Mid barrel primary choke? ... is this a thing??

[AirSmithCA]

I have an Ataman M2 in .25 cal. Been doing some barrel work to improve accuracy and discovered this thing had what I'm going to call a "primary choke" mid barrel, pretty much halfway, and then a very tight choke at the muzzle....ive never encountered this before.

I decided to fire lapp the barrel with JB bore paste on some slugs...success, couple dozen shots the middle choke reduced and pushing some pellets by hand I quickly discovered the muzzle half of the barrel was actually quite rough.

So... this got me questioning, is a midway primary choke actually a thing? Size that pellet down a little before the rough area and then size it down again at the muzzle? The OEM accuracy actually wasn't bad...just thought it could be better.


Photos are 50yds in heavy winds with 29gr JTS pellets and other 29gr NSA slugs.

 

[nervoustrig]

I would place the odds of a mid-barrel choke being intentional at 1:1000. It represents an unnecessary complication in the production of the barrel, carrying the risk that some percentage of barrels would end up with the tightness of the two chokes reversed, as compared to simply applying a single choke at the muzzle.

Many of the barrels I've lapped have tight regions at random places along the length, and some bad enough that they could reasonably described as chokes. I suspect your barrel is one of those.

Over time I have developed the opinion that finding a very tight muzzle choke (more than 1 - 1.5 thousandths) is an indication the manufacturer expects their bore dimensions to vary a lot.