Nick_C_S said:
The 38Spl case is cavernous with approved loads as it is. I'm concerned about squib loads and inconsistent ignitions.
The danger is in becoming, as the British say, too clever by half. This can be a real fooler. Take a look at the data from Hodgdon below. It shows the same 148 grain HBWC bullet loaded with 231/HP38 (same powder; different brands), both seated near the case mouths.
.38 Special, 1.16" COL, 231 or HP38, 7.7" barrel, Win SP primer
Start: 3.5 grains, 14,200 CUP 885 fps
MAX: 4.0 grains, 15,900 CUP 956 fps
.357 Magnum, 1.290" COL, 231 or HP38, 10" barrel, Win SPM primer
Start: 3.0 grains, 14,300 CUP, 845 fps
MAX: 3.4 grains, 17,600 CUP, 908 fps
Well, larger case, less powder, more pressure, but less velocity despite a longer barrel. The magnum primer could be part of it, but IME, not that big a part. What I think is happening is that in the shorter case the wadcutter is crowding the powder space so much the primer is unseating the bullet before the powder burn gets fully up to speed, so the actual case volume the pressure peaks in is higher for the .38 Special case than for the .357 Mag case. The way to tell for sure is to chronograph the loads and see which has the lower velocity standard deviation as a percent of muzzle velocity. Bullets that are jumping due to primer pressure (a common issue with the .22 Hornet, for example) tend to be more erratic in velocity because ignition is more erratic. Additionally, if a bullet jumps through a space wider than a normal freebore, as your .38 Colts will do in the wide part of the chamber, the amount of gas bypass gets larger and makes this worse, as that stalls out the build in pressure until the bullet plugs the escape route.
So, while you may think you are making for safer, less squib prone ignition by going to the shorter, tighter powder space in the loaded cartridge, it can work out the opposite is happening, depending on how high the primer pressure is. If you don't have a chronograph, you want to beg, borrow, or steal one to check the velocity regularity of your loads with the .38 Colt as compared to .357 Magnum cases loaded to the same velocity with an adjusted amount of the same powder. Same with the .38 Special cases. It's the only thing I know that will give you an indication of ignition consistency without pressure measuring gear.
Nick_C_S said:
And yes, when reloading manuals show "DNR" in their tables, that's a clue to not reduce the loads.
But you normally only see that with rifle powders and slow pistol powders, like H110/296.
Rifle powders generally don't like to be loaded much below 60% case fill, as pressure can get higher than better case fill gives. This is thought to be due to exposure of a larger ignition surface area to the primer flash, causing the powder to ignite more rapidly than normal and therefore make too much gas before expansion gets very far along. Use of case fillers like Dacron fiber tufts stops it, even though they don't remove much of the actual air volume. They just hold the powder over the flash hole more normally.
Slow pistol powders can be a squib risk in reduced loads in revolvers, especially. That's because pressure is still building when the base of the bullet clears the barrel/cylinder gap, allowing gas to start escaping. If enough powder isn't burning by then, that can drop pressure enough to cause the load to squib out.
But a fast pistol powder isn't normally at risk of the above. It normally burns up before the bullet base clears the barrel/cylinder gap, so it doesn't have to fight to keep burning during that gas bleed off. That's one reason I recommended a really fast powder for the .38 Colt loads. It's to try to get it peaking up before the bullet clears the case mouth or not long after. Clays, VV N310, and Norma R1 all would be good choices.
Anyway, have at it the way you propose. If you get some good chronograph data, please share it. I would be interested to hear how the short and long cases turned out to compare for velocity standard deviation in this instance. Maybe your light bullet is short enough not to crowd the .38 Colt much and the primer unseating won't turn out to be an issue. But I would like to know. My only point in this post is that the idea it is better or safer for powder ignition isn't a gimmie.
