The first sign of excessive pressure is...

[nheninge]

Field data is this most important and velocity is a feel good thing because drop data is the most important. However, I routinely use the ES and SD as validation of my methodology for reloading. But if you assume even a 2% error at 2800 fps then that is a 56 fps error rate. If your chrony is consistently high or consistently low, then your ES and SD are just an indirect measure of actual ES and SD. That is why it would be nice to have a set of known velocities (i.e. 2500, 2600, 2700, 2800 fps) to fire over the chrony and estimate actual accuracy and repeatability over a range of velocities. Would be nice if there was a service that you could send in your chrony to for this validation process!

 

[montana_native]

Youre welcome.

I was fortunate enough to have pulled my hair out with a smaller caliber that didnt eat my barrel up while I was trying to figure out what the he!! was going on.

I have actually done side by side comparisions for accuracy AND point of impact using two loads that I trust implicitly using the exact same powder but a different bullet type of the same or similar weight and two loads of the same bullet yet different powder. The results were very suprising.

For example, with my old 308 barrel, I had a 155 AMAX load of 42.5 grains of BENCHMARK and a 150 ACCUBOND load using the exact same charge weight and powder. Both loads from a clean barrel and fouled with one shot would shoot a very concistent 1/2 MOA. The POI was a bit different for each one. When I fouled with one or the other, it didnt matter which one I started with and shot a few more, then switched to the other bullet, the accuracy suffered quite a bit for a few shots then sometimes settled down. Whether or not it settled down depended on which bullet I started with. If I started with the AMAX, the ACCUBONDS would suck for a while and then settle in but if I started with the ACCUBONDS and switched to the AMAX, the AMAX never would settle in to normal levels. It is however way worse when you change powders. I have done ladder tests with one powder then switched to another using the same bullet and NOT cleaning only to come up with a "good" load, go home scrub her out, load more, go back to the range and never be able to duplicate the results without shooting 10 rounds of the load with the other powder.

I have read in magazines years ago that it didnt matter what you fouled with, just foul with 2 or three rounds of whatever and go hunting. I have never heard such bad advice as this. This is also why it took me a while to figure it out as I had bad info in my head.

Virtually everything you stated NOT TO DO, I have been doing with this gun. That has got to be why my "money load" will shoot 1/4 MOA one day and 1.25 MOA another.

 

[Shootin4fun]

Youre welcome.

I was fortunate enough to have pulled my hair out with a smaller caliber that didnt eat my barrel up while I was trying to figure out what the he!! was going on.

I have actually done side by side comparisions for accuracy AND point of impact using two loads that I trust implicitly using the exact same powder but a different bullet type of the same or similar weight and two loads of the same bullet yet different powder. The results were very suprising.

For example, with my old 308 barrel, I had a 155 AMAX load of 42.5 grains of BENCHMARK and a 150 ACCUBOND load using the exact same charge weight and powder. Both loads from a clean barrel and fouled with one shot would shoot a very concistent 1/2 MOA. The POI was a bit different for each one. When I fouled with one or the other, it didnt matter which one I started with and shot a few more, then switched to the other bullet, the accuracy suffered quite a bit for a few shots then sometimes settled down. Whether or not it settled down depended on which bullet I started with. If I started with the AMAX, the ACCUBONDS would suck for a while and then settle in but if I started with the ACCUBONDS and switched to the AMAX, the AMAX never would settle in to normal levels. It is however way worse when you change powders. I have done ladder tests with one powder then switched to another using the same bullet and NOT cleaning only to come up with a "good" load, go home scrub her out, load more, go back to the range and never be able to duplicate the results without shooting 10 rounds of the load with the other powder.

I have read in magazines years ago that it didnt matter what you fouled with, just foul with 2 or three rounds of whatever and go hunting. I have never heard such bad advice as this. This is also why it took me a while to figure it out as I had bad info in my head.

WOW, this is quite a revelation! I have heard tangentially that shooting different bullets made with different alloys can affect accuracy but I never really gave it much creedence. Your systematic tests shed some light on this, and I think I may have experienced it but just chalked up a less tight than expected group after a switch in ammo to my shooting, not the change in bullet. So now at least I know that there is some truth to the "mixed alloy" claim and I suppose powder changes. Well, something to watch for while shooting groups and experimenting with different loads on the same day. I guess it means cleaning & firing more fouling rounds when changing loads during the day.

 

[Shootin4fun]

I found this thread because I got unexpectedly high velocities in a 243 and I'm concerned about excessive pressure. Velocities came from a ChronoPro which seems to be close judging by drop tables.

100gr Hdy BTSP backed by 43.9 gr IMR 4831 yielded 3140 fps. This is about .9gr over max listed in the Hogdon manuals and there are no pressure signs except for flattened primers. No stiff bolt, no brass issues that I can detect. Maybe primer pocket sligthly expanded. ES 38 & SD 14. 8th use of brass. This seems to be an accurate node. 4/5 landed in .5" with 3 of those in a clover @100, 5th a 1" flier.

