Attempting HV through my Mosin

BHuij

Active Member
So maybe I can clarify, because I think we’re on the same page.

My Lee full length resizing die does three things.

First, it sizes the body of the brass below the neck to SAAMI spec, including bumping the shoulder, assuming it’s screwed in to the default setting. I can control the amount of body/shoulder sizing happening by unscrewing the die a bit.

Second, it reduces the diameter of the neck by applying force from the outside. I believe my die is reducing the neck diameter to smaller than it needs to, and this is what I mean by lapping it out, so there is less unnecessary working of the brass.

Third, it re-opens the neck by drawing the expander ball back through it on the downstroke. My problem is that this operation is not expanding the neck enough, since my expander ball is aimed at in internal diameter of .311” after springback is accounted for (meaning the actual diameter of the ball is probably one or two thousandths larger than .311”).

The NOE expander plug fits into a different die and expands the neck on the downstroke, to two different diameters. I actually prefer to avoid this “stepped” neck diameter.

Seems like if I could replace the expander ball/decapping pin piece of my existing full length sizing die with a larger expander ball, I could get my desired neck inner diameter in the same step as my sizing, and avoid the stepped neck diameter. Ideally my “sizing” step would not mess with the full body of the case (which is already fire formed to the chamber), just bump the shoulder back and get the neck set to the right diameter.

Lee will make me a custom expander ball for $10. But I don’t know exactly what size I should get, because I don’t know how to predict brass springback. If I want a tension of .002” on a bullet which is .317”, what does the actual diameter of the expander ball need to be?
 

Ian

Notorious member
So maybe I can clarify, because I think we’re on the same page.

My Lee full length resizing die does three things.

First, it sizes the body of the brass below the neck to SAAMI spec, including bumping the shoulder, assuming it’s screwed in to the default setting. I can control the amount of body/shoulder sizing happening by unscrewing the die a bit. Yes.

Second, it reduces the diameter of the neck by applying force from the outside. I believe my die is reducing the neck diameter to smaller than it needs to, and this is what I mean by lapping it out, so there is less unnecessary working of the brass. Yes.

Third, it re-opens the neck by drawing the expander ball back through it on the downstroke. My problem is that this operation is not expanding the neck enough, since my expander ball is aimed at in internal diameter of .311” after springback is accounted for (meaning the actual diameter of the ball is probably one or two thousandths larger than .311”). True. That's why I said buy a .323" somethingoruther Lee sizing die for cheap, rob the expander out of it, and turn it down to the size you need. If you enlarge the neck of your existing sizing die the correct amount, you will not need the expanding spud at all other than to knock out the spent primers.

The NOE expander plug fits into a different die and expands the neck on the downstroke, to two different diameters. I actually prefer to avoid this “stepped” neck diameter. The NOE part replaces the cone-shaped piece in your Lee "universal expanding" die. The difference in size between the steps is way to big IMO and the design is flawed, thanks to Lyman screwing it up in the first place. If you enlarge your sizing die the amount necessary to make your case neck INSIDES about .315" (including the springback), then you won't need an expander at all, just resize and then put a little bellmouth with the Lee universal die that you already have.

Seems like if I could replace the expander ball/decapping pin piece of my existing full length sizing die with a larger expander ball, I could get my desired neck inner diameter in the same step as my sizing, and avoid the stepped neck diameter. Ideally my “sizing” step would not mess with the full body of the case (which is already fire formed to the chamber), just bump the shoulder back and get the neck set to the right diameter. You won't be able to bump the shoulder without sizing the whole case body somewhat, unless you buy an expensive "shoulder bump" die that I'm not sure even exists for this cartridge.

Lee will make me a custom expander ball for $10. But I don’t know exactly what size I should get, because I don’t know how to predict brass springback. If I want a tension of .002” on a bullet which is .317”, what does the actual diameter of the expander ball need to be? It all depends on the state of your neck anneal and how much your sizing die squeezes the necks in the first place.

Click to expand the quote and read my notes.


I would start by modifying your existing FL resizing die.

First, you will need to know your rifle's chamber neck dimension, which you still haven't determined from a good pound cast or by measuring a case fired with a full-power load. You need that number, preferably from a pound cast that's fully upset in the neck area, to determine your maximum safe loaded neck diameter, which is bullet body diameter plus two maximum neck thicknesses plus about another thousandth.

Second, you need your throat entrance diameter. Subtract about half a thousandth from that, and you have the biggest bullet the throat will accept. Add two case neck thicknesses to that dimension, plus a thousandth, to make sure your rifle will safely chamber and fire a bullet ideally sized to fit the throat entrance.

Third, once you have established your bullet body diameter, you will need to enlarge the neck of the sizing die so it resizes fired brass to hold the bullet with about .002" interference fit, in ONE resizing operation. If you run the case in a second time, it will be a little tighter in the neck.

Fourth, to modify the sizing die, pull out the expanding mandrel and nut and size a case. Measure the outside and inside diameter of the case very carefully. Record those numbers. Go by the inside only in the future as you enlarge the die's neck a little at a time with sandpaper wrapped around a dowel. When you get the sizing die enlarged to the point that it's resizing necks to have an inside diameter of your max bullet diameter minus about .004", I'd say stop there and go through the grits to a 600 polish, you should have about .003" interference fit with your bullet size at that point, sort of a fudge factor on neck tension.

