At one time I altered a few mags to use longer OAL loads in certain rifles but had to be sure you marked long rounds well, had right mags for them when went in field but the coupdegrap was in real world testing. Once I nailed down the right process and load (all brass annealed, sized, trimmed, primer pockets uniformed flash holes deburred and sorted) discovered there was not enough additional accuracy to be worth the effort of modifying mags and loading long.
One of my most shot projectiles are Speer 90 grain TNTs. They are inexpensive and good for paper, training and varmints which is majority of my killing. Out of the box they shoot well but if going long distance they can be made much more accurate. Wife and I usually sit down with two to four 650 count boxes per session where all are "pointed" in a Whidden Bullet Pointing Die then meplat is trimmed in a meplat trimmer so tips of bullets are all perfectly centered and uniform. A TNT that's pointed and trimmed exhibits about 1" less drop at 500 yards and at 250 yards (my longest range close to house to train) group at least 1/2 MOA less or better. As I finish pointing and trimming wife sorts all by weight. We generally wait till have four boxes pointed and trimmed then she sorts all into four boxes, light, mid, heavy and short range training/barrel foulers if fall far enough out of the three main groups tolerances.
Use a scientific scale (got a $5,000 scale at auction when local defense plant making cruise missile parts closed) to sort the bullets so generally end up with about 400 to 600 in each pointed, trimmed and weight matched box. She also weight sorts all the cases into four groups and each bullet group is matched to a box of weight sorted brass. Drop our charges using a powder measure then trickle to dead nutts on. Wife will sit and pick out or add a single kernal of powder till the scale zeros. If she is not available when charging cases use a MEC automatic trickler to weigh charges as don't have her patience.
All bullets, cases and primer pockets are trimmed to most uninform we can do, all are weight sorted and matched with charges that fall within 1/10th of a grain (one to two kernals of powder) so all the work is done at the bench with a few extra steps that guarantee our loads are as consistent as humanly possible without having a million dollar ballistics lab as a major ammo manufacturer may have for development and data for reloading manuals. Able to load to standard OAL and still have first round cold bore accuracy out to 400 plus yards on varmints.
Having a magazine that lets me load to longer COAL doesn't do as much for accuracy as our meticulous bench work and don't have to worry about which magazines am using as long as the feed lips have been adjusted to present the bullet tips to the feed ramps at a consistent angle from magazine to magazine. Have all popular brands but know I have well over 100 ASCs as are inexpensive, stainless welded body and tough. The one thing I do as put them in service swap the factory springs for Tubb chrome silicone flat wire springs (learned this trick with AR 10 mags that may feed 6XC, 2 Fity-Hillbilly, 7mm-08, 308 or 338 Federal based on which rifle(s) chose to take to range or field. Before swapping to Tubb springs had mixed results and had to separate and tune mags to rifle/cartridge combo but not anymore. About to build a 358 Winchester AR 10 and not worried about mags at all. Same with my fat case AR 15s whether 6.8, 22 Nosler or others. In standard mags have at least six cartridges I run regularly and the Tubb springs have made that much easier. Buy what you want or can afford, if have issues return it or fix it. I have become a fan of stainless welded body mags that are inexpensive enough I can adjust till perfect then after swapping innthe Tubb springs I have a huge box of fresh springs for the day when or if I start having to replace worn springs like I do annually in my IPSC and IDPA single stack 1911s.