Effect of loads that are too hot?

5RWill · December 31, 2013, 09:19 PM

Here's the load
45.5gr Varget
Nosler Brass
Hornady 178Gr BTHP
Fed 210m Primers
COL 2.860

So when i grouped these in low temps the best group i got was 45.5, which i accidently loaded from the get go (max is 45.2gr). That said i saw no pressure signs at the time or maybe i wrote down 45.5 when it was actually 45.2. Either way I screwed up something this go around. So shot last spring and the first shot stuck. Decided to get rid of the remaining rounds i had left today. Was shooting out to 400yds and they were literally everywhere. Dialed 2.2Mils thinking it wouldn't be too far off my berger 175gr load and it was over. I ended up shooting 1.8 Mils and shooting high as hell, though still making hits.

None of them stuck, was just trying to get rid of them without having to pull them all. Can the pressure spike of a hot load cause this? They were all over the place i've never seen this rifle produce groups this bad at extended range.

SonOfGun · December 31, 2013, 10:02 PM

Do ya think it might help to know what you are shooting?
The data means nothing without knowing what caliber.

5RWill · December 31, 2013, 10:05 PM

.308 given the data i figured most would know but that's my bad.

Will be investing in a collet style bullet puller that's for sure.

Sierra280 · December 31, 2013, 10:05 PM

Absolutely. If i watch the chrono, I get to a point where accuracy just drops off suddenly, much more than the increase of velocity would make you think it should. I assume that at that point, chamber pressures have at least gone higher than optimal. In the worst case time I had the accuracy go to hell, and the primers flattened a little, but never any trouble extracting. Trouble extracting is a BIG sign that you have a load that's WAY TOO HOT.

Just use the puller and be safe.

Bart B. · January 1, 2014, 03:20 PM

Most loads' pressure curves are not all that repeatable when they're too hot. That is, above SAAMI specs by more than about 5%. And that causes them to be less accurate as measured by exteme dimensional spreads of many shots in a test group.

Case life gets less, too, as the brass is work hardened to extremes when fired then sized back down; especially with standard dies resizing cases too much after being fired in SAAMI spec chambers.

I think 42 grains of Varget is about max for 178's in a .308. Guessing at pressure from visible signs ain't the best thing to do, in my opinion. After shooting some proof loads in 7.62 NATO rifles noting no significant visible signs of pressure with the same lot and amount of powder, same case and primer used with 147-gr. bullets (50,000 cup) but with a 172-grain bullets (65,000 cup), that convinced me that visible signs are not good for judging pressure with.

Slamfire · January 1, 2014, 03:41 PM

Quote:

None of them stuck, was just trying to get rid of them without having to pull them all. Can the pressure spike of a hot load cause this? They were all over the place i've never seen this rifle produce groups this bad at extended range.

When conducting load development I now lubricate my cases. This does three things, firstly the transition from rounded primers to flat primers is more distinct. I found in my gas guns particularly, that dry cases gave flat primers but the lubricated cases gave rounded primers with the same load. Obviously what was happening was an effect due to the time it took the side walls of dry cases to stretch, because the front of a dry case firmly fixes the case to the chamber, versus with lubricated cases, the cases slide to the bolt face while pressures are still low. While primer roundness is a very unreliable indication of pressure, at least when you see a change, you know something is going on. While I have had leaky primers in a batch of cases where the other primers were round, at least the transition from round to flat is not being disguised by case to chamber friction. And this is helpful in evaluating loads in semi auto matic mechanisms as you don't have bolt lift as a guide.

Secondly, case friction disguises the load on the bolt face. With dry cases and dry chamber walls not only are you causing the cases to stretch, the stretched case is carrying some of the load. With lubricated cases the bolt face is carrying the full thrust of the case, as it is supposed to, and sticky bolt lift becomes apparent with over pressure loads. I think this could be part of your problem, over pressure loads (which the chamber sidewalls are carrying, it does not magically go away!) but the case load on the bolt face has been reduced by case friction.

Thirdly, when shooting new brass, such as I am currently loading new 30-30 brass, case lubrication keeps the side walls from excessive stretching on the first firing. This new 30-30 brass is excessively short for the rifle chamber. I determined that with a Wilson case gage and fired brass. The new brass headspaces at least 0.008” less than fired brass, and with a dry case in a dry chamber, the sidewalls are going to stretch that much on the first firing. This situation is particularly bad when firing new belted magnum ammunition as the shoulder distance is not controlled. You can have huge dimensional changes in shoulder position with belted magnum ammunition. The previous owner to a 300 H&H I have, he said the case heads came off on the third firing. I lubricated my cases and only pushed the shoulders back 0.000 to 0.003” and so far, no internal necking inside of the case.

I try my best to develop loads over a chronograph as it is an article of faith with me (that is, I have no way to prove this) that if my loads exceed factory or published values, then my pressures exceed factory or published values. I am certain you would have found that your loads were just smoking over the chronograph.

I have seen blown groups with over pressure loads, I don’t know what is going on really, it could be the dynamics of the rifle is such that the mechanism stretch and barrel vibrations are irregular. Or it could be the bullets are all getting deformed in unpredictable ways. Or maybe it is all due to Gremlins. Either guess is as supportable as any other. But the fix is easy: cut your loads.

