280 AI Reloading Input Needed

slas

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I've posted this in one other place but wanted to add it here for additional input. 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 (from my Cooper) 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 fired brass from my rifle, which is really of no concern but, it seems after buying several batches of previously fired brass about half have has 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...........
 

Jcann

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First you might want to try Cerrosafe in your chamber to get a more accurate measurement of your chamber. You can check it out on YouTube. It's not hard to do and will give you a baseline to begin with. Without a reamer print it's impossible to accurately know your chamber dimensions.

As far as gutting your bolt, I don't know how much not having your ejector in will effect your measurements. There is a constant forward pressure placed on the rim of the case with it in.
 

slas

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I tried this a while back and seemed to work. Poor man's way to check chamber measurement.
 

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swampratt

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Take a sharpie and color the entire case and bullet of the offending hard to chamber round.
Chamber it and remove it and look for wear spots in the marker.
This should tell you what is possibly going on.
I bump my shoulders back on my savage .308 .001" and have no issues with it.
I do have issues with my .243 and .223 bolt guns and Lapua cases..The necks are too thick. so thick in fact after firing a round I Can Not seat a bullet into the fired case with my fingers.

Too tight in the neck..Those cases get neck turned..Accuracy was horrible with the NON neck turned Lapua cases.. Like shot gun patterns.
You may need to neck turn the cases.
Get out the markers and see what you get.
 

Defcon Shooter

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Take a sharpie and color the entire case and bullet of the offending hard to chamber round.
Chamber it and remove it and look for wear spots in the marker.
This should tell you what is possibly going on.
I bump my shoulders back on my savage .308 .001" and have no issues with it.
I do have issues with my .243 and .223 bolt guns and Lapua cases..The necks are too thick. so thick in fact after firing a round I Can Not seat a bullet into the fired case with my fingers.

Too tight in the neck..Those cases get neck turned..Accuracy was horrible with the NON neck turned Lapua cases.. Like shot gun patterns.
You may need to neck turn the cases.
Get out the markers and see what you get.
I agree if you are moving brass around in the loading process you may need to use a neck turning/reaming tool
 

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