AR15 Front/Back Bolt Play

[VA_XTC_Shooter]

Just read Robert Whitley's article on teh bulletin and he mention front/back bolt play as an issue for accuracy.
http://bulletin.accurateshooter.com/2021/07/the-tack-driving-ar-secrets-to-ar-platform-accuracy/

If I am understanding correctly, he is saying to minimize the amount the bolt can move forward and backward in the barrel extension. How would you achieve this or make it work? Just test a bunch of bolt/barrel extension combos?

 

[DaveTooley]

The cartridge in the chamber limits the bolt movement. So I guess minimum amount of sizing on reloads. Custom chamber with a known lot of ammo.

 

[VA_XTC_Shooter]

The cartridge in the chamber limits the bolt movement. So I guess minimum amount of sizing on reloads. Custom chamber with a known lot of ammo.

I don’t think that is what he is getting at.

He advises that the bolt back and forth affects the brass, as in if there is too much back and forth play it will set the brass back more than desired.

he also doesn't recommend bumping shoulders, instead recommends 3-5 thousandths resizing.

 

[jelenko]

Just checked one of my uppers.
With the bolt locked in, it does move back and forth a bit. WAG is 5 thousandth or a bit more.

Even so, I'm not getting how that 'play' would impact the cartridge more than if there were no play at all.
Seems the cartridge would ride on the bolt face until the bolt stops forward movement - regardless of where the bolt stops.

 

[akajun]

IDK what he is talking about, I will tell you this, on an AR if you dont have enough clearance from the bolt nose face to the back of the barrel, you will have cycling and accuracy problems. Ive seen barrels from the factory on NM guns where that dimension was too tight, you can see where the build up of grit from normal shooting wears on the back of the barrel and will cause short stroking, failure to close, and accuracy problems. I always put about .005-.007 clearance in this area when chambering an ar-15 barrels. I got this number from disectting shot out service rifle NM barrels from two very trusted names in the industry.