9mm- oversize bullets and pressure?

I've been working on a 9mm load using a powder I don't normally use in this caliber since what I usually use has been hard to get.

I've been using 700X in 45 Colt, 45 ACP, and .38 Special. It seems less than ideal for 9mm but I figured a light load should be fine. I worked up a nice light load in my old HP clone (.358" barrel, slugged and measured with a micrometer):
125gr cast TC bullet, sized to .359", seated to 1.100" OAL, 3.5gr 700X. Velocity around 1000fps. Nice moderate load.

I then thought I'd try them in my other old HP. It has a replacement barrel that slugs at .355" (original barrel was dark), but the rounds dropped right into the chamber without resistance so I figured they should be fine.

Wrong, apparently. They shot and functioned fine, but the empty brass shows signs of what appear to be excessive pressure; the primers are flattened and even the headstamps looks flattened. I deprimed one and tried a new primer- it seated with minimal pressure so the pocket was definitely stretched a little.

I'm very particular with setting up my scale and powder measure, and check powder levels before seating bullets, so I'm confident that there are no problems there.

So, the bullet and round fit the chamber fine, but the bullet was oversize for the bore by about .004". Could this turn a light load into a dangerous one, with a fast powder like 700X, or is it likely to be something else?

I had another load using HS6, loaded a little hotter but still moderate, and using the same .359" bullets, that seems to work fine on both guns. Pressure this high on the 700X loads is a little scary and I'm a bit embarrassed about it, but any ideas?

You just ran into one of the triggers for working up a load in each gun when using a new powder.
HS6 is considerably slower burning than 700x. You get a lot more leeway with slower powders before you get pressure spikes.
With fast powders it sometimes takes very little to push them over the edge.
By the way, the Hodgdon site lists 3.4 grains as max for a 125 grain cast boolit. You are already over that.
You can't go by velocity to judge pressure in a load. While 1000fps mat be moderate with a slower powder, it is max with 700x. HS6 will give you another 120 fps safely because of the way it burns.

Thanks Tazman. Interesting that Hodgdon has 3.4 as max. Much less won't even function, and the several older manuals I looked in had max from 4.6 to 5.0 gr. Apparently Hodgdon must have seen that potential for spikes in this powder or something. Learned something there.

When working up this load I found numerous posts online from guys using this combination in higher charges with great success so I thought my moderate load should be fine. Clearly not.

I think I've decided it's a moot point. I'll leave the 700x for the revolvers, be patient and find something a little better for the 9mm and .40. I want a moderate load that's good in either gun. I'm rarely a fan of specifically tailored loads.

Sounds like you need a slower powder.
Since your HS6 load works in both guns, I would look at the burn rate chart and try to find something near that burn rate. There are 20 or more powders from Winchester 231 up to AA7 on the chart. Surely something will turn up.

I think you're right. I've used Unique as well as HS6 to good effect so I'll be patient and buy something in that range. I thought I'd never run out of HS6; I got most of an 8 lb keg from the estate of a shotgunner (and the 700x) a few years ago, but then let a friend use a bunch of it for loading a large quantity of .40S&W.

I just recently acquired a pound of HS6. It does indeed work well in the 40S&W and 9mm. So does WSF, CFE Pistol, and Herco, all of which fit right into your needed powder range. I also got a pound of Longshot last week but haven't had time to try it yet.
From the data sheets, it should be the magic powder for both those cartridges as well.

I'll keep an eye out for those. Funny thing, I was just going through my powder cupboard and found a mostly full can of AA#5 that I forgot I had. I've never used it for 9mm but it looks like the burn rate would make it just about right also. I think I'll give that a try and work up a load, with both guns at the same time, this time.

I'm also going to try the original barrel again. The gun is an old Inglis and the bore was less than pretty. I happened across a cheap replacement barrel at a gun show so I replaced it. That was the better part of a couple decades ago. I don't recall if there was any accuracy issues with the original barrel, just that the new one was nice and shiny so I put it in. I know a lot more now than I did then so I think the original barrel is worth revisiting. Bore diameter on it measures the same as the other gun.

That powder(AA5) should do the job nicely. The data I have shows 4.7 grains as starting load and 5.4 grains as max when used with a 125 grain boolit.
This data was from the Accurate Arms data site last January which still seems to be their current published data.