Now you can put the sizing die back together, resize fired brass, bell the mouth a little with the Lee expander, and be ready to prime, charge, and seat bullets with a near perfect fit.

I personally like to step up and put the correct-for-purpose expanding mandrel in the die, just as added insurance that I'm getting the perfect size necks. Also, if you happen to find boxer-primed range brass with dents in the necks or that has been stepped on, the correct-sized mandrel can often save the necks when you resize the cases.

Your only challenges now are getting a mould that fits the rifle, and a bullet sizing die that will ensure their uniformity. You will likely have to modify a Lee push-through sizing die or modify a lube-sizer die (if you have a lube-sizer) to final-size your bullets and gas checks. Hornady .30-caliber checks are about .319" at the largest part, so there is almost no crimping action going on when sizing say .317", so that may be a problem too.

I hear Thompson Center is selling new rifles in standard calibers for about $225 after rebates through Academy, so if you are trying to save money, tooling up for a very worn, custom-sized MN may not be the most cost-effective thing to do.
 

BHuij

Active Member
Okay, everything you said makes perfect sense. Your recommended approach is to lap out the sizing die so that it crushes down the neck to the exact right inner diameter and doesn't technically require the sizing ball to re-expand it on the downstroke. This probably would work since all my brass has been carefully kept in lots so that it's all fired the same number of times, trimmed the same number of times, etc. However, when I get new brass, especially if I go with another manufacturer (say, Sellier & Bellot instead of PPU), the neck thickness might not be exactly the same, and my inner diameter would then vary from what I expected.

I think I will still lap the sizing die out somewhat, so that it doesn't size down as much as it currently does. But I think I will avoid trying to manipulate the final inner diameter as a function of how much the outer diameter is crushed down. In other words, I will take your advice to get a correctly sized expanding ball/decapper pin as well, so that varying case neck thicknesses won't lead to significantly different neck tensions on my bullets. From what I can tell, Lee will make me a custom one for $10. If I want the final inner diameter to be as close to .315" as possible for various types of brass, states of neck hardness, etc. I'm thinking an expander ball with true diameter of .316" is probably about right? Or does the brass likely spring back more than my estimated .001"?

Gas checks were my last point of concern. You're saying Hornady checks have an OD of .319" and that crimping them down only .002" may not be enough for a secure hold? I thought maybe Gator checks would work better, but they are made for a .284" shank from .17" thick gilding metal. By my math that's .318" total OD, so perhaps even worse than Hornady checks. I guess I'll just have to try them and see how it works out. Another pet project I have going on is a custom gas check punching die, so if the commercial copper ones just absolutely won't stay on well, I suppose I can custom make my own slightly larger ones from thicker aluminum flashing or similar.

So with the Accurate mold and the custom Lee expander stem, I'm looking in the neighborhood of a little north of $100 so far, which is doable. But as much as I'm penny pinching on this, it's worth spending the money to make the Mosin work. I lived near Izhevsk for two years, so this rifle has some sentimental value.

Thanks as always for sharing your wealth of information. I am going to take a serious crack at getting my barrel spotless clean as recommended in the Jacketed Performance book, and then do that pound cast with properly soft lead.

In the meantime while I put pennies in jar for that Accurate mold, I think I will lap out the driving bands on the .312 185gr mold I have and see if I can't work up some super accurate gallery loads for practicing and plinking. I'll just expect to have a hard time getting much higher than 1400ish FPS with the bore rider design.
 
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Ian

Notorious member
I think you hace the best idea and would be better off making the neck of the sizing die a bit tighter than you need or want and then having an expander of some sort (custom mandrel or a separate die insert) to give you options with different lots of brass. As to what size, well, you need to obtain the mesurements I mentioned so you will know what size your bullets need to be in the first place. Making the expander the same size as the bullet size usually gets you in the ballpark.
 

fiver

Well-Known Member
your first step is to stop guessing at the rifles dimensions.
this isn't going to be easy, remember your going from 317 [if that's the throat size] down to ????

think through THIS very carefully.

the goal here is to get the bullet from the mold to the target with as little change as possible...
is that even possible with this rifle?
why?
why not?
 

BHuij

Active Member
Correct. From my first pound cast, I believe my throat is .317" and this tapers down to a groove of .314" Of course "I think" isn't good enough here, which is why a proper pound cast is necessary before I do anything like buying a mold.

A taper of .317" to .314" seems fairly substantial to me, but I wouldn't think it makes HV accuracy impossible. I'm not trying to win a benchrest competition here, just be comfortable about getting humane kills on game animals out to 100 yards or so.

When I have actual dimensions to show, I'll be back here to get everyone's insights on the best next steps before I go any further. Would you consider a 0.003" taper from widest to narrowest point inside my rifle to be too much to expect decent accuracy?
 

fiver

Well-Known Member
no, and you don't need a full 317.
you do 'need' to have a bullet that will take the rifling properly and straight.


as a side note.
100 yd game kills are easily accomplished without high velocity.
seriously, 1800 fps is more than enough with a 180-200gr bullet to totally penetrate 5-600 lb. animals without hesitation.
a little more velocity helps.
a lot more velocity actually makes things harder, and a whole new design criteria is necessary.
there is a reason why I don't take my 308 ramped up to 24 or 2600 fps deer hunting.
 

RBHarter

West Central AR
Ive made several expander balls , solid rods actually , with just files , wet dry sand paper , steel wool , and a drill press .