Old vs New rifling

Scottrh2 · #1 09-11-2020, 12:34 PM

I have a beautiful 5” M&P “s” prefix .38 and wondered if the pre 10 rifling was a little more shallow for only lead projectiles than more current barrels. Perhaps it is the older style muzzle being it does not have the pronounced crown cut like modern S&Ws have.

Scottrh2 · #2 09-12-2020, 08:35 PM

Gosh..... nothing?

Velle · #3 09-12-2020, 08:43 PM

My only experience with S&W rifling comes from an M&P made around 1948 and a new 637 Airweight. The M&P doesn't lead at all. The 637 leads like I dunno what. Long strands of lead get caught in the rifling. I dunno if it's because the old M&P has smoothed out over the years or the 637 hasn't been fired enough to smooth out but I never saw anything else lead up like the 637.

k22fan · #4 09-12-2020, 09:00 PM

I also have an S prefix M&P. Its grooves look just as deep as my most recently made Model 10s and 15s that are still old enough to have broach cut rifling. However, I have not measured any of their groove diameters. None have had accuracy difficulty to diagnose and if they'd had the first place to measure would have been cylinder throat diameter, not groove diameter. Also measuring a lead slug driven through a barrel that has an odd number of grooves is not easy.

Barrels designed for lead would have deeper grooves than barrels designed for jacketed bullets only. Besides, lead bullet .38 Special cartridges will be a big part of .38 Special cartridge production forever so I doubt S&W would change their rifling just to make it more suitable only for jacketed bullets.

The significant change in rifling occurred during the 1990s when S&W's standard method changed from broach cutting to eroding away metal with electricity. The effect on lead bullet accuracy and leading has been debated in the 1980 and newer revolver sub-forum.

Traditionally S&W revolver barrels were forged then the bore drilled, reamed and rifled. One piece barrels for K frames and larger frames are still made that way. J frame snub nose barrels have been metal injection molded (MIM) parts for a long time. If that 637 is fairly new it has a MIM barrel.

Velle · #5 09-13-2020, 04:14 AM

Quote:

Originally Posted by k22fan

If that 637 is fairly new it has a MIM barrel.

Bought it new last month. Nothing wrong with MIM these days. Practically everybody uses it to one degree or another. FWIW I have found no indication it is MIM but I'm not worried about it if it is. I've seen where it's supposed to be a two piece barrel. If it is that's no biggie either. I've also seen where the barrel is supposed to be a liner shrouded in aluminum. It wouldn't matter if it was but it isn't.

k22fan · #6 09-13-2020, 12:58 PM

I do not look at modern J frame snub noses. I do not think that I've ever handled a J frame that had a MIM barrel. My guess is they are rifled with electricity the same other standard production barrels. Two piece barrels are not the norm for all steel J frame snub noses. Two piece barrels are used on more expensive aluminum frame J frame snub noses when the lighter weight of an aluminum shroud is desirable. That's how S&W makes .357s recoil hard enough to kill the shooter before the bullet hits the bad guy. Two piece barrels were also used on all stainless steel 5" J frame .357s and no doubt other J frames that I've forgotten.

Two piece barrels are easy to spot by looking at the muzzle. The actual barrel is a round tube that is either threaded at the muzzle for a nut or more commonly has a flange. I've only seen the nut on huge X frames. Since they are round and tightened with a spanner nut is probably the wrong name. When the barrel is screwed in the nut or flange compresses the shroud against the frame. The shroud is prevented from rotating by a key that fits in a slot in the frame. Earlier shrouds were recessed at the muzzle so the flange did not show in a side view. Barrels that have a flange are screwed in with a tool that has the reverse image of the rifling.

The two piece barrel assembly puts the barrel under tension like a Dan Wesson. That has the potential to make them S&W's most accurate revolvers.

We have run this thread off the rails into subjects usually discussed in the modern revolver sub-forum. Getting back on topic, I've never seen any indication that S&W changed the diameters of .38 special rifling broaches.