First of all let me introduce myself, i shoot from the age of 6 (air and rimfire) and centerfire from 18 this year for 25 years.
I've been a rifle pro shooter for a while in the army. Had for duty Beretta 92 and at least 3 iterations of private 92ish models. I had Tanfoglio, Kimber, several Smith, STI Trubore (i actually use in open class) etc. Then i had a love affair with Glock.
The first i had was a 17 Gen 2 (in my strange country as civilians we use 9x21 while for duty 9x19... ) I shot maybe 25k rounds with only some basic maintenance and fresh recoil springs here and there. Then i had a G34 Gen 3, also nice, nothing special, no modifications except usual guide rod and springs. Shot through her maybe 8k rounds. Strange things of life i got rid of my Glocks and went for a while with Sig. Nice guns but not my thing, bore line too tall on the hand.
Few months ago, august 2020 in Corona event, remembering good old times, i bought 2 Gen 5 a G45 and a G34 both 9x21.
As usual the first thing i do with a factory new gun i do a little break in with 200 rounds before any polish and finish procedure.
The first thing i noticed was that the G45 had some "limp wrist-ish" symptoms with my standard loads. In the same session i added the gun light on the rail and the gun shot flawlessly 150 rounds.
Then we pulled off the G34 that had massive cycle problems both with my standard loads and both with factory ammo. No mods on the gun and factory magazines just out of the box. I may stop here because my previous Gens had fired downrange anything, from dummy rounds trough wurstels without any question.
But i went forward, since the 34 is an MOS i installed a dot and, as expected, with added mass to the slide with factory spring the gun wont cycle at all leaving the spent brass in the chamber several times. I know that is a good thing for suppressor use, but something is wrong for sporting use.
In the end, my last session was yesterday using a 13# on a Toni stainless rod and i've been able to fire say 10 rounds in a row without any feeding problem.
The load i'm using is the max suggested load for Fiocchi powder with FMJRN 123g balls that's a bit hotter than my usual training ammo. The config works flawlessly in any other gun i have or friends have (also PCC like Beretta CX4).
Do all that has to do with "marksman barrels"?
Give them back and buy a M&P CORE?