Thanks again Tazman; I appreciate the help. I realized I have about 1/3 can of very old Green Dot I can use up as well. Between the #5 and the GD, they should tide me over until I can find more. One benefit of this powder shortage is cleaning out the cans of old powder that have been languishing unused in the back of the cabinet for years!

Fatelk, I find HS-6 pretty easy up here in Lewis Co WA at the Chehalis gun show and the LGS in the Lewis county mall. I have almost 4 lbs of HS-6 and almost 5 pounds of Unique. Mark

How's it going Mark? We'll be driving by up your way in a month or so.

I sure wish I could find some powder for less than an arm and a leg around here. I just went to the show in Rickreall this morning and I might have seen half a dozen pounds of powder in the whole place, overpriced and not anything I use. I did find a good price on some primers, and bought my very first ever flintlock rifle, an old .50 cal Spanish "Jukar". It looks cheap and I don't know anything at all about them (or flintlocks in general) but figured I couldn't go too far wrong for $100.

I keep thinking pistol powder and .22 ammo will come back sooner or later. I don't keep close tabs on all that but take a glance at Bimart whenever I'm there. I was surprised to see absolutely zero pistol powder and minimum $50/brick .22 at the show, almost like it's gotten worse again all of a sudden. Crazy. I'm patient and really don't shoot a lot, so what I have should last me quite a while. If I get desperate it's really not the end of the world to pay $35/lb for a couple pounds of Unique if I have to, just work a couple extra hours of overtime to pay for it. :)

Powders are coming back somewhat in this area. I have been able to find many usable powders for decent prices even though they mat not be precisely what I wanted. Some of the mainstream pistol powders are coming back now as well.
Next few months will be interesting.
As far as 22lr ammo, if I am going to have to pay high prices for ammo, I am going to buy the really good stuff. I just bough a brick of match 22 ammo and it shoots extremely well in my revolver.

I use 700X for practice powder because its cheap and usually available, also impossible to double charge. My 9's do well with 3.2 grains under the Lee 356-120-TC. 3.4 grains flattens primers and causes the groups to get larger so I stick with 3.2. Its just practice ammo so no need for max velocity.

Accurate # 5 works well in the 9mm. I tried some last fall as I was running short of BlueDot. Tested loads in several 9mm pistols. XDs 9mm 5.25, S&W M&P, Tanfoglio TZ75 Series 88, and a PF9. Boolit was the H&G #275 09-125-SWCBB sized .357.

(fatelk) (How's it going Mark? We'll be driving by up your way in a month or so.) If you do and need some HS-6 I can sell you a lb and a LB of unique if you haven't found any. Have to go to Eugene/Spfld for GGD 1st BD the 29th of this month. Having another CT tomorrow. Got my shop/casting/reloading building built. Still have a few interior things to do.

I appreciate it Mark but I wouldn't want to dig into your supply. I'll be fine and should be able to find some before I'm desperate. Thanks for the offer though. I might try to stop and say hi if we have time, if it's OK.

I was just out to the range today and found a good load using Green Dot. I have enough of that for about 500 rounds, then a full pound of #5. If I get desperate, I even have my emergency can of Unique. I had forgotten about this can- it's an old square pop-top tin still sealed with the tear-off metal ring around the lid. It's a 13 oz can not a full pound but I expect it's still good. The can itself is probably "collectible" to someone out there. I just don't shoot a lot so a couple thousand rounds will last me a very long time.

Funny thing, I put the old original barrel back in the old Inglis and it shoots just as good or better than the replacement I stuck in it years ago. I guess I've learned to shoot a little better too.

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I use 700X for practice powder because its cheap and usually available, also impossible to double charge. My 9's do well with 3.2 grains under the Lee 356-120-TC. 3.4 grains flattens primers and causes the groups to get larger so I stick with 3.2. Its just practice ammo so no need for max velocity.

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Interesting, thanks for the info. That's about my experience with it. 3.0 gr wouldn't cycle, 3.2 would but barely, 3.5 cycled reliably but in the one gun flattened the case head. It's funny because one old manual I have shows 5.0gr with a 125gr bullet. That's scary! I think I could make 3.2 gr work OK but I only have a couple pounds of it so I'll just save it for the revolver stuff. 3.5gr and the same 125gr .359 TC bullet in a .38 Special is a nice mild load.