Bumping-How much?

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Ross Smith posted this 21 February 2023

The title says it all. When bumping bullets do you normally change the entire bullet shape, or just enough of the base to match the throat.??

My rifle was chambered by John Ardito and it has a long .62" throat then the leade and normal .300x.308 bore. The bullets that were sent with the rifle were completely reshaped in the bump die to the 1 degree taper except for the very nose that took on the shape of the cavity in the ejector rod.I also did not achieve my best accuracy till I bumped the bullets that much. Perhaps the whole bullet needs to be squished in order for the base to fill out and fit the throat?

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Shopdog posted this 21 February 2023

May be some help Ross?

I shoot rifle bore riders,and don't see that EVER changing. These are high intensity bolt rigs. Can not remember the last time I sized a bullet's body in a conventional in/out,or push through. I roll size some,but certainly not all. They see a Lyman 450 only for "crimping" as such,the body never fully enters the H die. And there are ways of "rolling" the upper edge of GC,very simple. Don't use it,but it's there as a tool if needed. As is crimping the GC in 5C collets in the shop....

Long way to say I don't bump the body.

The only bump gets applied to the bore ride sections. My definition of bump is,without splitting too many hairs.... "to increase diameter". Swaging is for reshape or to make smaller.

I am curious on your chamber however. Are you direct measuring, or are you measuring a pound cast or cerrosafe casting?

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John Alexander posted this 21 February 2023

"Roll sizing" sounds interesting, I can't remember hearing the term. But then I have forgotten a lot I have heard. What is it and how is it done? When is it helpful?

Thanks.

John

 

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Ross Smith posted this 21 February 2023

I measured the chamber and throat from a cerrosafe cast. Bullets were then bumped to match the taper in the throat which is.314 to .308. 

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Tom Acheson posted this 21 February 2023

This is a goofy “forum site”. I typed the following, was almost done, and had to step aside to shovel some snow. I came back and it was gone! Not the first time this happened. Have to get into the habit of developing the text in Word and when finally done, cut and paste it into the reply box.

 

At one time I “bumped” cast bullets for .30 and 6.5mm caliber. My “coach” (Dick Reese) in 2005 told me to do this: Bump the bullet, the nose along with the ogive, down to the middle of the driving band on the underside of the lube groove. This results in the bullet having a long, very gradual “taper” for much of its length. Then this “taper”, when the round is chambered, enters the mating “taper” in the chamber. Supposedly, a taper in a taper is a good step towards uniform round/bore concentricity.

 

This was for either an Eagan or an LBT bullet, both with similar profiles, 165-180 grains.

 

This approach worked very well in my XP-100 chambered in 30 PPC.

 

Comparing match results, when using my Savage .308 Winchester (Low Profile Varminteer), the groups were always much better with bumped bullets, compared to un-bumped bullets.

 

My current round in this XP-100 is a .22 BR but so far, no bullet bumping. However, my bump press is currently set-up to size the .22 bullet noses, my first experience @ doing this exercise. Lots of fun down the road!

 

Tom

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Ross Smith posted this 22 February 2023

That's about what I'm doing Tom, Eagan bullet and all. I want to hear from experienced bumpers-good or bad. Ross

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Glenn R. Latham posted this 22 February 2023

Ross, that's the way John intended bullets to be prepared for his chambers.  They won't shoot until bumped enough to seal the .314" at the beginning of the throat.

 He told me that when he started playing with a .32 (on the short 308 case) that until he got a 32 mould, he bumped his .30 cal. bullets up to 32!  They shot great.

Glenn

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Tom Acheson posted this 22 February 2023

Just a PS to my previous post…

The .30 cal. bullet was sized 0.311”. Bumping did not increase the diameter. It exited the bump die @ 0.311” and was very round. Traditional CB sizing dies do not always produce precisely, fully round bullets. With the correct “force” dialed into the bump die, the die makes the bullet base precisely round as it forces the bullet to confirm outwards into the ID of the bump die. That exertion and resultant effect is not available in a traditional CB sizing die.

Tom

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