7.62x39 .312 bullet in .310 neck?

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Mar 8, 2013
Columbia, SC
So I have finally gotten tired of loading .45acp and 9mm and have started to load some rounds for my Mini 30. The 3 bullets that I have chosen are Hornady 123 g. Z Max, Hornady 123 g. Soft Point, and Xtreme 123 g. plated flat point.

I know the Hornady bullets shoot great in my gun, but they are .310 diameter. The Xtreme plated are .312. Not sure what they are going to do for accuracy, but since they are just blasting rounds on the cheap it doesn't matter.

My question is about a slight bulge in the case after seating. I used my .310 neck sizer ball on all of the brass and the Xtreme bullets set fine, but have a slight bulge. Will this be ok? Obviously they have plenty of neck tension.:)


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It is fine, as long as they chamber freely in your rifle.

On the other hand, most 7.62x39 die sets come with two different size expanders.

And it's pretty easy to change to the right one for the bullets you are using.

I know, my set came with it. However in the heat of the moment processing a bunch of brass, I did not set a certain amount aside and size them correctly. In the future I will. To be honest I didn't even realize the diameter change until seating.
i know you probably already know this, but the plated bullets are supposed to be sent out slower than the jacketed. I've had great accuracy with just about everything. The plated bullets are treated a little more like cast bullets.

I've heard under 1500fps up to 1800fps for some is more ideal.
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The other thing you might want to check is to pull a couple of them and insure the tight case neck isn't scraping the plating off.

I have loaded some of those X-Treme 123 gr .312 bullets in 300 BLK to try. I was concerned about neck diameter, but they swaged down some and measured just slightly over the .310 123 Gr V Max my barrel likes. I have only loaded two so far to get a velocity, but am going to try some more. I feel like I'll probably just end up shooting the .308 150 X-Treme as a cheap plinker in 300 BLK. Two reasons, velocity, and size. Time will tell. I have a chamber cast of my barrel, so I know I am good to go in the neck area.

Chamfer the inside of the neck. Make absolutely sure the neck area of the chamber is large enough.
I am in the same boat so to speak. I am getting ready to do my first load of x39. My box of Hornady 123 gn z-max are supposed to be here Monday (all I could find in fmj). I have a follow-up question. I have the Lee die set which comes with two expander rods indicated on the website as .308 and .310. With my calipers they measure out more like .307 and .309. I assume this is correct and is that way to maintain neck tension. Am I correct that I need to use the larger of the two with the .310 Hornady bullets?

Belmont148 - I would be interested in hearing your experience and results with the X-treme plated bullets. I would like to be able to use them because they are a lot cheaper and available, but I couldn't get comfortable with any load data for them to keep the velocity down. Thanks.
I tried the 7.62x39 with the xtreme 123gr plated bullets and ran into several problems. The bullets are extemely short and going below 2.150 for the OAL causes feeding problems for me. I tried taper and FCD crimps, sized with the Lee .308 die and used light loads of AA1680. Several times the third round
bullet popped out when it hit the chamber. I was shooting a AK47 which is brutal on the rounds due to the recoil. Watch the OAL carefully if you're using an AK or varient. Also, the buldge is from "over crimping" as long as they fit in the chamber they seem to work fine.
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Thanks for all the help. I am using the same powder charge as my jacketed bullets. I have read online of a guy not having issues with my charge out of a 16" Mini 30 with these bullets, so I am going to give it a try. If I see any evidence of jacket separation I will work up something slower. I don't expect them to register much over 2000 fps.

I use the .308 expander for all of my Hornady .310 bullets. Depending on how these Xtremes do, I may stick to using the same expander for these .312's as well.
Well, they shot pretty good for a plinking load. Not as accurate as my Hornady loads, but I didn't expect them to be.

No signs of jacket separation, however I could
Not load my 20 round Ruger magazines to capacity. The spring tension sent the flat nose into the side of the magazine before clambering. Dropped back to 17 rounds and they functioned flawlessly.
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