And Yet Another Shoulder Bump Question

[FALex]

Hey all, so I am shooting a JP LRP-07 in .260. I have the Hornady gauge to measure shoulder bump. Long story short, I am obviously trying to mitigate the amount of bump in the shoulder while still being able to chamber and fire rounds, correct?

Assuming that is true, my fired cases are measuring right around 1.626-1.627. I have ran several through my RCBS FL die and have them at 1.626. I have made some dummy rounds with these cases and they chamber just fine.

Is it possible to have a rifle where the shoulder does not need to be bumped at all...especially in an auto loader? Is the FL die sizing only the neck at this point?

When I made my first attempt at this, I read with auto loaders, you should try to knock them back at least .005, so I had several cases where I ended up knocking the shoulder back to 1.620. Obviously, they shot okay, but the damn brass grew like it came out of Balco labs! I know enough to understand that can't be good...

Any help, information or direction, as always, is much appreciated.

 

[ZombieMonkey]

With FL sizing, you're always going to be doing some shoulder bump unless the shoulder is already pushed back further than your specified amount. In a semi-auto you're going to have to put up with this and obviously there are things you can try to do to mitigate the amount of bump necessary. I run 0.003 on my semi-autos, 0.004 would be as much as I would go personally if I were concerned about case life.

 

[FALex]

With FL sizing, you're always going to be doing some shoulder bump unless the shoulder is already pushed back further than your specified amount. In a semi-auto you're going to have to put up with this and obviously there are things you can try to do to mitigate the amount of bump necessary. I run 0.003 on my semi-autos, 0.004 would be as much as I would go personally if I were concerned about case life.

Is it then possible that the fired rounds have their shoulders pushed back to a point where the current setting of my FL die is not touching them? If those cases are able to be chambered, can I get away with that setting on the die?

 

[ZombieMonkey]

Yes, it is very possible that your FL die can be set to the point where it is sizing, but not bumping the shoulders back. Essentially your die would be acting as a both a body die and a neck die without the shoulder being bumped back.

For consistency's sake, I would take the average shoulder measurement and set that die to just bump back the shoulder to 0.003. A properly setup FL die has a lot of benefits with a semi-auto to ensure your gun is consistently able to chamber and extract your ammo.

 

[mdmp5]

Is it then possible that the fired rounds have their shoulders pushed back to a point where the current setting of my FL die is not touching them? If those cases are able to be chambered, can I get away with that setting on the die?

This is something commonly seen if you pick up a bunch of 1x fired brass. However, when you size a case that is of smaller dimension than that of the die, the shoulder will actually bump forward as if it is trying to fill the capacity of the die. It is seldom a complete fill to where the case shoulder touches the shoulder portion of the die. In my own experience in this scenario, I have had no problems when using loads that have been sized in the manner described.

It also is possible to set the die so that it sizes the body and the neck, but does not set back the shoulder. My 300 WM sizing die is set up like this, and I made a video showing it. I didn't try very hard to get it that way; using a Redding competition shell holder with some cam over, that is just where everything settled. If I wanted more setback, I would jump to the next shell holder.

 

[FALex]

awesome, thanks for the responses fellas. I will see if these rounds shoot well today...hopefully it all goes well.

 

[FALex]

Well shit, if I wasn't lost in the OP, I sure as hell am now...

So I took those loads out today, ten rounds. They all chambered, shot, and extracted without incident. These were the shoulders that were barely bumped, if they were bumped at all. According to my readings from the Hornady Headspace gauge, they were not bumped. What does not make sense is that prior to loading those cases, the shoulders measured 1.626-1.627. When I ran them through the FL die, the shoulders came out to 1.626. They were able to be chambered, so I ran with them.

Fast forward to today. Those same rounds were shot. The shoulders are now measuring around 1.628-1.634, most of them at the 1.633 range. The brass on most of them grew substantially. My trim to length is 2.025. The rounds are now at 2.030-2.040, most of them in the 2.035 range.

