280 AI Reloading Input

[slas]

After a hiatus I started reloading for my Cooper 280 AI again that I picked up quite a while back. Since it had been quite a while I basically wanted to start from scratch using better techniques than previously. One being to remove bolt innards, firing pin, ejector, etc in order to get an accurate shoulder bump size for a clean(loose) bolt close. After a couple days worth of work I have some questions and I'm sure some of you can help enlighten me.

One thing I have found is that it seems this Cooper is a bit more picky than my other rifles. For example, I've made several of the modified cases to use with the Hornady OAL gauge. After making this one with resized once fired brass I tested and the bolt closed accordingly. After I worked a bullet in to stretch the neck open I found the bolt wouldn't close on it. After repeating again, what I found was I had to keep the neck tight to the point where the bullet would just slide in/out with a little drag. Then I sanded the inside of the neck to keep the outside size consistent. After that I was finally able to cleanly chamber the round and use the gauge. The chamber seems very tight.

I was using the Hornady head space gauge marked C 375 to measure shoulder bump and Redding 280 AI FL die set to set should back and resize. All I currently have to work with is once or twice fired brass, which is really of no concern but, it seems after buying several batches of previously fired brass about half have been trimmed to 2.515 and the other half have been trimmed to 2.525. I may be guilty of the 2.515 but can't remember. I previously measured the actual length of my chamber and got 2.565, so I'm guessing I shouldn't be worried about using 2.525.
FIRST QUESTION: What affect will this length difference have on my loads as far as accuracy/consistency/speed/etc? I'm guessing I should separate the brass for testing and load development?

After getting the proper neck bump size for my chamber I ended up with 2.131 using the 375 head space gauge to measure. This was determined by taking a once fired brass and measuring the initial shoulder at 2.134. I know they say bump back .002 but after bumping to 2.132 and working with the gutted bolt, I was still not getting the clean bolt close, but after bumping down to 2.131 the bolt close cleanly without being tight or excessively loose. Length was 2.525. I did test one sized one down to 2.130 and bolt close was almost too easy.
SECOND QUESTION: Is using the Hornady 375 gauge and the method of gutting the bolt and using it to test sizing used by others here? I know there are different methods but wanted to use this one ever since watching a video on it and it appears to do exactly what you want, which is to get the cartridge shoulder sized to your chamber where the bolt just falls almost closed. I've seen this method also used for bullet seating, but I didn't use it for that.

One interesting thing to note is when trying to chamber a once fired cartridge with shoulder of 2.133 and length of 2.527 with the gutted bolt, it didn't want to close without a bit of force.
THIRD QUESTION: Is this expected behavior or could this be an indication of shooting loads that might have been a bit hot. There were a few times previously when using well under max loads I got a heavy bolt lift, that puzzled me since, again, on my other rifles the heavy bolt lift was expected. Maybe I had my bullets too far into the lands increasing pressure?

Again, it just seems this Cooper is much harder to develop loads for than my other rifles. I'm trying to get as specific (intimate) with it as possible and get it honed in for next hunting season since it's a beautiful rifle. I'm ready to load up some AccuBond 140's and some Berger VLD 168's. I was previously using Fed 215 primers only but found a bunch of Fed 210's so I'll be working with them also. I have a variety of powders on hand H4350, H4831sc, IMR4350, Retumbo, and lots of Varget. Please post any loads on the above bullets/powder combination if you have some. Always love seeing others loads.

Thanks to all on this site for you valuable input and information for those of us that are continually learning and forever chasing that rabbit down the reloading speed/accuracy hole...........

 

[cdherman]

-- lots of questions to answer here. I'll try to give my thoughts....

