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? About Compressed Charge


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Is there any way of knowing how much compression before a major pressure spike?

Here's my reason for confusion. I've been using HS7 for many years for 38 supercomp and 9 supercomp and it's always showed slight pressure signs on the primer with around 10.5 to 10.7. Since they dropped HS7 I'm trying 4756. I loaded 8.0 and it's a slightly compressed charge, but it shows no pressure signs at all. The load feels very soft and I don't think it will make major. The temperature is upper 30's to low 40,s so I don't want to chrono until it warms up some because of temp variations. I'm guessing another .3 to .5 grains to make major and that'll be pressed pretty good. Here's the stats:

9x23 supercomp starline brass

3 chamber comp, non hybrid and no popple holes

Zero 124 JHP

OAL is 1.247


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Some powders don't mind compression, some do. HS6 doesn't seem to mind a fair amount of compression in the testing I ran a few years back to develop my major 9 loading.

4756 may react differently than H7. I had no issues with a pressure spike using HS6 and went so far into compressed loadville for my testing that the rounds were lengthening after bullet seating and crimping (I don't really crimp, just flatten the case mouth back out).

I would say that slow steps up in charge weight and careful inspection for pressure sign and you oughta' be safe in your quest.

I would also recommend AA7 for a slow powder that loves full case charges. I run up to 10.5-11.0 of it in .38 stupor and it rocks a comp at that level of charge weight under a 124grainer JHP.

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i ran up to 9.2 grains of 4756 in my super (4 port hybrid) it was a compressed load, a bullet would barely sit on top of the case.

THat was a smokin load though like 1550 fps with a 124 FMJ and it still shot pretty soft. but the gun was a 50 oz 4 port hybrid with an 8 port comp!


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Like George says, HS6 doesn't seem to mind a little compression so you might want to give it a try.

I never could get a 9x21 load I liked with 4756. It may have been my loading or my chrono, but it seemed hard to get a consistent load without some of the rounds showing pressure signs. Maybe HS6 is a little more forgiving.

And I didn't know they dropped HS7. Sure hope they don't do the same with HS6.


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The rule of thumb is to proceed cautiously (esp. w/ double base powders) once you get into compression - things can get non-linear at that point. Most of the slower powders will do just fine, though, with a little compression. I think you could probably squash N105 until the cows came home and never have a problem... :) 4756 should be fine at any load that makes current major, obviously depending on all the variables in the loading process - proceed carefully, and stop if you start to see signs of pressure (cratered, flattened primers indicate an extreme situation, BTW...)

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I've run up to 10gr of 4756 in a Super under 121's and 125's (had to run mid 9's to make 165 PF). It's not fun to load, so I stopped, but pressures still weren't bad. 4756 does have quite a bit of lot variation, so do be cautious.

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Thanks for the help everyone.

I'm pressing 8.5 right now with no pressure signs. I feels like it might be getting close, but

I won't know until I chrono. I tried HS6 and 7625 before and I didn't like them as much as

HS7. I ran BlueDot with heavier bullets back in the old days, but it doesn't look like I can

get enough in the case for these lighter bullets. I used AA7 before HS7, so I might have to

revisit that. I'll let you know where I end up in the event it might help save someone else

some time and trouble.

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