Too much bump?

[L.Sherm]

Personally I like the Wheeler method of how much shoulder bump i dont like any resistance and in most cases it takes .003 for my stuff and always use the exact same comparator when you measure.
Watch Eric Cortina video on how he uses the Wheeler method and it took .004 to get the bolt handle to drop freely that being said I also agree .007 is to much.

 

[Webster]

The shoulder of the case is moved back.

Are you saying the shoulder gets moved without the location of the juncture of the body and shoulder moving?

 

[Dimner]

How much shoulder bump is considered too much?
When I set up my die I got butter smooth chambering. I have .002 headspace. After working up the load I'm very pleased with the ammo performance. I get .250" or less at 100yds, and .500 moa at 600yds.
I never checked how much bump I had.
I just did. From a fired case to a sized case, I have. 007" bump. It seems excessive to me, but I've read that some are over .010".
I'm so happy with my ammo performance that I'm hesitant to change anything.
What will excessive bump do? Reduce brass life?
Affect accuracy?

6 Dasher, Alpha brass, 105 Berger, Varget.

I have accidentally bumped too much many times. And I find it's not really that much of an issue.

if you have a really good load using a 0.007 bump, personally I would gladly give up any real or unreal degraded brass life* over the great results on target. Basically I'm saying, I would be fine keeping more brass on hand and having a great shooting load.

*brass life of your 0.007 shoulder bump might not even be an issue. There are some who will say it will impact brass life and there are some who will say it will not. If I were you, I would keep the load and shoot with it. If a year from now your are noticing issues with brass life and are super annoyed.... well that's when you can decide if new brass or load tweaking is the path you want to go down.

 

[Dimner]

Lots of good info in this thread for a new person to read.

For a while, when I heard the oft spoken '0.002" shoulder bump" I thought it was in regards to bumping back 0.002 from the fireformed shoulder. I did that for a year or two until I started having problems and I learned via the wheeler method videos that 0.002 is really the bump back from when the bolt drops freely.

So for those of you who, like me, just took 0.002 should bump as the instructions. It's a little misleading. Really, You need to take your fired brass and bump the shoulder back until the brass will chamber with the stripped bolt dropping freely. Only then, is when you bump 0.002.

I'm sure 99% of you know this, and It's covered in all the videos. But some punk like me will just roll with 0.002 shoulder bump as the only instructions and think it's all good.

 

[Rob01]

I have used .002” from fired cases for decades and no issues. I don’t worry about the bolt dropping freely as I have a hand and some arm strength and even at .002” off fired it drops easily with a round in the chamber. You guys do as you like but I will continue to do .002” off fired case as it’s not wrong in any way.

 

[memilanuk]

I have used .002” from fired cases for decades and no issues. I don’t worry about the bolt dropping freely as I have a hand and some arm strength and even at .002” off fired it drops easily with a round in the chamber. You guys do as you like but I will continue to do .002” off fired case as it’s not wrong in any way.

I don't disagree, as that's pretty much how I've done it for years as well.

I will say, that with a new gun I got recently I switched brands of brass and decided to tinker a little with a small sub-set of the new cases, rather than just proceeding to plow through the whole batch (four boxes).

After so many years of just taking the headspace from 1x fired cases, setting the die for 2 thou shoulder bump and calling it good... I was a little surprised to see the shoulder actually continued to grow a little ie the fired shoulder dimension didn't really stabilize until somewhere around 3x or 4x. So in the past, I probably was bumping the shoulder a little more than strictly needed. Did it hurt anything? Not really.

 

[BoydAllen]

Are you saying the shoulder gets moved without the location of the juncture of the body and shoulder moving?

No I am not. The brass at the top of the body is moved into the bottom of the shoulder, the brass at the top of the shoulder into the base of the neck, and the neck and OAL of the case get longer. Years ago, just for the fun of it, I made the longest necked .22-250 case from an old .30-06 case. That was an extreme case of what I described.

 

[Larry Koch]

Texas solo you had this question before. You should figure out how to measure shoulder bump. The way .007 will cause brass head separation in a short number of reloads.

How much bump is safe?

My bolt closure is tight, even with factory Fed GMM 168. I sized and trimmed new Hornady brass and set the seating depth at -.005" off the lands. It's also tight. Next I bumped the shoulder .002" and it's only slightly better, so I think I found the issue. Question is how much bump is...

forum.accurateshooter.com

 

[swd]

I like .002” headspace on a loaded round. And .003” is ok. I never want them any tighter or you run the chance of an inconsistent piece of brass being tight. Tight brass runs the risk of putting a shot out of the group.

 

[Webster]

I have used .002” from fired cases for decades and no issues. I don’t worry about the bolt dropping freely as I have a hand and some arm strength and even at .002” off fired it drops easily with a round in the chamber. You guys do as you like but I will continue to do .002” off fired case as it’s not wrong in any way.

Same thing for 50 years. It's not complicated. Don't care if the bolt falls down with almost zero push.

 

[gunsandgunsmithing]

No I am not. The brass at the top of the body is moved into the bottom of the shoulder, the brass at the top of the shoulder into the base of the neck, and the neck and OAL of the case get longer. Years ago, just for the fun of it, I made the longest necked .22-250 case from an old .30-06 case. That was an extreme case of what I described.

