Working up a decent 180 gr Accubond load for a .300 Win Rem 700.

Testing at 250 yds, factory loads about 2 MOA extract normally. Shoots ABs about 1 MOA, but slightly difficult to pull the bolt back (not difficult to lift handle). Empties look OK, primers ever so slightly flatter vs factory. No bright ring above belt. It was a really bright day, so didn't chrono. Micrometer readings (average of 3 casings/group) at pressure ring:

0.5139 on factory 180 gr Rem PSPCLs
0.5142 on Mex Match of above load w/ 180ABs seated (way) out to 0.010" off lands,
0.5143 on factory powder discards/factory primed brass with 72 gr of my IMR-4831 and 180 ABs to same 0.010" off lands.

After processing the empties new primer seats with normal resistance, ie., no loose pockets. Using a wire probe cannot feel any brass thinning post-resizing.

Question: would a reduction of 3% (from 72 gr to 70 gr IMR-4831) be a good bet to match factory brass expansion? Would like to nail it on the first try, if possible, instead of cutting back drastically and creeping back up. Looking for a check on my thinking here.

you don't know what the factory pressure is.
all you know is that they tested it to be UNDER maximum pressure.
the velocity & measurement is your only clue to what is happening with them.

I for sure cannot predict 3-4 ten thousands of an inch expansion based on powder reduction.
1 grain might do it, holding the micrometer slightly different might do it too.

Thanks, Lamar. I trust my micrometer technique, doing it as per Ken Waters - roll the case and take the largest OD. I should have mentioned there was no variation within each group. Eg. all the factory empties went 0.5139". You're right about the chrono, and am going to wait for an overcast day to test again. As much as I suspect 70 gr will work, will load up 3 each at 68 and 69 gr. If 70 gr "works" can dismantle them later.

Did you measure the base diameter "before" firing for a baseline of expansion.

Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.co...e-your-rifle-reloads

Also remember brass hardness in the base of the case governs how much the base will expand. Example military Lake City cases are harder than commercial cases in the base and show less base expansion.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshoote...base-hardness-tests/

Bottom line base expansion is like reading fired primers and both methods are ball park pressure estimates.

bigrdp51, Thanks for the links. You ask an interesting question. After reading the Hodgdon piece went back and reread Waters on the subject. No mention of measuring factory ammo prior to firing.

Wondered why, so just measured several new unfired RP factory and also new RP unprimed casings. Measurements ahead of the belt vary widely, from 0.509" to just about 0.512" (forget about the 4th decimal point). To be clear on this, this amount of variation is seen within single boxes of both a) unfired RP brass and b) factory 180 gr PSPCLs. So am not going to look at other .300 Win brass mfg.

IIRC, we had a recent thread on variations in .220 Swift brass diameters at the pressure ring, and the variations reported were impressive.

Next up, measured cases resized FL in my RCBS die. They are uniform and pretty much spot-on 0.5120". Waters insists on the need to start with factory loads as a benchmark, so cannot believe he was unaware that factory new brass/ammo is not uniform in that dimension.

There's also the observation that the fired cases within each group had identical OD at the pressure ring by my micrometer.

If you are just measuring your own brass before and after firing you are gaining no useful data upon which to base any pressure implications.
Is your brass easy to extract? Are the primer pockets tight?
Then your loads are fine.
I read everything Ken Waters wrote but I never held his case measuring theory in much regard.

If you need to load to the last few % of powder and pressure in hunt for the last 30-40fps, then you have selected to small a caliber/cartridge!

quote:

Originally posted by dpcd:
If you are just measuring your own brass before and after firing you are gaining no useful data upon which to base any pressure implications.
Is your brass easy to extract? Are the primer pockets tight?
Then your loads are fine.
I read everything Ken Waters wrote but I never held his case measuring theory in much regard.

Measuring the base diameter before and after shooting tells you when you reach the elastic limits of the brass. Its not a pressure measurement, but it tells you how much pressure the case can take before stretching beyond it elastic limits.

I would rather measure with a micrometer than wait until I see it first hand.



The thickness of the flash hole web also adds radial strength to the base. Below Federal was "known" for soft brass but the real problem for loose primer pockets was the thickness of the flash hole web. I have factory Federal .223 cases with over sized primer pockets after the first firing.



So actually measuring the base expansion before and after firing can tell you a great deal.

