How far off pressure are you loading?

[SloppyJ]

What's everyone's experience finding pressure in a certain rifle and then backing it off from there? I'm beginning to wane from riding the edge and chasing that top end velocity to loading something more conservative that will shoot well in a multitude of conditions.

How much headroom are you giving your ammo in terms of powder or velocity to account for environmentals, rain, dust/debris...etc? 99.9% of us can't measure pressure accurately so are you using another metric?

Thought this could be an interesting discussion. Climate is going to impact some things as well. I know that it's nothing for me to shoot the same load in 100°+ temps to negative temps.

 

[coyotekilla]

I bought a garmin zero chrono for that reason. I'm kinda new and don't need an expensive lesson. I think my hottest load is a 243, 85gr hpgk at 3333 with a 20" beretta brx1. Its a book max load.

 

[sdupontjr]

Most folks here in South Louisiana, or at least at m range, do load development in 90 - 95* weather. Because here, we have hot and muggy OR Hotter and muggier. The summers are brutal, so in my 7mag and 308's, I get as close to pressure as I can get with good accuracy and velo. Knowing that when winter comes and things cool down, my loads are still safe. It also allows me to shoot anytime I want and not have to worry about temps. I also use temp stable powers like H-1000, Varget and 8208xbr, so I don't get big fluctuations when the temps change.

 

[wind gypsy]

Ideally I never find pressure but rather get to a velocity that logic tells me is at a reasonable pressure and stop without looking for "max" before issue.. Since i started shooting more suppressed and more tikkas pressure signs seems to find me more often though.

I haven't poured water intentionally on ammo to do water test but have been shooting in rain/mist enough lately that I can just leave a loaded mag in the rain and then give it a shot to make sure it runs fine when wet.

 

[Hunter26]

I am curious what others are doing as well. I had been finding pressure and backing off .5 grains. However I had a load this year that was loaded up in mild temps and then shot it in warmer very humid weather and was getting pressure signs. I guess I will back it off another .5 grain and at some point try it in hot weather again.

 

[Harvey_NW]

Anymore, my approach is pretty conservative. With a new lot of brass I grab a charge about 2gr below the avg book max from a couple different sources, and do "load dev" by testing combinations (switching bullet or powder, not OCW) until one shoots acceptable. 10 shots into 1" or less is my goal. Load the rest, zero, true everything up, shoot.

After brass is formed, I bump the shoulders back .002" and load up a pressure ladder in .5gr increments with the winning combo, and try to do this test in warm weather or at least account for temp sensitivity. Drop 1gr from ejector marks, 2gr from bolt lift. Load the rest, adjust velocity in calculator, done.

 

[SloppyJ]

@T_Widdy quit liking everything and jump in here with some knowledge! Everything got home safe and sound last weekend so thank you again for that! I appreciate it so much.

I can understand the Louisiana thing for sure, it's only mildly better weather here in AR. The hot summer afternoons definitely provide a good testing environment to make sure that you're not going to get in trouble.

There was some feedback in the 25 western thread and someone said they had a rule of thumb for backing off of pressure signs on virgin brass. Their rule was to drop 1.5gr from where you found pressure on virgin brass to get in the ballpark for your fired brass. Now that's going to be wildly different depending on powder, cartridge, brass quality, and a myriad of other factors but from what I'm seeing, I might be able to get behind that as a generality. I still have plenty of testing left to do.

Powder selection plays a large part in it. I asked the question with the assumption that we were using relatively stable powder so Hodgdon Extreme line, N500 series...etc

 

[SloppyJ]

Anymore, my approach is pretty conservative. With a new lot of brass I grab a charge about 2gr below the avg book max from a couple different sources, and do "load dev" by testing combinations (switching bullet or powder, not OCW) until one shoots acceptable. 10 shots into 1" or less is my goal. Load the rest, zero, true everything up, shoot.

After brass is formed, I bump the shoulders back .002" and load up a pressure ladder in .5gr increments with the winning combo, and try to do this test in warm weather or at least account for temp sensitivity. Drop 1gr from ejector marks, 2gr from bolt lift. Load the rest, adjust velocity in calculator, done.

