I know that there are ratings say 10,000 or 20,000 rounds before a barrel is shot out and starts to lose accuracy.  If you were running a .22lr conversion kit with a bolt if you shot 5,000 or 10,000 rounds through it... would you be putting the same stresses on it as shooting the full size .223 through it?  If you were doing a high round count with the .22lr would it be pertinent to get a dedicated .22lr upper or would using just a conversion kit be sound?

22lr barrels can easily last 100k rounds. So shooting 22lr through your 5.56/223 barrel isn't going to damage it at all.

this.

only thing to watch out for is lead fouling... clean on a regular schedule and youll be fine.

This.
If it's your only / go to gun always shoot some full power ammo 5.56/223 through the rifle after using the conversion kit.

I have stopped up the gas port on three separate occasions with two separate brl's by firing large amounts of 22 before shooting real ammo.
I can't tell you when it stops up i just know it will happen every time i fired over 5k of 22 without cleaning it's made those guns single shots for a few rounds.
Not a big deal...... Just run the charging handle keep firing till it melts / blows out the lead. The most it's ever taken is 7rnds to be back functioning.

I can't tell it nor do i believe the 22lr is doing any harm to the brl.

Topic Moved

.22 doesn't fly fast enough to damage your 5.56 barrel. I recommend between 300 and 500 rounds, pulling a boresnake through the barrel then shooting 5 rounds of 5.56 to blow out the gas system.
Clean the rifle properly when you are finished.
Dave N

Great news.  I might be able to justify a standard AR then with a .22 kit : )

The .22 conversion has to be one of the greatest firearms ideas of modern times. Nothing is perfect but it comes close. Just follow some basic maintenance and keep it clean and you can live happily every after....or at least for a very long time.