HOW FULL IS A FULL CASE?

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John T
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HOW FULL IS A FULL CASE?

#1 Postby John T » Thu Sep 27, 2018 5:24 pm

Hello All.

For many decades, it has been axiomatic that to achieve maximum efficiency from a case, it should be loaded so that:-
1. the powder charge fills the powder chamber, that is, up to the body/shoulder junction;
2.the base of the projectile does not intrude into the powder column, that is, the base does not seat below the shoulder.

It seems that the old "principle" does not apply to the 7 RSAUM for F Open.

Popular 2209 loads go past the shoulder.

Popular slow powder loads, 2213 and 2217, go up to and beyond the shoulder/neck junction.

So, is the new "principle", load to the neck and damn the intrusion and the compression?

Regards,
John Tracey.
27.9.18

bruce moulds
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Re: HOW FULL IS A FULL CASE?

#2 Postby bruce moulds » Thu Sep 27, 2018 5:49 pm

john,
generally speaking, compression of powder is not a bad thing.
it is amazing how much you can compress powder if you do it working up loads, and it is also amazing how compression can be good for reducing velocity spread.
the biggest problems with too much compression is bulging cases such that they will no longer fit the chamber, and bullets pushing back out of cases.
different primers might shoot better with compressed loads.
ideally the rifle should be throated such that the bearing surface is above the neck/shoulder junction for target ammo, but this does not matter as much for hunting ammo.
monolithic bullets, e.g. copper, are longer than lead core ones of the same weight, making the problem even worse.
keep safe,
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

Tim L
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Re: HOW FULL IS A FULL CASE?

#3 Postby Tim L » Thu Sep 27, 2018 5:55 pm

I don't know where the original 'principle' comes from. My principle is to start load development from a known safe load from a book (I use adi powder so I use there book).
From there I work up loads that perform but don't show pressure signs.
Palmer brass isn't mentioned in any load development literature I've read but I have found the stronger case head allows larger loads with no pressure signs.

These cases (308 palmer) are "full" of 2209. They launch 200gn hybrids at a healthy velocity with single figure variation. I can get the same velocities from less 2208 but the 2209 gives me a smoother recoil. Cases have shot over 10 rounds each and show no signs of loose pockets, give no extraction issues and the primers have nicely rounded corners after firing with no cratering.

I think the general principle of reloading is to be safe.
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mike H
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Re: HOW FULL IS A FULL CASE?

#4 Postby mike H » Thu Sep 27, 2018 9:12 pm

Tim,
Do you use a drop tube to fill those cases?

Tim L
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Re: HOW FULL IS A FULL CASE?

#5 Postby Tim L » Thu Sep 27, 2018 9:28 pm

mike H wrote:Tim,
Do you use a drop tube to fill those cases?

Yes mate, a 1m long piece of carbon fiber tube has served me well for over 2 years now. It's slow pour as well, a fast pour brings it half way up the neck.

mike H
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Re: HOW FULL IS A FULL CASE?

#6 Postby mike H » Thu Sep 27, 2018 9:37 pm

Thanks Tim,I use an aluminium tube,also a metre long.

ben_g
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Re: HOW FULL IS A FULL CASE?

#7 Postby ben_g » Fri Sep 28, 2018 7:55 am

2209 in a 284 doesn’t reach the body/shoulder region. Last time I ran over the chronograph SD was 2.75 for 10shots??

williada
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Re: HOW FULL IS A FULL CASE?

#8 Postby williada » Sun Sep 30, 2018 10:32 pm

John, I was wondering how your SAUM was going? The important point that Tim makes is to be safe. To that end, whatever powder is used, determine the max load by working up to it observing the pressure signs. The other thing that is important is a complete powder burn to reduce SD's. Of course faster powders such as 2206 we used a few years back in .308 would completely burn with a considerable air gap and there was no need to compress loads or jam seat projectiles to improve burning efficiency. Bag handling was not an issue as TR shooting prone meant the body adapted. No such luck with a bipod so smooth recoil is important these days unless you can master the bag handling which is easier with a front rest.

These days when designing a reamer I like to have the mid point of the projectile boat tail seat at the junction of the neck and the shoulder. Not to be confused with the body shoulder junction. A couple of reasons. This junction often shrinks if you anneal and needs to be expanded and it is a common area for case donuts to form. Variable pressures occur in either scenario.

With an appropriate powder, its amazing how often the better loads fill the case so that the base of the projectile sits on the powder. A modern rule of thumb across a range of chamberings sees a 6% compression as maximum but I treat this value with caution. This figure will vary a tad depending on where the final seat is in relation to the lands and appropriate neck tension. I think 2209 is an accurate choice for the SAUM. If you want a longer barrel life and low SD's 2217 is a better choice than 2213 withe 180's.

John T
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Re: HOW FULL IS A FULL CASE?

#9 Postby John T » Tue Oct 02, 2018 5:40 pm

Williada,
the 7 RSAUM barrel is on the shelf while I play with my 6.5 WSSM wildcat at short ranges. Before I changed barrels, I fired some test loads of 183 SMK's with 60.5, 61.0, 61.5, 62.0 and 62.5 of RL-23, with little or no pressure signs. But the recoil was significantly heavier than the load of 2209/54.0. Also, they had about 3.75 MOA flatter elevation at 600 yards. When I get back to the SAUM in a couple of weeks, I will start with 58.0.

