Reloader 17 Narrow Nodes

[jasmay]

Any body considering running compressed loads is playing with fire. You may get away with it for a while but eventually the continued over stressing will cause something to let go. This could have disasterous effects, if not to the shooter, then to some body near by.
If a shooter in my club was considering doing this they would be taken aside and given a good talking to, and if they persisted in doing so would soon find themselves dismissed from the club. After all safety is of the utmost of importance. I cannot follow some peoples thinking that velocity is king. Quite often a accurate and well performing load can be found down from maximum loads, and is much easier on components. Do not try to beat the wind with velocity, just learn to read the wind.
My two bobs worth on the matter.
Cheers,
Trevor.

Not true! Slower burning bulky powders are often compressed & where such powders are used, such as 2209 in 308 cases, it is not dangerous to use compressed loads. However using 2209 compressed loads in 30/06 cases for example will cause dangerous pressures depending the bullet in use. That said I do not like loads that call for compressed charges in target loads due to variable compression raising ES to levels where long range accuracy can be affected.
Keith H.

Keith, I have often wondered about the relevance of SAAMI specs on modern target action, particularly when it comes to pressure maximum, although it is certainly a good base line for safety, weren't a lot of these developed decades ago?

[KHGS]

Any body considering running compressed loads is playing with fire. You may get away with it for a while but eventually the continued over stressing will cause something to let go. This could have disasterous effects, if not to the shooter, then to some body near by.
If a shooter in my club was considering doing this they would be taken aside and given a good talking to, and if they persisted in doing so would soon find themselves dismissed from the club. After all safety is of the utmost of importance. I cannot follow some peoples thinking that velocity is king. Quite often a accurate and well performing load can be found down from maximum loads, and is much easier on components. Do not try to beat the wind with velocity, just learn to read the wind.
My two bobs worth on the matter.
Cheers,
Trevor.

Not true! Slower burning bulky powders are often compressed & where such powders are used, such as 2209 in 308 cases, it is not dangerous to use compressed loads. However using 2209 compressed loads in 30/06 cases for example will cause dangerous pressures depending the bullet in use. That said I do not like loads that call for compressed charges in target loads due to variable compression raising ES to levels where long range accuracy can be affected.
Keith H.

Keith, I have often wondered about the relevance of SAAMI specs on modern target action, particularly when it comes to pressure maximum, although it is certainly a good base line for safety, weren't a lot of these developed decades ago?

True, but still relevant. Due to the strength & design of the better modern target actions in use today, many of the old home reloader pressure indicators are no longer relevant, which leads the home loader to push loads past where they should be in the pursuit of performance, a larger case at lower chamber pressure is what should be the goal, if the extra performance is deemed a requirement. An example of this is the recent 284 primer pocket problems which are a result of pushing to a higher node with that case than is prudent, all for the sake of a few fps higher velocity. Many 284's & 308's are inadvertently run on the edge due to the action design & strength masking the traditional pressure indicators. All cartridges have more than one accuracy node, three quarter throttle usually delivers a node that is wider & more flexible than the higher node. We need to be aware that the total failure of the brass cartridge case occurs in the vicinity of 70,000 psi cup. Standard factory chamber pressure for a 284 & 308 cartridge is 53,000 to 55,000 psi cup, manny shooters are exceeding these limits without realising it! Food for thought.
Keith H.

[Winston]

Hi Keith,

I thought the saami pressure spec for the 308w was 62k psi? Am I missing something?

[williada]

The bottom line is the legal system. Period! The great base of our negligence laws were founded in firearms mishaps. The courts and the insurance companies use binding precedents established for a long time and unless you have the money or the expertise to prove the facts are different then the precedent holds. The courts and insurance companies adhere to SAAMI and CIP guidelines in applying the reasonable person test, that is, what a reasonable person would do otherwise you hold the risk at your own peril. I certainly don't want to be squadded beside someone experimenting with unproven hot loads and I don't want to see our insurance placed in jeopardy either.

[jasmay]

Thanks for the words Keith, it is indeed a good reminder to keep things realistic.

It would be nice to see some perhaps more relevant/thorough information regarding this and Palma brass, so we do understand better our safety limits.

Williada's comments are also quite prudent and should be considered by all reloading.

My personal experience is pushing harder just makes everything harder to maintain for little gain.

I don't personally see an issue pushing as hard as you can if you wish, as long as you stay within those set guidelines, I think the biggest issue we have a lot of folk that don't know what those are.

[Winston]

Hi Folks,

A lot of informative replies from some very knowledgeable folk - thank you.

There seems to be a theme here that "this new guy is going to blow himself or someone else up", so to try and put some minds at ease, here is what I am working with.

While I understand that Quickload is simulation tool, not reloading manual, my results to date with several other rifles have been extremely encouraging. These simulations have the powder burn rate calibrated using results of chronographing simulated loads. All other input measurements are the average of multiple cases.

This load I have had fired 6 times on the one set of cases. 49k psi. Primer pockets still tight. Predicted velocity matches measured velocity. Safe as safe.





This is the load I will work up to today, weather permitting. 56.6kpsi. If this simulation was 62k psi, I wouldn't bother and just leave well enough alone. I figure that at 10% under the Saami spec, I should be fine while getting the most out of my rifle without causing undue stress on my rifle or components








For the sake of comparison, here is what a 2156 palma with 45,4gr of 2208 looks like. 56k psi





I'm proving my loads at the range, by myself, working up with caution. I have no intention of rocking up on a shoot day with something I hadn't proven first!

