Couple of reloading questions

[CTK]

I now would describe myself as functionally proficient at reloading. Have been doing it intermittently for 2 or 3 years. In this period, I have owned 3 different 280 Ackley rifles. The first one was chambered for the old 40 degree fireform wildcat. The other two have been supposedly chambered for the Sammi/ Nosler 280 Ack. Imp. These rifles have given me fits reloading during my general reloading learning curve. I would appreciate it if someone could answer a couple of my likely stupid questions. For some reason I still feel like I am missing something in my understanding of reloading this cartridge. My journey with reloading this cartridge has been somewhat ugly. Had had weird chamber/headspace issues in the first rifle. Second rifle showed very early pressure signs (likely my reloading mistakes). I have created screwed up shoulders on some brass. Last rifle from a revered gunsmith/maker was chambered too short to fit Nosler brass. Sent back and he corrected it. Now trying to figure out reloading for this chamber. My first loads for this rifle were done with virgin Nosler brass. They worked just fine. Now trying to figure out sizing the brass for the chamber. Have been using a barrel cutout provided by the gunsmith as a comparator. It is designed, in part, as a seating depth gauge and seats the cartridge to the top of the shoulder. I can only assume that it mimics the shoulder part of the rifle chamber. If it does not exactly, it at least is a comparator that hits at the top of the shoulder. Sorry for the long backstory but this chambering is testing my understanding of reloading principals. I think the fact that there is still confusion out there on the chamber 280 AI dimensions has not helped.

At what length should I trim the necks on the Sammi 280 ack imp? How much should they be trimmed? (min). Should virgin Nosler brass be used as a minimum or max guide or not at all?

Virgin Nosler brass is about 2 thousands longer at the shoulder than my fired brass. Virgin Nosler brass fits in my chamber. Why is my brass shrinking when do not have noticeable crush when closing the bolt? Where should I set the shoulder on my full length resized brass?

My loaded necks with virgin brass are measuring about .3095 to .310. I have .309 and .308 bushings. Which one should I use and why?

Thanks very much in advance!
Craig

 

[ireload2]

1. At what length should I trim the necks on the Sammi 280 ack imp?
Measure your chamber length and trim the FL sized brass .003 to .005 shorter than the chamber if you don't mind trimming fairly often.
The brass will get shorter when fired and longer when FL resized so check the length after each sizing unless you trim them way short.


2.How much should they be trimmed? (min).
I like my cases longer because I shoot cast bullets and it keeps the soft bullets from being expanded into the gap ahead of the case. You can trim .010 shorter than the chamber for a rule of thumb. For some cast bullet rifles I trim the case to the same length as the chamber for the first shot. The fired cases come out of the chamber .004 to .007 shorter. Keep an eye on the length. If your die is way smaller than the chamber (more than .004) at the shoulder the case may stretch faster than normal. Each time you fire a FL sized case that is sized smaller in diameter it will stretch diametrally. When sized it will get longer. Here I am trying to give you a little guidance so you can judge for yourself. This is not an exact to the .001 requirement. Decide what makes sense and trim them all the same.

3. Should virgin Nosler brass be used as a minimum or max guide or not at all?
I would NOT use the brass as a guide because it may/will vary. I would use your FL die as the guide and FL size each new lot of brass to fit your rifle before loading it.

4. Virgin Nosler brass is about 2 thousands longer at the shoulder than my fired brass.
I would size it to be a light dragging fit when the stripped bolt is turned down with a pinkie. Check your FL sized brass diameter at the shoulder and compare it to fired brass. If the 2 diameters are different by more than .004 your cases may change lengths when fired and resized.

5. Virgin Nosler brass fits in my chamber.
Why is my brass shrinking when do not have noticeable crush when closing the bolt?
Your brass virgin and sized brass body diameter may be a good bit smaller than the chamber diameter. Check your fired case's diameters at the pressure ring and at the shoulder. Compare to FL sized cases. Check 8 or 10 because they may vary a little. When new and FL sized brass is fired in a larger chamber the case inflates like a balloon and then contracts. The contraction or spring back may make the case length and the length from head to datum line shorter. This spring back will depend on your die setting, hardness of the brass and the difference in the diameters of your die and your chamber. Even so it will not be the same for every case. There is often .002 difference in the head to shoulder lengths.