BTW, Hodgdon loading data and Burn Rates give the following for a 175 bullet in a 7 RSAUM;
#117 H4350 (2209) 50.0-54.5
#128 H4831SC (2213SC) 54.0-58.0
#133 RL-22 (very close to RL-23)
#141 H1000 (2217) 61.0-65.5C

You say "it's amazing how often the better loads fill the case so that the base of the projectile sits on the powder." This is precisely the "old principle", save for the "fill", which is determined by the seating of the bullet.

You also say "I like to have the mid point of the projectile boat tail at the junction of the neck and the shoulder." In my view, this would case a problem with the short length of "grip" which the neck of the 7 RSAUM would have on a 180 Berger.

The 180 Berger boat tail is 0.245 (half, say 0.122).
The 7 RSAUM neck is 0.311. Shoulder to Mouth is 0.497.

If the 180 was seated to your preference, the length neck grip would be only 0.189 (.311 - .122). In my view, the very long 7mm bullets we use need a minimum of 0.25 grip to give the loaded cartridge integrity. (0.375 grip would be preferable but impractical in this case.)

If the base is seated at the body/shoulder the grip is 0.252 (.497 - .245). There is also compliance with the "old principle".

Regards,
John Tracey.
2.10.18

williada
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Joined: Wed Jul 22, 2009 12:37 am

Re: HOW FULL IS A FULL CASE?

#10 Postby williada » Tue Oct 02, 2018 8:49 pm

John, its always interesting to see how many do things differently and of course success can be had with many variations. Its an oldie now, but Stan Ware took his "Wolfpup" design to the extreme. Here is a link, its worth a read again to note his reasoning. http://bulletin.accurateshooter.com/201 ... benchrest/.

Like Stan, I pay close attention to the throat diameter to support and align the projectile. Sloppy wide throats lead to in-bore yaw. Alternatively, many shooters only neck size the last third of the neck, leaving the lower section to align the case to improve concentric release to reduce in-bore yaw. The latter method is beneficial in sloppy throats.

The photo below illustrates the variation of seating depth between the old and what I do. The length of the powder column will vary in either case but with the projectile seated lower and sitting on the powder there is a greater tendency for an air gap and change in powder density as rounds move about with carriage; whereas if the powder is compressed from the higher seating depth (particularly with slow burning powders which like to be compressed a tad) greater control on the required compression of the powder load can be had with the projectile sitting on top of it.

I hope you enjoy the SAUM. David.

Seating Depth.jpg
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John T
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Re: HOW FULL IS A FULL CASE?

#11 Postby John T » Wed Oct 03, 2018 6:31 pm

Hello David.

It may be ok to soft-seat light, short, flat based 30 cal. bullets in that case, but would it work with BT Bergers?

I am very interested that slow powders like a little compression. I have not used anything other than 2209 in my 7 RSAUM and my use of 2213 in my 284WIN did not involve compression.

What type of compression, drop tube or bullet seating? If the former, what length? If the latter, to what depth would the base intrude into the powder column?

Can complete ignition be an issue? I do not favour them, but would magnum primers produce better results?

Sorry for so many questions, but I have no useful experience with slow powders such as 2217.

Regards,
John Tracey.
3.10.18

williada
Posts: 729
Joined: Wed Jul 22, 2009 12:37 am

Re: HOW FULL IS A FULL CASE?

#12 Postby williada » Wed Oct 03, 2018 11:55 pm

John, those are boat tail Berger 180 hybrids in my picture above. They are not soft seated as such, but utilize a .002" neck tension seated into the lands .010" using 2209. I am a believer in firm neck tension to ensure full ignition of the powder. Seating into the lands also assists this process. However the total rifle lift may prefer another timing cycle with a jump of the projectile when combined with other components such as different primers and or powders. I found 2209 was the most accurate in my gear. The downside is of course reduced barrel life. Barrel length is also a factor in my holistic approach as is chamber design. There are many barrel profiles and lengths not to mention the variables in chamber dimensions out there so I limit comments to my gear. So if you put about 58.8 of 2213 (assuming it is safe in your SAUM barrel) you may get around 2950 with a .020" jump. Likewise a load of 62.8 with 2217.

To keep the seating on a sound footing I probably nip up the chamber more that most. In the case of the SAUM, the extreme accuracy or for that matter any of the other hot magnums there is a limited life. Not afraid to burn steel for a rifle to remain at the cutting edge of performance. Will go back to a smaller popgun in 6mm to keep my eye in and pull out the big guns for when it counts.

"Quickload" a computer program can take you through some scenarios which we used to do by trial and error, particularly in relation to compressed loads and safe pressures. Where you elect to seat your bullet will influence the volume of powder and the compression of it. How you stuff the powder in is up to you. Cheers, David.

John T
Posts: 152
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Location: Brisbane

Re: HOW FULL IS A FULL CASE?

#13 Postby John T » Thu Oct 04, 2018 4:01 pm

David,
sorry about being obtuse, my comments about the soft seated flat base bullets related to the Wolfpup, not to your load.

I take it that compressing slow burners when seating the bullet is par for the course, so I will develop my load in the usual way and not be concerned where the base is in relation to the powder level.

Thanks for your advice.

Regards,
John Tracey.
4.10.18


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