Crown question on new 627 PC

[FivePews]

Hello experts! I have a question for y'all.

I picked up a NIB 627 PC with the 2.6 inch barrel this week (I'm a big snubbie fan). It's literally a blast to shoot with full-house loads.

I've purchased 11 NIB Smiths since the beginning of 2023 and am very familiar with the current state of QC and the return process.

When I shoot .38 HBWC benched at 20 yards, the pistol hits dead-centered when the rear sight is centered. But, when I shoot Magtech 158s that are marked around 1400 fps on the box, the pistol shoots 5-inches left at 20 yards and 5-inches right with another brand of "full-house" 158s. I've never seen this happen before. Most of my experience is with J frames though. On those J frames, only elevation changes when switching between specials and mags. Sure, the mags might go an inch left or right with different loads....but not 5 inches.

My questions are these: Is the above behavior typical for a short-barreled .357 mag? Would you guys think that maybe something is off with the forcing cone or crown? To me, it looks like the barrel isn't crowned at all. It's sharp and I can see the ends of the lands/grooves cuts.

Anyway, I'd love to hear some opinions from those are familiar with hot loads in a short barrel. It's a fun pistol and pre-purchase inspection looked good (though I missed the crown).

Thanks!

 

[Protocall_Design]

The first thing I do when I get a new or used S&W revo is to recut the forcing cone and crown. So many of them are wrong from the factory. It's one of those things that has become a standard procedure. Just a minor cleanup can make a big difference. Five inches is a lot. Normally, you should only have minor left or right, most of the adjustment should be up or down, due to the amount of recoil.

 

[FivePews]

The first thing I do when I get a new or used S&W revo is to recut the forcing cone and crown. So many of them are wrong from the factory. It's one of those things that has become a standard procedure. Just a minor cleanup can make a big difference. Five inches is a lot. Normally, you should only have minor left or right, most of the adjustment should be up or down, due to the amount of recoil.

Thanks sir. I'm the type that would rather buy the proper tools and learn how to use them instead of waiting a month or two for Smith to MAYBE fix it. Knowing that an issue has been properly corrected goes a long way for me, regardless of my costs or time.

Do you have any suggestions on where I should look first to learn how to cut crowns and forcing cones myself? Browsing Brownells today resulted in a lot of options for crowning tools. Ultimately, I'd like to be able to deal with crown issues, forcing cone issues, and maybe chamfering cylinders for wadcutters....all that sort of stuff.

As an aside, I only plan to own revolvers in .22, .32 H&R, .38/.357, and .44/.44 Mag. Perhaps I can buy a chamfering kit that only covers pistol calibers? If so, can anyone recommend a good "master" kit?

 

[Protocall_Design]

I use the Brownell's 45 degree chamfering tool #8K51P79 with T handle and have barrel and cylinder pilots for all the calibers I work on. I use the steel pilots because the brass ones wear out too fast. The steel ones are smooth and will not hurt the barrel or cylinder in any way. That is all you need in that department.

There are 2 Brownell's kits for cutting forcing cones and back of barrel squaring cutters. One set is for .22 - .32 #8K201I24 and one set is for .38/9mm - .45, #8K230L61.

 

[FivePews]

It looks like those Brownell's numbers are no longer valid. They don't come up in a search, but I'll probably be able to cross-reference them. Thank you.

I've been doing a lot of Googling about this today, and as expected...I was a little confused about my terminology. After going down to inspect two L-frame PC guns at my LGS, they eyeball to have an 11º crown. My 627 PC eyeballs to have a 90º or "flat" crown. I'm nearly certain of this. I can't measure it because the end of the sleeved barrel is recessed into the sleeve. Heck, as of now, I don't have the tools to measure it anyway.

I was talking about putting a chamfer at the rifling to clean up the milling at the end of the lands/grooves. Perhaps at 45º as Protocall design suggested? I'm not even sure if this is something that is done, or is a good idea, or if it is of any benefit.

Thanks for bearing with me here. Obviously, I'm just getting started with this and have a lot of learning to do.

 

[Alk8944]

POI shifting left or right some, in addition to vertical change is not un-common when changing bullet weights, but 5" is quite surprising!

 

[FivePews]

POI shifting left or right some, in addition to vertical change is not un-common when changing bullet weights, but 5" is quite surprising!

I was surprised too, but I'm not an expert in any way, shape, or form.

The bullet weights were similar (148 WC and 158 plated HP), but the charge levels were wildly different.

Each shot nice and tight groups...just in very different places. Five inches is enough to miss what a fella is aiming at!

It may be the case that this is normal, and I'll just have to sight the gun in whenever I change loads. I don't have much experience with .375 mags.

 

[Protocall_Design]

If you're getting tight groups, and no leading, you're good to go. Just re sight when changing loads. I like to find a load I like and stick with it.

