Compressed loads; what are your warning signs on the bench?

WWWJD · August 12, 2012, 06:45 PM

I came across a box of 190gr SMK for my 700 SPS 20" .308. I've read that even with 1:12, some rifles have good luck with them. Not knowing where to start with Varget, I referred to Hodgdon's web site and to my Lyman 49th.

Lyman says 38.5 to 42.8C (60,200PSI), 2.775" COAL (which seems short to me), while Hodgdon says 41 to 44C (49100CUP) 2.74" COAL.

I loaded 10 each of 40, 41, 42, 43 and 44 at 2.8" COAL (.025-.06 over). Everyone was fine until I got to the 44s, which seated with a noticeable crunch. I would have expected that being loaded to a COAL beyond what's listed for both references, that I would have been ok at 44. Lyman's numbers suggest that I would have heard the crunch at a much lower charge weight.

I'm just a little weary of firing these rounds. Obviously, I'll be checking fired cartridges carefully across the board, but... IDK.

How much compression is generally acceptable? Or does it all boil down to watching for pressure signs when firing? Is this a dumb question?

Brian Pfleuger · August 12, 2012, 07:18 PM

There's nothing wrong with compressed loads if they're listed that way in the manual.

The only issue I see with your loads is that the increments are too large. 1/2gr would be excessive. A full grain is way too much.

mrawesome22 · August 12, 2012, 07:28 PM

A little crunch is a good thing. Takes powder position out of the equation.

sudo apt-get dist-upgrade

Mobuck · August 12, 2012, 07:33 PM

Drop the powder in slowly and/or use a vibrator to settle the powder. No need to crush the powder granules on many loads listed as compressed.
I can see a noticeable difference in the powder level depending on if I drop the full charge into the case or pour it in slowly from the scale pan.

FrankenMauser · August 13, 2012, 12:39 AM

They should be safe to shoot, unless you're using cases with a notably lower case capacity that those used to develop the data.

As far as consistency goes:
Pressure on the powder is fine. -It's just compression.
"Crunch" can be unpredictable. -You're breaking and/or crushing granules.

Use a drop tube to charge the cases, and you should be able to eliminate most (if not all) of the 'crunch'. In certain cartridges, with certain powders, my powder charges can be even with the case mouth if charged with a normal powder funnel. But, with a 6-8" drop tube and a slow pour, they are only slightly compressed. (With certain loads, it packs the powder well enough to actually leave an air space.)

Consistency at the target is far better with drop-tube charges, than the same load with a 'crunch'.

WWWJD · August 13, 2012, 12:46 PM

Ok. Thanks guys. I've been using the autodisk, but dumping, weighing and recharging each case with a funnel. Autodisk just gets me a rough start on final charge weight. We'll see what happens.

August 12, 2012, 06:45 PM	#1
WWWJD Senior Member Join Date: February 9, 2011 Location: Central KY Posts: 552	Compressed loads; what are your warning signs on the bench? I came across a box of 190gr SMK for my 700 SPS 20" .308. I've read that even with 1:12, some rifles have good luck with them. Not knowing where to start with Varget, I referred to Hodgdon's web site and to my Lyman 49th. Lyman says 38.5 to 42.8C (60,200PSI), 2.775" COAL (which seems short to me), while Hodgdon says 41 to 44C (49100CUP) 2.74" COAL. I loaded 10 each of 40, 41, 42, 43 and 44 at 2.8" COAL (.025-.06 over). Everyone was fine until I got to the 44s, which seated with a noticeable crunch. I would have expected that being loaded to a COAL beyond what's listed for both references, that I would have been ok at 44. Lyman's numbers suggest that I would have heard the crunch at a much lower charge weight. I'm just a little weary of firing these rounds. Obviously, I'll be checking fired cartridges carefully across the board, but... IDK. How much compression is generally acceptable? Or does it all boil down to watching for pressure signs when firing? Is this a dumb question? __________________ *~Mark* NRA Endowment FTW

August 12, 2012, 07:18 PM	#2
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	There's nothing wrong with compressed loads if they're listed that way in the manual. The only issue I see with your loads is that the increments are too large. 1/2gr would be excessive. A full grain is way too much. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

August 13, 2012, 12:39 AM	#5
FrankenMauser Senior Member Join Date: August 25, 2008 Location: In the valley above the plain Posts: 13,424	They should be safe to shoot, unless you're using cases with a notably lower case capacity that those used to develop the data. As far as consistency goes: Pressure on the powder is fine. -It's just compression. "Crunch" can be unpredictable. -You're breaking and/or crushing granules. Use a drop tube to charge the cases, and you should be able to eliminate most (if not all) of the 'crunch'. In certain cartridges, with certain powders, my powder charges can be even with the case mouth if charged with a normal powder funnel. But, with a 6-8" drop tube and a slow pour, they are only slightly compressed. (With certain loads, it packs the powder well enough to actually leave an air space.) Consistency at the target is far better with drop-tube charges, than the same load with a 'crunch'. __________________ Don't even try it. It's even worse than the internet would lead you to believe.

August 13, 2012, 12:46 PM	#6
WWWJD Senior Member Join Date: February 9, 2011 Location: Central KY Posts: 552	Ok. Thanks guys. I've been using the autodisk, but dumping, weighing and recharging each case with a funnel. Autodisk just gets me a rough start on final charge weight. We'll see what happens. __________________ *~Mark* NRA Endowment FTW

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August 12, 2012, 07:28 PM	#3
mrawesome22 Senior Member Join Date: November 9, 2005 Location: Ohio, Appalachia's foothills. Posts: 3,779	A little crunch is a good thing. Takes powder position out of the equation. sudo apt-get dist-upgrade

August 12, 2012, 07:33 PM	#4
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	Drop the powder in slowly and/or use a vibrator to settle the powder. No need to crush the powder granules on many loads listed as compressed. I can see a noticeable difference in the powder level depending on if I drop the full charge into the case or pour it in slowly from the scale pan.