An interesting result regarding OCW load and different case weights.

[MCMXI]

I've been working up loads for my .300 Win Mag and a few weeks ago weighed all 100 brand new Winchester W-W Super cases. I've been following the OCW method and in addition to shooting 30 rounds today (6 loads x 5), I wanted to see if a difference in case weights had a significant effect on POI with the same load. The question often arises here as to how much case weight variation is acceptable. When I weighed the cases, the lightest was 236.8 grains and the heaviest was 241.0 grains. So I loaded up 21 brand new cases (trimmed to 2.610") with 70.0gr of Reloder 22 since 70.0gr seems to be close to the OCW load for new brass based on my experience over the past few weeks. Target #1 shows the two "fouler" shots to start off the day ... case weights are 240.9 grains and 238.2 grains. The case weights for target #2 are shown on the second image along with the POI (and order shot) for each case weight/load. The case weight range for that target is 4.2 grains. I chose cases that were roughly 1 grain apart in weight for each of the five rounds.

Target #3 was shot with cases ranging from 237.4 grains to 238.1 grains ... a range of 0.7 grains. If I hadn't messed up the fourth shot, I could have had a 0.168" group!

Finally, target 2 (bottom) is a 9-shot group with cases ranging from 239.5 grains to 240.1 grains.

 

[BsChoy]

The OCW method isn't suppoesed to be affected by case weight or powder type I thought. I have noticed differences in case weight variations though.

 

[MCMXI]

The OCW method isn't suppoesed to be affected by case weight or powder type I thought. I have noticed differences in case weight variations though.

I realize that and that's why I posted the results. I guess I'm the only one impressed that five cases, all about 1 grain apart in weight, NEW, UNFIRED, AND UNSIZED can result in a group that's under 0.7"!! The other five-shot group perhaps shows the potential of sorting cases by weight but obviously, I can't assume much based on two targets and 10 shots.

 

[USSR]

1858,

Small differences in reloading components/methods do not typically show up at 100 yards. Move back to 300 yards, and I think your results will be more pronounced.

Don

 

[MCMXI]

Don,
I was thinking that the wind shouldn't have much effect on POI at 100 yards compared to longer distances. How do you know if the variation (at longer distances) is due to the components rather than the elements? Do you sort your cases by weight for your matches, or any other shooting for that matter? I do plan on moving out to 200 yards soon but that's as far as our range goes for paper targets. We have steel plates all over the place but they're more for fun rather than working up load data.

I have another question related to yesterday's shooting if you don't mind. I shot 30 rounds yesterday following the round-robin OCW method. Those 30 cases had been fired once in the new rifle so I necked sized them only, trimmed them to length and sorted they by weight. The results weren't what I was expecting. I got "better" results the previous week using new, unfired brass, with no sizing, no trimming etc. Is it possible that I didn't reduce the neck size enough? I reduced it by 0.001" i.e. the OD of the loaded neck is 0.335" and I used a 0.334" neck sizing bushing. There was some resistance when seating the bullet but a lot less compared to seating the bullet in the new cases.

I appreciate any help in this.

Thanks.

 

[kelbro]

That's pretty good for a +/- 1% variance. I'd bet that your once-fired capacities have changed. Tweak your OCW charge again if you plan to use neck-sized cases. I never try to determine OCW with new brass. I FLR with a ~.002 shoulder setback then start with OCW testing. Keeps things a little more uniform.

I like to use a -.002 bushing.

 

[MCMXI]

kelbro, thanks for the advice. It looks like the OCW load shifted up a little (maybe 0.2 grains or so) with the once-fired brass. The cases entered the chamber like new brass with no feeding problems at all but I'll measure the headspacing of each case to see where they're at and bump the shoulder back with a body die if they get hard to chamber. I do have .333, .332, .330, .329 and .328 neck-sizing bushings so I'll try a smaller bushing. I'll use the 0.333" bushing which will put the neck at -0.002". Hopefully that'll result in sufficient case neck tension.

 

[USSR]

I was thinking that the wind shouldn't have much effect on POI at 100 yards compared to longer distances. How do you know if the variation (at longer distances) is due to the components rather than the elements? Do you sort your cases by weight for your matches, or any other shooting for that matter? I do plan on moving out to 200 yards soon but that's as far as our range goes for paper targets. We have steel plates all over the place but they're more for fun rather than working up load data.

I have another question related to yesterday's shooting if you don't mind. I shot 30 rounds yesterday following the round-robin OCW method. Those 30 cases had been fired once in the new rifle so I necked sized them only, trimmed them to length and sorted they by weight. The results weren't what I was expecting. I got "better" results the previous week using new, unfired brass, with no sizing, no trimming etc. Is it possible that I didn't reduce the neck size enough? I reduced it by 0.001" i.e. the OD of the loaded neck is 0.335" and I used a 0.334" neck sizing bushing. There was some resistance when seating the bullet but a lot less compared to seating the bullet in the new cases.

1858,

Yeah, it helps to have one of those rare windless days. Yes, I sort my match cases (Lapua) by weight. You are not the first one to notice that new, never fired brass gives the best results. Although I prefer .001" to .002" neck tension, most new brass comes with quite high neck tension, so maybe increasing your neck tension now will help. What size is the OD of your necks after being fired in your chamber?

Don

 

[MCMXI]

You are not the first one to notice that new, never fired brass gives the best results.

But why is that? If it's true, would it indicate that neck tension is VERY important to accuracy and consistency and perhaps more important than other factors? I could see how insufficient neck tension might adversely affect case pressure and velocity.

