How fast is too fast?

F

FootSoldier

Sergeant
Full Member
Minuteman
Feb 29, 2008
128
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Phoenix, Arizona
#1
I am shooting a .308 FN SPR 24" with my loads:

#1--155 Scenar, IMR4895 45.4grs, Lapua brass, Fed 210M, 2.857" (.030 off the lands) I am getting solid MOA performance out to 785 yds (did it for the first time today) with an average 2902 fps, Es=17.42 and Sd=6.48.

#2--155 Scenar, Varget 44.0 grs, Lapua brass, Fed 210M, 2.857", 2795 fps, Es=23.29, Sd=12.28. Haven't shot this one at distance yet, but at 100 yds it's regularly just under 1 MOA.

My Lyman manual says the speeds are average, but the Sierra says I am pushing them hard with the IMR4895. I don't want to prematurely burn out a barrel, but I do like how they are shooting.

Am I pushing too hard?

Thanks,

Steve
 
#2
Re: How fast is too fast?

To me that would be to hard/fast, but what a Catch-22. I'm going to check the Hodgdon/IMR/Winc. website.

Well, their website says a max of 47.5 compressed gr IMR4895 w/ 155 Sie HPBT...

So as per their data, maybe it isn't that hot.

But I just looked at Sierras site and it is drasticlly lower...43.7...

Any pressure signs?...stiff bolt lift, primers cratered or loose,...
 
#4
Re: How fast is too fast?

Yes, but if copper fouling becomes a big deal, it might pay to back off the pressure somewhat, assuming it doesn't cause the bullet to go subsonic prior to impact.

A lot of this is a judgement call.
 
#5
Re: How fast is too fast?

The primers are a flatened, but they have not flowed in to completely fill up the radiused edge of the primer pocket. (If I explained that well enough)

In my load work up, I also found Sierra's info to be a much lower max, so I took Lyman, Sierra, Hodgdon's info and averaged them to get my "max" and started following the OCW system with that info. I shot loads as high as 47.1 of IMR4895.

The primers were much flatter and flowed the edges to fill the primer pocket completely flush. No loose or blown out primers though. I couldn't see any other signs of pressure. No problem opening bolt.

The load that performed the best was the 45.4, it just seems like 2902fps for a .308 is a little fast to me? Although I have been thinking that I may be getting too hung up on the numbers supplied by my $110 Chrony? Maybe my actual speeds are not really that high?

The 2902 was on a 10 shot string, bright sun, warmer temps. On my original testing day with a 3 shot string, I got 2886fps, Es=13.77, Sd=6.48, under cloudy skies, cooler day.

Maybe I am worrying about nothing?
 
#8
Re: How fast is too fast?

Not for me or anyone to say without seeing the cases in question, but without shiny circumferential rings a bit above the extraction groove, sharply flattened primer edges, firing pin indentation cratering, and shiny extractor/ejector marks on the base, the signs are sounding acceptable.

Those indicators, plus heavy coppering especially in the first half of the bore, evidence of significant case stretching/rim deformation on semiauto extraction, and a tendency for velocity increases to flatten out above a certain high charge would be telling you that max has been reached or exceeded.

I'll leave it to you to decide whether worrying is warranted. Having an experienced handloader present and observing the evidences when you're shooting certainly wouldn't hurt.

Greg
 
#11
Re: How fast is too fast?

I saved the brass in its fired state, in the hopes of having an experienced eye "read" the brass for me. I just don't have enough experience to have a good feeling that I am properly interpreting the information reflected on the brass.
 
#13
Re: How fast is too fast?

I think sierras manual states their loads are worked up in a military grade commercial brass which has less capacity and would yield higher pressures.
Their loads are gas gun safe loads as well.
 
#15
Re: How fast is too fast?

OK, got back to the range today.

The IMR4895 @ 45.4 grs averaged 2914fps and I now recognize some pressure signs. Primers are cratered. I can feel the "splash" edge of the firing pin indentation above the smooth surface of the primers. I fired 10 rds across my Chrony and had one with a sticky bolt lift. That case showed a slight ejector swipe on the base of the brass. (At least I think that's what I am seeing.)

The Varget @ 44.0, 44.5, and 45.0 was right at 100fps slower, but showed no such signs of pressure and shot almost as well as the IMR load.

I have fired 50 rds of the hotter IMR4895 load and it flat out performs in my rifle, but I don't like loading on the edge of high pressure signs. I love how it shoots, but I think I will go with a little less speed and use the Varget.

 
#16
Re: How fast is too fast?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FootSoldier</div><div class="ubbcode-body">The primers are a flatened,

The primers were much flatter and under cloudy skies, cooler day.

Maybe I am worrying about nothing? </div></div>

You have answered your own question if you think about it.

1. You are shooting some loads that are already showing signs of high pressures.

2. Your loads were developed under cool conditions.

3. You are shooting in AZ.

What is going to happen when it's 100(or higher) degrees F.(38 C.), sunny day, and the loaded cartridge sits in a hot chamber for a minute before discharge?

<span style="font-weight: bold">Forget loading manuals, look at the signs of high pressure that are already apparent.</span>

Here is a reference study: http://www.shootingsoftware.com/ftp/Pressure%20Factors.pdf
 
#18
Re: How fast is too fast?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FootSoldier</div><div class="ubbcode-body">Thanks Phil. I have never seen anything that detailed on the subject before. I just recently found a link to an article on the 6br website that helped a lot too.

I appreciate your response.

Steve </div></div>

You're welcome.

Sometimes the brain knows something but the cause-effect or most important factor dosn't come to mind. Here(Sask.) a load developed on a 90 degree(F) day is safe almost always. Especally so when its 40 degrees below!

Loading manuals are great but they always start with a disclaimer about starting loads(ususlly 5% less). Handloading is always safety(most important), accuracy(second most important), then speed(third in importance). Safety means back off the load(or don't exceed) at the <span style="font-weight: bold">first signs of pressure</span> not, see how far you can push it.

Imagine lending a hot load to a friend who has the same caliber. Making a slight mistake in a couple grains too much powder. Mistakenly putting in a magnum primer instead of a standard primer. At the maximum there are few parameters for error and failure of a chamber can be serious.
 
#19
Re: How fast is too fast?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Phil1</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FootSoldier</div><div class="ubbcode-body">Thanks Phil. I have never seen anything that detailed on the subject before. I just recently found a link to an article on the 6br website that helped a lot too.

I appreciate your response.

Steve </div></div>

You're welcome.

Sometimes the brain knows something but the cause-effect or most important factor dosn't come to mind. Here(Sask.) a load developed on a 90 degree(F) day is safe almost always. Especally so when its 40 degrees below!

Loading manuals are great but they always start with a disclaimer about starting loads(ususlly 5% less). Handloading is always safety, accuracy, then speed. Safety means back off the load(or don't exceed) at the <span style="font-weight: bold">first signs of pressure</span> not, see how far you can push it.

Imagine lending a hot load to a friend who has the same caliber. Making a slight mistake in a couple grains too much powder. Mistakenly putting in a magnum primer instead of a standard primer. At the maximum there are few parameters for error and failure of a chamber can be serious. </div></div>

+1

I would say fast is too fast when

1. Groups start to open up, or

2. Signs of pressure start appearing

Which ever one comes first. I know Im probably stating the obvious, and its not the most "scientific" answer, but regardless of what the manuals are stating, what matters is what your gun, ammo, and target is telling you. Manuals are a good starting point but what matters in the end is what you are experiencing with your groups and gun. Good luck with you loads bud.

Seth

 
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