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Thread: Necking down brass

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    Member shimano 33's Avatar
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    Default Necking down brass

    With the recent ongoing shortage of brass, how many of you are necking down brass that you can find for brass that you can't? For instance, I recently bought a 7mm-08 and it has become a pain to find brass for. I even went to the extent of hunting down some Cor-lokts to shoot for brass; until I noticed they were $32 a box!?!

    I have several batches of 308 brass and have contemplated on using these to neck down for the 7mm-08. I know it can be done but is it worth it? To take it a step further, would it even make sense to by "quality" 308 brass and then neck those down to use?

    I am shooting a stock Tikka, so I would think with the SAAMI specs I should be ok with the slightly thicker necks of the "once" 308 brass. I guess the only other concern would be with the converted 308 brass ending up slightly shorter than factory 7mm-08 specs. Plus the head stamps would be off..but nothing a slight notch in the rim couldn't solve.

    All comments on the topic are appreciated, Thanks!

    Mark

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    Moderator Paul H's Avatar
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    I've made .243 brass from .308 brass, necking the .308 down to 7-08 is very easy. Brass gets longer when you neck it down, so you shouldn't have to worry about short 7-08 brass when necking down, more than likely you'll be trimming them back.

    The only caveat is you might find that best accuracy with .308 based brass requires a slightly different charge than 7-08 brass. As with changing any component, back off and work up a new load.
    Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

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    Good advice. Also watch for neck-thickening when sizing down. If the neck gets so thick there's not sufficient room in the chamber for the neck to expand on firing and release the bullet properly, pressures will go right through the roof and get dangerous in a hurry in that case.

    Ideal is to get a tubing micrometer and check neck thickness after sizing. Without that, I'd size down one case and seat a bullet to make a dummy round, then try to chamber it. If you feel any resistance, odds are you're in neck trouble. If you don't feel any issues, load a single moderate charge and fire it. No excess pressure signs? You're not through yet. Take a bullet and the fired case and hand feed the bullet into the fired case. If it drags at all, you still have neck troubles.

    I got into real trouble sizing 7x57 brass to make 257 Roberts and 6mm Rem cases. Did the deed as I described above and everything seemed fine. But I failed to factor in that I have three rifles in 257 Roberts. Two of them were just fine, but one is a custom built for me by RCBS with a minimum chamber.

    Like a fool I loaded up my usual loads for that rifle in those cases and went out to sight it in before a hunting trip. Only time I've actually blown a primer in a round, and lotta gas floating around where it shouldn't have been. The primer pocket was expanded so badly that the remains of the primer simply fell out when I ejected the case. Happened to have the chrono set up when I fired that round. Sure was impressive to see it register 3642fps with that 100 grain bullet! But I'll not do that again, thank you very much!

    The real drag came next. Being so stupid, I'd loaded up 200 rounds of the stuff in those cases with too thick necks.

    Do you know what a drag it is to pull 199 bullets and all the rigamarole involved in getting the cases back to the point I could thin the neck walls like I should have done in the first place?

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    Member shimano 33's Avatar
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    Great tips so far! Much appreciated.

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    If you run into fat neck issues, bring them by the house and I'll fix them for you. Loaded or empty is fine Just bring a factory loaded round or a loaded real 7mm08 case.

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    Member shimano 33's Avatar
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    Quote Originally Posted by rbuck351 View Post
    If you run into fat neck issues, bring them by the house and I'll fix them for you. Loaded or empty is fine Just bring a factory loaded round or a loaded real 7mm08 case.
    Thanks for the offer! I will know for sure by this weekend if I run into neck issues and post the outcome.

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    BB:
    You can get by with just measuring the neck diameter of a loaded round.

    My LOADED 280 Rem. Necks measure .310, and Resized 30-06 cases, RESIZED to 280 measure the same.

    Let me run this by ya, and git your thoughts if you don't mind.

    A funny thing happened to me on the way to finishing the cases into 280 Rem.

    I resized 50, 30-06 cases with my 280 sizing die. The shoulder of the 280 is a bit longer than the 30-06, so it leaves a little shoulder there on the sized 30-06 case neck. Next step is to fireform it, in my rifle, and I did.

