Have just gone through this with my 7mm08 mod 7 I didn't even bother measuring maximum CBTO as I new I wouldn't get anywhere near it with the limited mag length of a mod 7.
I also dont think there is much if any more length to be gained by modding the mag box.
Another issue you will have with using a long projectile like the ABLR is that to seat it at mag length it will take up room in the case limiting powder capacity.
That being said my 708 using 150gn eldx seated at mag length shoots fantastic so it is possible you may get the ABLR to shoot even with a big jump.
If the ABLR don't work mabey the eldx would be worth a shot, whatever pill you use I dont think you will be able to seat it anywhere near the lands without single feeding due to the short mag length of the mod 7.
That shouldn't stop you from getting awesome results.
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