Saami specs and pushing the boundaries of case pressure ?

[plumbs7]

Well I wasn't going to post anything ! Even logged myself out so I could get out of the way and let someone else have a go! Well it seems I can't help myself lol! .

I thought I would start another thread that eventuated from 180vld v 168 vld and put it in its proper place ! So below is a copy of Kieth H's last post to kick it off.
Not , I'll be to let other have a go with comments . Regards Graham.


Post subject: Re: Berger 180gn VLD verses 168gn VLDPostPosted: Fri Oct 09, 2015 12:33 pm
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Location: Cowra NSW
plumbs7 wrote:
Longranger wrote:
That looks somewhere north of 62000PS... Just a guesstimate though.

I respect Keith's opinion a lot ! That was in the middle of the afternoon at Gundy opm. It shot very well!

I will be keeping an eye on it and will back the load of as Summer comes . 2209 does seem a little temp sensitive as much as 2208 in my 308 between winter and summer . It is pushing the limit for a medium cartridge . Anyway don't want to turn this into another blog as there is already 5 pages else where, enough to put any enthusiast asleep. If u like , I'll keep everyone posted on the 7-08 blog about load and pressure!
Still over the moon with it !

On the same note some of the velocties that Ftr guys pushing 215's and the amount of powder behind those pills makes me shake my head with the lil 308 win. But they are very successful . Pushing the boundaries I guess!
Regards Graham Sells.


Graham, there are several issues at play when we set out to develop an accurate load in any cartridge. The first issue to always consider is one of safety!!!! That is not only the shooter's safety but that of those around you, this is in fact a responsibility of the reloader which must never be undertaken lightly.
Please understand I am not criticising you or anyone else who frequents this site. The pic in the discussion indicates to me that the pressure MAY be above safe limits with that particular case! The fact that the load shoots well is NOT an indication of safety, many HOT loads display outstanding accuracy which is testament to the flexibility of the powders we have available to us today & can lead the uninformed down the path to unwittingly overloading their ammo in order to "up" the performance. There is a rule in engine performance that nothing outpaces "cubic inches" the same rule applies to cartridges, if you want speed safely use a bigger case!!
The "strength" of your action is only that of your brass case which is around 70000psi CUP or roughly 80000psi Piezio, both rates of pressure measuring methods are in use today. American manuals mostly (almost always) use the CUP measurement & ADI use mostly Piezio measurements, both are used in their latest handbook depending on the caliber. One should NEVER exceed 62000psi Piezio or 54000psi CUP no matter how well the load shoots.
I & others have spoken before of multiple accuracy nodes, the trick is to choose the right node! This node will be somewhere around 59 to 60000psi Piezio, in this range you will achieve good accuracy, case life & barrel life & you will preserve your safety & your action life will be extended.
All powders are temperature sensitive!!! Adi powders are LESS sensitive than others, if the load is maximum as so many are, the sensitivity will be more evident. This is why the node I have referred to above is wider than those at higher pressures.
In my many years as a full time professional gunsmith I have inspected & analysed many blown up rifles & pistols, not to mention other types of "firearm incidents" believe me nobody wants to risk being involved in any of these by "pushing the boundaries". In over 90% of these "incidents" human error was to blame. Now before the "experts" decide to jump on me, these are my opinions only & are based on observations during over 55 years of reloading & close to 40 years of professional gunsmithing.
Keith H.


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[Steve N]

Looks like Keith has some good advice there. Are high pressure loads worth the risk and associated problems with case life etc? Is the extra 100 fps or less any real advantage? Plenty of matches have been won by shooters using accurate loads at quite moderate velocities.

[Matt P]

The big question for me is what is the reason for running the small (for what you're trying to achieve) case ?
Is it to extend barrel life or just to be different, if it's to be different go for it (but do it with caution and some common sense) !!!
If it's to get better barrel life, well there are no free lunches !!!
Running the smaller case at higher pressure (even with less powder) will reduce barrel life probably more than using more powder in a bigger case at lower pressure.
Obviously case life will be better (except when using the 284 )and wear and tear on the action much reduced.
Regards
Matt P

[Brad Y]

I think the Americans have a huge case to answer here. Nobody over there shooting 284's or shehanes shoot the low nodes that we do. Everyone shoots 284's as close to 2850 as they can and shehanes are supposed to be useless if you dont run them at 2950. Nobody would think of running a 7-08AI there for f class because its just not big and fast enough.

Matt nailed it on the head perfectly. F open is great for experimentation, but the same principles as a 223 or 308 standard gun apply to open guns. You have BC on your side so use it.

[plumbs7]

Ok before I get banned from competitions with the 7-08ai below is a photo that I just took showing the fired she'll shot with 180's at Gundy opm hot afternoon!


On the right with the bit of blue paint is a case a shot today with 168's and a low 47.4 gr of 2209 @ 2860 fps .

IMO they both look the same . I think the light and the angle that the case was on made it look worse !

Why shoot the 7-08ai , it's different ! I have 9 yrs experiance with 308's . Just had a gut feeling that it was an effeciant case and inherently accurate .

look the jury is still out on this cartridge but it just the Wa Queens with a master pilot behind it !

