686 "PowerPort" Q's

[CHARLIE699]

Morning All! Question directed to those who own or have shot any S&W revolvers with "PowerPort" barrels.
A friend has been having issues with grouping on a recently acquired 686-4 6". Consistently groups three shots in 1.5-2" with rest flyers that expand group to 3-4". He tried several loadings, Factory & handload. Different bullet weights too. Group impact would change slightly between loads but spread remained consistent.
He asked me to try it. All were fired on my own range, 25 yd S/A from rest. I tried two factory JHP 125 & 158 loads and two of his 125 & 158 lead reloads. I got same results as he did. Nice group with three shots and then it opens up. I also tried my own 158 LSWC load. Same results.
No pin gauges but throats all appear consistent size. No evidence of spatter. Timing is excellent on all chambers and no forcing cone issues. No evidence of bullet strike in the "PowerPort" muzzle.
Is this just the nature of the "PowerPort" barrels? Something else?
While I realize many would still find this acceptable "Combat" accuracy,,,, It is puzzling.

 

[RGNewell]

I have the barrels recowned, forcing cone recut to 11 degrees and cylinder throats opened up if needed.

 

[twodog max]

IMO it is a little premature to start removing metal. Mark the chambers to determine if the same chambers are causing the dispersion.
In rifles barrels heating up can cause groups to open. I would think similar effect could occur in a revolver.
Don't do surgery until the problem is isolated.

 

[AveragEd]

I used to own several PowerPorts in Models 686 and 629. Shooting them back to back with my non-PowerPort models demonstrated a possible reason for the feature's discontinuance - it is ineffective in reducing felt recoil. Pressure in handgun loads is not great enough to allow a port that bleeds off pressure to reduce enough pressure to affect felt recoil. In rifles where you are dealing with 60,000 and more units of pressure, yes, it works.

Chronograph some PowerPort and non-PowerPort guns and you'll see very similar muzzle velocities. If the port was working, the ported gun's MVs would be significantly less but it isn't. They can reduce muzzle jump to some degree but in my experience, it is very slight. What the port does do well is allow an incoming breeze to blow combustion residue back into your face. Again, in rifles, you will see lower MVs from ported barrels and feel a difference.

I've since sold all my PP guns except one 686-4 that my S&W-trained gunsmith swears was not even fired at the factory so it remains so today.

Ed

 

[BLUEDOT37]

If you can get access to a pin gauge set I'd double check the throats more closely.

Next I'd check for a barrel constriction at the barrel-frame union by using the largest gage that will easily enter the muzzle & allow the gage to slide down the (clean) barrel & out the breech end.

If there's a constriction (from an over-tightened barrel) the gage will stop at that junction. I've found this problem on two of my brand new S&W revolvers, which I hand lapped out.

And definitely scrutinize the crown to verify that each of the rifling's lands/grooves are presented cleanly & equally at the point where they meet the crown.

Rarely they do & it's a pet peeve of mine. I end up chamfering the crown on most of mine.

I doubt the PowerPort has anything to do with the grouping issue.

.