Consistency, Precision, and Tolerances

[rduckwor]

We are all taught that consistency is the key when reloading precision rifle.

My question is what tolerances are acceptable to you with respect to tolerances you see on your bench?

Let's play based upon a 308 Win load, which most of us are familiar with. 175 grain projectile, primer and powder of your choice.

Your goal is to load the finest match grade 308 round you can.

What weight tolerances or variances will you accept with the following:

308 case: +/- grains variance

175 grain bullet: (your choice of brand) +/- variance

Powder charge: +/- grains variance


I realize that many will sort cases and bullets based upon weight, the key to answering this question is: What variance in each component would cause you to bump it into the next weight group.

Let's not get hung up on issues extraneous to this discussion (i.e. runout, COAL and OOAL). Stick to the parameters outlined

Convenient cut and paste for your answers:

Cases

Bullet

Powder charge


I will ask this same question on another forum and we will see what their thoughts are and how we compare.

 

[Greg Langelius *]

If your ten ring is 2MOA in diameter, how much less than 2MOA worth of consistent accuracy is mandatory? At what size does the additional reloading effort/expenditure approach the point of diminishing returns? Is producing the finest match grade round a necessary or realistic goal, or is something that is more economical and efficient to produce an adequate alternative? Can there be such a thing as too much precision?

My answers are:

If the ring is 2MOA and my personal capability is to shoot to 1MOA, then my load accuracy goal is 1MOA. I think that a slavish commitment to ideal accuracy is counterproductive. The expenditure beyond what's actually adequate detracts resources and attention from the overall goal.

If the firearm has a SAAMI chamber, concentricity differences in thousandths become immaterial, and seating depths become more a matter of whether all the bullets (within their factory tolerance range) do or don't jump, rather than one of differences in less than 5 or perhaps even 20 thousandths. I would strive, rather, for consistency in things like neck tension and charge weight.

Matters like bullet and case weight tolerances smaller than factory QC limits may not be especially pertinent. I don't sort anything, I believe the factory QC tolerances are good enough, and that imposing my own QC standards is redundant and may give a false sense of accomplishment. I reserve my measurements and QC checking for my own work, and not that of my suppliers; once I begin to doubt them, where do I stop?.

For SAAMI chambers, I believe 'standard' dies are clearly adequate, and the question becomes more (for me) one of why one would choose to use a non-SAAMI chamber. Yes, they can be more accurate, but they can also add levels of complexity, impose critical limitations, and allow room for more 'errors' than their more forgiving and less expensive cousins.

Again, where accuracy is the question, the answer must be driven by the application. IMHO, outside BR, where the ultimate is the goal, there is far more room for tradeoffs, and less room for intolerance.

For example, I have several Mosin-Nagant 91/30's, bought for between $114 and $169 apiece, fitted with $90 each worth of optics and mount, and another $15 worth of stock pack, shooting $.20/round Russian spamcan surplus fodder, delivering 2MOA at 200yd. Is such performance beneath significant consideration? IMHO, this could be considered as a threshold minimum degree of acceptable accuracy, if the wolves (or some other vile creatures) were scratching at the door.

For another example, I shoot in local club F(-ish) Class matches scheduled twice per month at 250yd. Competition is informal, comradely, and rather close. The V-ring is 1/2MOA and the 5 ring is 1MOA. My rifle is a custom chambered .30BR, I use Lapua brass, and my scores run in the 180-190's out of a possible 200, which puts me in the bottom half of competitors. Am I to despair and desert the field of competition, or chastise myself, because all of 40 rounds did not impact within 1 1/4" at 250yd?

Not likely...


Greg

 

[Rookie]

Back when I loaded 308 for tac rifle matches, I rejected any 175 SMK that varied in weight more than +/- 3/10ths of a grain. It was surprising how few were rejected. Always used the same headstamp - Black Hills, but didn't weigh them or measure water volume. Used an RCBS Chargemaster for weighing powder which I understand is +/- 1/2 of 1/10 grain accurate.

 

[lancetkenyon]

Take this for what it is worth, as I do not compete in BR or LR shooting matches. I hunt.

With that being said, I strive for accurate hunting loads to ensure (as much as possible) clean take of game. I am fairly meticulous with my hand loads, but I do not use match grade bullets for hunting. With that being said, all of my hunting loads are sub 1/2 MOA out to at least 500 yds. on a calm day. Some more so than others.

My personal process:
1. I do not weigh individual cases, but I do stick to same head stamp/manufacturer for each rifle. (except my AR. It gets what it gets)
2. I do weigh my bullets, and have a threshold of +/- .3 gr. for tolerance. I usually only find one to three out of 100 that do not fall into this tolerance.
3. For powder, I individually weigh each charge. I have an RCBS model 505 scale with a .1 gr increments of adjustment, but with the visual hash marks when weighing loads, I can see a difference that a single granule of extruded powder makes. I get charge weights close with a powder measure, and use a powder trickler to get it as exact as possible. My hand loads are all within 6 fps of each other, so I think that is working pretty well for me.

Tolerance for case length, neck thickness, COAL, etc. is .002". Tolerance for accuracy is sub 1/2" MOA maximum. Sub 1/4 MOA is preferred.

