CUP

[Ldigio21]

Working up a load for my 7mm-08 AI. Hodgdons lists max CUP of 49,900 with H4350 , 48 gr, and a 140 gr bullet in a standard cartridge. In rifles like the 300 Win mag max CUP is 54,000. So when loading a fire formed 7mm-08 AI starting at 48 gr and working up is it safe in a modern bolt action to approach 54,000 CUP?
I have a 20" benchmark barrel and 48 gr H4350 Garmin chrono at 2806 fps. Going to work up from there in fire formed brass. I use a MAC so can't use Quickload.

 

[308win]

No. It doesn't matter if it's a standard 7-08 or an improved 7-08AI, the max pressure is 49,900CUP. The 300WM was certified at 54,000CUP does not apply to your cartridge.

With the basic information given, Quickload is showing you to be slightly over max pressure. Understand that Quickload does not use CUP in its method, but Piezo. It states that "CUP units cannot be converted into piezoelectric pressure units that are useful in Quickload data". Regardless, the Piezo Pmax is 60191psi and your load is generating 60935psi. In my opinion I would not go above 48gr H4350, but look for a powder charge at a lower capacity. I'd you are into Optimal Barrel Timing (I've found this to be very useful for initial load development) then you need to be working around 47.2gr and 2763fps. This drops your pressure to 57884psi. Again, this is all a guess using Quickload, but will get you fairly close.

I also shoot a 7-08AI and would caution you when looking for pressure. AI cartridges tend to hide pressure until you get WAY up there!!!

Good luck with your process, proceed with caution

 

[Ldigio21]

No. It doesn't matter if it's a standard 7-08 or an improved 7-08AI, the max pressure is 49,900CUP. The 300WM was certified at 54,000CUP does not apply to your cartridge.

With the basic information given, Quickload is showing you to be slightly over max pressure. Understand that Quickload does not use CUP in its method, but Piezo. It states that "CUP units cannot be converted into piezoelectric pressure units that are useful in Quickload data". Regardless, the Piezo Pmax is 60191psi and your load is generating 60935psi. In my opinion I would not go above 48gr H4350, but look for a powder charge at a lower capacity. I'd you are into Optimal Barrel Timing (I've found this to be very useful for initial load development) then you need to be working around 47.2gr and 2763fps. This drops your pressure to 57884psi. Again, this is all a guess using Quickload, but will get you fairly close.

I also shoot a 7-08AI and would caution you when looking for pressure. AI cartridges tend to hide pressure until you get WAY up there!!!

Good luck with your process, proceed with caution

Is the pressure you are talking about in the standard 7mm-08 or the ai? Hodgdons lists 48 gr in the 7-08. I would think 48 in the fire formed case should be less.

 

[Ldigio21]

Is the pressure you are talking about in the standard 7mm-08 or the ai? Hodgdons lists 48 gr in the 7-08. I would think 48 in the fire formed case should be less.

Thank you by the way

 

[308win]

Is the pressure you are talking about in the standard 7mm-08 or the ai? Hodgdons lists 48 gr in the 7-08. I would think 48 in the fire formed case should be less.

You use the same max pressure as the 7-08. Just because you fire form a case does not give it a higher max pressure. You are limited to 49,900CUP in the 7-08AI

 

[308win]

Is the pressure you are talking about in the standard 7mm-08 or the ai? Hodgdons lists 48 gr in the 7-08. I would think 48 in the fire formed case should be less.

With a 3gr increase in powder capacity in the AI case, yes the pressure difference in about 2000psi lower.

 

[Ldigio21]

You use the same max pressure as the 7-08. Just because you fire form a case does not give it a higher max pressure. You are limited to 49,900CUP in the 7-08AI

Will you build the same pressure with the same powder charge in a larger case volume? If so, why ai it. The 280ai takes more powder than the parent cartridge for equivalent bullet.

 

[308win]

See the post above. It's rained me out today (thank the lord) so I don't mind running some numbers for you, but will need more specific information? Bullet used, Cartridge Overall Length, case length, water capacity.

