High velocity

zplinker

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Jul 1, 2021
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South Dakota
I had a 7UM, in Rem. Sendaro, factory gun, which just loved Swift Scirocco 150 gr. at 3542 fps. Going above that, it opened right up, as did another rig I loaded the same load for. Around 96 gr. of R-25 did the trick.
 

Baboltin

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Jul 25, 2017
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140
I had a 7UM, in Rem. Sendaro, factory gun, which just loved Swift Scirocco 150 gr. at 3542 fps. Going above that, it opened right up, as did another rig I loaded the same load for. Around 96 gr. of R-25 did the trick.
I feel as though this is the same situation with my rifle I was right on the cusp of velocity and once the barrel fully broke in and the brass formed it speed up and opened right up and so so I am going reload a few rounds -3 grains below what I was at and reload another few at -2 grains from what I was at and then go from there
 

johnnyk

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Dec 24, 2001
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The first thing that came to mind was your brass necks are getting thicker, causing excessive pressure. Hence the reason for 100fps velocity increase and accuracy gone to $4!+. The excess pressure has pushed your formerly golden load out of its node. "Not possible", you say, "with only two firings" but I think it depends on the brass.
I have experienced the above with my .270 Allen Magnum, using Norma .300 RUM brass. Initially, the virgin brass is run through the sizing die just enough to get it to fit the chamber where it can be fireformed w/COW method. I think I had about two firings on the Norma brass and I experienced what you described.
I had shot a couple/three rounds at a buddy's range and couldn't understand why I could barely connect on his 500yd gong. He and I were bouncing ideas around and he tried to put a .270 150gn Ballistic Tip bullet in one of my fired cases but it wouldn't begin to fit. All kinds of bells and whistle went off; .300 RUM necked down to .270, necks not turned, more than likely a tight chamber (Kirby built) or at best NO slop. After turning my brass necks down, my load has settled down and gone back to it's original accuracy.
Try a bullet first, then measure your neck thickness with ball micrometer.
 

Mikecr

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The first thing that came to mind was your brass necks are getting thicker, causing excessive pressure.
Necking down, if he did that, does thicken necks.
But for necks to thicken to problem with only additional reloading cycles takes extreme FL sizing, leading to a lot of trimming.
You really have to go out of your way to do that, as you're basically re-forming the cartridge with every cycle.
I know it works for some, but it just always seemed extreme to me. The brass would never reach a stable point in life.

In that situation, pressure won't go up due to lower neck clearance. ANY neck clearance is the same to bullet release, little or a lot.
But cases hold memory. When they're expanding a lot in a loose chamber, they want to go right where they have been. It takes far less energy for them to go where they've been, and that's less energy being absorbed. So the cases slam chamber walls (practically immovable object) sooner, causing ever higher peak pressures. This, regardless of further excess sizing.
And keep in mind that every bit of brass trimmed away means that much of the brass character is changing.
Thick body brass is moving upward, thick toward thin. This contributing further to case bodies slamming harder into chamber, as the bodies are getting thinner, while you're noticing necks getting thicker.
 

FEENIX

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Dec 20, 2008
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Great Falls, MT
7RM virgin brass has a way shorter headspace than fired brass. Meaning you use a lot of energy during the burn to form the brass. Usually something like (using a .420 headspace comparitor), virgin will be 2.107, and fired will be around 2.121".
Now, the 2nd firing, if you bumped shoulders back correctly, will be taking that wasted energy and putting it behind the bullet, instead of blowing out the case.
Also, if you now have 100+ rounds down the barrel, your barrel is breaking in, smoothing out, and speeding up.

Drop powder charge by about 1.5-2gr, and your velocity should come back down to the original speeds.
This is why you should have load developed with fire formed brass.
Changing seating may or may not affect MV. Depends on land relationship and load density. What does seating of .03 or .05 mean?
Going up in velocity does not decrease stability.

You just need to start over
^^^Yep!^^^
 

Baboltin

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Jul 25, 2017
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if you pull powder and chrono back up to just under that 3100 at the same seating , i bet you end up right where you wanna be

also 185 barnes ttx may be ready to clean it back to metal ??
I’m shooting 150 grain ttsx and I wish I could shoot 185 but I only have a 1:9 twist barrel
 

Seabeeken

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Apr 30, 2013
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West NC
Well I went ahead and seated the bullets from .30 to .50 to give them some more jump and it made things worse. The group at a 100 yards opened up and also velocity increased. Doesn’t make any sense to me but it’s clearly not the right answer or bandaid to get me by. I very well could have created a flinch since I haven’t shot much this year with the shortage of ammo and supplies.
Seating deeper increased speed by raising pressure and made it worse. Pressure equates to speed. Back off and do a ladder test to get back to your 3100 sweet spot and then see if the groups tighten back up again. Go back to your .030 jump.
As for copper, I shot thousands of Barnes bullets with minimal fouling in my barrels. Hammer bullets so far have no copper fouling at all. If your barrel is rough, the more fouling you'll get.
 

Baboltin

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I went ahead and put dry lube on the bullets when I seated them could this have any effect to my issue?

Also I took the expander ball out of my full length die, where as before I would have the full length die with the expander ball in it but changed my way of doing it by running the brass into the Rcbs full length die without the expander ball and then use a neck sizing die to get more consistent neck tension.

I didn’t think this would have a negative effect if it did and if anything I thought it would give me a more consistent neck tension resulting in better ES and make my groups better but maybe this has something to do with my issue?
 

Mikecr

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I went ahead and put dry lube on the bullets when I seated them could this have any effect to my issue?
No.
You should pick up a 'how to reload' kind of book (not a reloading manual).
The things you're doing and thinking so far amount to tail chasing.
 

Veteran

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Mar 10, 2021
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Michigan
All things being equal, seating the bullets deeper will just increase the velocity, = more pressure, more barrel time, and more velocity.

But as someone else already said, that may be 15 -20 fps, but not 100 fps. Best bet is to use as someone already said fire formed brass that has been shot several times, trim it to spec, and bump the shoulder back about .002.

So get your brass prep down 1st. Then work on what bullet seating depth gives you best groups , and then re work your charge weight to get the velocities you had before that worked. Good Luck!
 

fraz01

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Dec 9, 2020
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183
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washington
Something doesn't seem right with your load. Hodgdon's starting load for this bullet and powder is 67.2 gr. of H1000 @2847 fps. Max load is 73.8 @3083, they used winchester brass and wlrm primer. I would double check every thing about this load ie case length, charge weight, bullet weight, seating depth ect. Would also make sure the chamber, throat and barrel are not fouled.
 
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