 

[mkollman74]

I agree with what Greg has outlined (actually it is more akin to an essay than an outline). I see it like this: All of the component tolerance parameters are intended to be proxies/predictors for the true and only key performance indicator, i.e. - downrange accuracy. So, I don't spend too much time fussing over the predictors, and just look at the outcome. When I first started reloading I did slavishly pursue ideal accuracy (I like that turn of phrase Greg). After a while, I became curious as to which steps were really vital to the accuracy standards I had. I began to eliminate them one by one, and found that, for me, most of them did not make any real difference.

I now refer to myself as a lazy reloader. In other words, I do as little as possible to get the performance I need. I do not sort any component by weight (or anything else for that matter). I do not debur flasholes or uniform primer pockets. I do not measure runout. I do ID/OD chamfer after trimming. I FL size everything, everytime. I do not even sort my LC LR brass by year. Heck, when I was doing load develpoment for my 6 Creed, I took the brass (with absolutely no prep, net even sizing) straight from the box and loaded away. Some of the necks were not pristinely round - I loaded 'em anyhow. The accuracy was fine - less than 0.4MOA in some cases.

If I can't find a load that will meet my standards, I will begin to add some of the steps back in. I haven't had to do that yet.

The only OCD thing I still do (just can't seem to give it up) is weighing every single charge. I use a powder thrower to get close and then trickle up to the exact weight on the scale. This is probably not necessary, especially with a properly developed OCW load, but I still do it. It gives me some peace of mind...

 

[Enough Said]

The thought NOT to weigh my loads to exact clones never crosses my mind.
Precise neck tension
Precise seating depth (B2O)

 

[Graham]

Consistency, Precision, and Tolerances

OP, most of what you hear about reloading comes from Benchrest shooters. Note the capital 'B ' in Benchest.

When you anchor your rifle to a bench and shoot free recoil for a one-hole group, that stuff matters to the shot.

But I defy you to load ten random .308s with 175SMKs on a Dillon, then load ten of the same using weighed and measured brass, bullet and powder lots, shoot all twenty of them one after another through a practical precision rifle and see any difference on paper.

Why no difference? Because proper application of the fundamentals, not to mention things like barrel temp, have far more influence on the shot.

That said, I do my best to weigh accurate powder charges, keep uniform neck tension and not mix brands of brass, but only because I can, not because not doing it is fatal to my equipment.

 

[Greg Langelius *]

For match loads, I weigh charges. I will F/L resize, trim necks, and debur flash holes first time around, after that I use the same dies to partial length neck resize only about the last 1/3 of the neck length.

At last I think I can see some of the prevailing opinion here diverting slightly away from the 'maximum accuracy at any cost' train of thought toward a more practical approach. I've tried to champion the concept of reasonable limits on handloading zeal, and get some of that extra time reallocated back to the shooting side of marksmanship. I could die tomorrow and honestly believe I'd finally made a positive impact on my world.

...and now back to your regularly scheduled programming...

Greg

 

[AZ.noob]

I just chrono'd my 'summer' load... in ambient temperature 40 degrees cooler than when I'd developed it.
Even though MV was off by almost 100fps, SD was still 11fps. For my purposes, I'm happy with that low a standard deviation.
I measure and weigh each powder charge, and keep a very close eye on seated depth.

I do measure projectiles by bearing surface length, and sort those in batches not exceeding .002 variance
Any box of 30 cal SMKs usually winds up with three of those batches, with maybe three or four projectiles that are way off (like +/- .006, squeaked by QC I imagine). I set those aside for foulers
Maybe it's in my head, but I've found that sorting projectiles by bearing surface has done as much or more to cut down on the unexplainable flyers than anything else my OCD makes me do

 

[George63]

case for .308 2 grains - getting pickier than that by weighing has been proven meaningless - for that you have to check water volume

bullet .2 grains - for a 175 SMK, divide into 2 groups - there will be about 5% outliers

powder .03 gr - about 1 pc of 4064

 

[bigedp51]

When practicing for Zombie attacks with my AR15, constancy is being able to load as many 30 round mags as fast as possible without dropping one.

As you can see below consistency is the volume of fire you can lay down and consistently hitting the gray innocent non-bitten civilians.

Sorry, the devil made me do it.

 

[Dan Newberry]

People win matches with non-optimal loads all the time... you just need *enough* accuracy to beat the next score below you. You could take a mediocre load and actually beat a guy shooting a fully bench-rest prepped handload who simply fails to shoot as well as you did on that day. Or maybe he got some bad wind, and you didn't... it happens all the time.

Too, I'm reminded of Boots Obermeyer saying years ago how he sorted through all of his handloads and set out a box of those which had the most consistent weights and which had little to no runout... and he put the other "practice" shells into a separate box. The plan was to use those for practice, or sighters and foulers and use the "special" shells for the match.

He shot the culled out practice cartridges by mistake, won the match, and didn't realize it until the match was over!

What you should hope to see in a super-prepped match load is very minimal ES (extreme spread of velocity), which should translate to 1/2 MOA or less vertical dispersion on the target. Again, this isn't to say you cannot shoot your way into the winners circle with something less--you can win a match with a load spreading 1 MOA vertically, or worse. You've just gotta be hoping a shooter who can shoot just as well as you can doesn't show up with a tighter shooting load.

Dan