    I fireformed a couple, using a load that I'd used before, and didn't consider a HOT load. HOWEVER, I got a pressure sign, as in, the Primers were REELY flowed FLAT.

    I fireformed the rest with a lighter load, without incident, but I am puzzled as to why, the flattened primers.

    My chamber is SAMMI, and the necks were not too thick. The brass was not new, but frankly, I don't know how old it was.

    The case capacity was LESS, in the PRE-fireformed case, BUT, I would think that since it would/did fireform out to fill the chamber, it wouldn't be a pressure issue.

    I am at a loss here, because this is the FIRST time, I've actually necked down brass from large to small or vise versa. I actually didn't NEED to do this anyway, since I have sufficient 280 brass already, but I had always wanted to try it, and that's what happened.

    I talked to Andy about it, and I concluded that my fireforming load was too hot for fireforming, but not too hot for shooting is 280 brass.

    After reading of your experience with thick necks and a tight chamber, it prompted me to measure the neck diameters, and I found no difference in them, after fireforming.

    Thanks
    Smitty of the North
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    Yeah. I doubt there will be a problem but some brass is thicker than other and ya just don't know until you measure it. Factory chambers usually have plenty of room at the neck but it's always a good idea to check. If I needed 7mm08 brass, I would use 308 cases as they are easy to form and plentiful. If you use military 308 cases, back the charge down a bit as they have less case volume that commercial cases.

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    Quote Originally Posted by Smitty of the North View Post
    BB:
    You can get by with just measuring the neck diameter of a loaded round.
    I thought so too. That is until I fired the round from that custom 257 from RCBS with the minimum chamber dimension.

    The kicker is, lotta rifles built for accuracy have minimum chambers.

    Here's an easy "fix" for testing. After you fire the first round, try slipping the fired case over the bullet of an unfired round- If it drags, you're hosed.

    Note: That method is also a good test for cases that have grown too long for a particular rifle. If your cases get too long you'll have the same issue with overpressures when the case mouth starts pushing into the chamber mouth.

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    Quote Originally Posted by BrownBear View Post
    I thought so too. That is until I fired the round from that custom 257 from RCBS with the minimum chamber dimension.

    The kicker is, lotta rifles built for accuracy have minimum chambers.

    Here's an easy "fix" for testing. After you fire the first round, try slipping the fired case over the bullet of an unfired round- If it drags, you're hosed.

    Note: That method is also a good test for cases that have grown too long for a particular rifle. If your cases get too long you'll have the same issue with overpressures when the case mouth starts pushing into the chamber mouth.
    Thanks BB:

    I'll remember that.

    Yeah, bullets should slip in and out of a fired case. I've had some do that easy and some harder, depending on the particulars.

    I was hoping you could shed some light on the Fireforming experience I had, but there doesn't seem to be an explanation, other than that the load was too Hot. ??? And that fireforming increases pressure more than one would think. ??? (Supposedly, you can fire a Standard Load, FL, in an AI chamber and it fireforms safely. This is essentially what I was doin here.)

    Oh Well!

    It just bugs me.

    Thanks Again
    Smitty of the North
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    Quote Originally Posted by Smitty of the North View Post
    (Supposedly, you can fire a Standard Load, FL, in an AI chamber and it fireforms safely. This is essentially what I was doin here.)

    Smitty of the North
    Well when you fire a standerd round in an AI chamber it's a standerd powder charge not an AI charge. So when you drop a normal 280 powder charge in the necked 06 case it's like putting an AI load into a standerd case. I'd expect an altered presure signature with more presure than in a 280 case and would discourage the idea. It is a bit surprising that it would be that much more presure but the 06/280 case volume diferance is is a lot more than say 06/06AI or 280/280AI.
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    Quote Originally Posted by ADfields View Post
    Well when you fire a standerd round in an AI chamber it's a standerd powder charge not an AI charge. So when you drop a normal 280 powder charge in the necked 06 case it's like putting an AI load into a standerd case. I'd expect an altered presure signature with more presure than in a 280 case and would discourage the idea. It is a bit surprising that it would be that much more presure but the 06/280 case volume diferance is is a lot more than say 06/06AI or 280/280AI.
    The difference in capacity between 30-06 and 280 is LESS than the difference, 280-280AI,

    BUT, I would think it doesn't matter, since the chamber is 280 case capacity, not 30-06. So, it's putting a 280 charge, not a hot one, into a 280 chamber.

