SSA brass I am .8 MOA
At 28.8gr 1200R @ 2.28 OAL in S&B brass I am .8 MOA
I have been running the 2.29 Fed brass load.
LOL, I just noticed I should try 2.29 OAL with the SSA and S&B brass sometime
I found the .4 MOA load and called it good.
This is in my 16in Bison Recon.
This load is also very accurate in my new 3R 22in Triad barrel although I did not crono it yet
I have been specifically watching this load due to Xmans cautions and have not seen it do the variations Xman got.
This is the only projectile I am currently loading with 1200R.
I will be interested to see Xmans thoughts on this.