COAL vs Maximum Magazine Length

hugo121175

Sergeant
Full Member
Minuteman
Dec 16, 2009
592
0
46
Near Reading, PA
I have been reloading Lapua 250gr Scenar in virgin Lapua brass for my .338LM. I use a Hornady OAL Case Gauge with modified case to messure my head space. I use the Hornady Comparator to messure the bullet and modieied case, and get a messurement of 3.969". I would reduce this messurement and reload at 3.959" COAL.

I have since ran out of the Lapua Scenars and am starting to load test for 250gr SMK. I use the same method to get my COAL, but now the cartridge is too long for my magazine. I know I should have a COAL that is as close to magazine length, but how will this effect accuracy?

Rifle: Sako TRG 42 .338LM
Head Space: 3.992
Max Mag Length: 3.960"
Difference: 0.032"

Thanks,
Hugo
 

Fuzzball

Gunny Sergeant
Full Member
Minuteman
Jan 19, 2009
2,165
5
Re: COAL vs Maximum Magazine Length

" I know I should have a COAL that is as close to magazine length, but how will this effect accuracy?"

First, some termonology. Headspace relates to the chamber and that's all. What we have to do is try to make our ammo fit the headspace we have. The loaded cartridge has to fit the magazine, if any, and the chamber throat, or leade, neither are any part of headspace, as such.

Now, your Hornady tool can only tell you where your chosen bullet will touch the lands, and that's not normally the "best" seating depth. How you have been lead to believe you "should have a COAL that is as close to magazine length" OR throat length I don't know but, so far as accuracy goes, both are virtually irrelivant and none of us can honestly tell you what effect a change might have on your currect accuracy.

Obviously a round that's too long to feed from the magazine would be a mistake, you know that, but the common idea of seating close to the lands is usually a mistake also. MANY bullets shoot better by getting a running start before hitting the lands but only experimenting with YOUR rifle will tell you that.

None of my rifles shoot best closer than 25 thou off the lands and a couple prefer MUCH more than that, by a factor or 4 or 5.
 

vman

Gunny Sergeant
Full Member
Minuteman
Nov 23, 2009
3,719
3
38
Australia
www.google.com
Re: COAL vs Maximum Magazine Length

Certain projectiles can be fussy. I have found that for LR shooting i make rounds that sit close to the lands and require single feeding.

For hunting rounds, I will load to max mag length.

For LR hunting, I will single feed.

But thats just me. Using 155 Scenars.