** You have once and twice fired brass, but you didn't make it too clear if that brass was fired in your cooper or not. If you have acquired brass fired in a different gun, you MUST full length resize and start over with your gun. Neck sizing or just touching the the shoulder back is not an option. If the brass was fired in your gun, then you can try and just back the shoulder down by .002". But here's another problem -- if you are using the expander ball with a FL die and the neck is work hardened and/or the ball/neck is not well lubed, you will "pull" the shoulder back out. This could be happening to you. I personally measure my brass thickness, use bushing dies, and then use a final Sinclair mandrel to make the inside diameters identical. Its all about neck tension. Or so I have read and believe. You are correct to measure the shoulder at .375, as that bushing is what Hornady says to use in the 280 AI. BUT, if the expander ball is pulling the shoulder "out" closer to the neck, you will NOT detect that with the case comparator. You are measuring at .375. Not right next to the neck. Hope this is all making sense.

** You have several lengths of brass. The max length listed in my Hornady manual (and they state they are using SAAMI) is 2.590". Trim to length is 2.530. Your measured length of 2.560" seems "short", but regardless, you are no where close to the real dangerous event -- when brass exceeds the neck length of the chamber and "crimps" itself onto a bullet. THAT is a recipe for very dangerous pressures. Over trimming the brass cheats you out of neck on your cartridge, reducing the case capacity in some instances, since you have to seat the bullet deeper, But with even 140gr bullets in a 280 AI, you will not have trouble getting enough bullet in the neck for adequate neck stability (old rule is seat same distance as the diameter of bullet, so .284, NOT counting the boat tail). So your neck lengths are NOT the issue, IMO. I WOULD sort by manufacturer, then trim them all to the same length. If some are at 2.515, then cut them all that long. Or sort. But yes, using cases of varying length will affect neck tension and that affects accuracy, though not usually pressure.

** You have the Stoney River aka Hornady Case length comparator. It requires a modified case, which can be made yourself, as you are doing. I would NOT have FL resized. Instead, take a casse fired once or twice in YOUR gun (some cases don't reach full "fired" base to shoulder length till fired twice) case and just drill and tap the head. You should NOT have to be messing so much with sandpaper etc to get the neck to where it allows the bullet to move. That all being said, you probably have a decent test case now. I don't think its the case of your issues. See my top remarks first.

Finally, I too am new to the 280 AI, but not to reloading. I just posted up a thread here about best powders. I had tried RL-26 and was not overwhelmed, though that was in breaking it in. After reading a lot and based on some suggestions and two reloading manuals, I am going to try H4831sc next. Hornady and Nosler say max load of 60gr behind a 150grain bullet. Hodgdon's own site is more conservative at 57 grains. The usual caveats apply, start at least 10% below those numbers and work up. Caveat emptor. This powder choice does not give the most speed -- its reputed to give good accuracy which is my goal.

 

[slas]

-- lots of questions to answer here. I'll try to give my thoughts....

** You have once and twice fired brass, but you didn't make it too clear if that brass was fired in your cooper or not. If you have acquired brass fired in a different gun, you MUST full length resize and start over with your gun. Neck sizing or just touching the the shoulder back is not an option. If the brass was fired in your gun, then you can try and just back the shoulder down by .002". But here's another problem -- if you are using the expander ball with a FL die and the neck is work hardened and/or the ball/neck is not well lubed, you will "pull" the shoulder back out. This could be happening to you. I personally measure my brass thickness, use bushing dies, and then use a final Sinclair mandrel to make the inside diameters identical. Its all about neck tension. Or so I have read and believe. You are correct to measure the shoulder at .375, as that bushing is what Hornady says to use in the 280 AI. BUT, if the expander ball is pulling the shoulder "out" closer to the neck, you will NOT detect that with the case comparator. You are measuring at .375. Not right next to the neck. Hope this is all making sense.

