280 AI and IMR 4831

[sgt_zim]

did a pair of ladders today for my 280 AI

IMR 4831 for A Frame 160 and Oryx 156

Didn't find a decent node for Oryx, best one was around 2830 fps. I needed a node at 3K fps for that to be workable - BC on those is only .33

I did find a couple nodes for the A Frames, best one was from 57.9 gr to 58.3 gr, 2964 on the bottom and 2990 at the top. That will get me right to 600 yards with 1500 ft lbs and just north of 2K fps. Top load was 58.5 gr IMR 4831 for both. I probably could have gone another whole grain, no flattened primers or sticky extractions.

Will work up loads for next weekend for 175 gr Partition, Grand Slam, and Game King. Looking for something in the 2700 to 2750 range. Probably should have gotten some 175 gr A Frames, but figured at those lower velocities, the softer jackets of those 3 should work.

I had done some workups for those 2 bullets with Ramshot Magnum last Spring, but they were disappointing to say the least.

 

[Albert GRANT]

In 6.5mm I get better results with 4831 using lighter mono bullets pushed as hard as the particular gun will take. Doesn't seem to be as effective with the heavier 6.5 bullets. Not sure if that would hold true for the .280....

 

[112Savage]

I was shooting RL23 with 160’s and RL26 with 175’s today. I absolutely love my 280AI

the speeds these two powders give are scandalous and accuracy is amazing of course

 

[HuntingGold]

I've never tried 23 or 26. Might have to look into that.

 

[sgt_zim]

Curious what brass you guys are using.

I have Peterson, measured case H20 once-fired for a 5 brass average is 72.2. But sitting here looking at Nosler's data, they're showing 64.9 gr of H2O. Hard for me to believe there is THAT much difference between Peterson and Nosler. Peterson's unfired brass data for their last 3 or 4 lots runs from 70.5 to 70.9, so my 72.2 average on once-fired seems to be accurate

If any of you are using either GRT or QL, how close to 65K PSI do you get? Looking at Hodgdon's load data, they seem to stop at 61K PSI for their max loads, and they're getting different numbers on MV using same powders as Nosler, and also using Nosler brass and 175 gr partition.

Sure seems like my max safe loads are going to be a grain or 3 higher than what Nosler and Hodgdon are publishing.

 

[shootist~]

I think Nosler measures the remaining H2O volume with the bullet seated. I had the same confusion with their 9.3x62 measurement.

 

[sgt_zim]

I think Nosler measures the remaining H2O volume with the bullet seated. I had the same confusion with their 9.3x62 measurement.

Is that the standard? I had thought you were supposed to measure the volume of an empty, once-fired case.

 

[sgt_zim]

All right, I think I have it figured out. Peterson's brass is thicker. If I show 74.0 gr of water capacity and a 175 gr parition, GRT shows an effective case volume of 64.94, and the brass is 89% full with 54 gr of IMR4831, for example.

What doesn't line up at all are the MV and pressure with GRT vs Nosler and GRT vs Hodgdon.

I know there's variation from lot to lot with powders, but that seems like a bigger difference than could be accounted by lot variation.

 

[Albert GRANT]

Possible bad batch of powder? Is it new or old?

 

[112Savage]

I use nosler brass. I get 73.7gr H2O capacity on an unsized case that has more than 3 firings

175ABLR 59.5gr RL26 2920fps
160 BT/AB 57.5gr RL23 3032fps
24” carbon6 barrel

im going to back off both of these 0.5 gr due to sticky extraction on the older brass.

 

[shootist~]

Is that the standard? I had thought you were supposed to measure the volume of an empty, once-fired case.

The light turned on when I noticed Nosler has different H2O volumes for every change in bullet weights.

 

[sgt_zim]

Possible bad batch of powder? Is it new or old?

Powder is new, less than 2 years old.

I'm not concerned about the powder, only what GRT is showing relative to what I can infer from Nosler's and Hodgdon's load data.

