Different ammo,
make sure to clean the assembly lube and copper out of the barrels with a good copper solvent like Sweets copper solvent,
make sure to clean the chambers with chamber brushes, and put the rifles in someone else hands that is used to shooting an HP auto loader to weed out if you are fighting recoil of the rifles off the bench.

Lead sled can be a bit tricky if the forearms are not free floating.  Here, if the front of the handgaurd is attached to the front of the barrel with the front hand gaurd clip, you need to sand back up as close as you can to the upper receiver with sand bags.  Hence the farther down the guard towards the front sight with a suport, the more is going to flex torque the barrel from shot to shot instead.

Small glitch here,

When running the rifle for long periods and needed first break in, need to run the rifle on the wetter side with CLP to help combat the power fouling so it does not build up to the point that the rifle will gun power fouling choke out.  CLP has a cleaning agent in it that will dissolve the gun powder fouling as it tried to build up under live fire conditions.

The down side, beside the cleaning agent, CLP has Teflon in it as well, and it takes about 14 rounds of live fire burn out any CLP Teflon in the bore (used as the short term storage lube) until the barrel will group settle in. If you have the rifle lube on the wetter side with CLP, some CLP will migrate to the bullet tips from the lube on the upper receiver bearing areas, and you really never get the Teflon burned out of the barrel so the barrel can settle down.

So for groups, Sweets copper solvent to clean the chamber (with chamber brush) and bore (bore brush needed here, but only for a couple of passes), dry patches down the bore to get them bone dry, and only every so lightly lube the upper receiver bearing areas instead.

Once at the range, single round down the barrel to bullet foul the barrel as a start point, then start shooting your groups with a slow rate of fire (should take you around a  few mins to get off 10 shots).  Now let the barrel cool down for a few mins, then you can start the next shot string for another 10 shots.    What a few more mins, and then get off a third 10 shot string.  Keep shooting 10 round groups until the barrel starts to copper foul to the point that the groups start to open up (keep a note pad so you can keep track of your self induced fliers.

Also to point out, on a new production barrel that has not been hand lapped, it can take up to 300 rounds before the barrel has self unified the rifling, knocked off any burs at the throat and crown, and heat stress relieved the barrel.  On a custom hand lapped barrel, should shoot it best from the first round down the barrel instead.



Bluntly, we are working in 10 shot strings to see what that rifle will group with that many shoots, and the extra strings are to see the amount of rounds (next short strings) the barrel will stay clean before fouling builds up to the point that it starts to open up the groups.  And don't rapid shoot the HP rifle like it a 22lr.  It will just heat up the barrel to start to change the barrel harmonic, and will cause enlarged groups.