** You have several lengths of brass. The max length listed in my Hornady manual (and they state they are using SAAMI) is 2.590". Trim to length is 2.530. Your measured length of 2.560" seems "short", but regardless, you are no where close to the real dangerous event -- when brass exceeds the neck length of the chamber and "crimps" itself onto a bullet. THAT is a recipe for very dangerous pressures. Over trimming the brass cheats you out of neck on your cartridge, reducing the case capacity in some instances, since you have to seat the bullet deeper, But with even 140gr bullets in a 280 AI, you will not have trouble getting enough bullet in the neck for adequate neck stability (old rule is seat same distance as the diameter of bullet, so .284, NOT counting the boat tail). So your neck lengths are NOT the issue, IMO. I WOULD sort by manufacturer, then trim them all to the same length. If some are at 2.515, then cut them all that long. Or sort. But yes, using cases of varying length will affect neck tension and that affects accuracy, though not usually pressure.

** You have the Stoney River aka Hornady Case length comparator. It requires a modified case, which can be made yourself, as you are doing. I would NOT have FL resized. Instead, take a casse fired once or twice in YOUR gun (some cases don't reach full "fired" base to shoulder length till fired twice) case and just drill and tap the head. You should NOT have to be messing so much with sandpaper etc to get the neck to where it allows the bullet to move. That all being said, you probably have a decent test case now. I don't think its the case of your issues. See my top remarks first.

Finally, I too am new to the 280 AI, but not to reloading. I just posted up a thread here about best powders. I had tried RL-26 and was not overwhelmed, though that was in breaking it in. After reading a lot and based on some suggestions and two reloading manuals, I am going to try H4831sc next. Hornady and Nosler say max load of 60gr behind a 150grain bullet. Hodgdon's own site is more conservative at 57 grains. The usual caveats apply, start at least 10% below those numbers and work up. Caveat emptor. This powder choice does not give the most speed -- its reputed to give good accuracy which is my goal.

Thanks for all the welcome input. All the brass I'm testing with has been fired in my Cooper rifle and is all Nosler, which show trim to as 2.525. I've had some tell me trim to .010 below trim to, not sure why they've given that advice. I did find an old post I did asking about it here

280 AI trim to length

I noticed in my research than many post the trim to length for the 280 AI at 2.525, whereas the Sierra manual post it as 2.515. I then noticed in the manual diagram the case size showed 2.525 also. Then read else where you're supposed to trim .010 below max case length. I guess I never paid much...

www.longrangehunting.com

On the modified case. When I took one that had been fired in my rifle and tried to chamber the round, mind you with the bolt stripped, the bolt needed a bit of force to close. I guess what I was going for was a cartridge sized just so, where the bolt would close without pressure. In the video that seemed to be the whole point of stripping the bolt and working the cartridge in order to get that "just right" size where the bolt just falls over about half way requiring almost no pressure to close the rest of the way.

 

[DucNutz]

I've recently begun reloading for the 280 AI. Powder wise i'm getting good results from 4831SC with 160 accubonds. I've got a load of 168 bergers with R-23 ready to shoot.

All of the Trim to length I've seen is 2.525" with a max of 2.530. 2.590 sounds really long to me.

For measuring head space, I've been using the A330 comparator bushing as it measures closet to the neck/shoulder junction. (this may very well be the wrong tool to use, but it seems to be working for me.) My thoughts when using this bushing was that my understanding of the original design of the 280 AI was for it to head space off the neck/shoulder junction. Curious if you have any thoughts or opinions on this.

 

[slas]

I've recently begun reloading for the 280 AI. Powder wise i'm getting good results from 4831SC with 160 accubonds. I've got a load of 168 bergers with R-23 ready to shoot.

All of the Trim to length I've seen is 2.525" with a max of 2.530. 2.590 sounds really long to me.

For measuring head space, I've been using the A330 comparator bushing as it measures closet to the neck/shoulder junction. (this may very well be the wrong tool to use, but it seems to be working for me.) My thoughts when using this bushing was that my understanding of the original design of the 280 AI was for it to head space off the neck/shoulder junction. Curious if you have any thoughts or opinions on this.

Not sure I'm qualified to comment on the best comparator bushing to use. I just basically researched looking for what others used and worked for them. Maybe someone with more experience can provide additional info on them.