Over expand neck affects accuracy?

[longrangeprecisionshooter]

I noticed that 35 of my 6 dasher rounds I loaded yesterday went everywhere on paper during seating depth test with 5 shots groups between 0.7-1.5MOA, mostly around or over 1 MOA at about 100 yards from prone. Never had this bad of groups in the past, most of the time I got is around half MOA, range is between 0.4-0.8.

The only difference is this batch of brass when I first expanded, I used the wrong mandrel, instead of 0.242 one I used 0.262 for 6.5creedmoor.

When I realized that I FL resized(didn't anneal again) all the brass again and expanded again using the correct mandrel.

The seating force is pretty consistent around 40-50lb.

I am wondering how likely my bad groups are related to the wrong mandrel used at first time? And is it still worth to load and shoot the rest of the batch of brass(65 left) I prepared?

Thanks.

 

[bozo699]

I’m not sure where to start…. First of all your Dasher should easily shoot in the .200’s-.300’s and with the right bullet and tune less than that. If you already have them all sized back to your desired dimensions I would anneal and try a few more. What bullet powder combo are you using?
Wayne

 

[longrangeprecisionshooter]

I’m not sure where to start…. First of all your Dasher should easily shoot in the .200’s-.300’s and with the right bullet and tune less than that. If you already have them all sized back to your desired dimensions I would anneal and try a few more. What bullet powder combo are you using?
Wayne

108ELD with varget. I loaded with same components from the same batch in the past without any issue, also tried 107 SMK with varget, same thing.

I hope the brass length processed by Giraud slightly shorter than not trimmed could be another reason? Brass was at around 1.533, I was adjusting Giraud's brass holder depth to get the chamfer angle I want, trimmed a little bit over than I expected (1.530) down to 1.528.

 

[longrangeprecisionshooter]

Shot another 30rounds today using the same seating depth test yesterday. The group size are pretty much in the same range.

By looking at today's groups, it's always 3-4 rounds are much closer(0.3-0.6MOA) without the 1-2rounds flyers(0.8-1.2MOA).

One thing I noticed the front action screw(shorter) on my ACC is less tight than the rear one(longer). I don't have the tool head for my digital Wheeler torque screwdriver, so couldn't confirm how much torque I have on the action screws, only hand tight with an allen key.

Have re-tighten the action screws and will try again.

 

[fkimble@charter.net]

If you used a .262 mandrel, then the 6mm bullets would probably fall out of the necks if held bullet pointed down. Or another way to put it, you would have zero neck tension. Trimming a hair shorter than others would probably not show up on a target. A loose front action screw can create havoc with your accuracy.

Frank

 

[Fire Dog]

If you used a .262 mandrel, then the 6mm bullets would probably fall out of the necks if held bullet pointed down. Or another way to put it, you would have zero neck tension. Trimming a hair shorter than others would probably not show up on a target. A loose front action screw can create havoc with your accuracy.

Frank

Oh yes, loose screws... Have you also checked the ones securing your scope?
Had my Anschutz 64 suddenly just start shooting random fliers and it turned out to be the screw on the front scope mount...
You did say that you had resized the brass and then used the correct mandrel to get neck sizing just right...
I use the same mandrel size for my 6BR F Open rifle and that gives me about .0015" neck tension on my Peterson brass that is cleaned and annealed @ time. AMP annealer so that annealing is totally consistent rather than "Flaming" guesswork... {:~)

 

[bozo699]

108ELD with varget. I loaded with same components from the same batch in the past without any issue, also tried 107 SMK with varget, same thing.

I hope the brass length processed by Giraud slightly shorter than not trimmed could be another reason? Brass was at around 1.533, I was adjusting Giraud's brass holder depth to get the chamfer angle I want, trimmed a little bit over than I expected (1.530) down to 1.528.