How do you account for temperature during testing? If you complete this process in the winter, do you repeat it to verify in the summer or back your charge off a little to account for that?

It seems there's no good way getting around doing almost 2 different sets of load dev. One on a new barrel with new brass and one on fired brass and a broken in barrel.

 

[Jimbee]

I'm basically doing the same as WindGypsy. I used to chase velocity and max book loads. It caused issues. I recently started dumping water on my ammo and shooting it.

 

[T_Widdy]

@T_Widdy quit liking everything and jump in here with some knowledge! Everything got home safe and sound last weekend so thank you again for that! I appreciate it so much.

I can understand the Louisiana thing for sure, it's only mildly better weather here in AR. The hot summer afternoons definitely provide a good testing environment to make sure that you're not going to get in trouble.

There was some feedback in the 25 western thread and someone said they had a rule of thumb for backing off of pressure signs on virgin brass. Their rule was to drop 1.5gr from where you found pressure on virgin brass to get in the ballpark for your fired brass. Now that's going to be wildly different depending on powder, cartridge, brass quality, and a myriad of other factors but from what I'm seeing, I might be able to get behind that as a generality. I still have plenty of testing left to do.

Powder selection plays a large part in it. I asked the question with the assumption that we were using relatively stable powder so Hodgdon Extreme line, N500 series...etc

Good deal! I forgot to check the delivery.

I now find heavy bolt lift or ejector marks, back off 2-3 grains, spray a light mist of water on the case and shoot to check for heavy bolt lift again. 2-3 grains off pressure signs has seemed to work. I sometimes have 1 or 2 out of a 10 shot test that requires primary extraction with the sprayed cases but nothing that fights me running the bolt.

 

[FoggyScope]

Im 2.5 grains under where i first saw ejector swipes on virgin brass. At 1.5g under i got heavy lift on wet days so i dropped another grain. Funny enough this puts me just under book max velocity.
im going to do a wet ammo test next time i work up a load. Thats a good idea to find that out at the start. I have been doing the freezer and dash heater trick depending on what time of year it is to make sure i didnt have pressure at high or low temps.

 

[TaperPin]

I like to load hot enough that cheap soft brass starts to develop thinning near the case head or opens primer pockets after 10 reloads. If the load kills cases after 5 shots it’s too hot, and if most cases are going well over 10 it could handle a little more powder. This has served me well, never resulted in a blown primer or full case head separation and velocities usually at or slightly above published max. It’s easier to measure case head expansion than the number of loads, but either work. A lot of brass is soft enough to leave multiple ejector marks and still survive 10 reloads, so I dont ignore them, but don’t see them as the mark of a max load. One batch of brass had 8 ejector marks on some of the cases.

Lapua brass is hard enough the primer often becomes the weak link, so I just work up to what most books are getting for max velocity and call it good to avoid
leaking primers, or blanking primers with my loose fitting firing pins. Ejector marks take a lot more pressure than on soft brass.

If I ever had a rifle disabled by over pressure I’d be more conservative, but it’s worked for 40 years so no reason changing it if it ain’t broke.

 

[Harvey_NW]

There was some feedback in the 25 western thread and someone said they had a rule of thumb for backing off of pressure signs on virgin brass. Their rule was to drop 1.5gr from where you found pressure on virgin brass to get in the ballpark for your fired brass.

That was me.

Powder selection plays a large part in it. I asked the question with the assumption that we were using relatively stable powder so Hodgdon Extreme line, N500 series...etc

Agreed, I'm only using Hodgdon's Extreme, or VV N560/565/570, and also ADG brass, which I find to be a bit tougher. If I get ejector marks on ADG I call it there and drop at least 1gr.

How do you account for temperature during testing? If you complete this process in the winter, do you repeat it to verify in the summer or back your charge off a little to account for that?