From what I have read, getting the shoulder bumped back with as small of a measurement as possible should make it to where I my brass barely grows, if at all, but it looks like I am way off on whatever I am doing.

At any rate, I hope this is making sense. It's driving me nuts.

Any thoughts?

 

[ZombieMonkey]

Your cases are probably now closer to being fire formed to your chamber. Can you easily chamber the spent cases with where they sit now?

 

[damoncali]

I've sometimes found newish brass to be inconsistent on the first firing or two. I have no idea that would be, because it doesn't make sense to me without a little hand-waving. I wouldn't be surprised to see the next firing have them all come out at 1.633. Bump them back two thous, and give it another whirl.

(I say two thous, because if you don't bump it enough, your'e going to kick yourself one day when the bolt gets stuck half open on a live round.)

Edit- two thous is good for a bolt gun. Semis need 3-5. You can get by with less, but you're playing with fire.

 

[FALex]

Your cases are probably now closer to being fire formed to your chamber. Can you easily chamber the spent cases with where they sit now?

not sure, but I will give it a try tomorrow and report back.

How about the brass growth issue, is that rate of growth normal? Is it different when speaking about auto loaders vs bolt guns?

Damoncali - I have had that issue on one of my other AR's long time ago... I absolutely destroyed a CAA buttstock by trying to get it out with pounding it on the ground. I hit it twice and a piece came flying off the stock. I got so pissed off at it (it was a pile of ass with other issues, anyway) that I just proceeded to obliterate the thing. Not something I am interested in doing with my 3500.00 rifle, honestly.

 

[bigedp51]

On a over gassed semi-auto there is still pressure in the barrel as the bolt is moving to the rear, and it is possible for the fired case to be longer than the chamber when ejected. This is because the pressure in the barrel blows the case shoulder forward as the bolt moves to the rear.

If you take a full length resized case and place a fired spent primer in the primer pocket with just finger pressure and then chamber this test case. The amount the primer is protruding from the rear of the case is your head clearance which correlates to your shoulder bump.

1. Measure the case from the base to case mouth and write it down.

2. Seat a fired spent primer with just finger pressure just starting it into the primer pocket.

3. Now chamber this test cartridge allowing the bolt to seat the primer as the bolt fully closes.
4. Remove the case and remeasure and write it down.
5. Now subtract the first case measurement from the second and this is your head clearance "AND" the amount of shoulder bump.
6. Adjust sizing die for the correct amount of shoulder bump and retest using the primer trick until .002 to .003 shoulder bump (head clearance) is achieved.

You can also measure using your Hornady cartridge case headspace gauge with and without the primer to get the same readings only from the shoulder to the base of the case.

Note, the higher the port pressure the higher the chance of the shoulder of the case being moved forward and becoming longer than the chamber when fired. Also the location of the gas port affects the amount of shoulder movement along with the burning rate of the powder.

This problem increases with the shorter length gas systems and with slower burning powders, meaning higher port pressures.

I just looked up your rifle and they "may" come with a adjustable gas block and you can lower your port pressure and not be over gassed and not have this problem. But remember new freshly annealed cases will have softer brass at the shoulder and can be pushed forward at lower pressures. This will also cause different spring back rates in your brass after firing. I check the fired cases with the Hornady gauge and use the shortest cases for my "average" shoulder bump.

 

[FALex]

On a over gassed semi-auto there is still pressure in the barrel as the bolt is moving to the rear, and it is possible for the fired case to be longer than the chamber when ejected. This is because the pressure in the barrel blows the case shoulder forward as the bolt moves to the rear.

If you take a full length resized case and place a fired spent primer in the primer pocket with just finger pressure and then chamber this test case. The amount the primer is protruding from the rear of the case is your head clearance which correlates to your shoulder bump.