I’m sorry I never got back to this,… I myself never have found Hornaday bullets to be very consistent and I’ve never seen anyone other than Hornaday using them on the 1000 yard line. If you don’t want to go custom you should give the 105 Berger’s a try. Varget is my powder of choice in the 6brx but in the Dasher H4895 worked better for me. I don’t think your trim length will hurt your accuracy or at least not by much. I have had good luck with the 107 smk but I had to sort them to do well.
Not to be mean but have you tried dry firing your rifle to see if your cross hairs stay on target?… are you useing a good front rest and rear bag setup?… I find it strange your getting moa with a Dasher.
Wayne

 

[JFrank]

If the OP is using a.242 mandrel for a .243/6 mm caliber , having erratic grouping does surprise me at all. Personally I would test smaller bushings or mandrel sizes, .239 -.240-.241

 

[longrangeprecisionshooter]

If you used a .262 mandrel, then the 6mm bullets would probably fall out of the necks if held bullet pointed down. Or another way to put it, you would have zero neck tension. Trimming a hair shorter than others would probably not show up on a target. A loose front action screw can create havoc with your accuracy.

Frank

I didn't notice that until I was going to chamfer/debur(trim) using Giraud.

So I resized all the brass and used the correct mandrel again, the press shows consistent seating force so I doubt it is neck tension. But couldn't figure out why until pen of the gentleman pointed out could be bedding issue or scope mounting related.

I checked all the screws again, scope part is all good, action screw could be the problem as I noticed the front one is slightly less tight like the rear one.

Anyway, would try again next week.

 

[longrangeprecisionshooter]

I’m sorry I never got back to this,… I myself never have found Hornaday bullets to be very consistent and I’ve never seen anyone other than Hornaday using them on the 1000 yard line. If you don’t want to go custom you should give the 105 Berger’s a try. Varget is my powder of choice in the 6brx but in the Dasher H4895 worked better for me. I don’t think your trim length will hurt your accuracy or at least not by much. I have had good luck with the 107 smk but I had to sort them to do well.
Not to be mean but have you tried dry firing your rifle to see if your cross hairs stay on target?… are you useing a good front rest and rear bag setup?… I find it strange your getting moa with a Dasher.
Wayne

No pressure.

The ELD and SMK were my initial purchase during pandemic when everything is in shortage. I only used it for break in, testing, and practicing purposes.

For serious match, definitely I will use Berger, maybe A-tip, or at least Lapua bullets. H4895 is almost cannot be found in my area, I have lots of varget, but may try N140 or similar for Dasher.

I didn't try dry firing but my past experience with the rifle giving me satisfied result. I can hold the rifle md control recoil properly, the point of aim is still within the sight at high magnification after firing. I am not setting up this rifle for purpose F class or Benchrest, more like a PRS/tactical one, so Ckypod is used for front support and a hand hold rear bag from precision underground is what I have now. Will replace by a Neo-X and a rabbit ear rear bag when I find the suitable filling sand.

I found my front action screw is slightly loose or less tight than the rear one, have fixed it will see what it can do next time.

Thanks a lot for all the info.

 

[longrangeprecisionshooter]

If the OP is using a.242 mandrel for a .243/6 mm caliber , having erratic grouping does surprise me at all. Personally I would test smaller bushings or mandrel sizes, .239 -.240-.241

I tried 241, 2415 and 242 mandrels in the past, not significantly difference like what I had, has tighten the actions crews, will see what happen next time.

 

[JFrank]

.001-.002 neck tension / bullet hold or whatever you call it , isn’t much if you experience any spring back or softening of the brass from annealing. Along with the action screws I’d certainly be looking at increased bullet hold.
Please report back with your findings.

 

[longrangeprecisionshooter]

.001-.002 neck tension / bullet hold or whatever you call it , isn’t much if you experience any spring back or softening of the brass from annealing. Along with the action screws I’d certainly be looking at increased bullet hold.
Please report back with your findings.