Pretty much, like I said I like to try to do this in warmer temps. Last year I did "load dev" on a barrel that was "broken in" @ 88°F. Found pressure on new brass, dropped 1gr from ejector marks, called it good and trued up. Then shot over a chrono early morning just before season and got a temp factor of .77fps/1°F (6.5 PRC, N565). Then tested in 29°F over winter and it was right on track. Sized my lot of brass and tested my original load in cold temps and it was spicy, ejector marks and slightly sticky extraction. Dropped 1.5gr and haven't touched it since.

It seems there's no good way getting around doing almost 2 different sets of load dev. One on a new barrel with new brass and one on fired brass and a broken in barrel.

I agree for the most part, except I don't really consider it load dev because I don't believe in nodes or chasing tiny sample sizes around. If pressure shows up, I drop the charge. The biggest change I've seen is from new vs formed brass. I haven't witnessed much velocity migration on barrels that I've developed safe loads for. I have 2 new ones coming in that I'll start a thread and post all the data as I track them.

 

[waspocrew]

I don’t chase max, but I’ll work up to pressure then back it down at least 1 gr.

 

[BigNate]

I agree for the most part, except I don't really consider it load dev because I don't believe in nodes or chasing tiny sample sizes around.

I find this interesting. Would like to understand better what you think is going on.

I'll type out a longer explanation if I think it's warranted, but I think I do believe in nodes so I'm curious about your school of thought.

 

[SloppyJ]

I haven't witnessed much velocity migration on barrels that I've developed safe loads for. I have 2 new ones coming in that I'll start a thread and post all the data as I track them.

I had a really nice load in my 6 creed comp gun after about 50 shots. I loaded up 150 and went and shot a match the next month. About halfway through I noticed my bolt started to get funky. I setup my chrono on the next stage and I was about 40fps faster than when I started. I finished the match but had to go pull the rest of the bullets and drop the charge. Temp could be a slight variable but we're talking only roughly 15° difference between the different days. That's not enough to account for that velocity swing.

I think some tests and logs on new barrels going through load development would be extremely interesting and I'll join you on the next one I do too.

 

[Wprinkle]

When the bolt gets sticky back off a ticky

 

[Harvey_NW]

I find this interesting. Would like to understand better what you think is going on.

I'll type out a longer explanation if I think it's warranted, but I think I do believe in nodes so I'm curious about your school of thought.

To put it shortly, nodes have never been proven to exist with statistical validity. Dropping a near max powder charge can decrease dispersion, if it's worth the sacrifice in velocity. What most people observe as "nodes" from 3-5 shot OCW tests is just random distribution with up to 70% variability, meaning the same load (with a 1" average) could produce groups as small as .3" or as large as 1.7". Upping your sample size drives the variability down, and gives you a much better picture of the actual size of the cone of fire. I load ~.050" off the lands and do a small pressure test to make sure it's safe, then I shoot 10. If it's 1" or less, I'm done. If it's over 1", I'll repeat with a different powder or bullet. The combo either shoots or it doesn't.

This episode of The Hornady Podcast explains it in statistical detail, and the results they got when looking for nodes.

Can't post pics right now, but the results of the safe loads I tested in 88°, and adjusted and checked at 29°, both were ~.7" group ES for 10 shots.

 

[wyosam]

Quite a ways. Very descriptive, I know. I used to load right up to the ragged edge, but anymore I’d rather determine my need, and use enough cartridge to get there easily when considering bullet/barrel length etc.


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[jfk69]

I run pressure ladders and do load development in the summer, try for 70+ degrees, 80+ is even better. If I find pressure signs I back down 1 grain and test again. I shoot 10 round groups to determine accuracy. I don’t have any precision custom guns, and I don’t feel comfortable shooting beyond 500 yards at live game, so if my 10 round groups are under 1.3” MOA, I call development done. I always use a chrono during load development, I don’t chase velocity because my hunting scopes almost all dial (at least those I’ll use at longer ranges). I want enough velocity for reliable bullet performance at the ranges I’ll shoot. I don’t need anything faster than that.