How accurate should COL be?

[siegrisj]

I've been having an annoying problem where I can't seem to get my die to consistently seat bullets to the same depth. These are being measured at the ogive with a comparator.

If it matters, most of the brass is reused federal and the bullets are SMK HPBT 175's. Hornady dies, RCBS press.

The closest accuracy I can seem to get with depth is +/-.01. I'll get some that are really close, within .001 and then all of a sudden one will be .005 too short. Then the next one might be long. It's maddening.

Competition dies are supposedly adjustable to .001 so is this kind of variance normal with regular dies? And would a competition die really fix the problem?

At the end of the day, am I really going to see the difference on paper?

 

[Kevin Thomas]

Siegrisj,

The dies are adjustable, and I'll bet you that they aren't varying a bit. The bullets are another matter. From what you've described, I'd say the ogives are varying on you, and that's what's showing up when you measure them. Remember, the seating plug hits the ogive far closer to the meplat than the major diameter where your gage is checking the ogive. Whatever variation there is in the bullets, is probably what you're seeing when you take the measurments. I'd suggest trying Bergers or (dare I say) Lapuas and see if that doesn't drastically reduce these measurments. Not all manufacturers pay as close attention as they should to base/ogive variation.

 

[siegrisj]

Kevin,
Thanks for the response. So if I am following your logic correctly, I should be able to measure a sample of bullets at their ogives and see the same kind of variation with just bullets themselves right?

I might have to take you up on trying something different, although I thought Sierra's were supposed to be the bullet by which all others are judged. Which I guess translates into some will be better and some will be worse.

Thanks

 

[Mikecr]

Kevin hit on a good one & it could be other things, or a combination of them.
It could be the press, an issue with the die setting or seater plug, greatly varying seating force, or an issue with measurement.
Describe each condition & let's rule these out.

 

[Kevin Thomas]

Lots fo things involved here, but most of them can be overcome by consistent operation of the press. If the dies are properly locked and not moving within the press, the seating stem is tight and not moving, then this part of the system won't be an issue. I have seen many presses with enough slop or play in the linkage system that it would effect uniform seating, bu this could usually be eliminated by exerting a little lateral pressure on the handle when you seat. That is, pushing the handle consistely to the left or right while operating it through its stroke. That said, I'll still put my money on the bullets themselves as being the most likely culprits here. As I said, not everyone puts the same degree of care into base/ogive consistency as they should. Worth trying some others, just to see if this reduces or even eliminates the variation.

 

[siegrisj]

The press can't entirely be ruled out cause I have it set up in a ghetto fashion where it isn't firmly bolted to the desk. If the press isn't 100% firmly bolted, isn't that still a separate system from what happens internally in the press?

That seems to be an obvious thing to clean up and has been on my list for awhile.

 

[Kevin Thomas]

Shouldn't be an issue, but it certaily will make it more difficult to operate. Bolt that sucker down, tight!

 

[siegrisj]

One thing that I question is the Hornady dies have rubber washers on the adjustment screws, and that seems to me it should introduce some sloppiness in the system. But then anyone with a Hornady die would have the same problem I would think.

 

[feelinducky]

I get the same problem with Barnes and it absolutly drives me nuts. I figured it was a bullet issue. It did make me more consistant with pressure through the stroke of the press and at the end of the stroke.

 

[siegrisj]

Glad I'm not the only one.


For the other question there... how much does it matter? Which parts of the process are important to get the most consistent for results down range? (As opposed to warm fuzzy feelings. Don't get me wrong, I love warm fuzzies too)

 

[Mikecr]

How much does it matter?
VERY much if you care to get the best of your gun's accuracy potential.
Seating depth is the single biggest performance adjustment.

If your load shoots best with bullets off the lands, you need to hold that distance within +/- 1thou.
Luckily, this is not difficult once the bugs are worked out.
You need to isolate the issue.

 

[siegrisj]

I've been trying to just keep a consistent OAL which obviously hasn't been working.

Maybe I'll try to make getting that press properly mounted a project for the weekend.

I haven't delved into loading off the lands yet since I'm still pretty new to reloading. Have only done a few hundred rounds. As I get more experienced that might be next

ETA: I also read recently that primer pocket uniforming is another big variable in keeping rounds consistent. That really surprised me since I thought the primer wouldn't have much affect on paper. Any opinion on that matter?

 

[boomtube]

I've found that there's usually a window of seating from 15 to 20 thou wide that really doesn't make much difference in accuracy, at least not out to 300 yards or so. I find the full range of tolerance and seat in the middle of it, then the normal variations won't mean a thing.

 

[siegrisj]

So I just measured a box of Federal GMM 168gr using the same comperator. Here were the numbers

* 2.222 2.223 2.224 2.225 2.225 2.225 2.225 2.226 2.226 2.226 2.228 2.228 2.228 2.228 2.228 2.230 2.230 2.230 2.231 2.232
Looks like their range of tolerance isn't too far off from what I am getting. Even though I still want mine to be tighter. (Who doesn't? )