Having to bump shoulder an excessive amount?

[Never Forget]

I discovered this well over a year ago and realized today why don’t I post and maybe find out why.

I had my factory Rem 700 5R 300 win mag dialed in as far as I thought I could with Hornady and Sierra bullets shooting just under an inch at 240 yards which is the max at my range. At the time I was satisfied because I couldn’t find a way to improve no matter what I tried. I purchased some new Remington brass at a gun show and decided to try some 190 VLD Bergers. It didn’t take long and I was down to ½" groups at 240 yards.

When all the brass was fire formed I neck sized as that is what I did at the time and my groups opened up to just under 1” again. I had been reading about guys getting better groups full sizing bumping the shoulder back between .0015/.003 and decided to give it a try. I purchased the gages from Sinclair and gave that dimension a shot, groups opened up to 1 ½. Played with tweeking the charge and no improvement. Frustrated I let the project sit. I had some really old mixed brass that was getting tough to chamber from several neck sizes so I decided to give it a full size. Out of habit I set my Lee full size die up the way the book says, screw it down to touch the shell holder then a ¼ turn more to cam over. After sizing all the cases (about 40) I remembered to check it with my gage and found out I had moved the shoulder back .013, that seems really excessive. Pissed at myself I loaded them up to re-fire form and low and behold my 1/2" groups came back. I did a test and bumped shoulders at .0015, .003 and so on out to .015 in 3 shot groups. From .0015 to .007 groups were over an inch and from .011 to .015 groups are ½"again. I chose .013 in the middle and had fun from there on.

My question is why do I have to bump so far back and over work my brass where most people see results with much less. Is something wrong with my rifles head space?

 

[savagedasher]

I discovered this well over a year ago and realized today why don’t I post and maybe find out why.

I had my factory Rem 700 5R 300 win mag dialed in as far as I thought I could with Hornady and Sierra bullets shooting just under an inch at 240 yards which is the max at my range. At the time I was satisfied because I couldn’t find a way to improve no matter what I tried. I purchased some new Remington brass at a gun show and decided to try some 190 VLD Bergers. It didn’t take long and I was down to ½" groups at 240 yards.

When all the brass was fire formed I neck sized as that is what I did at the time and my groups opened up to just under 1” again. I had been reading about guys getting better groups full sizing bumping the shoulder back between .0015/.003 and decided to give it a try. I purchased the gages from Sinclair and gave that dimension a shot, groups opened up to 1 ½. Played with tweeking the charge and no improvement. Frustrated I let the project sit. I had some really old mixed brass that was getting tough to chamber from several neck sizes so I decided to give it a full size. Out of habit I set my Lee full size die up the way the book says, screw it down to touch the shell holder then a ¼ turn more to cam over. After sizing all the cases (about 40) I remembered to check it with my gage and found out I had moved the shoulder back .013, that seems really excessive. Pissed at myself I loaded them up to re-fire form and low and behold my 1/2" groups came back. I did a test and bumped shoulders at .0015, .003 and so on out to .015 in 3 shot groups. From .0015 to .007 groups were over an inch and from .011 to .015 groups are ½"again. I chose .013 in the middle and had fun from there on.

My question is why do I have to bump so far back and over work my brass where most people see results with much less. Is something wrong with my rifles head space?

What way did they opens up vertical or horizontal . ? Larry

 

[SheepDog]

That is a hard question to answer without having the rifle to inspect. I suspect that your load was worked up with the room for the case expansion and when you take away that room you need another load or powder to make up for the cushioning effect of the expanding brass.

 

[Never Forget]

What way did they opens up vertical or horizontal . ? Larry

More of a triangular pattern.

 

[Never Forget]

That is a hard question to answer without having the rifle to inspect. I suspect that your load was worked up with the room for the case expansion and when you take away that room you need another load or powder to make up for the cushioning effect of the expanding brass.

I did try adjusting powder and seating depths when bumping less but nothing helped the groups, only made them worse.

 

[savagedasher]

More of a triangular pattern.

I can only guess but the powder Can have a spike at ignition. Like sheep dog said the case is absorbing the pressure . Larry

 

[RonAKA]

I can't think of any explanation. 1/2" groups at 240 yards is pretty darn small, at about 0.2 MOA. Are you sure you are not just having good days and bad days at the range due to the effect of wind?