    I would expect, or I EXPECTED, that fireforming wouldn't make much difference in pressure. Fireforming is often done with light charges of a fast powder, even without a bullet.

    However, I can't say that you're wrong. Especially, since I have no other explanation. But, just that it doesn't seem to compute with the information I've gathered so far.

    I shall endeavor to study it further. As I said before, maybe it takes more to fireform than I thought. ????

    Thanks
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    I haven't done the math but the 280s shoulder is .052" farther out than 06 which I'd sure think accounts for more volume than AIing ether chamber would.

    At any rate it alters the pressure curve, pressure will come up faster (before bullet moves or case forms) and would act a lot like putting an extreme crimp on a load that was developed with no crimp. The faster initial pressure comes up the better burn you will get so the sooner peak pressure will be made and peak pressure is also apt to be much higher due to fastermore efficient burn.
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    Quote Originally Posted by ADfields View Post
    I haven't done the math but the 280s shoulder is .052" farther out than 06 which I'd sure think accounts for more volume than AIing ether chamber would.

    At any rate it alters the pressure curve, pressure will come up faster (before bullet moves or case forms) and would act a lot like putting an extreme crimp on a load that was developed with no crimp. The faster initial pressure comes up the better burn you will get so the sooner peak pressure will be made and peak pressure is also apt to be much higher due to fastermore efficient burn.
    I looked up the case capacites of the 280, 30-06, and the 280AI.

    I think the bullet would release 1st, and the continuing pressure would expand the shoulder. I can't see any back pressure like with a crimp. In any case, the pressure was too high in those 2 loads for fireforming. At least, a lighter load corrected the problem.

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    I was just thinking. Ya I know that is dangerous. But what if the case was a tad short for the custom chamber and upon firing the was pushed forward some as the primer fired. The vented gas would keep the case forward during firing causing higher pressure and then add the effect of the case mouth pushed into the rifle bore which also increased pressure. That could also cause the popped primer and the flattened primers.

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    Quote Originally Posted by redale View Post
    I was just thinking. Ya I know that is dangerous. But what if the case was a tad short for the custom chamber and upon firing the was pushed forward some as the primer fired. The vented gas would keep the case forward during firing causing higher pressure and then add the effect of the case mouth pushed into the rifle bore which also increased pressure. That could also cause the popped primer and the flattened primers.
    First of all, I'm not the one with the Custom tight-neck chamber. That was BB. My chamber is SAMMI spec.

    HOWEVER, when you size a 30-06 case in a 280 die, there is left on the neck a tiny shoulder that serves for controlling the headspace.

    It is possible then, because of the small surface of this shoulder, that the case was pushed forward by chambering or the firing pin blow enough to create some headspace. The primer would then have protruded, initially, and then later when the case head is forced into the bolt face the primer would flatten. BUT this flattening was extreme, apparently, a sign of pressure, and it doesn't explain why subsequent loads, howbeit lighter charged didn't act in the same way.

    Those 2 rounds, for initial testing, were of a load I had used just previously, in 280 cases and I was already set up for them, so I just loaded a couple in the resized 06 cases. They were just too HOT for the purpose, no matter they were NOT too hot for regular 280 loads in 280 brass.

    I'm looking for a reason these 2 rounds showed pressure signs. Or, anything that would shed some light. Because I want to stay outta trouble in the future, and I'm curious.

    Thanks for your input.
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    Quote Originally Posted by Smitty of the North View Post

    I think the bullet would release 1st, and the continuing pressure would expand the shoulder. I can't see any back pressure like with a crimp. In any case, the pressure was too high in those 2 loads for fireforming. At least, a lighter load corrected the problem.

