Shoulder Bumping ???

[hoz53]

I am wondering if there are any negatives to bumping the shoulder back farther than what it was as new brass. Im not talking about brass life, or forming to a different case. Im wondering about case runout-concentricity ect issues or mabie something else I havent thought of on a case youre just reloading. Thanks Hoz

 

[Jose_Luis_G]

My opinion is that you don't get any advantage doing that. Concentricity is based on other subjects and the only thing you get, by doing that, is to stress the case beyond the natural limits of use.

 

[ireload2]

Moving the shoulder back adds shoulder clearance to the loaded round. This would permit the round to float back and forth longitudinally in the chamber even more.
This float would permit variations in firing pin strike and variations in the location of the bullet off of the lands when the round fires.
Depending on the type of extractor and ejector you have this might be significant. A plunger ejector would always push the round forward until it either registers on the shoulder of the chamber or it is caught on the rim by the extractor.

 

['Freak]

The case will likely require multiple firings, with no shoulder setback performed between those firings, before a fire formed case will finally exit the chamber having retained, after spring back, a case head to shoulder datum length very near same as the distance from the bolt face to the chamber’s shoulder datum.

Thereon, setback [“bump”] the shoulder only enough to maintain a thousandth or so clearance betwixt the bolt face and the case head, minimizing stretch of the case mid-body when the forward section of the case body gets blown outwards, grabbing hold to and sealing against the chamber wall, all the while the rearmost portion of the case body and case head gets blown rearwards, backing the case head up against the bolt face.

 

[Steve Ladino]

I am wondering if there are any negatives to bumping the shoulder back farther than what it was as new brass. Im not talking about brass life, or forming to a different case. Im wondering about case runout-concentricity ect issues or mabie something else I havent thought of on a case youre just reloading. Thanks Hoz

To much shoulder set back will swell the case body and will be felt when bolting over.

 

[jepp2]

I am wondering if there are any negatives to bumping the shoulder back farther than what it was as new brass

My first question would be why? I have found some new factory brass to have a datum to case head measurement of as much as 0.010" less than chamber headspace. If you happen to have that brass, just curious why you want to set the shoulder back that much.

 

[K22]

Shoulder set back is performed to assure flawless functioning, i.e. chambering. Typically the shoulder is set back approx. .001 to .002" (bolt rifles) from a fired case in the specific rifle you are loading for. To do this properly you need a gauge such as the Hornady headspace tool measure the amount of set back.

 

[M-61]

If the fired (in your rifle) brass chambers flawlessly (after firing) I see no reason to 'bump' the shoulder.

 

[mikecr]

Im not talking about brass life, or forming to a different case.

With this you ARE forming a different case(cold forming, analogous to hydraulic forming).

 

[K22]

If the fired (in your rifle) brass chambers flawlessly (after firing) I see no reason to 'bump' the shoulder.

True but without chambering every case how are you going to know. If you are a hunter, you don't want to find out in the field that the cartridge won't chamber. Eventually, after repeated reloads you will have to bump the shoulder to chamber the case. By using the .001 to .002 shoulder bump you don't have to guess or wait until you experince chambering difficulties in the field. Also, bumping the shoulder back this slight amount, while assuring flawless chambering, will NOT reduce case life. I see no negatives and all positives using this method of sizing especially for the hunter.

 

[hoz53]

True but without chambering every case how are you going to know. If you are a hunter, you don't want to find out in the field that the cartridge won't chamber. Eventually, after repeated reloads you will have to bump the shoulder to chamber the case. By using the .001 to .002 shoulder bump you don't have to guess or wait until you experince chambering difficulties in the field. Also, bumping the shoulder back this slight amount, while assuring flawless chambering, will NOT reduce case life. I see no negatives and all positives using this method of sizing especially for the hunter.

OK Guys--Thank You all for the responses to my question. I appreciate you all taking the time to do so.

 

[hunter243sgk]

Just ask fguffey he is our local expert on this.

 

[hoz53]

Just ask fguffey he is our local expert on this.

Yes Ive had the pleasure of reading some of Guffeys Junk quite awhile back. The trouble is he has no "headspace" so I think this question would be out of his area of expertise.

 

[jlow]

I am wondering if there are any negatives to bumping the shoulder back farther than what it was as new brass. Im not talking about brass life, or forming to a different case. Im wondering about case runout-concentricity ect issues or mabie something else I havent thought of on a case youre just reloading. Thanks Hoz

First of all, new brass tends to be slightly shorter than what you need i.e. SAAMI specs, this is to ensure that the case will work for most rifles. So if you bump the shoulder back more than what comes in a new case, you might have problems with either reliable firing and/or increase likelyhood of flat primers even for loads that are not overly hot or even case head separation.

The reason is since you have bumped the shoulders more than required, the firing pin will be able to push the case forward when it hits the primer. This will decrease the strength of the hit on the primer. If it push the case forward enough, it might result in a weak hit and no ignition. Even if the hit is hard enough to result in ignition, the pressure in the case can push the primer out of the primer pocket until it hits the bolt face which will give you a what looks like a flatten primer.

Of course a significant bump will also mean the case will have to stretch to fit when it is fired, significant degree of stretching will cause case head separation.

