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High pressure signs in a 270

charliehorse27

Silver $$ Contributor
Good afternoon,

I have a Tikka T3 chambered in 270 that I use primarily for hunting, and have endeavored to make it as accurate as possible. In this process, I have found a load that seems to perform the best in the gun: 50.5 grains of IMR 4350 paired with a Nosler Accubond 140 grain bullet and CCI large rifle #200 primers. Using this setup, I'm achieving average velocities of 2650 fps, which is about 75 fps slower than the Nosler manual indicates should be expected for this combination (2723).

I have been experimenting with bullet seating depth as it pertains to accuracy. Therein is where my issue lies. SAAMI specs for the 270 call for a max OAL of 3.340. Currently, my bullets are seated at 3.380 OAL to achieve .007 off the lands. The gun prefers this length, even though they don't fit in the magazine. However, I am getting high pressure signs, even though it is not touching the lands. Some primer flattening, and some, but not all of the brass is showing one-sided expansion just above the casing web. This is all brand-new brass.

The max powder charge for this load is 52.5 grains, so I am well below that. With the already lower-than-expected velocity, I would rather not lower it if I can help it. Do I need to seat the bullet deeper?

Thanks for your input!
 
Last edited:
If when you say "CCI standard rifle primers" you mean CCI400, that's your problem. Those primers are well known to have thin cups and would flatten even at min loads...

FWIW, bullets seated longer (unless they are jammed) usually give you LESS pressure.
 
They are the CCI #200 primers.

That was the impression I was under that pressures should be less, so I'm confused why the brass is expanding at the web section visibly, even though it's brand new and never weakened. I've never seen brass do this before.
 
There could be a number of potential problems that cause what you are seeing.
  1. 7 thousands off can be pretty close depending on how accurate you measure touch distance i.e. you could actually be jamming. Jamming = significantly higher pressure.

  2. Any possibility of a carbon ring in your chamber – that can cause pressure problem.

  3. Lube on your case can also be a problem.
For the first two, manually insert (with your fingers) a loaded round or better yet a dummy round into your chamber, push it in gently (so that it does not get stuck hard), and see if it will come out by gravity. If it gets stuck, you have one or two of the above problem. The round can be pushed out with a wood dowel.
 
Check the increase in length, measuring from the case head to the case shoulder datum. Compare new still untouched cases to fired cases, both before and after resizing with your current resize die setup.
 
I kind of sounds like the brass may be too short at the shoulder. It would certainly do what you're describing.
 
charliehorse27 said:
Good afternoon,

I have a Tikka T3 chambered in 270 that I use primarily for hunting, and have endeavored to make it as accurate as possible. In this process, I have found a load that seems to perform the best in the gun: 50.5 grains of IMR 4350 paired with a Nosler Accubond 140 grain bullet and CCI large rifle #200 primers. Using this setup, I'm achieving average velocities of 2650 fps, which is about 75 fps slower than the Nosler manual indicates should be expected for this combination (2723).

I have been experimenting with bullet seating depth as it pertains to accuracy. Therein is where my issue lies. SAAMI specs for the 270 call for a max OAL of 3.340. Currently, my bullets are seated at 3.380 OAL to achieve .007 off the lands. The gun prefers this length, even though they don't fit in the magazine. However, I am getting high pressure signs, even though it is not touching the lands. Some primer flattening, and some, but not all of the brass is showing one-sided expansion just above the casing web. This is all brand-new brass.

The max powder charge for this load is 52.5 grains, so I am well below that. With the already lower-than-expected velocity, I would rather not lower it if I can help it. Do I need to seat the bullet deeper?
Click to expand...

I'm guessing you have a 22" barrel? If so the Nosler load data is for a 24" Shilen, and losing 40 or so fps would be expected. Also consider that IMR powder is sensitive to temperature changes, and pressure changes based on the cartridge temperature at time of firing. That is not ideal for hunting. Both for hunting and target shooting, I prefer the Hodgdon powder over the IMR. Looking at the load data from Nosler I would choose the H4831SC powder for your 270 with a 140 grain.

Your unfired brass is going to be loose in the chamber both in diameter and length. I would not get too concerned with what you are seeing. When you reload these fired cases only bump the shoulder back 0.001", and I suspect they will not grow again on the second firing.
 