Thanks again blokes, hopefully that helps put some minds at ease. I don't want to wear my bolt as a piece of jewelry anymore than anyone else does.

Alex

[williada]

Winston, its good to see you taking a careful approach with the heavy projectiles in this chambering that is stretched to the limit with their use. The pressure issues can be solved more readily by lengthening the throat bit by bit with a universal throat reamer. It is trial and error for several reasons.

If your goal is to max out the charge within SAAMI limits, you will have little room to move unless you relieve pressure by increasing throat volume. Ideally the throat needs to remain minimal in terms of diameter to align the projectile with the bore and achieve greater volume by lengthening it.

There is greater inertia with heavy projectiles. As such, a greater dwell time is sufficient to get a full powder burn. Many people use a compressed load to get a full and efficient powder burn, but in this situation it is not necessary (a very mild one maybe) if you can match the throat length with the powder burn efficiency. It is analogous to a rocket launch where the rocket seems to pause on the launch pad, slowly moves forward and accelerates with smooth transition to maximum speed. You don’t want wasted energy popping primers and you want a smooth transition in acceleration as the projectile engages the rifling and beyond. You want to contain it and use the energy in a sustained long burn to increase your velocity.

BC is irrelevant if the gear will not group. Firstly, the longer throat is less inclined to create excessive harmonic noise from wasted energy where the shockwave donut can interfere with group size as it can interfere with muzzle shape on bullet exit. Secondly, you want those heavy bullets positively compensating at long range where you will use them, so the launch angle of the muzzle has to be controlled in the vertical plane. This is a different concept compared to the muzzle waggle or distortion of poor harmonics and sometimes wrong powder choice. You may of course add weight to the muzzle to control launch angle for compensation purposes rather than keep chewing into the throat in an effort to find the right cycle of the muzzle whip.

In summary, with lighter projectiles the powder charge can place us where we want to be because we can adjust it, and we can also finesse with small seating depth adjustments, but with full loads and heavy pills that choice is gone. The initial difficulty is therefore getting the ignition process right to reduce extreme spread, not pop primers and remain safe; then you must achieve (probably a further) suitable throat lengthening that controls bullet exit timing in terms of both harmonics and launch angle. These are very advanced skills both in armouring correctly and application of positive compensation theory when normal load development won’t get you there. David.

[Winston]

David - many thanks for a detailed reply and some good Tech stuff to sink my teeth into.

Please correct me if I am wrong, but the inertial differences (and subsequently dwell time) between light and heavy projectiles is something that quickload accounts for? If it didn't, we'd be fed the same load data for any projectile occupying the same amount of case volume. Or was your comment with reference to muzzle distortion as a result of the increase in dwell time?

I have read Geoffrey Kolbe's work with great interest, but without the access to laboratory equipment costing more than most people's rifles, positive compensation to a meaningful degree like he describes seems unattainable unless one has a ton of experience with the particular load and rifle or stumbles upon it with a crap shoot.

Can you recommend any books that may help a man get a more detailed understanding?

I'm not necessarily looking to max out the charge within saami limits. With any luck, I can find a charge that still has me enough wiggle room to adjust up or down to find a load at a harmonic node with good vertical.

Another question, if I may - do the principals you discuss apply to shooting 80s and 90s in a 223? Proportional to the differences in the cube of the bore size, they are fairly similar.

Lastly, am I really trying something wildly out of the box here? Bryan Litz has said on the long range Hunter forum that the only reason he doesn't use 230s in his ftr rig (he uses 215s) is recoil. I figured with a 10kg gun, I could cope. With that said, Litz has the benefit of an aerospace degree, so he can probably get things to work a bit easier than most!

Thanks again

[mike H]

Winston,
Match Rifle shooters or most of them,use heavier bullets usually 208 or210 grains,a good many use 2209 powder,all have long throats to allow longer bullet seating and to give more powder capacity.What I do is give the gunsmith a dummy cartridge loaded with the projectile of choice and enough length of seating to hold the bullet.If you overdo it,you will either have next to no case neck holding the bullet,or a lot of bullet jump.
All of the 2209 loads would be compressed to some degree,I don't like heavy compression and prefer to have the powder just touching the bullet base.
Your heavy bullet project is very interesting .
Mike.

[Winston]

Winston,
Match Rifle shooters or most of them,use heavier bullets usually 208 or210 grains,a good many use 2209 powder,all have long throats to allow longer bullet seating and to give more powder capacity.What I do is give the gunsmith a dummy cartridge loaded with the projectile of choice and enough length of seating to hold the bullet.If you overdo it,you will either have next to no case neck holding the bullet,or a lot of bullet jump.
All of the 2209 loads would be compressed to some degree,I don't like heavy compression and prefer to have the powder just touching the bullet base.
Your heavy bullet project is very interesting .
Mike.

Cheers Mike! I did just as you suggested. Barrel is throated so the pressure ring if the projectile is just above the neck/shoulder junction so I have basically a full neck gripping the projectile, while still not compromising powder space too much (seating at an oal of ~3.150"). This chamber also gives me the flexibility to shoot 215 hybrids with a short jump and still have plwnty shank in the case.

I'll keep posting my results here and keep learning from the brainstrust.

[KHGS]

Hi Keith,

I thought the saami pressure spec for the 308w was 62k psi? Am I missing something?

That is the piesio rating which is roughly equivalent to 53,000 cup. confusing, isn't it? You need to know the different modes of measurement, web sites & loading manuals rarely tell you which method they are using!!!!!!
Keith H.