How do reloads in .38 Special+P (as listed in various reloading manuels) compare with say Remington or Winchester? (in terms of power and velocity?

I made the same question. I could not find any re loading recipe to launch bullets at 1.350 feet per second with 9 x 23 Winchester, a cartridge said designed for that and higher speeds. They just kist loads for 1.200 and a little more fps.-

I've never compared directly with factory ammo,(chronograph). I will say, as we all know, that '+P' loads are not all that more than regular 38 spcl loads. The data is just a tad more powder. How many +p loads are shot in guns not designed for +p ammo? I'd say the likelihood is high. Then it's a big jump to 357 mag max loads.

Most of the time I'm shooting +Ps in a 357, so I don't worry about it. If I go above 38 +P loadings, I go with a 357 mag case to be safe. You never really know where the ammo may end up down the calender.

sourdough44 got it right! If there's any chance they'll be warmer than +P, load'em in 357 brass.

I loaded Skeeter's old stand-by of 13.5 gr. 2400 with the Lyman 358156 seated out to the rear grease groove in 38 brass (for use in 357 guns only) for years. My Model 60-9 (marked .357) prefers Taffin's 11 gr. load.

I always tried to keep these loads hidden out of harm's way in the loading building.

I must have dropped one or left it in my pocket, or ???, because just the other day I caught my lovely wife with one of'em loaded in her Airweight. The little gun is +P-rated but I doubt if it would withstand the heavier charge.

I'll never again assemble this favored load in 38 cases. Aint worth the risk.

As a seasoned reloader with a chronograph, I have no trouble loading to any safe power I want, including duplicating factory loads.
However, you can't just go by published data from factory loads to determine what you are duplicating.
I shoot the factory loadin MY gun to get a baseline, then select an appropriate powder, build the load, and chrono in MY gun to get the power factor right.

People who try to set reloading standards without a chrono are just reading and speculating, and frustrating themselves.
Comparing different loads baed on different tests in different guns by different people are misleading at best, and dangerous at worst.

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Science plus Art

I've used factory +P loads in my K-frames (158 grain LSWCHP) from Winchester, Remington and Buffalo Bore. The Buffalo Bore seems more powerful.

That said, my handloads using current +P recipes seem more stout than either the Winchester or Remington loads.

YMMV

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I believe in the wadcutter.

Just out of curiosity I spent the big $$, bought some of the BB "FBI" 158 LHP +P loads

Shot out of a 642 Airweight +P rated, they are brutal and I am not handgun recoil sensitive. I fired 10 and the others went in the 357 M 640.

Yes, they can be duplicated up in the notable threads there is lots of info, but as mentioned a Chronograph is a must.

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Still Running Against the Wind

I use the standard pressure Buffalo Bore in my Airweight. To be specific, the first five are the 150 grain wadcutters, and the five in the speed-loader are the 158 grain LSWCHP. (I'd use the wadcutters all the way around, but the LSWCHP's are easier to load in the gun.)

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I believe in the wadcutter.

First, you need to know what pressure level the factory ammunition is loaded to. In other words, is it really +P, or just marked that way! You need to know what +P standard is being referred to. I know that seems inane, but you will find figures from 17,500 PSI to 20,000 PSI published in various loading manuals and reference sources. Likewise you will find standard pressure shown anywhere from 15,000 PSI to 17,000 PSI.

Assuming that whatever load you want to compare is really a +P load, then you need to know what velocity the ammunition really delivers in a specific revolver/pistol. That takes a chronograph. Then you need to load and shoot the published load recipe you are curious about. This has to be in the same gun, same conditions. Preferably same day and fired consecutively with the factory load.

Can factory +P loads be duplicated? Yes. For .38 Special Unique, 4756, WSF, Universal, Herco, HS-6, and several others will safely equal +P performance with lead bullets, but not necessarily directly using data from the published manuals.

So far as you original question is concerned, who knows! Some published reloading data may very well surpass "factory" loads. This is just too open ended a question to answer any more completely than, again, who knows!!

You want to know, buy a chronograph.

FWIW, Federal and Winchester 158 LSWCHP +P have both chronographed at 821 FPS from 2 Model 12s I own, Federal from one, Winchester from the other. The same load ran 945/936 FPS from my 6" 10-4 on the same day. These were relatively small samples in all cases, only 6 rounds for each string. Larger samples will give a more statistically significant result, but these results should be in very close proximity to results with larger samples