I think you did this, but figured I might as well make it a point too.
you want the brass to be from the same lot.
this pretty much means pulling down some factory rounds to use in the experiment.

Thanks for the responses. I trust pressure ring mic measurements, sensibly applied, and have done so long-term.

As mentioned brass was from one box RP used as: factory baseline, Mex Match, powder discard/replace with 72 gr IMR-4831.

Often we can exceed factory pressures with no pressure signs beyond chrono results. I generally view things like sticky extraction and loose pockets as evidence of greatly excessive pressure. My hunch is this particular rifle is just sensitive. 0.0004" is not much over, IME. Charge is within ballpark according to my manuals, though one manual has it as maximum.

72 gr works in other .300s I own or have played with. But again, will have some 68 and 69 gr just in case (no pun) 70 gr is not sufficient reduction. And a chronograph, definitely next time. Will post results. I'm smack in deer season so may be awhile.

Thanks again to all.

The biggest problem with belted cases is the case diameter just above the belt is at SAAMI minimum diameter. And many sizing dies have problems sizing the case above the belt.

You then have a case rubbing the chamber above the belt causing chambering and extraction problems.

Bigrpd51, I had this problem with a few of my belted cartridges, and purchased a Larry Willks die for belted mags. Does a good job of reducing the area just ahead of the belt.

http://www.larrywillis.com/

Got to play with it today. 35 deg F. < 5mph variable crosswind.

All RP brass, WLRM, 180 gr AB as described. Each test = 3 rounds fired.

68 gr IMR 4831 - avg 2850 fps, ES > 90 fps, 5" at 250 yds. Mic reading 0.5135" Most vertical dispersion

69 gr IMR 4831 - avg 2890 fps, ES 15 fps, 1.9" at 250 yds. Mic reading 0.5139" (matches factory load expansion at pressure ring)

70 gr IMR 4831 - avg 2915 fps, ES 25 fps, 2.4" at 250 yds. Mic reading 0.5140" No pressure signs.


Will settle on 69 or 70 gr IMR-4831.

Looks like you can still increase the charge some more.
Watch for velocity leveling off or decreasing with heavier charge.
Then back off a grain or more from the peak velocity.
Inspect every case every way you can soon as it comes out of the gun.
Primers especially are an indicator I've found.

Main thing is be safe first!! Then have fun.

George

Thanks George, but the problem with this particular .300 is sticky extraction at a 72 gr charge. Except for that, I'd have called it good. Am happy with the accuracy at the 69 and 70 gr levels, though. May just split the difference at 69.5 gr.

Sam,

With those mild velocities for 180 bullets you shouldn't be having pressure problems with a 300 WM. I have two of them.

IMO, your case sticking is more likely related to a "resizing problem", which occurs just in front of the belt. It shows up as soon as after 2 or 3 firings with some factory resizing dies.

For a discussion and solution to this "sticky" case problem go to...

http://www.larrywillis.com/

And read about what he says regarding...Belted Magnum: Collet Resizing Die. "Finally a resizing die that works on belted magnum cases."

A bit expensive, but worth the money - IT WORKS!!

AIU

Thanks, AIU. Alot to read, just took a cursory look.

This gun's sticky extraction manifests even with new non-resized factory primed brass casings. When I substituted 180 gr ABs for the 180 gr CLs they gave sticky extraction. Expansion at the pressure ring was just slightly greater with the Mex Match ABs than with the factory load.

I haven't tried to correlate pre-fired diameter at pressure ring of factory casings/ammo with stickiness - pre-fired diameters are all over the map - but maybe??? FWIW, my sizer takes the pressure ring diam down to 0.5120" and there is no difficulty chambering loads resized in this die.

Will read the info thoroughly next week (last week of deer season). Thanks again!

73 grs. with a 180 gr. bullet is a max charge in most 300 win mags.d and about all the H4831 you can get in a case.. My 300 Wins have shot up to 74 grs. of the new stuff and 76 of the old Milsurp 4831 that I have on hand, the stuff that Jack O'Connor shot, which is my hunting load.

In your case the first thing I would do is start over with 68 grs. of modern SC 4831 and see where it goes on the chronograph..A tight chamber can get you the same velocity with less powder and thick Rem cases can do the same as a matter of fact. When get a comfortable load shot the same case over and over until it show stress and primer pockets get loose, then back off a gr. or two and your good to go and you know YOUR guns max. IMO everyone should KNOW their guns max..