What size is the OD of your necks after being fired in your chamber?

Good question and I have no idea. It never occurred to me to measure them but I will when I get home. Will these measurements help me in some way e.g. to figure out the correct neck-sizing bushing to use?

 

[USSR]

Quote:
Originally Posted by USSR
What size is the OD of your necks after being fired in your chamber?

Good question and I have no idea. It never occurred to me to measure them but I will when I get home. Will these measurements help me in some way e.g. to figure out the correct neck-sizing bushing to use?

Yep. When you are taking the neck down quite a bit in one pass, the resulting OD is smaller than what the bushing size is. Example: The OD of a case fired in my .308 FN SPR is about .346". When I use my .338" bushing, the OD comes out at .337", which is perfect for my M118LR brass. Sometimes you need to take the OD down in steps by using an intermediate size bushing, followed by the bushing in the size that you actually need. I believe this happens when you try to reduce the neck OD by over .005".

Don

 

[MCMXI]

Don,
I measured the OD of the necks of the fired cases and they're at 0.340". The OD of a loaded 208gr A-MAX is 0.335" so if I need to be at 0.333" perhaps I need to neck size at something like 0.336" followed by 0.333". I'll give it a try this week.

As I was cleaning the case necks with Brasso prior to measuring them, I did notice that the once-fired cases were a lot dirtier (carbon black etc) around the neck compared to the new brass cases. Is this significant? Maybe the powder isn't burning efficiently with insufficient case neck tension.

Thanks for the help.

 

[Ridgerunner665]

If it's true, would it indicate that neck tension is VERY important to accuracy and consistency and perhaps more important than other factors?

It is true...and is just as important as the other factors.

I like my neck tension to be at least .002 and no more than .003, but opinions vary on that (so do rifles)

 

[MCMXI]

Ridgerunner665, well I'm going to measure the neck OD after sizing this time. When I ran them through the 0.334" bushing I just assumed that they were good to go .... the significant reduction in seated effort over the new cases should have raised the alarm.

I like my neck tension to be at least .002 and no more than .003, but opinions vary on that (so do rifles)

ANOTHER variable to consider in the "relentless pursuit of perfection". This barrel will but shot out by the time I get it all figured out!! At least I'm having fun doing it.

 

[Ridgerunner665]

One thing...just a theory of mine that I've never tested, so take it with a grain of salt.

If you load "kissing the lands", then neck tension is all but removed as a variable...the more jump, the more neck tension matters.

Again, just an untested theory of mine.

 

[USSR]

As I was cleaning the case necks with Brasso prior to measuring them, I did notice that the once-fired cases were a lot dirtier (carbon black etc) around the neck compared to the new brass cases. Is this significant? Maybe the powder isn't burning efficiently with insufficient case neck tension.

Uh, not a good idea to use Brasso on your brass due to the ammonia it contains (it weakens brass). I don't think your neck tension is causing the soot around your necks, but it could be a result of underpowered loads. Any idea as to what velocity you are running those Amax's at? I know alot of guys use about 72.0gr of RL22 with 190SMK's, so it seems to me you might be able to use a bit more powder.

Don

 

[MCMXI]

If you load "kissing the lands", then neck tension is all but removed as a variable...the more jump, the more neck tension matters. Again, just an untested theory of mine.

I can see the logic behind that theory and you're probably correct about that. I have no intention of having the bullet touch the lands so I need to be diligent with neck size and tension.

Any idea as to what velocity you are running those Amax's at? I know alot of guys use about 72.0gr of RL22 with 190SMK's, so it seems to me you might be able to use a bit more powder.

I just recently managed to borrow a chronograph and will measure the velocities in the very near future ... maybe this weekend ... but for now I'd just be guessing based on the load data from Walt Berger. The max load he listed for RL22 and the 210 grain VLD is 71.1gr, however, his COAL is 3.340" whereas mine is 3.578" ... still not sure if that shifts the safe load range up by some significant amount. I had five loads at 70.7gr and those necks had the same sooty ring on them. The starting load for the VLD is 67.5gr and I'm well above that. Also, there's quite a bit of room in the case even at 71.5gr (tried that last week).

I had this notion that I'd find the "best" load and then chronograph 10 rounds to get the velocity, then using ballistic software calculate bullet drop every 100 yards out to 1000 yards and use that information to get me started in shooting matches. Now I'm starting to think that I need to use the chronograph in the load development stage rather than just at the end since I have NO IDEA what the velocities are and I could be a couple of grains under the max and not even know it!

 

[USSR]

I had this notion that I'd find the "best" load and then chronograph 10 rounds to get the velocity, then using ballistic software calculate bullet drop every 100 yards out to 1000 yards and use that information to get me started in shooting matches. Now I'm starting to think that I need to use the chronograph in the load development stage rather than just at the end since I have NO IDEA what the velocities are and I could be a couple of grains under the max and not even know it!

Yeah, that's why I load 3 cartridges with a certain charge weight, then load 3 more with 0.5gr more powder, and keep going until about what's listed as a max load. Then I chronograph them, starting with the lower charge weight loads and working up. I've ended up tearing down a bunch of loaded shells that had too much powder in them, but I've gotten directly to where I want to be velocity-wise. Once there, I can play around with the charge weight to find a good load.

Don

 

[MCMXI]

Don, thanks for tip ... I'll make up five each of 71.0, 71.3, 71.6, 71.9, 72.2 and 72.5 gr loads and chronograph them this weekend as I'm going through the OCW method.

Also, thanks for setting me straight re the Brasso. I usually just add a little in the tumbler but will stop using it altogether now.