1. Measure the case from the base to case mouth and write it down.

2. Seat a fired spent primer with just finger pressure just starting it into the primer pocket.

3. Now chamber this test cartridge allowing the bolt to seat the primer as the bolt fully closes.
4. Remove the case and remeasure and write it down.
5. Now subtract the first case measurement from the second and this is your head clearance "AND" the amount of shoulder bump.
6. Adjust sizing die for the correct amount of shoulder bump and retest using the primer trick until .002 to .003 shoulder bump (head clearance) is achieved.

You can also measure using your Hornady cartridge case headspace gauge with and without the primer to get the same readings only from the shoulder to the base of the case.

Note, the higher the port pressure the higher the chance of the shoulder of the case being moved forward and becoming longer than the chamber when fired. Also the location of the gas port affects the amount of shoulder movement along with the burning rate of the powder.

This problem increases with the shorter length gas systems and with slower burning powders, meaning higher port pressures.

If I use the Hornady gauge for this, do I perform the same steps with the primers (seating them with the bolt, etc...) or would I perform a different process?

very nice, thank you for that, I will give that a try tomorrow, also.

I just read something that has me thinking. I read that if I am using a standard shellholder and running the case through a FL die, that it is likely creating too much headspace. The solution, is to get a Redding competition shellholder to decrease the headspace.

If that is true, how would I go about knowing which shellholder I would need?

 

[ZombieMonkey]

As your headspace grows your case OAL is going to grow as well, that brass all has to go somewhere. Once the cases more closely resemble the size of your chamber you will likely see the case growth slow a bit. If after the second firing most of your cases are reading 1.633 on your gauge, that's probably going to be about where you're going to level off. With it being a semi-auto, it is much more difficult to determine if the case is chambering or extracting hard until you've already started seeing problems. I'd probably do some test cases with the shoulders bumped back to 1.630 and see where the group of test cases end up. I'm willing to bet you'll find they are going to hover around that 1.633 mark on that third firing.

Do make sure that your OAL case length is not getting over max though, you do not want to have a kaboom from a pressure spike.

 

[ZombieMonkey]

No special shell holder is needed unless you prefer to have the die bottomed out onto the shell holder. Most people will set the FL die by screwing it down closer to the shell holder until they obtain the desired amount of shoulder bump.

 

[damoncali]

not sure, but I will give it a try tomorrow and report back.

How about the brass growth issue, is that rate of growth normal? Is it different when speaking about auto loaders vs bolt guns?

Yes, it's normal. Again, I've found it to be strangely inconsistent. But it's not unusual to see that kind of growth in a bolt gun. It's tough to predict, especially if your brass is not coming out at a consistent size because brass growth depends on the chamber fit and the brass having somewhere else to go.

I have a strong feeling that after another firing, your brass will come out all the same size, and when you run it through the sizer they will all be the same size. Length will continue to grow somewhat erratically. Sometimes brass does weird things. I had a batch that would not size equally (it varied by .003") after the first firing. After the 2nd, It was all the same - at least as close as I could measure - within about half a thou.

Edit: Oops - I just realized you're on a semi (sometimes I read too fast). Everything still works the same, except the numbers are a little tougher to pin down. I'd bump semi cases back 3 to 5 thous, not 2 as I said above.

 

[bigedp51]

Below the shorter average of my fired .223/5.56 cases, some are .003 longer "but" I want the case to chamber in three different AR15 rifles so the shorter length is used.

Below the same case resized with .003 shoulder bump.

Below a new unfired Federal M193 cartridge in the Hornady gauge.

 

[Icewater]

The reloading world is so much more complex then I ever thought. I could be wrong but I doubt there are any books covering the variety and complexities of the various situations encountered in these threads. Good thing for knowledgable and experienced people will to help. Always interesting to learn from other's situations

 

[FALex]

The reloading world is so much more complex then I ever thought. I could be wrong but I doubt there are any books covering the variety and complexities of the various situations encountered in these threads. Good thing for knowledgable and experienced people will to help. Always interesting to learn from other's situations

Amen to that brother! My RCBS DVD didn't cover any of this

I spent the last two years just putting rounds together, which has worked, to a degree. I have done so much reading on the subject that I sometimes wonder if I will ever understand ALL of the nuances involved in reloading. To be honest, this whole shoulder bump issue has come from the fact that I can't purchase the Remington-branded .260 brass that I love so much.

