Home Forums Hunting & Shooting Handguns 357 Magnum revolver conundrum

Hey guys I've got a Smith & Wesson from the performance center it's a 327 8 shot with a 5-in barrel. No matter what loads I have put into it so far it's always very very slow. I tried the 125 XTP with 19.4 grains of little gun and it gave me 1,200 ft per second. It shoots the 158 close to a thousand feet per second. Any idea what's going on cuz this thing's going to drive me nuts.

I've seen huge variations in velocity when it comes to rifles but never ever in a revolver.

Get a feeler gage set and measure the barrel cylinder gap first. If that is within normal specs, I wonder if your chamber or barrel are over sized? How is the accuracy?

Mark in GA

I agree with start measuring up stuff! Tried any other powders?

18 gr imr 4227 125 xtp 960 fps

Something is seriously wrong and it's not the chrono.

What would be normal?

What is your baseline?

By that I mean have you tested various ammo that you have shot in the S&W through other guns, to determine that it is fact slow?

Sometimes people ask me various questions, believing X when they have a completely different issue, such as a chronograph issue, or a powder issue, or a problem with their press.

A number of times I have been at guys houses and they have been complaining about their terrible loading press, (how they just don't make them like they used to) or bad lot of powder and inconsistent charges, seating depths etc. If they ask me to look at their setup, I almost always inspect their dies, and pretty much every single time, their dies have substantial buildup in them. The seating dies, and powder drops are consistently dirty.

Or they have left powder in a powder drop for who knows how long. 6 months, a year, whatever.

Also powder is hygroscopic. It will absorb moisture from the air. How much depends on the environment. Guys will wonder why their loads are slow. Thinking they have a bad lot of powder, when in fact their powder has absorbed moisture over time. The same volume of powder (powder drops measure by volume not weight) gives a lower velocity due to the moisture content. Or worse, a guy thinks he has a "slow barrel". Nope.


Plus most guys really have a hard time using a chronograph properly. You will get substantial variations, depending on if there are shadows, cloud cover, etc. Using multiple chronos simultaneously is really the best way to tell if your readings are accurate.

You could have a slow gun, with a large BC gap, but there are a BUNCH of other things that can be a factor as well.

Establish a baseline and test only one thing at a time and eliminate the variables.

Hope this helps.

Cylinder gap looks normal to me 0.006 of an inch

I do have a 357 Dan Wesson pistol pack with all the barrels and it seems to be just fine velocity wise with the same loads same thing with my 686 Plus Smith & Wesson

That is well within spec for a Smith.



Interesting to note about your Dan Wesson pistol pack.

In theory your slow barrel could be one with a slightly larger bore diameter. (projectile and bore diameters not matching/good fit, gas escaping causing reduced velocities)

I have seen rough barrels that needed lapping (or cleaning) that were initially shooting lower velocities, but not as low as you describe.

I just shot some factory ammo 125 and 158 out of the 5-in 327 and 6" 686 Plus the 686 Plus with one more inch of barrel is yielding a little over 200 ft per second more than the 327

Is your fired brass bulged? (Oversized chambers)

Did you check the cylinder throats. (Bullet, especially a slightly large cast one makes a decent “pin gauge” to compare the throats with your other revolvers.)

Maybe double patch a cleaning jag to compare barrel dimensions with your others too.

I have a recent thread on this very same issue with the exact same model of revolver, I also bought a second 627, the 4” Pro Series after my frustration with the first 5”. The 4” was also slow. Best I can come up with as a reason for this is from Brian Pearce who states in multiple articles that the EDM rifling process currently used by S&W produces lower velocities. Best way I found around it in both revolvers was going with cast bullets, I use the 358156 w/gc from MBW and obtain magnum level velocities.

Loads?????

Max loads of 2400, H110, MP-300, Enforcer off the top of my head couldn’t crack 1200fps with 158 XTP. 140’s and 125’s all were tried with max loads of everything mentioned and while velocities increased as bullet weights dropped they too were off the mark from where they could/should be. For instance I could not achieve 1400 fps with the 125’s out of the 5” revolver, much less the 4”.
All weights however in both revolvers with their preferred powders are EXTREMELY accurate and I have chosen to just get on with shooting them and not chasing a few fps, real world results haven’t shown me it makes much difference. If I need the fps, I put aside the XTP’s and go cast.

Brass looks good

That is indicative of what I was posting about above.

That perhaps the bore is oversized. The reason the cast were working best was that they were obturating and sealing the bore.

Fotis, I suppose it depends on what your ultimate usage is for the gun. If it is paper punching, or hunting or what. How much does the velocity matter if you can find an accurate load. Perhaps just sell the gun to a paper puncher and replace it with one built in a traditional manner. An older one perhaps?

I wonder if the EDM barrels are actually oversize or if it has something to do with the finish which is left on the bore’s surface?

One could be fixed with lapping while the other could not and dimensions could be tweaked on future production while the EDM finish will probably remain as long as S&W use that process.

A bore slugging would be interesting.

A couple of thoughts….

A quick, easy thing to check (maybe you already have) is the accuracy of the scale you are checking your powder measure against. If you don’t have weights, use a good quality bullet (I usually use a 55 grain Sierra or Nosler.224.)

The other thing is the bore, as some have mentioned. EDM has always seemed to me a bizarre way to do a bore. I say this as someone with more than a little EDM experience. As a tool and die maker I’ve used the process a lot over the years. For one period of about 3 years I did almost nothing but very high precision die cavity sinking with EDM. There are so many variables that need to be controlled and monitored during the process that it leaves me scratching my head as to why S&W would use it to replace a pretty mature, straightforward and quick production process with EDM. It’s never made sense to me and if someone could explain it, I’d be grateful. All that’s just to say I wouldn’t be at all surprised to find anomalies in an EDM generated bore that could cause the problem under consideration.

Thank you fellas.

Tried a couple of more loads last weekend.

165 Matt bullet cast 14 gr Enforcer I got 1088 fps....should have been 1350 or so.
125 XTP 22.5 MP 300. I got 1250 fps....should have been around 1500.
165 Matt cast bullet with 17 gr MP300 I got 1110 fps should have been in the 1300's.

After thinking on it a while I decided to measure the cylinder gap again. It measured .006.
I pulled my SW 686 out and I could BARELY fit a .003 gap gauge through it.
The 327 has a removable/adjustable barrel like the Dan Wesson pistol kits so I can change the gap.


Can this be the issue?