639 Accuracy Issues

[That One Guy]

I have a 639 that I love, but for whatever reason, it's just not accurate at all. I have a few other S&W autos, and they are all great shooters, but this one just plain sucks. I've tried piles of different ammo thru it with no luck whatsoever. The target below was sandbagged at 10 yds... that's roughly a 7" group. It usually averages around 4"-5" at 10yds no matter what ammo I use. I don't think it's me, cause I can shoot a ragged hole with any other Smith auto I have and the right ammo at 10 yds.

The muzzle crown looks fine to me. Not sure what else to check. I'd really like to get this gun sorted out for a multitude of reasons. Any ideas?

 

[Sevens]

I'm not really qualified to answer genuine gunsmithing type questions, but if it were me, I suppose I would look first at the bore an absolutely ensure that it's not full of lead from a previous owner. If the pistol has eaten jacketed ammo for it's entire life, this will not be an issue, but if someone else had fed it lead bullet ammo, especially lead bullet ammo that wasn't well-suited to that bore, it could be full of lead which will even more than disturb potential accuracy.

If that definitely isn't the case, I would inspect the relationship of the barrel to the bushing. Unlike a 3rd Gen pistol, the bushing on full size 1st and 2nd Gen 9mm S&W pistols is a removable part, comes out as part of a routine field strip.

The barrel bushing is an obviously key part to putting the pistol back in a "repeatable" lock-up. If there is excessive play then the barrel cannot necessarily get placed back in the "SAME" spot for the next shot.

I would genuinely doubt that wear has made the bushing loose, I would suspect more that it was never a very good fit from the start if it happens to be the case. I would try other S&W 1st/2nd Gen barrel bushings to see if you can close the tolerance and relationship to the barrel.

The best way to do something like this would be to field strip other 1st/2nd Gen S&W pistols that you may own and check for fit. Obviously, if you have no others, that's not an option. Tracking down and buying other bushings is certainly possible but we'd be talking about parts that haven't been made since the late 1980's. They aren't totally rare, but won't be find easily either.

Good luck, please report back and I'm eager to hear other suggestions as well.

 

[Sevens]

One quick addition...
I definitely have found, especially in 9mm, that some pistols -hate- the 147 grain ammo when it comes to accuracy. I'd otherwise guess that you are feeding it more typical 115/124gr ammo, but I figured I would throw that in as well. Any time we are talking about accuracy results and what we may do to improve, it's important that we make it clear what ammo we are talking about.

 

[That One Guy]

One quick addition...
I definitely have found, especially in 9mm, that some pistols -hate- the 147 grain ammo when it comes to accuracy. I'd otherwise guess that you are feeding it more typical 115/124gr ammo, but I figured I would throw that in as well. Any time we are talking about accuracy results and what we may do to improve, it's important that we make it clear what ammo we are talking about.

Only reason I didn't mention the ammo specifically is because I've tried so many different types/brands/weights that it didn't seem pertinent to me. Doesn't really seem to make a huge difference what I put thru it, group size generally hovers right around 4" at 10 yds. The only notable exception is the target I posted above, which was PMC 115gr fmj, IIRC. That's the worst group I've ever shot with it.

 

[That One Guy]

Just how tight should the barrel/bushing/slide relationship be? It seems to be loose in my opinion. Are there any specs around so I could check the dimensions?

 

[jsbethel]

How old is the recoil spring? It really can make a difference.

Range report: new to me 639

 

[That One Guy]

I replaced the recoil spring when I got the gun 2 years ago. It has less than 500 rounds thru it.

 

[stansdds]

Some pistols simply are not very accurate, while others are tack drivers. I had a 39-2 that would not group well at all, but my 439 is far better, but still not a tack driver.

Semi-auto pistol accuracy requires a good and consistent trigger, good sights, and consistent lockup of the barrel at the muzzle, at the slide stop pin and at the locking lugs. This creates three points of contact with the barrel. If the lockup is sloppy, then odds are the pistol is going to pattern rather than print groups.

The barrel bushing in the first and second generation pistols is removable and most seem to have tons of clearance between the bushing and the slide and the bushing and the barrel. Sadly, there are no aftermarket match grade bushings for these pistols. You might be able to buy a replacement bushing and it might be tighter, it might be looser, it might be the same.

Then there is the possibility that you might have a bad barrel. If the bore and/or rifling are rough or out of spec, you are likely to have accuracy problems. A sloppy chamber can also cause problems. Again, there are no aftermarket barrels for the S&W metal frame pistols.

If you happen to have or have access to other S&W first or second generation 9mm pistols, you might try comparing those barrels and bushings to those of this inaccurate 639.

 

[TAROMAN]

I had a 639 that shot exactly like yours. 8 inches at 10 yards at best.
Posted the issue here.
A nice member advised me to measure the headspace with the gun in battery (unloaded).
I could move the barrel about .025" fore and aft, IIRC.
Posted my measurement.
He mentioned my 24th Infantry avatar and said "your Christmas just came early" and shipped me a complete top end, gratis.

After the fix, it was all good. 100 rounds rapid fire.
Thanks, Nyteman44!

 

[BLACKHAWKNJ]

How about a replacement barrel ?