 

[Ldigio21]

You use the same max pressure as the 7-08. Just because you fire form a case does not give it a higher max pressure. You are limited to 49,900CUP in the 7-08AI

I get the max pressure being the same, that was my point. I started my load in the fire formed case at 48 gr. When i was fire forming i used the minimum load ( 42 gr 4831) and am burning up some old Hornady 154 to keep pressure low and not shoot the cream out of the barrel
in the ai: COL: 2.795"
140gr accubond bullet
fed 210M primer
Not exactly sure of the case capacity but 52.5 gr powder fills case to top of neck

 

[308win]

Standby

 

[308win]

Just a quick clarification (as I got confused when you were asking about a 300WM) when you were wanting pressures for a 7-08AI? I think this is what you were asking?

7-08 (20" barrel) w/140accubond and 48gr H4350 @ 2806fps = 64,303psi

7-08AI (20" barrel) w/140accubond and 48gr H4350 @ 2806fps = 61,524psi

A difference of 2,779psi

This is using Quickloads 55gr case capacity for a standard 7-08 and 58.3gr for 7-08AI. Both of these outcomes are over the listed Max pressure of 60,191psi.

Now with that behind us, let's see what YOUR load is doing with the information given? I'll use my Alpha brass case capacity of 56.62gr since you do not have that information.
7-0AI (20") w/140accubond and 48gr H4350 @ 2806fps = 62,707psi. Approximately 2,516psi over pressure. With that information I would back the charge down to 46.8gr @ 2733fps and 57,616psi. 2800fps with a 140gr bullet out of a 20" barrel is really leaning on it, I would be careful. Good luck

 

[Ldigio21]

Just a quick clarification (as I got confused when you were asking about a 300WM) when you were wanting pressures for a 7-08AI? I think this is what you were asking?

7-08 (20" barrel) w/140accubond and 48gr H4350 @ 2806fps = 64,303psi

7-08AI (20" barrel) w/140accubond and 48gr H4350 @ 2806fps = 61,524psi

A difference of 2,779psi

This is using Quickloads 55gr case capacity for a standard 7-08 and 58.3gr for 7-08AI. Both of these outcomes are over the listed Max pressure of 60,191psi.

Now with that behind us, let's see what YOUR load is doing with the information given? I'll use my Alpha brass case capacity of 56.62gr since you do not have that information.
7-0AI (20") w/140accubond and 48gr H4350 @ 2806fps = 62,707psi. Approximately 2,516psi over pressure. With that information I would back the charge down to 46.8gr @ 2733fps and 57,616psi. 2800fps with a 140gr bullet out of a 20" barrel is really leaning on it, I would be careful. Good luck

First of all, thank you for doing this. Hope the weather was very crappy so you didn't waste a day. Interesting that Hodgdons lists 48 gr in the standard 7mm-08 as the max load, they are usually conservative. I would think they actually measure the pressure.
I actually got 2806.2 fps with a standard deviation of 2.5 . Great vertical spread of 1/2" 1.2" horizontal which I think was me on a less than perfect rest.

 

[308win]

Take the information with a grain of salt, not saying it's the gospel....just what Quickload is spitting out. Have to watch those different lots of powder. I have some Staball6.5 that's got 2.5gr difference between lots. Had me scratching my head till I ran my loads again trying the the two out. Lots of other variables there too. Anyway, not sure if this is your first AI cartridge, but most people are trying to get that "100-150fps" more out of it? Don't think of it that way, think of it like you were in the beginning....lower pressure for a given load as to the parent case. As far as the weather, couldn't be better, been raining all day. We'll take every last drop here in Texas. Good day to be in the loading room

 

[Ldigio21]

I have 2 280 ai's . Downloaded the link someone posted on this site for the 280 ai data from quick loads. Thought it was conservative and not in the marginal area for RE26. Primers were falling out of the case when I opened the bolt. Chroned 3215 with a 160 gr TBT. Needless to say I pulled way back and now am at 3014 out of a 23" barrel.
Thanks again and love Texas