270 high pressure question

[fastchicken]

I loaded up some 130gr Hornady interlocks for my .270 on Sat. with Fed brass, CCI 200 primers and 56, 57 , 58, &58.5 gr of H4831sc seated to 3.180. No high pressure signs and the 58 and 58.5 shot good so I loaded up another batch, 58.5, 59, 59.5 H4831sc seated to 3.180, and one batch of 58.5 seated to 3.210.
   No high pressure signs except for the 3.210 58.5gr load, flattened primer and an ejector mark on the primer. Can .03in seating depth variation really have more of an effect on pressure that 1 gr of powder? I'm new to all of this and still at the bottom of an increasingly large learning curve.
Another issue that may or may not have had any effect is that all the 3.180 loads had to be crimped because as soon as the bullet was seated past the beginning of the cannelure [3.20], neck tension relaxed and the bullet could be moved within the cannelure with hand pressure. The 3.210 load seated at the beginning of the cannelure but not into it and neck tension was good. Any thoughts? Thanks

[charles p]

What your should be searching for is the most accurate load.  A few extra fps will not matter at all, even out to ranges that most of us can't accurately estimate.

[LONGTOM]

With out looking into my manuals to see how close to max he is I would say he is doing what most would do in search of a load.
The only thing is after finding a pretty good load (58, 58.5) I might work a little closer to that each way to fine tune it. 1/4gr, 1/10gr.
As long as the loads are under max enough to not have to worry about differences in chambers I think you are fine.

Now as far as changing the seating depth on the higher load may not have been a good idea.
If you wanted to try a different length you should have dropped back a couple of grains to allow for the increased pressure that you might encounter by having the bullet closer to the lands.
In fact, if you change anything on a load, bullet type or brand, primer, brass, or length you should drop back to a starting load and work up again.

That is the way I do it but is not the only way by no means, just the way I do it.



LONGTOM  

[Autorim]

How are you determining seating depth? This can be a crucial issue on near max loads. I determine maximum cartridge OAL on all rifles individually then seat accordingly. Max OAL as determined by throating may not feed from your magazine. Maximum OAL in my Sierra manual for the .270 Win is 3.340 inches so you are well under max and may benefit from longer seating.

My reloads with the 150 Nosler Partition in one of my .270's measure 3.358 inches OAL. They feed from the magazine and do not contact the rifling leade. Also very accurate with RL22 powder.

[fastchicken]

 My interest with this problem has nothing to do with accuracy, only with pressure in a lighter charge load with longer OAL compared to the same charge with a shorter OAL [seated deeper, decreased case capacity]
   Max load in Lyman is 58gr, [that is with Sierra]  w/ OAL @ 3.250, max in Hornady is 62 gr w/OAL @ 3.210 and max in Hodgdon [w/ a Hornady bullet] is 60 gr w/OAL @ 3.180, so I think I'm within the max with all 3 at 58.5 gr. I figured pressure would increase with DECREASED case capacity, IE seated deeper [ OAL @3.180] rather than seated @ 3.210. I did not think pressure would increase by increasing seating depth. The 3.210 load shot worse that the 3.180 so it really isn't a load I'm going to be working with, but the high pressure signs, by only decreasing seating depth, confused me, but my coffee maker confuses me as well . I just got it, seated shallower= closer to lands= higher pressure DUH! But the load I seated shallower was not the high end load, it was the lower the my last 3, 59.5 was the highest @ 3.180, and that one had no signs of high pressure.

[Smokin Joe]

My interest with this problem has nothing to do with accuracy, only with pressure in a lighter charge load with longer OAL compared to the same charge with a shorter OAL [seated deeper, decreased case capacity]

The difference is caused by the bullet having a better "run" at the rifling and thereby reducing pressure. Check a Hornady manual; they explain it there.

[bobg]

   fastchicken. I am shooting the same brass,powder and primers as you in my Vanguard 270 Win. I settled on 58.5 grains of H4831. My old Lyman lists a top load as 60 grains and an aol of .340. That is the exact aol i needed to feed through the magazine and to stay just off the lands. I have never seen any high pressure signs so i can't answer that one.
            bobg

[Catfish]

Your missing something. It sounds like you have seated the bullets into the rifleings, but with the oal you gave you should be way short of that. Are you sure of the powder charge?

[shot1]

Yes you get a quicker pressure spike with the bullet seated closer to the lands as well as seating the bullet deep in the case to decrease case capacity will increase the actual pressure. When the bullet is closer to the lands it hits the lands quicker than a bullet seated deeper. When the bullet hits the lands it is slowed down for a nanno-second and allows the pressure to spike quicker than a bullet that has to travel a little farther to the lands that allows the pressure to rise at a different rate and the pressure will spike farther down the barrel and put less back thrust on the case. That is the reason that Weatherby Magnum rifles have looooog throats. It allows more velocity to be gained with less pressure spike for the bullet to jump a ways before it hits the lands.

My standard load for the 270 Win in many rifles with cup and core 130 gr bullets has been 60 grs H-4831 with the bullet seated 10 thousands off the lands. This load has always shot very accurately and will run 3000 to 3200 fps depending on barrel length 22 to 24". A 130 Sierra or Nosler ballistic tip will really do a number on a deer.