Seating depth blackout

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Morne
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Re: Seating depth blackout

Post by Morne »

Here is a visual comparison of three bullets that I am using for my blackout loads. On the far left is the 130 grain open tip match barrier bullet. In the middle is the 150 grain copperplated flat point bullet from X-treme. On the far right is a 163 grain AP bullet.

Image

They measure in length:
130-gr = 1.014"
150-gr = 0.847"
163-gr = 1.382"
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JustaShooter
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Re: Seating depth blackout

Post by JustaShooter »

Morne wrote:What does the neck tell you and how? I'll post pics of necks, too, since you suggest it.

Too low? I figured that aside from a barrel blockage or a failure to cycle too low wasn't an issue.

FYI - 130-gr OTM Lil' Gun loads (in grains):
15.1
16.5
17.9
18.5
19.0

Published max is 20.0-gr (Hornady 9e) or 19.5 (Hodgdon online).
If the necks are sooty then the pressure is too low to get a proper seal of the neck brass against the chamber walls. It can cause inconsistent velocities, accuracy issues, and premature wear of the chamber.

Oh, and I'm not that familiar with Lil' Gun, but starting at 75% of max published load sounds really light. I'm used to seeing starting loads around 90% of max or so.

ETA: Hodgdon (http://www.hodgdonreloading.com/data/rifle" onclick="window.open(this.href);return false;) lists the starting load as 18.3 grains of Lil' Gun for a 130 grain projectile. How did you determine your starting load?
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Morne
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Re: Seating depth blackout

Post by Morne »

Hornady shows a much wider band of loadings.
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stephen45-70
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Re: Seating depth blackout

Post by stephen45-70 »

i am going to throw a curve ball at you concerning low pressure loads and bottleneck cases . as when using very light loads just sticking a bullet in the bore is not the only potential problem you may have

as we all hopefully know bottleneck cases for the most part head space off of the shoulder , this is important to remember because things work a very tiny bit differently inside the chamber with light loads . i am going to do a very poor job of explain what happens so be easy on me here .

ok here goes with a normal load when you pull the trigger .. the sear releases the firing pin witch then strikes the primer , the firing pins inertia then pushes the case forward slightly off the bolt face and once the shoulder is tight against the chamber wall the primer dents and it fires the primer .. good we all already know this correct ,
when the powder ignights it expands the case to grip against the chamber walls and pushes the case head back against the bolt face ( this causes case stretch and is why we need to trim every now an then ) .. still following along i hope .

now what happens with light loads is when the firing pins inertia pushes the case forward it also sets the shoulder back a very tiny bit .. and yes it is a very tiny amount of set back but that isn't the problem a this is normal , the problem is that pressures aren't high enough to do either of the two thing that need to happen to push the shoulder back out

one of two things happen here upon ignition either the case does not expand enough to grip the chamber walls and just slams back into the bolt face , or the case grips the chamber but doesn't have enough pressure to expand the case back into contact with the bolt face .

now i am sure everyone is scratching their head and wondering where the problem is .... the problem is more of a cumulative effect with light loads .. if you keep shooting light loads you never get high enough pressures to push the shoulder back out to where its supposed to be so after a few loading you end up with slightly excessive head space due to the to short shoulder .
this isn't a problem at all if you dedicate these cases to light loads only

the problem is when you use these case with light loads enough to set the shoulder back and then load up some high pressure loads in cases that now do not head space properly and you end up with case separations and or excessive bolt thrust .

now how was that for a poor explanation .... before i get flamed for this keep in mind that this is only a potential problem with very light loads , and doesn't happen with only one or two firings usualy
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Morne
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Re: Seating depth blackout

Post by Morne »

Thanks for that explanation!

I'm just doing load workup, here. Once I find a load recipe that works well (for all 3 of these bullets) I'll probably stop fiddling with it.
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