How are "bump" dies made ?

  • Last Post 05 January 2019
Slug Gun posted this 02 January 2019

 I did a search on bump dies and saw some good pictures of dies but no drawings with dimensions or a print showing the internal area of bump dies with any dimensions. I'm wanting to make some bump dies for a new 30BR rifle build and can make the dies (have a lathe) if I had some idea of what they look like on the inside as some appear to be made to resize the nose only and some are made to size the bullets base and square up the gas check. Maybe one die does both ? I already have a bar of 12L14 steel from when I used to make all my bullet dies for a slug gun I shot which used a two-piece cross paper patch bullet. I have the general idea; just need the particulars. Looks like the die is an insert that fits into a Lee die from the pictures. Any help would be greatly appreciated and thanks.

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M3 Mitch posted this 03 January 2019

OK I have no direct experience with bump dies, but, my understanding is that they are used primarily to "bump up" the diameter on bore riding bullet noses, when said noses are cast undersized.  In today's mold market, where you can get a mold from several custom makers that will cast to the diameter you ask for in the alloy you specify - not quite certain why you would need a bump die in the first place.  If your bases are good, the gas check should go on square to begin with. 

Maybe someone with actual experience with bump dies will post up.  But since no one has said anything so far, I wanted to offer the above idea.

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muley posted this 03 January 2019

get a blank die and drill a thru hole to fit the pilot of ur throating reamer. use ur throating reamer to a depth  where ur bullet u will be using goes into the die up to the gas check when ur press is at top dead center. this will taper ur bullet to fit the throat of ur rifle. e.g. throat and bullet taper are now the same angle.

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David Reiss CBA Membership Director posted this 03 January 2019

Check this thread out.

David Reiss - NRA Life Member & PSC Range Member Retired Police Firearms Instructor/Armorer
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OU812 posted this 03 January 2019

You want the bullet to chamber inline and fit throat and bore like a snug glove. I think the mx-4 bullet requires one degree per side taper. You can use one of PTG's 30 caliber blank resizing dies to make die. Extraction punch can be machined from aluminum . The punch can also be used to bump bullet larger diameter when press is at top dead center and before extraction. If bullet is too fat the die will swages down smaller. Bore of die is important for snug slip fit of bullet into throat.

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OU812 posted this 03 January 2019

Cut your extracting punch to match nose shape of bullet.

You can use a 30 caliber Lee sizing stem to press bullet into die. I like to shorten and square face.

Get a PTG .310 diameter throater with one degree per side taper (2 degree included) . I would cut freebore about .100" deep. Cutting it in line is on you.

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Ken Campbell Iowa posted this 03 January 2019

just a thought on materials ... i have made bumping/swaging dies from 416 stainless ( old gun barrels , heh, very pretty !!  and already have a guide hole ...), 4340, 12l14, 8620 ( way way better than needed ) , and::  aluminum 6061, 2024, 7075 ...  

so far, the aluminum dies and pusher-inner and pusher-outers ...  have worked just fine ....   and aluminum tends to not gall with lead ....

AND::  aluminum is 10 times easier to cut ... important to me, as usually my first 6 designs are obsolete as soon as i try them out ...   and sometimes before i even get them finished ...

i often use threaded rod from ace hardware ... it comes in 7/8-14 cold rolled ....  for simple dies just for me, works fine, just ugly threads and nasty to cut on a small hobby lathe ...  mine is a 13 inch southbend and it still squeals on cold rolled ... ( g ) ...


design-wise ( i always wanted to say that ) ....  the die should ideally totally re-form the bullet ... so the forming cavity should look just like the bullet you want to shoot ...

with alloys up to non-heat-treated hardball, a good reloading press adjusted to max leverage can work fine ... the casting only swages a few thousandths ...  oh, lube the grooves before swaging or lose them ... my old herter's 3, with not much leverage, runs out of goodie at about a 220 grain 30 cal. hardball casting.  i do 44 hardball castings on an arbor press with a long pipe handle.   brittle heat treated alloys are essentially not swageable. 

i like to make shallow angle lead-ins for the pushers and the casting itself ... you can bore these but i prefer tapered reamers ... pin reamers come in many sizes, i get mine from * drills and cutters . com " ... 

 the above are just some thoughts, hope this helps...