 

[stansdds]

If accuracy remains good and it is only the point of impact changing when changing loads, that is a function of bullet velocity and recoil control. There is a massive difference in both velocity and recoil between 148 grain 38 Special target wadcutter ammo and full power 158 grain 357 Magnum ammo.

 

[BLUEDOT37]

I picked up a NIB 627 PC with the 2.6 inch barrel this week (I'm a big snubbie fan).
To me, it looks like the barrel isn't crowned at all. It's sharp and I can see the ends of the lands/grooves cuts.
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My 627 PC eyeballs to have a 90º or "flat" crown. I'm nearly certain of this. I can't measure it because the end of the sleeved barrel is recessed into the sleeve.

The 627PCs don't have a sleeved or two-piece barrel, they're one-piece.

Did you mean you can't see the lands/grooves? Ideally you should be able too see them.

I was unhappy with the crown of my 5" 627PC right out of the box so I chamfered the muzzle as well as the forcing cone using the Brownell's kit I previously bought to remedy similar maladies.

Yes it shouldn't need to be done on a new revolver, & the kits aren't cheap, but what's piece of mind worth?

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PC627-5 muzzle before chamfering, 5" bbl
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PC627-5 muzzle after chamfering, 5" bbl
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[FivePews]

The 627PCs don't have a sleeved or two-piece barrel, they're one-piece.

Did you mean you can't see the lands/grooves? Ideally you should be able too see them.

I was unhappy with the crown of my 5" 627PC right out of the box so I chamfered the muzzle as well as the forcing cone using the Brownell's kit I previously bought to remedy similar maladies.

Yes it shouldn't need to be done on a new revolver, & the kits aren't cheap, but what's piece of mind worth?

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PC627-5 muzzle before chamfering, 5" bbl
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PC627-5 muzzle after chamfering, 5" bbl
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That's great info and great pictures! I had no idea what these barrels are one-piece.

Your crown looks good. Did you notice any shift in POI or change in grouping after doing the work?

I'll try to get a closeup picture of my crown today and find a hosting site to put it up here. Maybe it's just fine?

Did you happen to notice if your pistol had an 11º or 90º crown before you added the 45º cut? As I mentioned earlier, my pistol looks to be a flat-crown, but the two L-frame PC guns at the store look like they both have 11º crowns.

 

[BLUEDOT37]

Thanks. The muzzle was flat from the factory, as best as I can tell, with almost a raised ridge at the bore line instead of being smooth across the face.

I made the changes before I ever fired it. I knew doing so would only make it shoot better, not worse, so I wasn't worried.

By the way, these one-piece 5" PC barrels are broach cut verses the electrochemically etched (EDM/ECM) rifling found on the two-piece barrels.

You can see its sharper lands/grooves even in my after picture above.

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[FivePews]

An update here, it turns out that my new 627 suffers from light-strikes. I've ordered an extended firing pin from TK and will report back when it's installed to see if things improve.

OEM pin =
Length = .4885, diameter = .155

I haven't got around to ordering tools to deal with the forcing cone or crown yet...but I will.

 

[FivePews]

If you're getting tight groups, and no leading, you're good to go. Just re sight when changing loads. I like to find a load I like and stick with it.

I haven't checked for leading yet, but I'm waiting for some moon clips, a holster, and assorted goodies for the 627. Once they are here, I'll put some rounds through it and report back.

 

[6string]

Hmmm…..
So, everyone is assuming the gun is at fault?

I’m surprised that nobody has asked, “What size groups are you shooting?”
At 20 yards with any good brand of 148 gr. HBWCs, groups should be consistently 1” or less for 5 shots. Most, if not all, of the bullet holes should be touching. There shouldn’t be any vertical or horizontal stringing.
Anything else suggests there is a human error/technique issue.
Even a holster-worn, police surplus Model 10 can easily satisfy the 1” @ 20 yd accuracy criteria.

As the power, and hence recoil, increases there will be a tendency to accentuate any errors in technique. At the same time, the recoil and blast totally conceals any errors.

Here’s a suggestion: play the “ball and dummy” game. Get someone to load your cylinder with an undisclosed mix of empties and loaded cartridges. (You can try it yourself if you load the cylinder blind, spin it, then close it.)
When you shoot, make sure you’re really watching that front sight. When it goes “click” instead of “bang”, any movement of the front sight will indicate a technique issue.

Another suggestion after exploring the above, would be to repeat the bench shooting process using an optical sight.
Again, the idea is to reduce or eliminate the human factor first.

Here’s a quote from Doug Wesson’s book, “Burning Powder”, pub. 1938:
“It might be well to say at this point that the same barrels, cylinders, chambering, rifling and reaming that are used in our target arms are found in our service arms, and the accuracy of the two types of arms is identical.”

