Cooper 280AI loads hot

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canoetrpr

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I'm loading for my new Cooper. Using 150g TTSX with IMR7828SCC.

Now Barnes does not have load data for the Ackley so I used Noslers. Didn't quite realize that it seems pressures for the TTSX tend to be higher and even plain ol 280 min, max numbers in Barnes book are quite a bit lower than for the same bullet weight Nosler.

I started at some 58g and worked up to 63g which is the max in the Nosler book. One good group at 59 then 61 was good one day and another time 61.5 was the best. I went as high as 62.5 and noticed that opening the bolt was a bit hard there. Primers were flat for the first two in the 62.5 string and then the third blew the primer right off so I stopped there.

A friend at the range pointed out that my cases all had extractor marks.

The cases for 61 and 61.5 still do have light extractor marks but there is no problem opening the bolt. The primers are flat but I wouldn't say they look bad - not loose certainly on these rounds.

I am using fire formed Remington brass from factory 280 Remington.

My question is that I think that my most accurate load is somewhere between 61 and 61.5. How much should I be concerned if my still have light extractor marks there as long as the primer is just nice and flat but not loose?

I have not chronographed the load; plan to do it next time. My wild guess is that it is ~3000 fps or above; maybe 3100 fps. It is a hot load but my novice instinct says it is just fine at 61-61.5.

Appreciate any suggestions from others? Anyone else using TTSX in a Cooper 280AI who could share their loads?
 
Primers are not a good indication of pressure, extractor marks are. You very likely are in excess of 70000psi and I bet you are running more velocity than you think, but you will never know without a chronograph. I think a chrono is necessary if you pushing max loads. Warmer weather could push pressures into dangerous territory. I do not load light in any caliber but stiff bolt lift and extractor marks are a definite sign you are way to hot. In my experience extractor marks show up first and then stiff bolt lift. Any time I see extractor marks, velocity is usually well beyond max loads.
 
My Coopers in 280AI had tighter chambers than normal, and I could not use the maximum loads in the Nosler manual, without pressure signs. I would back off the loads until the extractor marks disappear.
 
I concur that Nosler lists 59.0 gr. - 63.0 gr. for their 150 grain BT's, Partitions & CT BST's with IMR7828.

Hodgdon's data for IMR7828SSC and the 150 gr. Barnes TSX lists 54.0 - 57.5 gr. (59,200 psi)
showing their max. velocity as 2863 fps.
Even with IMR4350, (54.5) the max velocity listing given for the 150 TSX is 2893 fps at 60,100 psi !

Sounds like you need to back down a bit from Nosler's listings with the Barnes TSX's ... or switch to Nosler bullets if you're chasing velocity.
Either way, extractor marks & flattened primers are not a good thing !
 
If you have good accuracy at 59gr then why not stop right there?
Another indicator of high pressure is when after three or four shots your primer pocket becomes loose.
Out of good brand of brass you should get at least ten safe reloads.
 
I see you are currently using Remington fire-formed brass.

I've found Remington cases (in 25-06) tend to average as much as 17 grains heavier (thus less case capacity) than say Winchester cases,
thus taking a little less powder to generate the same pressure.

Many have found for example they can get more of a certain powder into a Winchester case than they can Remington.
Jack O'Connor reported this with H-4831 and 270 Remington/Winchester cases back in the 60's.

Lapua & I suspect, Norma/Nosler will be on the heavy side for comparative case weights too.

I like your plan to back off the Nosler data and start with Hodgdon's specifically for the TSX.
And don't forget, a max. load at 0C this time of year may well lock up your bolt at +30C in the summer.

What primers are you using ???
 
shorttrac said:
Primers are not a good indication of pressure, extractor marks are. You very likely are in excess of 70000psi and I bet you are running more velocity than you think, but you will never know without a chronograph. I think a chrono is necessary if you pushing max loads. Warmer weather could push pressures into dangerous territory. I do not load light in any caliber but stiff bolt lift and extractor marks are a definite sign you are way to hot. In my experience extractor marks show up first and then stiff bolt lift. Any time I see extractor marks, velocity is usually well beyond max loads.
Click to expand...

Aside from pressure-testing equipment, a chronograph is by far the most accurate indicator of high pressure - all the rest are subjective and deceptive. If you had one, you would have seen very high MV's 3-4 grs below the top loads you tried.
 
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