On the Hodgdon load data site they list a pressure rating of the Min. & Max. listed loads.
Does anyone know what pressure the FGMM 168 and 175 are loaded to ?
Does anyone know what pressure the FGMM 168 and 175 are loaded to ?
- Thread starter Baddog0302
- Start date
No one knows. I’m guessing it’s close to max.
Your question begs another question.
Do you own or have access to a pressure test barrel and the software?
If your answer is no, then the answer to your question is moot.
It's pretty easy to do the math and get a ballpark on pressure. The problem is that even using all the exact components, including the transducer, you could swap test barrels and get different pressure.
Change the lot of powder, that'll change your pressure.
Change the ambient temperature, that'll change your pressure.
Change brand of brass, guess what? Yeah, that'll change pressure.
Shoot the ammo out of different rifles, that gives different pressure.
You'd be much better off if you just forgot all about the question and focus on things that matter.
Do you own or have access to a pressure test barrel and the software?
If your answer is no, then the answer to your question is moot.
It's pretty easy to do the math and get a ballpark on pressure. The problem is that even using all the exact components, including the transducer, you could swap test barrels and get different pressure.
Change the lot of powder, that'll change your pressure.
Change the ambient temperature, that'll change your pressure.
Change brand of brass, guess what? Yeah, that'll change pressure.
Shoot the ammo out of different rifles, that gives different pressure.
You'd be much better off if you just forgot all about the question and focus on things that matter.
Based on what I see in terms of velocity (2650 for 168gr) I think its short of maximum. I'm assuming that you are in reference to 308 and that round(s) is suitable for the M1A. Based on Hodgdon data for 4064 and 168 SMK it would look to be around 52 kpsi for 43.9 gr and 2653 fps. 308 load data is 45 gr and 2743 fps and 58.9 psi.
Hodgdon data is for Winchester brass. Federal uses Federal brass. Because FC brass is thicker the pressure will be higher at the same velocity.
The last time I cracked open a 175gr FGMM round it had 40.7grs of what looked like AR-Comp and ran around 2700 FPS. That’s pretty close to max pressure especially for FC brass.
Unless they changed it it's been 4064 for a while, was reloder-15 before that.
There are two lines if 175grFGMM. The one with 4064 is GM762M2. The other one, GM308M2, uses different powder.
It's been well over a year since I heard that Federal is using AR-Comp now in place of 4064 in their 168 and 175 FGMM cartridges. And if I recall correctly, that report also mentioned that the military 20cal cases are using AR-Comp. But . . . I've never seen any confirmation of this and it hasn't mattered to me since I only shoot my reloads using AR-Comp. Out of a 24" Krieger barrel using 41.6 AR-Comp to push 175 SMK's, I was getting just a hair under 2700 fps and pressue per my QuickLoad is showing that at max pressure.
I chose 4064 because it was the powder used at one point and that was prior to the introduction of the 7.62 variant which is only the 175. In the 175 both are rated at 2600fps. The comment on the case is correct.