I need to be able to preserve the small amount of cases I have, and if I ever come across any others, be able to treat them correctly right from the get go. I also want to know what I am doing with my cases when I have to start buying Nosler brass. I am too poor to be messing up cases that cost 1.10 a pop.

 

[Mad_Charlie]

Bear in mind that the Hornady tool is just a comparator. bigedp51 uses a headspace guage to set his up, that stupid little bevel that Hornady puts on it messes up the linear measurements.

 

[Graham]

And Yet Another Shoulder Bump Question

It's an auto loader: If your goal is to mitigate the amount of shoulder bump, then when the bolt slams forward it's going to bump the shoulder anyway.

 

[elfster1234]

The one thing you need to remember is my hornady headspace guage might show a different measurement than your guage....... All you are trying to do is bump back back the semi auto fired brass .003 to .005

Amen to that brother! My RCBS DVD didn't cover any of this

I spent the last two years just putting rounds together, which has worked, to a degree. I have done so much reading on the subject that I sometimes wonder if I will ever understand ALL of the nuances involved in reloading. To be honest, this whole shoulder bump issue has come from the fact that I can't purchase the Remington-branded .260 brass that I love so much.

I need to be able to preserve the small amount of cases I have, and if I ever come across any others, be able to treat them correctly right from the get go. I also want to know what I am doing with my cases when I have to start buying Nosler brass. I am too poor to be messing up cases that cost 1.10 a pop.

 

[Icewater]

Bear in mind that the Hornady tool is just a comparator. bigedp51 uses a headspace guage to set his up, that stupid little bevel that Hornady puts on it messes up the linear measurements.

Looking at the photos in post #16 to me looks like the hornady headspace comparator, but is it actually a headspace gage? Or how does someone set those up?

 

[Mad_Charlie]

Looking at the photos in post #16 to me looks like the hornady headspace comparator, but is it actually a headspace gage? Or how does someone set those up?

Just zero it on an average of 10 fired cases if you don't know your chamber's actual dimensions. Or use bigedp51's method above.

 

[mdmp5]

Well shit, if I wasn't lost in the OP, I sure as hell am now...

So I took those loads out today, ten rounds. They all chambered, shot, and extracted without incident. These were the shoulders that were barely bumped, if they were bumped at all. According to my readings from the Hornady Headspace gauge, they were not bumped. What does not make sense is that prior to loading those cases, the shoulders measured 1.626-1.627. When I ran them through the FL die, the shoulders came out to 1.626. They were able to be chambered, so I ran with them.

Fast forward to today. Those same rounds were shot. The shoulders are now measuring around 1.628-1.634, most of them at the 1.633 range. The brass on most of them grew substantially. My trim to length is 2.025. The rounds are now at 2.030-2.040, most of them in the 2.035 range.

From what I have read, getting the shoulder bumped back with as small of a measurement as possible should make it to where I my brass barely grows, if at all, but it looks like I am way off on whatever I am doing.

At any rate, I hope this is making sense. It's driving me nuts.

Any thoughts?

Don't overthink it. Your brass is now at its new starting point. Set the shoulder back relative to the current dimensions. Trim the brass back to 2.025. Set the shoulder back .001.

 

[FALex]

It's an auto loader: If your goal is to mitigate the amount of shoulder bump, then when the bolt slams forward it's going to bump the shoulder anyway.

The gauge was not reflective of this when I made those dummy rounds and chambered them a few times...they indicated no movement of the shoulder. I'm not trying to argue, just trying to understand. I do appreciate the input.

 

[FALex]

Looking at the photos in post #16 to me looks like the hornady headspace comparator, but is it actually a headspace gage? Or how does someone set those up?

Yes, it is a headspace gauge. I do have the comparators too.

 

[bruddah]

Tag for good info.