627 S&W accuracy problems

[1972RedNeck]

I have a 5" 627 Smith and Wesson that I have never shot well. Always suspected the gun as I am a decent shot with the rest of my hand guns. Following advice on here, I finally had a chance to take it out and shoot 3 shot groups from each chamber.

At 7 yards, 7 of the 8 chambers grouped well, but only 4 of 8 put the group at point of aim. 2 chambers were an inch high and one was an inch left.

The last one was a little high left but won't group at all. 2" + spread. Tried several times, could not get it to group. Lockup is the same as the rest of the chambers.

This was my first revolver and was a birthday gift so I won't get rid of it. Is there anyway to make it shoot better? Would Taylor throating help? Get a new cylinder fitted?

Suggestions?

[Recycled bullet]

Try different bullet weights and different powder charges and then see if you're getting the same results.

[1972RedNeck]

I have tried every different ammo I could buy and a half a dozen different bullets with several powders and who knows how many different weights. This revolver has never made a single decent group until I went chamber by chamber this morning.

[wild cat mccane]

S&W will fix it and send you an RMA based on accuracy.

Remember, they updated the entire M&P line because of accuracy issues. They will fix it.

[Don P]

Honestly I can't see the chambers being that far out of spec to cause the issues you are having. Are you getting any spit back while shooting. Generally that's a good indication that there are problems with the chamber alignment to the forcing cone

[Webleymkv]

Have you measured the chamber throats? If the chambers which don't group well have undersized chamber throats, then they're swaging the bullet down to a size that's undersized for the bore before it enters the barrel which would, in turn, negatively affect accuracy. An undersized chamber throat would be relatively easy for S&W or a qualified gunsmith to fix as all that would be necessary would be simply opening the chamber throat up to the appropriate size.

[74A95]

Originally Posted by 1972RedNeck

I have a 5" 627 Smith and Wesson that I have never shot well.

1972RedNeck, How are you doing the test? Your distance is 7 yards, but are you shooting offhand or from a bench rest?

Webleymkv, Undersize bullets don't necessarily shoot poorly, as shown in a recent article in Shooting Times where .355 bullets were as accurate as .357 bullets (all jacketed) in a .3571" barrel.

[1972RedNeck]

Off hand. Replicated the results several times.

[bamaranger]

l would not fully trust any accuracy test 'til I shot it off bags, fully supported at a bit more distance than 7 yds. Bags should (mostly) eliminate human factor. A bit more distance, will further illuminate if you've got wonky cylinders. Sure, you can shoot it at 7 yds if you wanna, but I'd think a bit further back would make variation easier to see.

[74A95]

Originally Posted by bamaranger

l would not fully trust any accuracy test 'til I shot it off bags, fully supported at a bit more distance than 7 yds. Bags should (mostly) eliminate human factor. A bit more distance, will further illuminate if you've got wonky cylinders. Sure, you can shoot it at 7 yds if you wanna, but I'd think a bit further back would make variation easier to see.

And more than 3 shots. 10 minimum.

[Webleymkv]

Originally posted by 74A95
Webleymkv, Undersize bullets don't necessarily shoot poorly, as shown in a recent article in Shooting Times where .355 bullets were as accurate as .357 bullets (all jacketed) in a .3571" barrel.

It depends on the gun and the bullets, but just because undersized bullets shot well in one gun doesn't mean they will in another. I haven't seen the article you reference, but I'd be interested to know exactly what kind of gun and what specific bullets they were using and what sort of accuracy they got. Some guns have tighter bores than others, for example I've seen older Colts in both .38 Special and even .38 Colt New Police (aka .38 S&W) which had bores as tight as .356". If you're shooting a revolver with a particularly tight bore, you might be able to get decent accuracy with .355" bullets even though they should, by textbook at least, be undersized for a .38 Special or .357 Magnum.

Also, the jacket thickness, lead hardness and manner in which the bullet is constructed can also play a role. If you take a typical .355" FMJ bullet designed for 9mm or .380, you'll have a jacket which is open at the rear and filled with a soft swaged lead core. If the jacket is thin enough and the core soft enough, you might be able to get it to obturate enough to still get acceptable accuracy from a .357" bore. .357 Magnum ammunition, on the other hand, is less common with FMJ bullets and much more widely available with JSP or JHP bullets which normally have jackets that completely enclose the base of the bullet and are, instead, open at the front. Also, because they're made to be shot at .357 Magnum velocities, many of the bullets commonly loaded in .357 Magnum ammunition have harder lead used in their cores to prevent over-expansion. With a bullet like that, it is unlikely to obturate much at handgun pressures and thus wouldn't likely give very good accuracy if swaged to an undersized diameter by an overly tight chamber throat.

[74A95]

The SAAMI specs for 38/357 jacketed bullets is 0.3580 - .0030. So, anything between .3550 and .3580 is within spec.

For lead bullets it's 0.3590 - .0030.

For 38 Special match (think wadcutter) the spec is 0.0360 - .0030.

https://saami.org/wp-content/uploads...12-13-2022.pdf


Some Colts are tighter than .356. I've seen them reported as small as .353.

[74A95]

Originally Posted by Webleymkv

Some guns have tighter bores than others, for example I've seen older Colts in both .38 Special and even .38 Colt New Police (aka .38 S&W) which had bores as tight as .356". If you're shooting a revolver with a particularly tight bore, you might be able to get decent accuracy with .355" bullets even though they should, by textbook at least, be undersized for a .38 Special or .357 Magnum.

EDIT: I'll assume you're talking about the groove diameter and not the bore diameter. Correct me if I'm wrong.

.356 is not tight when you consider that SAAMI specs for 38/357 barrels is a groove diameter of .355 + .004. That means any groove diameter between .355 and .359 is within SAAMi specs. This, by the way, is the exact same spec for 9mm barrels.

see the link to the SAAMI document in the previous post.