I tried the same load again last weekend, it didn't change much, the only difference is there are a couple of groups are pretty small (0.3-0.5MOA) if doesn't count that one or two flyers(4+1 or 3+2 situation).

I even tried to re-tight the action screws at range with some other experienced shooter's help, it didn't make much difference.

I have just re-process the same batch of brass again, but this time, I will use my original lyman xpress case prep center to chamfer/debur the brass instead of using Giraud. (Not saying Giraud causes the issue, as the seating force is pretty consistent between the 30-40lbs range)

By the way, if I ever over tighten the front action screw, say I used 80-90ft/lb torque instead of 65ft/lb, could that cause any damage to the thread inside the action screw hole? If yes, could this be one of the cause of this accuracy issue?

 

[bozo699]

I tried the same load again last weekend, it didn't change much, the only difference is there are a couple of groups are pretty small (0.3-0.5MOA) if doesn't count that one or two flyers(4+1 or 3+2 situation).

I even tried to re-tight the action screws at range with some other experienced shooter's help, it didn't make much difference.

I have just re-process the same batch of brass again, but this time, I will use my original lyman xpress case prep center to chamfer/debur the brass instead of using Giraud. (Not saying Giraud causes the issue, as the seating force is pretty consistent between the 30-40lbs range)

By the way, if I ever over tighten the front action screw, say I used 80-90ft/lb torque instead of 65ft/lb, could that cause any damage to the thread inside the action screw hole? If yes, could this be one of the cause of this accuracy issue?

Unless you absolutely know you pulled a shot you have to count the flyers….. why wouldn’t you?… I’m guessing your meaning 65 inch pounds because there’s no way you can put 90ft/lbs on a action screw
Wayne

 

[Bill Norris]

I tried the same load again last weekend, it didn't change much, the only difference is there are a couple of groups are pretty small (0.3-0.5MOA) if doesn't count that one or two flyers(4+1 or 3+2 situation).

I even tried to re-tight the action screws at range with some other experienced shooter's help, it didn't make much difference.

I have just re-process the same batch of brass again, but this time, I will use my original lyman xpress case prep center to chamfer/debur the brass instead of using Giraud. (Not saying Giraud causes the issue, as the seating force is pretty consistent between the 30-40lbs range)

By the way, if I ever over tighten the front action screw, say I used 80-90ft/lb torque instead of 65ft/lb, could that cause any damage to the thread inside the action screw hole? If yes, could this be one of the cause of this accuracy issue?

No experience at all with one action screw considerably tighter than the other but it would seem to put un-due pressure on the stock/action. Minimum torque differences between the two would probably not be an issue unless you were dealing with a Rem Model 7 where specs. are recommended to be 35 in/pds. on the front and 15in/pds. on the rear.

 

[JFrank]

I tried the same load again last weekend, it didn't change much, the only difference is there are a couple of groups are pretty small (0.3-0.5MOA) if doesn't count that one or two flyers(4+1 or 3+2 situation).

I even tried to re-tight the action screws at range with some other experienced shooter's help, it didn't make much difference.

I have just re-process the same batch of brass again, but this time, I will use my original lyman xpress case prep center to chamfer/debur the brass instead of using Giraud. (Not saying Giraud causes the issue, as the seating force is pretty consistent between the 30-40lbs range)

By the way, if I ever over tighten the front action screw, say I used 80-90ft/lb torque instead of 65ft/lb, could that cause any damage to the thread inside the action screw hole? If yes, could this be one of the cause of this accuracy issue?

Maybe’ …I don’t recall ever tightening action screws much beyond 35-40 in pounds and never really had any issues that traced back to action screws.

 

[Clancy]

How do your other rifles shoot?
Can you post a picture of the rifle?
A dasher shooting bigger than mid .3s on average (so some teens and some half moa mixed in) sounds like a mechanical problem, probably a scope.

It could also be your experience level and that’s ok too. I’m definitely not judging.