 

[longbow]

If your not using at least one or two wind flags , its a crap shoot. One more variable to work out.

 

[22BRGUY]

Have you tried removing the firing pin from the bolt and seeing how much resistance there is in bolt drop at the various shoulder bump dimensions? Alex Wheeler posted an excellent vid a while back about how to set the headspace using this method. Just thinking maybe the die is somehow pushing the shoulders back but not sizing some other part of the case that needs to be resized as well....just a guess but you may want to try it.

 

[BoydAllen]

Back in the day, before shoulder bump comparitors were commercially available, except for Wilson, I knew shooters who lost belted magnum cases after three or four firings. They were following RCBS's directions for setting their FL dies, and not understanding what that was doing chalked up their short case life to "magnum pressure". If you bump .014 you will lose cases because of it. Belted cases do not move forward during firing like rimless do, but even so, repeated blowing forward of the shoulder will shorten brass life considerably. The couple of times that I compared belted once fired in factory chamber brass with new brass (.300 WM, and 7mmRM) shoulders had been blown forward .021 on first firing. Brass manufacturers do this because there is no standard spec for shoulder to head dimension, and they want to cover the variation that is out there. One firing with that much stretch is not dangerous. Repeat a long stretch over and over and brass life will be short.

 

[Never Forget]

Have you tried removing the firing pin from the bolt and seeing how much resistance there is in bolt drop at the various shoulder bump dimensions? Alex Wheeler posted an excellent vid a while back about how to set the headspace using this method. Just thinking maybe the die is somehow pushing the shoulders back but not sizing some other part of the case that needs to be resized as well....just a guess but you may want to try it.

That's a great idea, I will give it a shot. I may have caught that video last night. I don't remember his name but he did what you explained on a 700 bullpup style rifle and used redding competition shell holders to get the correct headspace.

 

[John Russell]

Back in the day, before shoulder bump comparitors were commercially available, except for Wilson, I knew shooters who lost belted magnum cases after three or four firings. They were following RCBS's directions for setting their FL dies, and not understanding what that was doing chalked up their short case life to "magnum pressure". If you bump .014 you will lose cases because of it. Belted cases do not move forward during firing like rimless do, but even so, repeated blowing forward of the shoulder will shorten brass life considerably. The couple of times that I compared belted once fired in factory chamber brass with new brass (.300 WM, and 7mmRM) shoulders had been blown forward .021 on first firing. Brass manufacturers do this because there is no standard spec for shoulder to head dimension, and they want to cover the variation that is out there. One firing with that much stretch is not dangerous. Repeat a long stretch over and over and brass life will be short.

My 264 WM blows the shoulder forward 32 thou on new cases... and I leave it there.

 

[Never Forget]

Back in the day, before shoulder bump comparitors were commercially available, except for Wilson, I knew shooters who lost belted magnum cases after three or four firings. They were following RCBS's directions for setting their FL dies, and not understanding what that was doing chalked up their short case life to "magnum pressure". If you bump .014 you will lose cases because of it. Belted cases do not move forward during firing like rimless do, but even so, repeated blowing forward of the shoulder will shorten brass life considerably. The couple of times that I compared belted once fired in factory chamber brass with new brass (.300 WM, and 7mmRM) shoulders had been blown forward .021 on first firing. Brass manufacturers do this because there is no standard spec for shoulder to head dimension, and they want to cover the variation that is out there. One firing with that much stretch is not dangerous. Repeat a long stretch over and over and brass life will be short.

Yah I have a feeling the brass life will be short but for groups that small it might be worth it.

 

[BoydAllen]

One thing that I think has already been mentioned, that is a good idea to keep in mind is that 240 yard group differences shot without flags are as likely to represent differences in conditions, rather than differences in loads. Shooters that do not have experience shooting over a full set of flags, which at that distance would be about six, really do not understand how different and varied (at the same instant) the wind can be at various distances between the shooter and target. Another thing, for big game calibers, given the size of the targets that they are generally used for, I try to discourage shooters from spending a lot of barrel steel to get below three shot groups of around 3/4" at 100 yards. All they end up doing is wearing out perfectly good barrels to achieve a goal that has nothing to do with what the tool is used for. Instead, I suggest that they pick something smaller, with a top barrel and chamber to use as a range and reloading toy. Years back, I made a decision to separate my varmint rifles from a range only rifle, and that has been one of the best decisions that I have made for my gun hobby. I built up a tight neck, Hart barreled .222 on a tuned up Remington action, added a 2 oz. trigger and a 36X scope and started using home made flags, and loading at the range. As a result, my understanding, shooting skills, and consistency took a big step forward, and my varmint rifles continue to be plenty accurate for the task for which they were designed, smaller calibers in the high twos and threes, larger ones comfortably under an half inch, all five shots.