5RWill · January 1, 2014, 04:51 PM

Yeah I'm backing down to 45 or 45.2 as the manual states. As I said I'm not sure how I loaded 45.5 but I did: carelessness or stupidity I guess. 45gr shot well enough though here's how 45.5 shot last winter.

Max load in the books is 45.2 which is what I'll be backing down to. I ran Berger 175gr BT LRs before this at 44.5 with great results at distance holding a tad above half MOA out to 400yds. MOA at 500yds and at 600 they started to open up though I blame that on my inexperience with wind and distance shooting. 600 and up my groups start to open.

I appreciate the responses guys. Kind of wanted to assure it wasn't my rifle.

The first bolt stick I had last spring was very noticeable it took some force to get it out honestly. I have a collet style puller in my cart now as we're about to build a setup at the house finally.

What's the jump to the lands on factory rifles? Quite a bit right? I have these seated to run out of AI mags at 2.860 I doubt they're anywhere near the lands but if they were coupled with hot loads that could be a serious problem and the source as well.

December 31, 2013, 09:19 PM	#1
5RWill Senior Member Join Date: July 20, 2008 Location: Mississippi Posts: 2,654	Effect of loads that are too hot? Here's the load 45.5gr Varget Nosler Brass Hornady 178Gr BTHP Fed 210m Primers COL 2.860 So when i grouped these in low temps the best group i got was 45.5, which i accidently loaded from the get go (max is 45.2gr). That said i saw no pressure signs at the time or maybe i wrote down 45.5 when it was actually 45.2. Either way I screwed up something this go around. So shot last spring and the first shot stuck. Decided to get rid of the remaining rounds i had left today. Was shooting out to 400yds and they were literally everywhere. Dialed 2.2Mils thinking it wouldn't be too far off my berger 175gr load and it was over. I ended up shooting 1.8 Mils and shooting high as hell, though still making hits. None of them stuck, was just trying to get rid of them without having to pull them all. Can the pressure spike of a hot load cause this? They were all over the place i've never seen this rifle produce groups this bad at extended range. __________________ Then I heard the voice of the Lord saying, "Whom shall I send? And who will go for us?" And I said, "Here am I. Send me." Last edited by 5RWill; December 31, 2013 at 10:07 PM.

December 31, 2013, 10:05 PM	#3
5RWill Senior Member Join Date: July 20, 2008 Location: Mississippi Posts: 2,654	.308 given the data i figured most would know but that's my bad. Will be investing in a collet style bullet puller that's for sure. __________________ Then I heard the voice of the Lord saying, "Whom shall I send? And who will go for us?" And I said, "Here am I. Send me."

January 1, 2014, 03:20 PM	#5
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Most loads' pressure curves are not all that repeatable when they're too hot. That is, above SAAMI specs by more than about 5%. And that causes them to be less accurate as measured by exteme dimensional spreads of many shots in a test group. Case life gets less, too, as the brass is work hardened to extremes when fired then sized back down; especially with standard dies resizing cases too much after being fired in SAAMI spec chambers. I think 42 grains of Varget is about max for 178's in a .308. Guessing at pressure from visible signs ain't the best thing to do, in my opinion. After shooting some proof loads in 7.62 NATO rifles noting no significant visible signs of pressure with the same lot and amount of powder, same case and primer used with 147-gr. bullets (50,000 cup) but with a 172-grain bullets (65,000 cup), that convinced me that visible signs are not good for judging pressure with. Last edited by Bart B.; January 1, 2014 at 03:27 PM.

January 1, 2014, 04:51 PM	#7
5RWill Senior Member Join Date: July 20, 2008 Location: Mississippi Posts: 2,654	Effect of loads that are too hot? Yeah I'm backing down to 45 or 45.2 as the manual states. As I said I'm not sure how I loaded 45.5 but I did: carelessness or stupidity I guess. 45gr shot well enough though here's how 45.5 shot last winter. Max load in the books is 45.2 which is what I'll be backing down to. I ran Berger 175gr BT LRs before this at 44.5 with great results at distance holding a tad above half MOA out to 400yds. MOA at 500yds and at 600 they started to open up though I blame that on my inexperience with wind and distance shooting. 600 and up my groups start to open. I appreciate the responses guys. Kind of wanted to assure it wasn't my rifle. The first bolt stick I had last spring was very noticeable it took some force to get it out honestly. I have a collet style puller in my cart now as we're about to build a setup at the house finally. What's the jump to the lands on factory rifles? Quite a bit right? I have these seated to run out of AI mags at 2.860 I doubt they're anywhere near the lands but if they were coupled with hot loads that could be a serious problem and the source as well.

December 31, 2013, 10:02 PM	#2
SonOfGun Senior Member Join Date: February 25, 2012 Location: Utah Posts: 111	Do ya think it might help to know what you are shooting? The data means nothing without knowing what caliber.

December 31, 2013, 10:05 PM	#4
Sierra280 Junior member Join Date: July 29, 2013 Location: Gardnerville, NV Posts: 569	Absolutely. If i watch the chrono, I get to a point where accuracy just drops off suddenly, much more than the increase of velocity would make you think it should. I assume that at that point, chamber pressures have at least gone higher than optimal. In the worst case time I had the accuracy go to hell, and the primers flattened a little, but never any trouble extracting. Trouble extracting is a BIG sign that you have a load that's WAY TOO HOT. Just use the puller and be safe.