[Julian D]

Edited , not related to topic .

[Norm]

Graham don't get stressed over this. You are not the one that hijacked the other thread.
Just use a bit of common sense when reloading and back off when you see obvious signs of high pressure.

There is quite a bit of variation in the pressure that calibres can be run at. For industry standards have a look at
http://saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf

Cases designed for say a 7x57 have a Maximum Average Pressure of 51,000psi while the various WSM and RUM cartridges have a MAP of 65,000psi. The common F-Open cartridge .284 Winchester has a MAP of only 56,000psi.

Looking at the .308 cartridge its SAAMI standard safe MAP is 62,000psi. SAAMI tested this cartridge at this pressure with 165gn bullets put of a 15" barrel and came up with an average velocity of 2880fps. This is with standard LR primer brass.

It is common for TR shooters to run at over 3000fps with 155gn bullets. Lapua introduced the much stronger Palma case so that these shooters could run at these speeds with longer case life.

If a .308 can safely run 165gn bullets at an industry standard of 2880fps with 165gn bullets from a 15" barrel. Then an Ackley Improved 7-08 with its larger powder capacity, should be able to run 168gn bullets at 2900fps from a 30" barrel, without excessive pressure. Especially when using the much stronger Palma brass that is designed for 65,000psi.

I would be more worried those that use the .284 Winchester and its wildcats. SAAMI specify 2845fps for a 150gn bullet out of a 15" barrel at safe MAP limit of only 56,000psi. Those that are running 180gn pills at over 2800fps with a standard .284 would be pushing these limits and anyone shooting a .284 Shehane up near 2900fps with a 180gn bullet, would also be pushing it well over the SAAMI safe MAP limit, yet I don't hear about people not wanting to shoot next to them!

[DenisA]

I think its important to add to this thread that if anyone's going to run a cartridge case towards the top end of the limit, then there's little to no room for error when trying to keep your ammo dry when forced to shoot in the rain. I think it was one of the 2013 or 2014 Queens at Belmont that was VERY wet and straight .284 Win's were dropping primers on extraction. Even some of the most experienced shooters I know were seeing this.

Shooting in the rain rarely happens for many of us, especially in load development and it's a likely situation to catch us unaware.

Based on other threads, I don't think that "bullet proof" (for want of a better term) weather shelters protecting the ammo box to the breach and the loading hand have been adopted by many.

[plumbs7]

I think its important to add to this thread that if anyone's going to run a cartridge case towards the top end of the limit, then there's little to no room for error when trying to keep your ammo dry when forced to shoot in the rain. I think it was one of the 2013 or 2014 Queens at Belmont that was VERY wet and straight .284 Win's were dropping primers on extraction. Even some of the most experienced shooters I know were seeing this.

Shooting in the rain rarely happens for many of us, especially in load development and it's a likely situation to catch us unaware.

Based on other threads, I don't think that "bullet proof" (for want of a better term) weather shelters protecting the ammo box to the breach and the loading hand have been adopted by many.

Yes Dennis , I remember that . It was happening to 308's as well! They ended up stopping the shoot eventually . But was very dangerous .
It was good to see John and his RO team act a lot sooner from post shoots from then on !

I hate shooting in the rain !

[Brad Y]

Norm

The only problem with those figures are that we often dont shoot SAAMI chambers. Ours are long throated, chamber specs are probably on the tighter side of the scale, and we also have barrels that are twice as long as tested, probably using slower powders in the longer barrels too which will produce extra velocity, and barrels can vary in bore and groove diameter. Each gun is different and must be loaded for accordingly and back off when pressure signs show like you said.

[Norm]

Norm

The only problem with those figures are that we often dont shoot SAAMI chambers. Ours are long throated, chamber specs are probably on the tighter side of the scale, and we also have barrels that are twice as long as tested, probably using slower powders in the longer barrels too which will produce extra velocity, and barrels can vary in bore and groove diameter. Each gun is different and must be loaded for accordingly and back off when pressure signs show like you said.

I agree with you Brad.
There is a lot of things that the reloader needs to take into account when working up a load. Chamber dimensions are one and case design specifications is another.
I recently had two 7mm barrels that were made by the same company and had the same twist. They both had the same groove diameter but one had a bore diameter 1.4 thou tighter than the other! Needless to say they will not be running the same load.

[Matt P]

Also some of the Saami spec pressure limits have to do with the actions most common to the calibers, for example the 7x57 and 6.5x55 both have low pressure limits, but remember there are a lot of turn of the last century built M38's in those calibers.
Matt P

[Brad Y]

I agree with you Brad.
There is a lot of things that the reloader needs to take into account when working up a load. Chamber dimensions are one and case design specifications is another.
I recently had two 7mm barrels that were made by the same company and had the same twist. They both had the same groove diameter but one had a bore diameter 1.4 thou tighter than the other! Needless to say they will not be running the same load.

Yes I have two maddcos here chambered for my new gun, one needed another pilot to be sent from USA for the reamer as my gunsmith didnt have one to suit that diameter.