effect of small differences in OAL

[artemistrad]

Hi,
I am reloading a Compressed load and I think therefor I need to adjust by every bullet I seat the Micrometer bulletseater of Forster. Think because of the difference in counterpressure by seating or difference in ogive of the LRX bullets. I still though have OAL differences between some cartridges of 0.0016". Does this cause accuracy loss? How much difference may be there before you notice that? Who can help me? Gr Mark

 

[Mikecr]

The tightest seating window I've run across for tune has been +/- 3thou. Some would think this is a risky condition but I never had a problem setting exact seating.

There has been some great testing done w/regard to case charging. I think Boyd Allen posted some.
Anyway, he found that a slow pouring of powder produced a denser charge than a longer drop tube and full dump into funnel. You might experiment with this to relieve compression on seating.

 

[Damascus]

The tightest seating window I've run across for tune has been +/- 3thou. Some would think this is a risky condition but I never had a problem setting exact seating.

There has been some great testing done w/regard to case charging. I think Boyd Allen posted some.
Anyway, he found that a slow pouring of powder produced a denser charge than a longer drop tube and full dump into funnel. You might experiment with this to relieve compression on seating.

+1 Took the words right out of my mouth as I was reading Pour your charge into the funnel very slowly. This allows the grain kernels to "work into" the area much more efficiently, down around the primer, etc.. I beleive you'll be suprised at how much room it can save by changing your fill style. You can also lightly tap the sides of the shoulder or body of the case with something to help the powder "settle" down the best it can. Perhaps with will help with your OAL runout.

 

[Trickymissfit]

I've been preaching to the masses for years over accurate seating depth, and actual gap between the lands and the ogive. Many felt it was over the top, and others knew.
Now when I want to be serious about seating locations, I use my K&M press with inline dies. I have little trouble holding the window in the .0015" range with just about any bullet. Custom match stuff will be even tighter. Now in my Forster press, and using a Forster seater, I can usually do less than two thousandths 80% of the time (window). But some bullets will vary a little in shape, and that window expands. Flat nosed bullets drive me crazy in my big bore rifles. I think bullet manufacturers could do a better job than they are doing right now, but then they'd have to rebuild those forty year old presses! Let alone the die sets.
gary

 

[bill123]

Anyone try placing the bullet over the case mouth and tapping the base of the case on the bench a few times gently? I've noticed this compresses the charge a bit. Not sure how repeatable this is though.

 

[Gene]

Compressed loads will change the OAL because the bullet base in hard contact with top of the powder column pushes the bullet back out slightly. If you are jamming those loads, the bullet will push back again when it contacts the leade.

 

[jsthntn247]

After you find your powder charge, load up a seating depth test in .003-.005 increments. Example: my .308 with 175 gr SMK's shot a bad group high and left of the dot at a touch, then a one hole group dead center of the dot .005 off, then went high and left with a bad group at .010 off, then a good group dead center low at .015. then another good group dead center low at .020 off, then another decent group dead center low at .025, then all over after that. I would pick .017 as my seating depth to give me .002 either way and still have the same point of impact and group size. If .025 had shot just as good as .015 and .020, then .020 would be my seating depth and I could have .005 either way of wiggle room. A seating depth test will tell you where you want to be and how much wiggle room you have for errorr without affecting poi. Even though .005 off shot the best group, it will not be as easy to load for (0 wiggle room) and not as consistent from day to day.