M14 Forum

Larry Gibson

Bill

Here's the very problem with that site and several others just like it that say basically the same thing;

'The most commonly-cited explanation asserts that .308 Winchester operates at higher pressure than 7.62x51mm. SAAMI specifies a maximum average pressure for .308 Winchester of 62,000 PSI, but the oft-cited pressure of 7.62.51mm is 50,000 PSI--almost 25% less."

The problem being that the "psi" refered to is with piezo transducer measurement for the .308W and for C.U.P. (Copper Unit Pressure) for the 7.62 NATO. If you use the same pressure measuring method for both then they are the same; either 60,000 psi for a piezo transducer measurement or 50,000 C.U.P. for the Copper Unit Pressure method.. Comparing piezo transducer psi's to C.U.P. psi's is comparing apples to oranges. There is no correlation between the two as one site would have you believe either BTW.

Also comparing velocities obtained out of different length barrels some of which are production barrels and some of which are test barrels is a futile process.

Also you should quantify your statement;

"Now with bullet weights the lighter bullet moves faster out of the case when fired so there is less breech pressure. The lighter bullet moves sooner as the round is fired. With the heavier bullet it has a higher breech pressure because the heavier bullet takes a longer time to move out of the brass case. There is a higher peak breech pressure. This is why some semi auto's don't like the heavier bullets."

with your premiss only would apply if the same powder and same charge of that powder were used for both the light weight and heavy weight bullets. If not quantified it is all to easy to demonstrate where the heavier bullet, with a slower burning powder, will actually have less "breach pressure".

Larry Gibson

jake2far

Larry, I found this and was wondering if you have any experience with this double pressure spike?

http://www.shootingsoftware.com/barrel.htm


Jim

Larry Gibson

I have recorded "spikes" as they are common with loads that have ignition problems or the pressure is not sufficient for uniform burning of the powder. However, I have not recorded anything as dramatic as they show with the RSA equipment, particularly with the almost identical loads in the same cartridges. I've discussed this with a couple RSA owners but have not worked with an RSA set up specifically. There are several other things besides pressure that can cause such "spikes" to appear also. Understand that the strain gauge must be securely attached to the barrel. If not such "spikes" can appear. Also the computor and/or the RSA "box" may be suseptable to shock from muzzle blast if not positioned correctly.

As mentioned though I've measured some pretty sporatic time pressure curves with some cartridges. They are not all smooth lines going up and then down in a nice curve. Some "spiking" can be expected but the average peak pressure of such should not excede the SAAMI MAP. You see a lot of "pressure spiking with light cast bullet loads with some powders and with mild handgun cartridges such as "cowboy action loads". Recently I measured some factory match handguns loads and you'ld be surprised how "spiky" the time pressure traces were.

Larry Gibson

MTU1980

What is the price $$$ for the Quick Load data software??? And how often do they upgrade it? I wonder if they have the new Hodgon (spelling?) CFE 223 powder in Quick Load software now.....??? thanx

TheTinMan

Google

RAMMAC

Find it at

http://www.neconos.com/details3.htm

Cost is about $153

They update the data when they feel it's necessary, there is no schedule to their updates. The current data does NOT include CFE 223.

mustanggt

For the purposes of the m14 or m1 can it be simply put that the difference to understand is to use the medium burn powders because its all about not over stressing the gas system on these rifles? In essence 7.62 is to distinguish from 308 which is more referring to that chambering for bolt action rifles? You can use a wider array of powders for the bolt gun vs the gas guns. Or am I all wet? This is what I think in my mind to distinguish between the two.

RAMMAC

I think that with your kind of shooting in mind, that would be a valid way of managing the ammo so that it is used in the most appropriate weapon.

For my purposes my rule of thumb is that the difference between .308 Winchester and 7.62x51mm as a quality control issue.

Those that manufacture .308 Winchester ammo have better quality control which means that their loads will be more consistent and stay within SAAMI safety standards.

7.62x51mm ammo is normally military surplus and as such it was rejected by the country of origin because it exceeded some standard. It has most likely exceeded one of the standards for manufacturing, transportation, storage, or testing. It could simply be a manufacturing overrun, too many rounds were produced and the extra were sold as military surplus. Or it could mean that the ammo was stored in an overheated warehouse in Afghanistan and the powder degraded due to high temperatures. In that case nobody can tell you honestly how that powder will perform, it might simply burn inconsistently and produce terrible group sizes or it might burn too fast and over-pressure the barrel.

mustanggt

RAMMAC, that surplus don't sound like a good deal after all does it???

RAMMAC

It's not too bad of a deal most of the time. I know quite a few people that use milsurp almost exclusively. But once in a while it can do weird things. I use commercial ammo and hand loads almost exclusively. The only milsurp I've fired were FN and I was very impressed with both their performance and their reliability.

My recommendation is that if you buy milsurp do a little research first and only use the stuff that has a reputation for not having problems.

Then once you get the ammo remove it from it's original packing and check for corrosion and proper sizing. Use a Wilson style cartridge gauge to check the sizing, it provides you with a fast way to verify safe head space and trim to lengths even though the cartridge is completely assembled with powder and bullet.

If it passes those checks then I'd test fire a couple of rounds, one at a time, and look for any obvious problems with chambering, ejection, or extraction. After firing, check those first couple of cases for signs of excessive pressure. I would check the inside for an excessive pressure ridge and measure around the base for excessive expansion.

If all that looks good then I'd say that the ammo is safe, at least that lot. Definitely keep a record of the lot numbers, some will be great while other lots might be questionable.

sgj2025

Damn, show me a 7.62 die and I will kissyour ass! For Our beloved m14 keep the bullet weight below 178 and you will be fine! Hornady 178 I do not suggest they are on the are on the warm side!!!

SILENCED556

OK, So.... been in the military for going on 19 years now. I suppose you could say I've had my fair share of experience with the M14, M4, SSR and now our EBR's. Over the years I've developed quite the fetish for the M14 base. I've owned M1 carbines and Mini-14's but never had the capital to drop on an M1A until recently. Went with a loaded that will get turned over to one of my armorers here shortly for a little "tuning". Over the years I guess you could say that I've really taken for granted the fact that all I need to do is walk into the armory, grab a rifle and a case of AA11 (or A130) and be on our merry little way. Start out the day with a 100yd cold bore and move to 600 and out with a few tweaks here and there. Never really grasping all the work that went on behind the scenes to get me there. So now that I've got my own personal toy, what do I use to feed the beast? A little bit of searching around the .net led me to this forum and I must say (especially after reading this post), I officially feel a little more retarded. I mean, it's one thing to get your dope, punch a few numbers from your book and send it, but I never stopped to think about the actual intricacies involved beyond headspace and timing. I've reloaded in the past. Mostly .357, 45 ACP and 45 Colt done on a old rock chucker that my grandfather gave me. But even then, simple numbers and settings from a book. Nothing as complex as this. I can see there is a wealth of knowledge floating around in the forum here. Can't wait to pick a few brains and learn more!
BTW... leaning towards Fed. Match 168's for now. Not the 175's that I'm used to, but it's an M1A, not an SSR.....yet.

Cheers!

nf1e@snet.net

GMM 168's are top notch. Can't go wrong with the best.
Semper Fi

Dredsen

I REALLY think the mods need to take your best post with drawings, or let you write up a new one and STICKY that sucker, so this question doesn't come up and confuse more people when someone chimes in on page 3 with opposite information.