Are you getting any kind of an imprint on the head from the extractor recess on your bolt face? I consider that one of the more reliable signs of pressure. If it is just barely there, I don't get too worried. If it is quite obvious, then yes there is an issue.
 
charliehorse27 said:
Good afternoon,

I have a Tikka T3 chambered in 270 that I use primarily for hunting, and have endeavored to make it as accurate as possible. In this process, I have found a load that seems to perform the best in the gun: 50.5 grains of IMR 4350 paired with a Nosler Accubond 140 grain bullet and CCI large rifle #200 primers. Using this setup, I'm achieving average velocities of 2650 fps, which is about 75 fps slower than the Nosler manual indicates should be expected for this combination (2723).

I have been experimenting with bullet seating depth as it pertains to accuracy. Therein is where my issue lies. SAAMI specs for the 270 call for a max OAL of 3.340. Currently, my bullets are seated at 3.380 OAL to achieve .007 off the lands. The gun prefers this length, even though they don't fit in the magazine. However, I am getting high pressure signs, even though it is not touching the lands. Some primer flattening, and some, but not all of the brass is showing one-sided expansion just above the casing web. This is all brand-new brass.

The max powder charge for this load is 52.5 grains, so I am well below that. With the already lower-than-expected velocity, I would rather not lower it if I can help it. Do I need to seat the bullet deeper?

Thanks for your input!
Click to expand...


SAAMI specs are a guideline, not "The Law"... If you don't need to use the magazine, then use whatever OAL you like. But remember, it is a hunting rifle, not a bench rest rifle.

"However, I am getting high pressure signs, even though it is not touching the lands. Some primer flattening, and some, but not all of the brass is showing one-sided expansion just above the casing web. This is all brand-new brass."

You are NOT having high pressure signs - flattening of primers is is not a sign of high pressure - it is a sign of a tiny bit of headspace, which can be normal on first time fired cases - see what they look on the second and third firing.

The swelling on one side of the web is also normal and happens with a majority of rifles... it is caused by the case lying at the bottom of the chamber, and when it is fired, the top side of the case wall expands up into the empty space above the case - it can be a little if the case has a max SAAMI body and the rifle has a minimum chamber... and visa-versa, if it is a min case body and a max chamber, the expansion can look like a lot - but it is nothing to fret about.

You are worrying about nothing :) :) :)
 
John Russell said:
SAAMI specs are a guideline, not "The Law"... If you don't need to use the magazine, then use whatever OAL you like. But remember, it is a hunting rifle, not a bench rest rifle.

"However, I am getting high pressure signs, even though it is not touching the lands. Some primer flattening, and some, but not all of the brass is showing one-sided expansion just above the casing web. This is all brand-new brass."

You are NOT having high pressure signs - flattening of primers is is not a sign of high pressure - it is a sign of a tiny bit of headspace, which can be normal on first time fired cases - see what they look on the second and third firing.

The swelling on one side of the web is also normal and happens with a majority of rifles... it is caused by the case lying at the bottom of the chamber, and when it is fired, the top side of the case wall expands up into the empty space above the case - it can be a little if the case has a max SAAMI body and the rifle has a minimum chamber... and visa-versa, if it is a min case body and a max chamber, the expansion can look like a lot - but it is nothing to fret about.

You are worrying about nothing :) :) :)
Click to expand...

+++1
-
 
The barrel is a 22 inch barrel so that could certainly be the reason for the lower than published velocity...

'Freak said:
Check the increase in length, measuring from the case head to the case shoulder datum. Compare new still untouched cases to fired cases, both before and after resizing with your current resize die setup.
Click to expand...

I measured the headspace on a group of 5 random new cases, never been fired or sized, and found the average length to be 2.046 in. It varied +/- .001 either way. Another random lot of once-fired cases from this gun had average length of 2.0466. After resizing them in the press, the average length was 2.0465. Again, the differences between the measurements within the groups were generally within .001 each way. This said, all of the fire-formed cases fit easily into the gun prior to resizing. Does this mean that the chamber actually has a headspace larger than any of the actual measurements, and over repeated firings, the brass will slowly grow to fit it? I've measured older, used several times brass, and usually get fire-formed measurements between 2.047-2.049.
 
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