Bump gauges and their use.

[Lonny in ID]

I recently got two Sinclair bump gauges for a .270 Win and 22-250 Rem. I had never used these gauges before in my reloading. After watching a resizing video(link below) by Panhandle Precision-"Headspace, Full-length resizing and Shoulder Bump" I went with his recommendation of .002" of shoulder set-back when resizing cases for my 270 and 22-250.

I'm a hunter first and foremost and don't want any trouble chambering handloads in the field, if that makes a difference?

What do you recommend for a shoulder bump? What is your application? Hunting, varmints, targets, etc?

Thanks for any advice.

 

[K22]

Like you, I'm a hunter primarily varmints / predators but also big game thus functionality is at the top of my list along with accuracy.

Before I address your question a couple of remarks on full length sizing using a shoulder bump, points which you may already be aware of but I wanted to cover them just in case.

1. Having cases from the same lot will help in achieving consistent shoulder bump.

2. Obviously, the cases must be dedicated to a specific rifle and the bump based on the dimensions of a fired case from that rifle.

3. As cases age, some adjustment to the sizing die may be required to achieve the same degree of bump. I use Skip Shims to adjust the amount of sizing if and when needed. Some use the Redding competition shell holders for this purpose albeit considerably more expensive but a good choice.

4. Sized cases w/ bump should be periodically checked in the rifle for ease of chambering. The best way to do this is to remove the firing pin assembly so you can get a "feel" of the degree of effort needed to chamber the case. The case should chamber with only slight resistance. I spot recheck every 3 or 4th sizing.

Now for you question, I strive for a .001" shoulder bump (bolt rifle). You want the minimum about of shoulder set back that will produce ease of chambering. While .002" is alright, some variation will occur that's why I like to set my die for a .001" set back to minimize the amount of sizing.

 

[Lonny in ID]

Thank you K22 for that detailed response.

All cases are only used in a specific rifle.

I did notice some variation for sure... Like .001" more. So even though I was going for .002" I also got a .003" on some WW cases for the 270. This was a mix of firings and lots also.

The Lapua brass seemed to hold the tolerances better and all of those cases came from the same lot.

Because I am just getting into this, I'm going to try for .001-ish

Again, thank you for the help here.

 

[madmixerman]

For deer I bumped .003 so there would be no hangups if a quick second shot was needed. For varmint I did .002 and on my competition rifles .001 .

 

[Lonny in ID]

madmixer, Good to know what your numbers are on the rifles and intended use. Thank you!

 

[Uncle Ed]

Standard bump for bolt action is .001 to .003 and for semi-auto .003 to .006.

And if you have ever hunted in freezing inclement weather firing the first shot the warmth can cause condensation in your chamber. And with the second shot you will hear crunching ice sounds when you chamber the next rounds.

Bottom line, when hunting a little extra shoulder bump will not hurt anything.

Cold weather humor.

Do you know what the meanest bear in the world is?

A Polar bear.

If you had your balls in ice cold water all day long you would be a mean son of a bitch too.

Now ask yourself if you were hunting a polar bear would you want .001 shoulder bump or .003 to .006 bump.

 

[Ccrider]

Measure will differ depending on where you measure from on the brass. Amount needed will vary from chamber to chamber.

 

[BoydAllen]

A number of years ago I was helping the owner of the business that I worked for reload ammo for a 7mm WSM to take on safari in Africa. As I had many times before, I used a fired case to set the shoulder bump at .001. After they had returned from the trip, his wife complained that some of the rounds had been hard to chamber. Looking into it, I realized that the variations in the hardness of the brass had resulted in some cases not being bumped at all. Some time after that, we decided that an annealing machine would be needed to solve the problem for that rifle and a .338 LM, which it did. We were careful to set the time in flames to the very minimum required for the variation in shoulder bump to be +-.0005 which was several times better than it was before annealing. The brass was only partially annealed so the necks were hard enough for heavy bullets fed from a magazine. My advice to game hunters is to measure every round, or pull the firing pin assembly and run them all through the rifle to make sure that they will all function properly, this after setting the die to bump .002 from a tight case, or .001 from once fired.

 

[Old Navy]

And with the second shot you will hear crunching ice sounds when you chamber the next rounds.

I just have to call BS on that one.

 

[Surfgent]

Great discussion

 

[Lonny in ID]

Good stuff guys. Thank you all.

 

[Dusty Stevens]

For hunting guns ill go with .003-.004. Any more than that you may get unreliable ignition. If its an important hunt ill chamber every single loaded round with the firing pin removed

 

[Uncle Ed]

And with the second shot you will hear crunching ice sounds when you chamber the next rounds.

I just have to call BS on that one.

Funny thing the case shoulder and body had small dents on them from the ice after firing and the case was wet when extracted that quickly froze.

I will chalk up your BS to lack experience with cold, heat and frozen condensation.

 

[tnek13]

Like K22 I use my rifle to confirm chambering. Set back is .001, dedicated lot of brass, annealed every third firing and I measure to the point of obsession.

 

[K22]

Never had a chambering problem with targeting a .001" bump in bolt rifles but I'm saying it can't happen, I just never experienced loading thousands of 223's, 243's and 308's. A .003 - .004 is a lot of bump (working of the brass) for a bolt rifle and I'd be uncomfortable with that amount of set back for cases that are reloaded numerous time because of concern for head separation. (I have no experience sizing belted magnums so my comments are restricted to non-belted cases).

In my experience, where you can encounter problems is when you full size and don't contact the shoulder. In some instances, the case can be extruded and actually grow in head space dimension thereby creating a chambering difficulty.

As others have said, check each round you intend to take on a costly and important hunt, the last thing you want to find in the wilderness of Alaska is that a round won't chamber especially if you're hunting dangerous game. Worst if you need a second shot when a Grizzly is about to pounce on you.

 

[Tommie]

This subject throws reloader ls to the street....

Sorry. My inner Guffey leaked out.