Interesting chronograph data with 4756

[JohnK]

I found some old sheets listing some chronograph testing I did with .38 Special loads with 4756. Testing done about 1997.

I still had a couple of boxes of loads, completed in the late 60's, with a powder lot OF THAT TIME.

8.0 grs. 4756 (old powder lot, late 60's))
125 Rem. H.P.
Winchester cases.

Shot through a 2.5" Model 66 aver. velocity 1396 fps

8.0 grs. 4756 (new powder lot, 1990's)
125 Rem H.P.
Winchester cases

Shot through the same Smith 2.5" Model 66 aver. velocity 1034 fps

I pulled bullets from the respective loads, the powder charges were correct, bullets were identical,and the powder appeared identical.

I present this, with no desire to start controversy, but it does relate somewhat, to "The Load" controversy of the past.

My starting loads, (reduced 2.0 grs. from the top load listed) with 4756 (late 60's lot)), in a .357 Mag, were so hot, that I popped of a letter to Speer, questioning their data. This was the Speer # 8 manual. I have never done that before, or since.

I never heard from them.

I wish I had the chronograph way back then.

I am NOT recommending ANY load, just presenting some data.

 

[Erich]

John, that is very interesting, and I thank you for mentioning it. Nice to have the datum to file away - very kind of you to share.

 

[SuperMan]

As to SR4756...Dupont changed the burning rate significantly back in the early 1980s I believe. Originally it was a little slower than Blue Dot but the "new" 4756 was more like Unique.

It was one of those powders that made "Magnums" out of "Specials". I had lots of loads in .45 AR, .38 Special, .38 Super, .44 Special and .45 Colt that were equaling what CorBon gets for velocity today with zero pressure signs.

I found out almost the hard way that the burn rate had changed. Had been loading I believe 16 or 17 grains in a .41 Magnum with a 170 grain Sierra JHC bullet and was getting close to 1600 fps from a 4"...the shells would drop right out. Using a new 4# can of powder the brass had to pounded out. Upon inquiry I found out they had changed the burn rate and not even bothered to list it on the can...

Bob

 

[JohnK]

Superman, I have never heard that. Did you talk directly with Dupont ?

From the early data, I surmised, that the early lots were a lot "slower", than the later ones. Or the guy that tested for the the #8 data was having a bad hair day.

It is my strong impression, that pressure measuring devices, were not used by most of the loading companies, till much later than say, 1970.

I was younger, and dumb (er) then. This was a thing that looked to good to be true (.357 Mag. velocities, at .38 Special pressures), and it was.

Good Lord, I shot a bunch of the early lot ammo, in a Model 15. So much for them having weak cylinders.

It would sure kill those Texas pigs deader than a doornail !

 

[Paul5388]

I have 5 different lots of SR 4756 and 4 of them are DuPont varieties. The lot numbers are P75AP27B, P77MY18C, P82AP26A and P84--13A (I can't read all of the last lot). I know I bought the last two lots in the early 1980s, so it's reasonable to assume they were made in 1982 and 1984. That would make the other two made in 1975 and 1977. Due to additional numbers of 10156, I thought the 1975 lot was made in 1956 and reported it that way in this range session.

As you can see, the 1975 DuPont lot chronographed almost the same as the IMR Lot I have from 2004. The data is very close to what Speer #8 would indicate is the norm for 8.0 gr with a 158 gr LSWC (1140 fps).

 

[RH45]

I've found that 4756 varies quite a bit, from lot to lot.

 

[noylj]

Remember, when you find a lot your gun likes, stockpile that lot number of powder.
When the lot number changes, assume it is a new powder and work up your load again--particularly if the load is near-Max.