Explain Sudden Velocity Increase PLEASE

[Doc88]

how far is your chrono from your muzzle? Muzzle blast can cause accuracy issues.

It's a Labradar so 6" beside a Vais break.

I want to say I really appreciate everyone's input. Gives me a lot to think about and work on.

 

[g0rd0]

it sounds as if you have your ducks all in a row. So, first I would get a good beam scale set it up, cal your charge master with the beam scales pan and throw a few charges just to find out if there is any difference. If you do see a huge difference then I would sugest that like myself you have developed a flinch factor.
If there still is no difference your barrel just might be hot, I have a 7rm with a sporter barrel and by the 4th shot the barrel is just too hot to grab and the flyers come out to play

 

[Alex Wheeler]

If you look at all the speeds, I dont see 3145 as being out of that group, you had a 3141 as well. A 25 fps ES is not terrible, you could shave a little off but that is not why your shot went off 2". Velocity/ES only have some effect on accuracy and almost none at close range. If you were on the top edge of a velocity node and "broke out" you would have seen a larger jump in speed. I would look more at things like, if it cooked in the chamber longer of lighting changes, but like I said I dont think its out of you "group" with regards to velocity. My personal charge master is only good to +/- .2 grains. Thats a .4 grain window of error. Even if the scale shows its dead on. I trickle on a lab scale (fx 120i) to the .02gn. So that could be some of your ES. Seating depth has a huge effect on ES as well. Do not overlook Neck tension and primer choice when trying to reduce ES. However I think your close enough that a slight tweak in charge or seating will be all you need. Under 20 ft es and theres no gains.

 

[Doc88]

Thanks guys for all your help. I did compare yesterday my charge master to my beam scale and it is NOT throwing consistant charges. So I through the charge with the charge master then fine tuned with the beam scale and trickler. Things were a lot better both with accuracy and ES/SD.

 

[Doc88]

Continuing the saga...so I started over with new brass today and did a ladder/Chrono test from 75-77.4gr in .3gr increments. 200 yd shooting(that's all I have) at a 2" circle. 100fps spread but all impacts within or touching the circle. Found a velocity node around 3125 fps and loaded up 4 rounds. All of this is NOT rapid fire (remember 7STW). Come back to shoot at a 1" circle at 200yds. First 2 shots within the circle and 3123/3125 fps. Next 2 shots high right and 3168/3145 fps. So I think hot barrel. Run back to house and load 3 more rounds while rifle is cooling. All 3 shots in a little 3/4" group high right of my point of aim (close to the last 2 shots of my first group). Shots were 3125 to 3135fps. I'm shooting from a Bipod with off hand on rear bag only. Gun appears to be tracking very well. Now... still me the shooter or scope issue? I have recently checked all bases rings etc and the edge of my IPSC target is level to check my cross hairs with. Talley bases and rings, Zeiss Diavari scope. New to all this and really do appreciate the great help I've gotten so far.

Back to my original post and problems, I think a lot of the issue I was having with velocity spike were probably due to old brass/neck tension problems as the new brass seemed to iron a lot of it out. Please let me know if you agree or disagree. Thanks.

 

[Doc88]

On a side note. I don't claim to be the best shooter by any means but I have a couple other pretty good setups in various calibers and don't seen to have quite the issue as I've had with this particular rig.

 

[Wedgy]

Yes, I think the velocity changes were from scale and neck tension issues. Not sure what power you have the scope on but parallax/head position as well as how the rifle recoils into your shoulder(right handed tend to pull shots right) are the next things that come to mind. Also, once this brass is formed to your chamber the velocity should increase a bit, assuming you are just resizing minimally.

 

[Doc88]

Yes, I think the velocity changes were from scale and neck tension issues. Not sure what power you have the scope on but parallax/head position as well as how the rifle recoils into your shoulder(right handed tend to pull shots right) are the next things that come to mind. Also, once this brass is formed to your chamber the velocity should increase a bit, assuming you are just resizing minimally.

Scope is 6-24. I usually shoot around 14-16X for fine tuning. Parallex is checked frequently. It does seem that either I'm dead on or to the right so it prolly is just me needing more practice experience behind the trigger. Thanks for your help Wedgy.

 

[Alaska2006]

shoot a smaller bullseye, 2" at 200yrd way to larger if you have you scope cranked up.
honesty this may seem like BS but I had the same issue with grouping some months ago with one of my 300WM that would cut holes all day long with a proven load. I couldn't but my finger on the issue as all things were the same as previous 100s of rounds. Finally sitting at my reloading bench disgusted with my performance and looking at past and present targets it hit me the only thing different was target--- color and target bullseye size. I switched back to the cardboard brown colored targets with 1/2" bullseye and shazam my groups were back. This is a real life no ******** story. Try it, what are you out but a few rounds.

 

[HARPERC]

.......This is a real life no ******** story. Try it, what are you out but a few rounds.......

Aim small, miss small! Forces a little more focus.

 

[Doc88]

Aim small, miss small! Forces a little more focus.

My post indicates that once I found my load I came back to shoot groups at a smaller 1" circle. Much smaller and the reticle covers it up at any power. Shoot 2 on target and 3 high right but still small group. I thinks it must be some change in positioning, shoulder tension, trigger control etc. Scope issue would have shots sort of scattered wouldn't you think?

 

[HARPERC]

.......Scope issue would have shots sort of scattered wouldn't you think?.........

Generally, but not absolutely.

It takes so little to move POI at distance, we maybe should marvel over when it happens instead of questioning when it doesn't.

 

[Alex Wheeler]

Back off .3gn and shoot another group. Let me know what happens. Is this rifle bedded and free floated? Factory or aftermarket barrel?

 

[Doc88]

Custom action. Bartlein 3b barrel floated, action pillar bedded in McMillan stock. It's a REM 700 clone action. All the good stuff. I'll load some at lunch and shoot and get back to you Alex. Thanks.