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Redleged posted this 03 January 2019

Hi. I've read the thread that David referenced above, and I'm still a little confused. In one of the comments, you said:

"Bullet on left is not bumped. Nose measures .2205 and bands measure .2265.

Bullet on right is bumped 3/4 turn inward of adjusting bolt. Bore ride section after bumping now measures .2205 the full length of bore ride section and bands measure .2275.

Alloy is 13-14 bhn."

If bumping doesn't change the bore-riding section, and only increases the driving bands, what's the difference between that and casting a little over and sizing to the .2275 diameter? Or, is the purpose of the bump die to uniform the diameter of the bore riding section to a point above the first band? The results are obviously impressive based on the before/after targets, just curious about what's being done.



Growing old is mandatory, growing up, however, is totally optional!

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OU812 posted this 03 January 2019

A good die and punch reshapes bullet to a more perfect diameter and shape. A lathe will allow you to experiment and test to see what works and what doesn't.

Working with the 223 Remington is most interesting to me.

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Ken Campbell Iowa posted this 04 January 2019

it might be good to consider what good shooters of a hundred years ago knew and told those who would listen::

the rear end of the bullet is 30 times more important than the front.

just for fun, take a good shooting load and crimp the nose with a pair of pliers ....  still shoots good at least at 100 yards  ...  johna has a rack of trophies won by shooting bullets oval shaped at the front ... and even middle...  it has to hurt to get beat by a guy with crooked bullets ...  ( g ) ...


back when i was more serious, the consistent thing to improve accuracy was better bases   (  oh, and rule 1 ::  snug fit in throat ) ....

so a bump die has to do 2 things for sure: ... snug fit in throat and perfect bases ....  since roundness is easy enough with reamers and lathes, the roundness up front  is pretty much a free ride ...  


 while making, sketching, or thinking about a swaging/bumping die, you will notice there is a difficult area ( the only real problem in a simple die set ) where the nose punch meets the main body of the bullet ....  so it is good to have this junction as far forward on the bullet as possible ...   ( the further forward any matching error, the less it affects accuracy ) ... on a $750 custom benchrest die set, the nose punches are about $650 of that work ....  but for homebuilt cast bullet scrunchers, we can get 99 per cent of the goodie out of a $19,  3 or 4 piece set with a teensy matching error of nose punch to main body.     the coward's ( my ) way out is to make the nose punch about twice the bullet nose diameter, and machine the nose shape EN BLOC with the punch inserted into the die body.  you could then form with the nose punch indexed, but i doubt if it really matters .  hah, if you get it too tight, you have to scratch the punch to let the air out ..  kinda neat.

just some trivia, i never run out ... ken

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OU812 posted this 04 January 2019

Throat erosion

Designing a bullet and cutting a throat that is not sensitive to throat erosion is important. The mx-4 is a good example. It has both a tapered and bore ride section on bullet. As erosion increases and makes throat larger you can simply bump bullet larger for better fit.

I plan on ordering a couple PTG throating reamers with the following specs.

.225 diameter 2 degrees included taper.

.310 diameter 2 degrees included taper.

These reamers will help make the bump dies and cut throat to match for good accuracy.

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OU812 posted this 04 January 2019

I ordered chucking reamers from McMaster Carr to cut bore diameter of bump dies (.218, .219, .220, .221, .222, .299, .300, .301, .302). After bumping diameter is usually .0005 larger so do the math. Sanding helps gets diameter more perfect also.

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OU812 posted this 04 January 2019

OR you can just use a softer alloy and let the obturation of quick powder blast do the bumping for you.

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Ken Campbell Iowa posted this 05 January 2019

ou812::  ...   consider reamers from manson ...   ppg is possibly suffering from over-expansion ....  the rumors are ...

.... and i used to order almost all my reamers from ppg ...  when you talked to Dave or his wife about what you wanted ... ... and 2 weeks later BAM there they were ... exactly what you ordered ...




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