Pressures 7mm vs 270

[Handwerk]

Can someone give me the difference in pressures created Between the 7mm rem mag and standard .270. Lets say they are both shooting .140 grain accubonds out of the same gun and barrel length.

[EsoxLucius]

The SAAMI MAP pressure specification for the 270 Winchester is 65,000 psi or 52,000 CUP and 61,000 psi for the 7mm Remington Magnum.

Hodgdon lists a 270 Win load using H1000 with a 140 grain bullet which yields 2979 fps and 50,800 CUP from a 24" test barrel and a 7mm RM load using H1000 with a 140 grain bullet which yields 3036fps and 50,600 CUP from a 24" test barrel.

Accurate Powder lists a 270 Win load using AA4350 with a 140 grain bullet which yields 2988 fps and 52,000 CUP from a 24" barrel and a 7mm rm load using AA4350 with a 140 grain bullet which yields 3028 fps and 54,900 psi from a 24" barrel.

Hence, one can conclude that the 270 Win will usually require more pressure to achieve less velocity than the 7mm Remington Magnum.  Kinda obvious given the respective standard operating pressures and difference in case capacity.

[Handwerk]

so does that mean the 7 mag is actually easier on the barrel than the .270? thanks for your help!

[Graybeard]

so does that mean the 7 mag is actually easier on the barrel than the .270? thanks for your help!

Nope. Cuz what he DIDN'T tell you was it takes about 10 grains more powder in the 7MM Mag to reach that extra 50 fps or so it averages more than the lowly .270 with same weight bullets. Wow boy do we ever need those magnums or what.

Another point to conside is that the same weight .277" bullet has an advantage in BC over the .284" bullet so that out past 200-250 yards the .270 will actually have more velocity and of course KE or paper energy for those of you so enamored with paper energy. :roll:

[Handwerk]

Well my 7 mag continues to be my favorite for over 20 years, fps in one thing but the 7 mags sure has more energy down the road and I really don't notice a lot of difference in recoil. What I was after was more of a question of barrel life under the same conditons between the 2.

[EsoxLucius]

Five to seven grains, not ten grains.  But I also believe the standard cartridges aren't improved upon by much by the magnums.  There are trade offs which many people seem to accept when choosing the magnums.

[Ramrod]

so does that mean the 7 mag is actually easier on the barrel than the .270? thanks for your help!

Chamber pressure has nothing to do with it. I'll try to explain what Graybeard was alluding to about the powder charge. Trying to force more powder to burn through the same or similar size hole is akin to holding a hotter blowtorch for a longer perion of time to a given piece of steel. You can bet it will do more damage than one with less flame, applied for less time.