Accumark ?'s continue..#4 -crowns and muzzle brakes

[elkeater2]

I've seen a bunch of different crown styles, but I'm curious about something. Many crowns have been machined, or had the brass ball treatment, so the juncture at the end of the bore has a slight chamfer or bevel. This creates a countersunk edge which is enough to effect both the lands and the grooves, but often that's all. Others (and this Accumark is one) have had no visible machining or modifying in this area - it goes straight from the bore to outside edge of the barrel. I wonder if there is anything in this latter style that is not conducive to accuracy:

 

[Dr. Vette]

Entirely normal.

In reality the shape of a crown has little to do with its accuracy.
How well the crown was made has everything to do with its accuracy.

 

[elkeater2]

What we discovered is that when fired with the brake installed, there is a layer of carbon fouling that builds on the flat between the bore and the outer edge of the 'crown'. If that fouling isn't totally removed when cleaning, one can leave a bump or two of it in places which creates an assymetry I don't like. I did some minimal polishing there in hopes the fouling wouldn't build up like it has in the past.
EE2

 

[IdahoCTD]

Even highly polished crowns get the carbon build up. It's totally normal and brakes can cause it to build up sooner.

When I'm building a gun and cutting the crown I either do a 90 degree/flat crown or a 11 degree crown. I make a cut as slow and as smooth as I can. Then I polish the face of the crown and the final step is to polish the edge of the bore. I just hit this edge lightly with 1000 grit sand paper

 

[Oldtrader3]

The important feature of a crown is its smooth tansition from barrel to air. The configurations of crowns run the gamet from straight cut to angled cut to various chamfer styles. The goal is no gas blowouts at the muzzle and smooth gas and ejecta transition at the muzzle with minimum turbulence caused by burrs and tool marks.

All of the different shapes seem to have their adherents and critics. I am not sure what works best from all of the various shapes that I have owned but dead nuts machining and TP and smooth transition angles are the important part of this transition. I happen to think that Sako has one of the better cut geometries for muzzle crowns myself but the is just MHO.