Hodgdon is showing 55 gr of IMR4831 under a NP 175 as generating 61K PSI, but that's using a Nosler case, presumed water mass of 74 gr (that shows 64.9 gr of usable space under the bullet in GRT, which tracks with what Nosler shows).

GRT is showing that same load at 49K PSI

Pretty sure the issue is with GRT.

With the 160 gr A Frames, I started at 55.7 gr IMR 4831 and progressed up in .2 gr increments to 58.5, COAL of 3.33 (which I think is too long by a little). GRT says I should have been around 2825 at the top end, but my magnetospeed showed me right at 3K fps on the highest load. No signs of pressure on the brass or anything.

I'm not too concerned about over-pressuring on the 175s, will take the same baby steps to progress up, just seems odd to me the disparities I'm seeing.

One thing for certain with 160 gr SAF....my rifle seems to like pushing them pretty hard. Both of those 4 shot clusters are over 2900 fps, one almost 3K fps.

 

[Albert GRANT]

Hard to say what pressures actually are for your combination of components and rifle, but if you aren't seeing pressure signs, you should be fine. My 6.5 load is 3gr over max for what I'm using and showing zero pressure. I stopped there because I didn't need to push it any harder, but guessing I could have gone a bit more. It sounds right on that you are getting your best groups pushing it hard with 4831, it's exactly what I found with the 6.5. I take published data with a grain of salt and proceed with an abundance of caution when reloading. When different published sources give you a 5-6+ grain spread on max for identical components, it's hard to put a lot of faith in it.

 

[112Savage]

My suggestion is to use the nosler manual. It has lined up the most with my personal experiences.

 

[Nevada Mike]

Thanks for posting this data - I am currently awaiting delivery of my M70 in 280 AI from the stocker. I have Nosler brass and plenty of IMR 4831 and N560.

Anybody using N560 in their 280 AI loads?

 

[sgt_zim]

My suggestion is to use the nosler manual. It has lined up the most with my personal experiences.

That's the plan for the Partitions, but I also have 175 gr Grand Slams and Game Kings. I'll use partition data for those, but like with the Oryx and A Frames, I'll do 0.2 gr increment ladders and see where I start getting pressure signs, if I even get any. I'll start at 52.7 and go to 55.5 - that's only .5 higher than Hodgdon's data for the same bullet, powder, and brass.

 

[Ray B]

A fellow Hunter Ed instructor got a 280AI built about 10 years ago and he is ecstatic about it. I think he uses WW brass, 160 gr Partitions and IMR4831 powder- uncertain of primer. I don't think he has chronographed it but he has killed deer with it at measured 400+ yards. I forget the 'smiths name but he is in Pendleton, OR.

 

[sgt_zim]

A fellow Hunter Ed instructor got a 280AI built about 10 years ago and he is ecstatic about it. I think he uses WW brass, 160 gr Partitions and IMR4831 powder- uncertain of primer. I don't think he has chronographed it but he has killed deer with it at measured 400+ yards. I forget the 'smiths name but he is in Pendleton, OR.

The one real challenge with it is there is still very little published data on load development for it. The only 2 major publishers are Hornady and Nosler - well, Sierra does as well, but their load data seems overly cautious, and scant advantage over 280 Rem. Everybody has published loads to 280 Rem.

I wouldn't recommend a 280 AI for a novice hand loader, but with experience, patience, and an abundance of caution, it's certainly possible to develop loads that compare to 7mm RM on equal footing. Looking at Hornady and particularly Nosler load data, there is HUGE overlap in performance between the AI and the 7mm RM. Casual observation - no difference. Astute observation, the larger powder loads are the only tell. But it shouldn't be lost on anyone that for a 175 gr bullet, velocities range from a little over 2500 fps for both on the low end, to 2900+ fps on the high end.

 

[HuntingGold]

I just gave my 280 AI to my son in law. He is over the moon excited. In fact, we will be shooting it again just before he takes it home across the country.
To reward myself for the generosity, I'm going to build myself another one.

 

[Ray B]

I'm going to build myself another one.

From S Central Oregon, too bad CP Donnelly isn't still around to make the barrel.