Case trimming

[Robin]

When I am not getting good groups, I like to know I have done everything I can to make all my bullets as exactly the same as I can. So trimming is something I just do as a matter of course. The case I am trimming, according to SAAMI is 1.600", +0, -.020. I have a mixture of Starline and American Eagle brass, both once fired. To keep within accepted tolerance I am taking them to 1.585" and even at that length, .005" above the minimum, many of the AE brand brass are not long enough to trim.
If SAAMI establishes tolerances for these cartridge casings, why don't manufacturer's follow them. It make me think this is not a critical measurement as far as functionality goes. Me, I just want them all the same. Anyone have thoughts on this?
Robin

 

[Carlos Hathcock]

I'm not an expert but I like to think all chambers are somewhat unique no matter what the SAAMI specs are. I typically trim to published length but find I don't always need to trim.

I was curious recently and pulled out my shiny new scope to see what I was actually doing in there.....



Posted elsewhere and was told all is well. My mind tells me a tighter "fit" should mitigate gas / pressure variations and therefore stabilize accuracy to some degree. I also understand there needs to be some room for case expansion but again, I don't trim very often with fire formed cases.

Shot some decent groups today with this setup....



I suppose chamber dimensions depend on the tolerances to which that reamer was produced, and maybe how long it6s run before dimensions start to change as a result of tool wear.

Not sure if that helps or answers any questions....or created new ones.

 

[Robin]

I think I understand. This is a rifle I put together to test myself on accuracy first and hunting second, till now the reverse has been the rule. So I'm very particular in everything I do. I even bought one of those Vortex Vipers with the adjustable parallax, which I'm still getting used to. It is in .224 Valkyrie.
Robin

 

[Carlos Hathcock]

I have 3 Vipers, 1 Strike Eagle, and 2 Crossfires. Excellent products. Parallax is simple. Keep dialing until the crosshairs don't move when you move your head.

 

[kev74]

I don't think case length matters so much as longs as things are uniform. Its got to be short enough that it doesn't meet that rifling (pressure spike) but short enough that case neck tesion isn't negatively effected - but that's a pretty big spread.

I usually trim to a healthy margin below the maximum overall case length. I never experimented with varying the cases length to maximize accuracy.

@Carlos Hathcock , is the picture above of a fired case or a freshly trimmed case?

 

[Carlos Hathcock]

I don't think case length matters so much as longs as things are uniform. Its got to be short enough that it doesn't meet that rifling (pressure spike) but short enough that case neck tesion isn't negatively effected - but that's a pretty big spread.

I usually trim to a healthy margin below the maximum overall case length. I never experimented with varying the cases length to maximize accuracy.

@Carlos Hathcock , is the picture above of a fired case or a freshly trimmed case?

Multiple firing case trimmed to spec length or maybe .001 under.

 

[squib]

Are you controlling neck tension?

 

[Mosinitis]

As long as you are within specs, you are fine. There is no evidence it has any measurable effect on accuracy.

 

[Robin]

I have 3 Vipers, 1 Strike Eagle, and 2 Crossfires. Excellent products. Parallax is simple. Keep dialing until the crosshairs don't move when you move your head.

Yeah, I get that, but holding my rifle steady while moving my head around puts me in conflict like, hmmmm, was that me and the gun moving or was it the crosshair. Yeah I tend to make things difficult for myself. I should borrow my BIL's lead sled till I get it nailed down, HAH!
Robin

 

[Robin]

Are you controlling neck tension?

That brings to mind something from long past but I can't remember the meat of it. Can you expand on this?

 

[Robin]

Just doing a diopter check on my hundred yard range out back. Using the preset at 100 on the diopter dial the crosshairs do seem to hold steady. Like Reagan use to say, "Trust, but Verify". Later.
Robin

 

[Carlos Hathcock]

Yeah, I get that, but holding my rifle steady while moving my head around puts me in conflict like, hmmmm, was that me and the gun moving or was it the crosshair. Yeah I tend to make things difficult for myself. I should borrow my BIL's lead sled till I get it nailed down, HAH!
Robin

Easiest way is to find even some decent eye relief, and take your cheek off. This way you're not moving the scope. I now do this every time I start a session. Worth the effort when you can see just how much the reticle is "moving".

 

[Robin]

Easiest way is to find even some decent eye relief, and take your cheek off. This way your not moving the scope.

I have read this numerous times and don't know what it means.
Robin

 

[Carlos Hathcock]

I have read this numerous times and don't know what it means.
Robin

Just get your eye where you can see a decent amount of the reticle and still be able to keep from touching the rifle. You don't need to move your head much to see if the crosshairs are moving, especially of you have a target with lots of lines on it. I like to line up the crosshairs on a line so its easy to notice movement of the reticle.

 

[Robin]

Ooooooooooh, okay, got it!
Nice group!
Robin

 

[Robin]

My home made bench is a tad shaky but I'm pretty happy with the results. I think I got the scope situation figured out too.

Ten rounds and I even called the two high ones. Thanks for the help fellows.
Robin

 

[Carlos Hathcock]

My home made bench is a tad shaky but I'm pretty happy with the results. I think I got the scope situation figured out too.
View attachment 66048
Ten rounds and I even called the two high ones. Thanks for the help fellows.
Robin

Perdy respectable. Safe to say your groups are improving? I don't know how many people are aware of parallax and how to address it. Hoping that was most of your problem.

 

[Mosinitis]

The scopes that I am familiar with come with a parallax adjustment or parallax free from a specified distance and out. I prefer to use the later. If I need to use it at a shorter distance, I just add an aperture disc to the front of the scope. It helps with astigmatism as well.