I’ve attached a few images showing 6-shot, 20 yd group sizes using the then-new S&W .357 Magnum.

 

[chief38]

Overt the years I've found that shorter barreled guns change more radically with hotter ammo than their longer barreled cousins. In your case you went from the mildest 38 special WC loading which was designed only for accuracy and target shooting to the Magtech magnums at 1,400 fps. That is almost the most drastic difference you could shoot out of your short barreled M627.

Secondly, you are shooting at 20 yards (60 ft) which for the shorter barrel and magnum ammo is a good distance. As said above, groupings are more telling than POI at 60 ft. I've also never been very impressed with Magtech ammo. Nothing particularly wrong with it but I have never had great accuracy with it as compared to other brands or my hand loads.

Third, you also stated you are shooting from a bench position. I personally no longer sight a handgun in from the bench - for at least 35+ years now. For some reason I find when benching a handgun, I rarely get POA=POI or the best groupings. Yes, I've always thought that was counter intuitive and does bewilder me, but I just shoot handguns much better from a standing position - can't really get a handle on that one but suggest trying that.

Last but not least, the longer I shoot the more I see just how ammunition makes a big difference in different handguns. I am not negating Protocall Design's advise about cleaning up the forcing cone but if you are not experiencing any other issues or leading I wouldn't expect a major POA/POI difference. Would not hurt to try it through as many S&W forcing cones are indeed a bit crude as Protocall Design stated and just one more thing to eliminate.

If this gun was mine I'd shoot it at 50 feet with Federal, CCI, Remington or Winchester ammo from the standing two handed position and see what happens. Cleaning up the forcing cone could theoretically help too, but IMHO ammo sometimes makes a pretty fair difference! I have a CZ "tack driver" .22 rifle that when shot with Eley top grade target ammo, prints all over the paper! Switch to CCI Mini-mags out of the same rifle and it will put 5 rounds in the same hole at 75 or 100 feet. Go figure - but I have been told from the manufacturer the barrel is kept to tighter tolerances and much prefers higher velocity ammunition.

Please let us know how you proceed and the results.

 

[BLUEDOT37]

OEM pin =
Length = .4885, diameter = .155

Generally S&W firing pins that are shorter than .492" are suspect, though I have shorter FPs in a few revolvers that have run fine for years. Other factors come into play on this subject though.

S&W replacement FPs ideally run .495"-.498".

APEX extended firing pins historically run right at .500" & C&S run .510".

I've never bought any FPs from TK so I have no data on them. Let us know what theirs measure.

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[FivePews]

Generally S&W firing pins that are shorter than .492" are suspect, though I have shorter FPs in a few revolvers that have run fine for years. Other factors come into play on this subject though.

S&W replacement FPs ideally run .495"-.498".

APEX extended firing pins historically run right at .500" & C&S run .510".

I've never bought any FPs from TK so I have no data on them. Let us know what theirs measure.

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Thanks for the info. I installed the TK extended pin/reduced power firing pin spring a couple of minutes ago. It measured .505, so I guess I'll be in the ballpark.

What's the only downside of an extended pin? Puncturing primers?

Funny how no matter how many times a fella emails or calls TK with a question, they never get back to him. At least they are quick to ship.

I'll give the 627 a run later this week to see if it becomes reliable and report back.

 

[FivePews]

I appreciate all the replies from folks. You've given me a lot to think about, and I'm leaning towards agreeing with all of you.

Last week I picked up another N-frame .357 (327 R8), and when benched it, the same darn thing is happening...so it must be me. I'da betcha a dollar two weeks ago that I'm not anticipating with Magnums and now I know that I'd probably lose that dollar.

First, I'm not really on a bench. I'm using a camping table with a low-budget collapsing rest while sitting on my knees in the dirt. Not really professional. Or comfortable. It works with my Centennial J-frames though and I assumed it would work the same with larger pistols. Maybe it doesn't.

I also noticed that when I started shooting drills offhand, I was getting good hits. Somehow or other, I'm pooching the bench process.

I put a Holosun 508T on the R8 and will give that a try from the bench this week. I'll also try running my standard 50-round timed drills with the 627 to see what happens. I'm really, really hesitant to modify the 627 any more than adding the extended firing pin...for now.

 

[BLUEDOT37]

What's the only downside of an extended pin? Puncturing primers?

Once, maybe twice (?), I had to remove the C&S extended firing pin I installed because the nose of the FP would hangup in the primer, after firing, & you couldn't cock the hammer for the next shot as the cylinder wouldn't rotate.

After a couple attempts at cocking the FP would release & operate normally. The primers weren't getting pierced but the FP impact was deep.

Going to a shorter FP eliminated the problem in that revolver. In others the C&S worked fine so it just depends.

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