 

[Never Forget]

One thing that I think has already been mentioned, that is a good idea to keep in mind is that 240 yard group differences shot without flags are as likely to represent differences in conditions, rather than differences in loads. Shooters that do not have experience shooting over a full set of flags, which at that distance would be about six, really do not understand how different and varied (at the same instant) the wind can be at various distances between the shooter and target. Another thing, for big game calibers, given the size of the targets that they are generally used for, I try to discourage shooters from spending a lot of barrel steel to get below three shot groups of around 3/4" at 100 yards. All they end up doing is wearing out perfectly good barrels to achieve a goal that has nothing to do with what the tool is used for. Instead, I suggest that they pick something smaller, with a top barrel and chamber to use as a range and reloading toy. Years back, I made a decision to separate my varmint rifles from a range only rifle, and that has been one of the best decisions that I have made for my gun hobby. I built up a tight neck, Hart barreled .222 on a tuned up Remington action, added a 2 oz. trigger and a 36X scope and started using home made flags, and loading at the range. As a result, my understanding, shooting skills, and consistency took a big step forward, and my varmint rifles continue to be plenty accurate for the task for which they were designed, smaller calibers in the high twos and threes, larger ones comfortably under an half inch, all five shots.

I should have mentioned this earlier, all groups were shot from a Farley rest with rear bags over a field of flags. I do shoot on windy days but I chose not to do load development on those days, I shoot early in the morning or late to beat the wind. I also run Jewel triggers with 1 1/2 OZ triggers. I want to take as many things out of the equation as possible. And I know there are better calibers than a 300 win mag for what I'm doing, I have many other rifles like my 6br to shoot tiny groups. I just find it fun and have the money and time to do it with big stuff too, I'm a very lucky person in that regard with a very understanding wife. These results were not a fluke that happened once, when I find something that works I try it a few times to see if it repeats then tweek from there. I just found this one very odd as none of my other rifles work in this manor nor have I ever read about someone having to do this. Not being a gunsmith I was wondering if something was wrong with it.

 

[Ggmac]

Could your factory setup have a non square bolt face ? Have you checked after firing how true your case base is ? Having full or bump sized could , COULD give enough to improve accuracy and not be pushing the case off center . Just a WAG

 

[mikecr]

You went to new Rem brass, firing XX results, and after fire forming and neck sizing you had YY results. It doesn't sound like there was any load development there, and it's 2 changes.
Then you went to experimenting in a way affecting your pressure curve twice at least(both higher load density and excess case expansion on firing).
I would get the head space back to right, and then start over with load development -while maintaining correct case dimensions as stable, and changing one thing in your load at a time.

 

[pete1955]

If your case wall thickness was not a even thickness just above the belt the egg shaped case may have been pushing the case out of alignment with the axis of the bore. Meaning when you size all the way down the body of the case it was better aligned with the bore.

If you want the case to headspace on the shoulder then you may want to try the Larry Willis collet die. You might have warped banana shaped cases. Normally a full length resized case is .003 to .005 smaller in diameter than the chamber.

Belted Magnum Collet Resizing Die
"Finally a resizing die that works on belted magnum cases."

http://www.larrywillis.com/

 

[Eric Leonard]

at ,013 be on the lookout for case head separation,,

 

[pete1955]

at ,013 be on the lookout for case head separation,,

The OP is talking about pushing/bumping the shoulder back .013, and his belted case headspaces on the belt and not the shoulder.
I think what happened was he reduced the case diameter more by pushing the case further into the die.

I would measure a new case just above the belt and then a fired case and see how much it expanded. I would then blacken this area with a black felt tip marker on the fired case and see if the case is rubbing in this area and pushing the base of the case off center.