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Importance of OAL

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 03:58
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This week-end I started to work on a load for 200gr Nosler Partitions for my 300H&H. To begin with I am using the cheaper 200gr Sierra Gameking (aprox 1/3 of the cost). The idea is that once I have come to a satisfactory load, to then switch to the Nosler Part. Hopefully the 2 bullets will not be to far off.

What stood out once again is the importance of OAL (Overall cartidge length) or seating depth. For my particular rifle, the OAL seems to be more important then the amount of powder. By keeping everything the same, but changing the seating depth by only 0,5mm or 19thou of an inch, the grouping improved dramatically.

The powder load of 67gr S385 should be chronographing at about 2800ft per sec with the 200gr bullet.

I am posting this info, hopefully it will help someone else struggling to tighten up the grouping and have not yet tried altering the OAL. The OAL of 89mm I am using is way of the lands, about 3mm or 118 thou of an inch. 

 

The first target is using a 165 gr monolithic, with a reduced load. This shows the capabilities of the rifle (and the shooter, which is the real subtle reason for the post wink wink)

The second target is 66,5 gr powder and an OAL of 89,5mm

The third target is 66,5 gr powder and an OAL of 89 mm.

The fourth target is 67 gr powder and an OAL of 89 mm

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 06:41
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I am surprised that your worst grouping is at your longest OAL. Considering that you are around .078" off the lands, I would think reducing freebore would give a substantial improvement. 

Reducing OAL by .040 made a substantial difference. This goes against my experience. I haven't done load develpment with the .300 H&H but have done quite a bit with the 7mm Rem mag and my freebore is under .040" for my standard loading.

I hope to see more results 8shots.

 

Good luck,

Doug

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 09:46
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I know this might seem out of place, but in the search for accuracy it seems we often ignore statistics. Any rifle and load can fire a single 0.25 MOA group. In fact, if you shoot enough rounds eventually every rifle (no matter how inaccurate) will fire such a group. If one assumes that rounds are even somewhat randomly distributed around the point of aim then basic statistics tells us that some groups will be larger or smaller than others even given the same rifle and ammo - it's just dumb luck.

Personally, this is why I am not a fan of three shoot groups, the math just makes it too likely that the group will make it appear that rifle is more accurate than it really is. Before being certain that any change to a load/rifle was a positive one (it is my opinion) that you need at least the average of three (5 shot) groups. Of course, the level of confidence required for each person's application varies.

Again, just my two cents.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 10:08
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Graysteel, I agree with you that 3 shot groups are statistically speaking not good enough. The truth and the whole truth in this specific grouping is that I shot the above 3 shot group and "chickened out". On a separate target I shot numbers 4 and 5 of which shot 4 went into the same group, and shot 5 slightly lower. It would still have been a sub 1/2 MOA with 5 shots.

 

Jokes aside, you are totally correct. I am however trying to find the load and OAL that would give me that 5 shot grouping. As I get nearer to that load I will shoot 5 shot groups.

 

Yes. Tahqua, I also initially lengthened the OAL, and matters got worse. My 30-06 is the exact opposite and likes the bullet in the lands.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 10:31
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I have to salute you for owning up to that 8shots... I have done that before myself... the first 3 shots are so good, you just can't bear to shoot again and risk opening up that perfect group. I thought I was the only one who ever did that.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 10:56
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yup, got the nasty goobys-- at increases of oal the ogive is "lifting" the rd.in relation to the bore alignment. with shorter oal the extractor is holding the case back against the bolt face and the bullet axis is more in line with bore. agree on the 5 rds. though, 7 even better. (although this would upset the symmetry in mtm ammo box).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 11:35
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Originally posted by Dale Clifford Dale Clifford wrote:

(although this would upset the symmetry in mtm ammo box).

 

I've never heard that one and it makes sense. It's still funny..................that's good, Dale.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/15/2007 at 13:29
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Originally posted by tahqua tahqua wrote:

Originally posted by Dale Clifford Dale Clifford wrote:

(although this would upset the symmetry in mtm ammo box).

 

I've never heard that one and it makes sense. It's still funny..................that's good, Dale.

 

That is funny, because I've used that exact same justification for how many shots I fired during load testing. 

 

Thanks for posting your observations, 8shots!  Varying the seating depth/ COAL has a tremendous effect on group size, and reducing the amount of freebore doesn't always improve accuracy as you've demonstrated.  What works best seems to be totally random and varies from rifle to rifle, load to load.  A buddy of mine has the exact same varmint rifle in .223 as I do, yet mine shoots best with an entirely different load recipe and bullet seating depth than his does, despite the fact the 2 rifles are identical in all respects.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/16/2007 at 04:57
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Graysteel, yes I am to honest for my own good, and the very reason I am called 8 shots! I took 8 shots to kill a Barbary sheep some time ago. I told this epic hunting story around a campfire. There were some guys around who I had met for the first time. After telling the story they shook their heads and my hand, saying that this is the first honest hunter they have met! Usually it is of 500yds running 1 shot headshot kills people talk about, not the stuff I talk about.

 

 

 

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/17/2007 at 01:51
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Same here 8shots.  I got lost on my first hunt in NZ - great joke - untill my mates also got lost!  That was really funny - especially since I got lost again!  Sorry, nothing to do with seating depth.

 

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/17/2007 at 03:50
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Maybe we should start a thread called "Great confessions" or "Coming clean"!!!!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/17/2007 at 08:09
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It would end up in a pissin contest about which cleaning rod was best.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/17/2007 at 11:45
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I've made too many boo boo's - I might embarrass myself!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/18/2007 at 16:13
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will anyone admit to having a "X" on their forhead from scope kiss?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/18/2007 at 22:14
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Uhmm....... maybe...

 

My 303 has a long butt piece and the scope mounted 'far' forward - or so I thought!  I fixed that real quick.  Now I have to reach forward to see through it.  Sweet!

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