Where should I set the shoulder on my full length resized brass?
For a range rifle I set it at .000 and it takes a while to get it just right. You also have to use extra care when sizing the cases to make sure they are all exactly the same. If you are hunting they should be .001 to .002 shorter. You might prefer more space with a pump, lever or autoloader.

6.My loaded necks with virgin brass are measuring about .3095 to .310. I have .309 and .308 bushings. Which one should I use and why?
Check your bushings to see if they are what is marked. I would use a .308 bushing especially if you are running the rounds through a magazine.
You should learn your rifle well enough that you can answer this. You might consider getting a .307 bushing too.

Thanks very much in advance!
Craig

 

[CTK]

Thanks

Will digest and apply. Is a Sinclair chamber gauge good enough?

 

[JRS]

You really need to ascertain the actual chamber you have. There are two different dies for those chamberings. The original will be marked 280 Imp 40 Degrees, and the SAAMI/Nosler version will be marked 280 Ackley Imp. Headspace of the SAAMI cartridge is shorter.

 

[Sheldon N]

I load for a SAAMI 280AI.

I trim to the standard spec for the traditional 280 Remington, just using a cheap Lee cutter stud. Trim length is 2.5325. I rarely have to trim and brass stretching is minimal due to the 40 degree shoulder.

If you are getting shorter brass post firing with your chamber gauge, but bolt close is easy, I would guess that you've got some sort of contact point on the chamber gauge that isn't exactly on the shoulder when checking the Nosler brass. Might get a "cleaner" measurement when using a simple bushing like the Hornady tool offers. If you wanted to keep using your chamber gauge, I'd ignore the initial Nosler measurement and just measure fired brass vs sized brass.

I bump the shoulder about .001-.002 from a fired case, which also gives me a light bolt close. This method is how I set up my full length sizing die, combination of measurement and feel.

With regard to neck bushing choice, my personal preference is for a bushing that gives me .002 tension on the resulting sized brass. For me I found that was actually a bushing that was marked at .001 smaller than my average loaded round OD. Just measure the brass neck after sizing with the .308 and .309 bushings and see which one gets you closest to the .308 neck OD that would give you .002 tension from a .310 loaded round OD. You can tune neck tension from there, if you wanted to refine your load development with neck tension adjustments.

 

[ireload2]

I usually use a longer case to measure my chambers.
It looks like regular .280 Rem brass is longer than the SAMMI AI brass. If that is true you can use an over length .280 Rem case if you have one or expand a .270 neck. Then expand the case mouth into a funnel with a .50 cal BMG or other large caliber spitzer. Expand the case mouth about .020 to .030 oversize. Shove this case into the chamber with the bolt. if the bolt will not close pull the case out and trim it about .020 and try it again in your chamber.
Keep expanding checking and trimming your case until the bolt barely closes with the case mouth jammed against the end of the chamber. Double check this length with 3 or 4 more cases until you know exactly what your chamber length is. Write the number down and save it. This dim is your absolute longest possible case length.

Thanks

Will digest and apply. Is a Sinclair chamber gauge good enough?

 

[CTK]

You really need to ascertain the actual chamber you have. There are two different dies for those chamberings. The original will be marked 280 Imp 40 Degrees, and the SAAMI/Nosler version will be marked 280 Ackley Imp. Headspace of the SAAMI cartridge is shorter.

I know that this is a SAMMI/NOSLER chamber. Strangely it was initially cut shorter than the already shorter SAMMI chamber. Had to go back to gunsmith. Gunsmith cited a communication error with the maker of his custom headspace gauge. I think the gauge was built 14 thou shorter than the SAMMI chamber rather than the 40 degree Rem chamber. He fixed the error immediately.