It’s like most things in life, a little especially if it is the correct amount is good, too much is almost always bad…

 

[hoz53]

First of all, new brass tends to be slightly shorter than what you need i.e. SAAMI specs, this is to ensure that the case will work for most rifles. So if you bump the shoulder back more than what comes in a new case, you might have problems with either reliable firing and/or increase likelyhood of flat primers even for loads that are not overly hot or even case head separation.

The reason is since you have bumped the shoulders more than required, the firing pin will be able to push the case forward when it hits the primer. This will decrease the strength of the hit on the primer. If it push the case forward enough, it might result in a weak hit and no ignition. Even if the hit is hard enough to result in ignition, the pressure in the case can push the primer out of the primer pocket until it hits the bolt face which will give you a what looks like a flatten primer.

Of course a significant bump will also mean the case will have to stretch to fit when it is fired, significant degree of stretching will cause case head separation.

It’s like most things in life, a little especially if it is the correct amount is good, too much is almost always bad…

Thanks for this info--Happy Holidays

 

[Sgt 45]

Thanks for this info--Happy Holidays

What if you are loading for two different rifles? I have both a 6.5x47 Lapua and a .338 Lapua where brass fired in one rifle simply will not chamber in the other even using full length sizing dies.

 

[Webster]

True but without chambering every case how are you going to know. If you are a hunter, you don't want to find out in the field that the cartridge won't chamber. Eventually, after repeated reloads you will have to bump the shoulder to chamber the case. By using the .001 to .002 shoulder bump you don't have to guess or wait until you experince chambering difficulties in the field. Also, bumping the shoulder back this slight amount, while assuring flawless chambering, will NOT reduce case life. I see no negatives and all positives using this method of sizing especially for the hunter.

If you are worried about functioning in the field what's the problem with running each loaded round thru the rifle? How many cartridges do you need to kill a deer? Sounds like you are imagining a problem that doesn't exist. If you can extract a fired case easily and rechamber it you don't have a tight fit. Adjust your die using the closing the bolt without a firing pin in the bolt method and you will get the proper die adjustment. The case should be fired several times without any shoulder bump so the case fits the chamber.

 

[hoz53]

What if you are loading for two different rifles? I have both a 6.5x47 Lapua and a .338 Lapua where brass fired in one rifle simply will not chamber in the other even using full length sizing dies.

this thread is a year old-anyway I dont quite understand youre question. you want to make sure you use the cartridge in the rifle it was chambered for

 

[LCazador]

What if you are loading for two different rifles? I have both a 6.5x47 Lapua and a .338 Lapua where brass fired in one rifle simply will not chamber in the other even using full length sizing dies.

Like mentioned before most new brass is undersized. Proper sizing to the dimension of your chamber is critical. If you don't know the exact dimension as in most factory rifles, your best bet is a chamber cast. Don't do any set back until you have some sort of idea of the chamber dimensions. If it's new brass and you can't do a chamber cast , fireform only a couple of rounds to get a idea what the chamber dimensions are. This is especially true of new brass in a factory chamber. Don't do any setback unless the brass goes into the chamber really tight. Remove the firing pin assembly from your bolt and check the fit of your new brass. If it closes with no effort than it is undersized. Because of brass spring back, fire form at least twice before measuring the base to shoulder datum dimension. Only after doing this should you consider how much bump is needed. Of course if you have a custom reamer ask for a blueprint of the reamer dimensions. As for that brass that fits in one rifle but not another, keep a record of the setback needed for each rifle. I mark my brass and I don't mix it up when dealing with two different rifles. I use different brands for this situation but if I can't afford different brands of brass than I will mark each piece of the same brass for each rifle and keep a record of such. Been doing this for 50 plus years, happy reloading!! And Happy New Year to all!!

 

[Webster]

Like mentioned before most new brass is undersized. Proper sizing to the dimension of your chamber is critical. If you don't know the exact dimension as in most factory rifles, your best bet is a chamber cast. Don't do any set back until you have some sort of idea of the chamber dimensions. If it's new brass and you can't do a chamber cast , fireform only a couple of rounds to get a idea what the chamber dimensions are. This is especially true of new brass in a factory chamber. Don't do any setback unless the brass goes into the chamber really tight. Remove the firing pin assembly from your bolt and check the fit of your new brass. If it closes with no effort than it is undersized. Because of brass spring back, fire form at least twice before measuring the base to shoulder datum dimension. Only after doing this should you consider how much bump is needed. Of course if you have a custom reamer ask for a blueprint of the reamer dimensions. As for that brass that fits in one rifle but not another, keep a record of the setback needed for each rifle. I mark my brass and I don't mix it up when dealing with two different rifles. I use different brands for this situation but if I can't afford different brands of brass than I will mark each piece of the same brass for each rifle and keep a record of such. Been doing this for 50 plus years, happy reloading!! And Happy New Year to all!!

Hate to reply to a year old post but I will. Might help someone? I found a good way to get a good head to shoulder measurement with a bump gauge is to take a twice fired case, primer, powder, bullet no sizing die at all. The case will chamber easily if you are not firing hot loads. Fire twice without using a die. The case will then fill the chamber as good as it will ever fit. As long as the case still chambers easily as it should this measurement should give you a good bump to dimension if the dimension gets longer. I still use the bolt close method but record a few bump measurements for comparison.