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Old April 13, 2019, 19:53   #1
Falfan2017
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What caused my pressures and speeds to spike?

Loading for a benchrest custom rifle with a Brux barrel chambered in 6 br. Iíve used the same load for several months and it always chrono at 2960 which is where I want it. I changed the stock on it but changed nothing else. I took it out to test and it was shooting from 3000-3180 FPS which is the ragged edge of whatís possible for a 6 br with 105 bullets. Also had hard bolt lift. Why did changing the stock change the pressure that much?
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Old April 14, 2019, 00:29   #2
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It didn't. You have something else going on.
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Old April 14, 2019, 00:42   #3
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It didn't. You have something else going on.
About sums it up...

Is the ambient temp higher?

Of course, 'always' chronos at 2960 is a bit unclear, since you then mention a range of 3000 - 3180 with presumably the same load.

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Old April 14, 2019, 01:29   #4
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Range temperature?
Bullet jump?
Same loading, same primer, powder?
Jacket fouling/powder fouling?
Same case length?

Something is different, you just need to find out what it is.
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Old April 14, 2019, 01:32   #5
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Did you bed this new stock and how did you do it???
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Old April 14, 2019, 08:34   #6
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Did you bed this new stock and how did you do it???
Glass bedded the stock. I didnít do it a gunsmith did who knows what heís doing.

When I say it always chronos around 2960 I mean the last few months Iíve been using the load it was consistently at that speed. Itís only yesterday after changing the stock that the speeds became erratic and up to 3150+.
Nothing else changed. I have a similar gun that uses the same bullets, powder and primers and I shot it yesterday too and it had no problems.
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Old April 14, 2019, 09:25   #7
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I'd suspect your loads. Different lot of powder, bullets, seating depth, primer, etc.
Might try weighing empty cases that show high velocity/pressure compared to cases that register normal vel/pressure.

As the others have said, I have never heard of a rifle changing ballistics due to a stock change.

A load going from 2960 to 3000~3150 is not a great deal of difference. Some minor change in any of the variables could account for it. Powder sensitivity to temperature for one.
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Old April 14, 2019, 09:54   #8
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I'd suspect your loads. Different lot of powder, bullets, seating depth, primer, etc.
Might try weighing empty cases that show high velocity/pressure compared to cases that register normal vel/pressure.

As the others have said, I have never heard of a rifle changing ballistics due to a stock change.

A load going from 2960 to 3000~3150 is not a great deal of difference. Some minor change in any of the variables could account for it. Powder sensitivity to temperature for one.
This is a benchrest gun in a small cartridge. 20 FPS would be normal variation from temp or conditions. 200 is crazy. Under normal conditions Iíd have to add 2 full grains to get the speed up that high which would hardly fit in the case. Thereís been no change in components Iíve only got one 8 pound jug of powder open and Iíve been using it for months. Iíve been using the same box of 1000 bullets for months and Iíve got thousands of primers from the same lot Iíve been using for months. Iím totally baffled
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Old April 14, 2019, 10:28   #9
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You should be asking this on benchrest.com.
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Old April 14, 2019, 10:47   #10
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Originally Posted by Falfan2017 View Post
Iím totally baffled

I can see why.

You have answered all the ammo variables that I can think of. That leaves the rifle it would seem, but aside from changing group accuracy or POI, I can't think of anything that would effect internal ballistics by changing the rifle stock. Barrel harmonics would be different, but......?

Be interesting to see what has happened, but meanwhile, I would back off the load a grain or two to see what the chrony reads with less powder.

Good luck with this one.
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Old April 14, 2019, 13:53   #11
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Quote:
Originally Posted by Falfan2017 View Post
Glass bedded the stock. I didnít do it a gunsmith did who knows what heís doing.

When I say it always chronos around 2960 I mean the last few months Iíve been using the load it was consistently at that speed. Itís only yesterday after changing the stock that the speeds became erratic and up to 3150+.
Nothing else changed. I have a similar gun that uses the same bullets, powder and primers and I shot it yesterday too and it had no problems.

As others have said, if your ammo and WEATHER conditions have not changed, then that ONLY leaves the "gunsmith" and the "new stock".

Any gunsmith that knows what they are doing, normally is very busy, and also has some "help' in the shop.

Do you have your old stock?
Change it back to the old one, see what happens.
I would not expect it to make a difference,but,,,rule it out of the equation.

The gunsmith;

Bolt tight:
Ammo changes in speed:

After it returns from gunsmith.

WHO actually worked on the rifle????

Was something done to the rifle by "mistake"???

Did your rifle get "mixed" up with another "job" in the shop???

Was there a "shop accident"????

Was is "practiced upon" while in the shop????


IF your ammo did not change,,,,the weather did not change dramatically,,,,
And all that's left is the time spent with the gunsmith,,,,,,,,,,,,,,,,,,then,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,????


There is an answer somewhere.
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Old April 14, 2019, 13:54   #12
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And to add:

Did your chronograph break????
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Old April 14, 2019, 16:08   #13
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What action ? Is it a glue in or does it have action/receiver screws ?
About all I can think of offhand is maybe release agent on bolt face or in chamber,,,have you cleaned it well ?
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Old April 14, 2019, 20:17   #14
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Maybe the pressure went up because you squeezed the trigger too hard..

Don't start on me guys, I am just having some fun.
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Old April 15, 2019, 14:59   #15
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Took it back out yesterday after a thorough cleaning. Speeds settled back in to where they should be. I think the craziest readings may have been chrono related. Played with the torque settings on the action screws and that tightened groups up quite a bit so all is good again.
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Old April 15, 2019, 16:03   #16
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Originally Posted by Falfan2017 View Post
Took it back out yesterday after a thorough cleaning. Speeds settled back in to where they should be. I think the craziest readings may have been chrono related. Played with the torque settings on the action screws and that tightened groups up quite a bit so all is good again.
Mine got haywire once, for no reason, kept showing insane FPS for 3006.

Happy its all good now.
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Old April 16, 2019, 02:33   #17
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Sounds like fouling as in jacket fouling.
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Old April 16, 2019, 11:33   #18
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seating depth variation...
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Old April 16, 2019, 13:53   #19
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Sounds like it was mostly a chronograph problem to me...

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Old April 16, 2019, 15:45   #20
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Sounds like it was mostly a chronograph problem to me...

Forrest
Most of my problems have been traced back to the nut behind the trigger.
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Old April 17, 2019, 04:47   #21
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If you are using an optical chronograph, I would guess that the variations in fps you noticed were possibly due to environmental conditions.
I started using a Lab-radar awhile back for the sole purpose of getting consistent readings that did not depend on clouds or sun.
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Old April 17, 2019, 05:23   #22
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Lots of good info here and chronys can have issues,,,,but,,

None of that goes far to causing the HARD BOLT LIFT the OP stated,,,,
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Old April 17, 2019, 05:54   #23
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Lots of good info here and chronys can have issues,,,,but,,

None of that goes far to causing the HARD BOLT LIFT the OP stated,,,,
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