Even the max load of 43.0 gives me 3075, 110fps faster than the manual. And my barrel is 2" shorter, a 22 rather than 24" in the book.

Something I haven't seen before is in this ladder test that I haven't seen before is a nonliner progression of velocities with increasing powder charges. Charges and average MVs were:

42.7gr = 3055 fps
43.0gr = 3075 fps
43.3gr = 3037
43.6gr = 3139 poorest group
43.9gr = 3140 tight group 1 flier

I need to run another round of tests to verify these results but really want to know if I'm treading on thin ice at the upper end here. Like someone said speed is nice but there's no free lunch.

Does this indicate that I'm approaching excessive pressure?

 

[MontanaRifleman]

It's true there is no free lunch but there are a lot of variables that will produce different pressure/velocity ratios such as chamber/throat spec, bore spec, length of barrel, type and twist of rifling, primers, primer lot, powder lot, bullet make and manufacturer to name a few. Not to mention, chrony's will give different reading from same lots of ammo under different light conditions, not to mention your $100 off the shelf chrony is not the most reliable and accurate piece of precision equipment available. A 1% margin of error is equivalent to 30 fps with an MV of 3000 fps.

In the final analysis, During load development, I look for the usual sings of flattened primers, craters around firing pin holes and sticky bolts. These are not perfect indicators and also vary from rifle to rifle but they usually give you an idea of about when you are approaching excessive pressure.

My final indicator is primer pocket life. I like to see 5-6 firings before the pockets are gone. 2-3 and I'm backing down. This would be in warm weather.

 

[Bart B]

Anyone ever consider the huge average muzzle velocity spread a given rifle and load has across several shooters? I've seen almost a 100 fps spread.

 

[MontanaRifleman]

I've seen almost a 100 fps spread.

Easily

 

[Shootin4fun]

Different shooters?? Ok, that's enough now! No more variables please! gun)

Right, all those factors are going to affect the velocity. I just started checking the primer pockets from my hot loads early this morning to see if they were expanded. These are only on their 4th firing and the primers are going in pretty easy. Equal to about 8 firings of a milder load.

Is it OK to use some kind of adhesive that won't flow into the primer - like nail polish or a locktite of some sort to be sure the primer won't fall out- if you want to make use of cases with easy primer pockets?

 

[MontanaRifleman]

Different shooters?? Ok, that's enough now! No more variables please! gun)

Right, all those factors are going to affect the velocity. I just started checking the primer pockets from my hot loads early this morning to see if they were expanded. These are only on their 4th firing and the primers are going in pretty easy. Equal to about 8 firings of a milder load.

Is it OK to use some kind of adhesive that won't flow into the primer - like nail polish or a locktite of some sort to be sure the primer won't fall out- if you want to make use of cases with easy primer pockets?

I have heard of guys using super glue, nail polish or whatever, but I never have. I seat my primers using an RCBS hand priming tool and I can feel them pretty good. I usually have a good idea which ones will hold and which wont. If i have a doubt, I take the case, tilt it, and tap the head firmly on the hard surface of my reloading bench. If it holds, it's good. If it doesn't, I pitch it.

 

[Shootin4fun]

In another thread there is talk of expanded primer pockets, and what happens if they get to the point where gas leaks out around the edges of the primer back to the bolt. Not a pretty thing.

Then there is talk of the primer swager device Hart makes. Seems like there are +s and -s to that. It would be nice if there was a reliable cost/time effective way to renew the primer pockets, but at this point tossing them seems like the most expedient way to go.

Most of my experience with expanded primer pockets is with Federal brass, and that seems to be the consensus in the other thread.

 

[MontanaRifleman]

Over all, Federal brass seems to be the cheapest/weekest in my experience. I usually go with WW if I can't get something like Lapua or Norma. Hornady is good too for the most part.

IMO, Swaging primer pockets is not worth it. Once they're stretched, that's it.

 

[Clark]

I chambered a Uberti 1885 action for 257RAI rimmed last year.
I thought I would be getting 80 kpsi before I had to back off.
But the Norma 7x57mm rimmed brass I used was weaker than 257 Roberts rimless brass.
I had loose primer pockets in rimmed brass.
I shot 4 deer in 2012 with wimpy 65kpsi loads.

 

[ehryk]

I let pressure trace let me know. The hard part was taking all the measurements, which I spent hours on, but once done was well worth the time. The next part was looking for a load with components I had that had full measurements and pressure included. Once I adjusted the powder charge to give the velocity listed I was able to make my correction which was only about 130psi. Now I work up the load until PT says I am at or near max then work down for accuracy. Most often PT shows I am at max with no apparent pressure signs at all. Cases mic fine, no ejector or extractor marks, primers are fine, etc. Pressure Trace is a bit pricy but I feel it has been WELL worth the expense.

 

[PBR driver]

When you achieve .0001" case expansion over a factory round in your chamber.gun)