    Smitty of the North
    Well boss by that logic bullet seating depth (seating deep vs shallow) dosnt matter to case capacity . . . But we know it does, right? So why wouldn't your unformed sholder act the very same way?
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    Quote Originally Posted by ADfields View Post
    Well boss by that logic bullet seating depth (seating deep vs shallow) dosnt matter to case capacity . . . But we know it does, right? So why wouldn't your unformed sholder act the very same way?
    Why would it be the same logic?

    I used the SAME seating depth that I had used for the previous loads using the 280 cases, and since the case expands to fit the chamber, I'm suggesting that case capacity equals the capacity that the "chamber" allows. Which is 280, not 30-06.

    Therefore, it is not a function of the 30-06 case capacity, versus 280 case capacity.

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    Quote Originally Posted by Smitty of the North View Post
    Why would it be the same logic?

    I used the SAME seating depth that I had used for the previous loads using the 280 cases, and since the case expands to fit the chamber, I'm suggesting that case capacity equals the capacity that the "chamber" allows. Which is 280, not 30-06.

    Therefore, it is not a function of the 30-06 case capacity, versus 280 case capacity.

    Smitty of the North
    Same logic because it takes a cretin amount of pressure to start the bullet moving in the very same way it does to fire form the case. Yes it eventually gets out to 280 capacity but starting out at 30-06 capacity is changing the clock on the pressure/time curve in the exact same way as altering seating depth alters the pressure time curve.

    Seating depth, bullet weight, crimp, and bullet bearing surface all effect pressure because they all affect the case volume and/or total chamber and bore volume. A bullet moving more slowly for whatever reason means there is less space for gas to fill at a given time in the curve so there will be greater pressure at that same time in the curve.

    Itís the very same thing with your necked 30-06 case, pressure becomes higher sooner in the curve because it has less room until there is enough pressure to shove the neck out. It takes a lot of pressure to shove that neck out, like 20Kpsi so from zero to 20Kpsi there is reduced case volume. This is giving less space for the gas to fill.

    Less space for the same quaintly of gas means higher pressure sooner in the curve . . .
    Higher pressure means more heat sooner . . .
    More heat sooner means more efficient and faster burnning of powder charge . . .
    More efficient and faster burn means even more gas in the limited space . . .
    This means higher peak pressure can be reached befor bullet exit vints off pressure . . .
    And Smitty sees him some flat primers.
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    Quote Originally Posted by ADfields View Post
    Same logic because it takes a cretin amount of pressure to start the bullet moving in the very same way it does to fire form the case. Yes it eventually gets out to 280 capacity but starting out at 30-06 capacity is changing the clock on the pressure/time curve in the exact same way as altering seating depth alters the pressure time curve.

    Seating depth, bullet weight, crimp, and bullet bearing surface all effect pressure because they all affect the case volume and/or total chamber and bore volume. A bullet moving more slowly for whatever reason means there is less space for gas to fill at a given time in the curve so there will be greater pressure at that same time in the curve.

    Itís the very same thing with your necked 30-06 case, pressure becomes higher sooner in the curve because it has less room until there is enough pressure to shove the neck out. It takes a lot of pressure to shove that neck out, like 20Kpsi so from zero to 20Kpsi there is reduced case volume. This is giving less space for the gas to fill.

    Less space for the same quaintly of gas means higher pressure sooner in the curve . . .
    Higher pressure means more heat sooner . . .
    More heat sooner means more efficient and faster burnning of powder charge . . .
    More efficient and faster burn means even more gas in the limited space . . .
    This means higher peak pressure can be reached befor bullet exit vints off pressure . . .
    And Smitty sees him some flat primers.
    I can go with "pressure/time curve" as the cause of higher pressures, indicated by the flattened primers.

    There just doesn't seem to be another plausible explanation. I weighed those TWO charges, and I don't think that I was off or had the wrong powder charge.

    However, I don't see that as the Same Thing, as having less case capacity, since the case is elastic and the Expansion Ratio is the same with the chamber, no matter which case, the case.

    As I've said before in different ways, Fireforming must have a greater effect on pressure, somehow, some way, than I imagined. I had figgered that the fireforming should be done with a full charge, so the case would be fully formed.

    I have another 50, 06 cases to do, and I'll make sure I use a lighter fireforming charge from the get-go.

    Thanks Andy.
    Smitty of the North
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