As usual Boyd, you bring up good points that can get people a bit confused with what they measure vs what actually can happen.

While I've never seen the body to shoulder area vary much, I have often seen the shoulder to neck area vary by quite a bit in length, especially so with bushing dies.

What happens is that the hole thru the bushing shelf is commonly quite a bit larger than neck diameter and if you're loading hot or just after several firings of the same brass, you can see that area at the top of the shoulder, just below the neck..that never gets touched by the die, grow in length. It's typically above the actual datum for a cartridge, so it doesn't get measured there and will create bump error as well as bolt closure and even extraction issues that can be hard to detect with some combinations. Bottom line, if the die can't get to it, it will not bump back and if using a datum diameter comparator, it can't get measured either.

Will have to look but I might have some extreme examples laying around where it's quite visible. I'll check if I remember. Lol!

 

[JMayo]

Has anybody said .002 is all you need.
Wheeler bolt method, if bolt drops freely you're there.
I personally like a little bit of scrub with the Wheeler method

 

[TIMO]

Has anybody said .002 is all you need.
Wheeler bolt method, if bolt drops freely you're there.
I personally like a little bit of scrub with the Wheeler method

Here as well.

Tim

 

[Mike TackleBerry]

I bumped my shoulders back .001-.002 max. If you bump it back to far the case have to expand and stretch to fill the void and the case will eventually tear apart at the case head, Hence case head seperations.

 

[Dimefox]

Not to high jack the thread, but tangentially related... I've been measuring my fired Lapua brass for my 260 Rem I've been working with and they seem to vary by 2 or 3 thou. If one were to bump 2 thou during resizing, do you set the die to bump 2 though based on the longest fired case or shortest fired case?

FWIW I set it based on the shortest case this last time. It's also a hunting rig so I might be splitting hairs for the intended purpose but enjoy trying to make it shoot the smallest groups possible.

 

[TSFineGuns]

Not to high jack the thread, but tangentially related... I've been measuring my fired Lapua brass for my 260 Rem I've been working with and they seem to vary by 2 or 3 thou. If one were to bump 2 thou during resizing, do you set the die to bump 2 though based on the longest fired case or shortest fired case?

FWIW I set it based on the shortest case this last time. It's also a hunting rig so I might be splitting hairs for the intended purpose but enjoy trying to make it shoot the smallest groups possible.

**Subscribed**

 

[Webster]

As usual Boyd, you bring up good points that can get people a bit confused with what they measure vs what actually can happen.

While I've never seen the body to shoulder area vary much, I have often seen the shoulder to neck area vary by quite a bit in length, especially so with bushing dies.

What happens is that the hole thru the bushing shelf is commonly quite a bit larger than neck diameter and if you're loading hot or just after several firings of the same brass, you can see that area at the top of the shoulder, just below the neck..that never gets touched by the die, grow in length. It's typically above the actual datum for a cartridge, so it doesn't get measured there and will create bump error as well as bolt closure and even extraction issues that can be hard to detect with some combinations. Bottom line, if the die can't get to it, it will not bump back and if using a datum diameter comparator, it can't get measured either.

Will have to look but I might have some extreme examples laying around where it's quite visible. I'll check if I remember. Lol!

It might be interesting to make three bump gauges with different dimeter holes just because no-one’s ever done it. . Measure bump at the bottom, middle and top of the shoulder. Would you get different numbers? Are the bump gauges arbitrarily made to reference at mid- length of the shoulder? I really don’t care about any of this, I just have an interest in details. I adjusted my die by measuring and averaging 10 fired cases and that’s what I go with (0.002” bump). Bolt closure method sounds very good, but I don’t want to take my bolt apart to do it.

 

[Rob01]

You could just use different bushings in the Hornady kit if you wanted.

 

[gunsandgunsmithing]

It might be interesting to make three bump gauges with different dimeter holes just because no-one’s ever done it. . Measure bump at the bottom, middle and top of the shoulder. Would you get different numbers? Are the bump gauges arbitrarily made to reference at mid- length of the shoulder? I really don’t care about any of this, I just have an interest in details. I adjusted my die by measuring and averaging 10 fired cases and that’s what I go with (0.002” bump). Bolt closure method sounds very good, but I don’t want to take my bolt apart to do it.

Lots of folks have what many call a "bbl gizzy", made from the bbl cutoff, with the same reamer that cut the chamber. The reamer is just run in deep enough to form most of the shoulder. It can then be used like a comparator but is specific to your chamber. IMO, it doesn't get much better than that. It can also be used to verify neck clearance and seating depth. Simple and easy to use tool that is quite handy and accurate. As you can imagine, it does away with datum issues etc. Lots of smiths used to provide them to customers, often as part of the chamber job.

 

[BoydAllen]

Lots of folks have what many call a "bbl gizzy", made from the bbl cutoff, with the same reamer that cut the chamber. The reamer is just run in deep enough to form most of the shoulder. It can then be used like a comparator but is specific to your chamber. IMO, it doesn't get much better than that. It can also be used to verify neck clearance and seating depth. Simple and easy to use tool that is quite handy and accurate. As you can imagine, it does away with datum issues etc. Lots of smiths used to provide them to customers, often as part of the chamber job.

With any barrel job, I always ask for a "gizzy". IMO they are the best tool for several jobs, not just measuring bump.