Case Length Variability and Accuracy

[Significent]

Not sure what happened the first time I posted this. Here it is again.

I'm working up some loads for a brand new 270Win bolt gun I purchased recently. In the process, I discovered that my case trimmer wasn't doing as consistent a job as I thought it was. I set up up and tested the first few which were within 1/1000"s of each other. During the process of trimming 150 of them, I noticed one came up short. Instead of 2.531" (where I set it) this one came up 2.527". I double-check to see that everything was set up properly. It was. So then I went back through all of the cases and checked them. Most were between 2.530" and 2.532" but about equal numbers were short or long by as much as 5/1000"s. I put the long ones back in the trimmer making sure everything was just right in the way the cases were seated in the trimmer. Nothing additional was removed. Obviously, I couldn't do anything with the cases that were too short. I was able to move the longer cases out of the case clamp a bit to get them down to 2.531".

So, now I have about a dozen cases that are 2.526" to 2.529". (2.530" is the trim-to length). I'm not too worried about them being safe to shoot but I'm concerned about what they're gonna do to my group sizes. I plan to seperate them out and see if they behave any differently than the more uniform length cases (after I've worked up an accurate load).

Can anyone quantify the relationship between case length variability and accuracy so I know what to expect? Does anyone see a problem shooting the cases that are 4/1000"s too short?

BTW, I'm using Federal brass with no crimp.

Thanks for your help.

 

[dakotasin]

shoot 'em w/ confidence. they'll be fine. they are not grossly short.

i made a mistake w/ a 7 rem mag last year, and had about 50 new cases that were .01 inches short... i shot 'em up, and accuracy was same/same.

your group sizes might suffer a little if your gun is extremely finicky, but i can't imagine it would. shoot 'em up - they'll stretch out fine. get a new trimmer, and trim more consistent next time.

 

[Significent]

dakotasin: That's what I was hoping someone would say. I'll probably shoot the short-cased rounds separately anyway just to see if my new rifle treats them differently. I've heard good things about L.E. Wilson's trimmers. I'll probably buy one of them. They're cheaper than the one I have. Thanks for the info!

 

[swifter]

Its a lot more important that the case mouth be square than the cases be exactly the same length.

Tom

 

[strambo]

I don't see any problems, and I expect the short ones will be just as accurate. Since accuracy is all about consistency, the only possible problem would be if they were all mixed up, but even then the seating die would seat all the bullets to the same OAL regardless of minor case trim variations. I guess neck tension might be different based on how far each bullet is seated in the case due to length...post your results, especially if something weird happens

 

[Archie]

Shouldn't make much difference.

If you were crimping, the lengths would influence the crimping proceedure.

Be sure and seat the bullets relative to either "over-all length", or "to ogive" length; do not seat the bullets relative to " x deep in case from mouth".

Another factor to consider regarding meticulous case preparation: All the detail work on cases is pretty much irrelevant if your rifle is not equally prepared. That is, is your rifle free floated, pillar bedded, trued and a serious trigger installed? If you have a pretty much factory rifle, you can still get impressive (sub MOA) groups, but don't sweat the ultra case prep routine.

 

[labgrade]

Shoot them all & I wouldnt even worry about any case segregations at all.

Accuracy "problems" will be with bullet seating depth & powders charges - that & the type bullet loaded.

A couple 1/1000s brass length, if even measured properly, isn't going to make one hoot's difference in your outcome.

 

[Significent]

How bout case weight?

Thanks for all the input guys. Seems I have a lot more time to reload than I do to shoot. So, I generally go overboard on the case prep work. I always tumble, trim, clean primer pockets, uniform flash holes (1st time only), and debur. I have an inexpensive .223Rem (Howa) that I've got shooting 0.4MOA, 5-shot groups. The trigger on it isn' the best. I've been shooting Speer bullets and H335. I'm gonna try Sierra bullets to see if I can get it down to one hole.

I don't know what to expect out of the new 270Win. It's a Swiss-made rifle, pillar bedded, free floating barrel. An interesting feature on the rifle has to do with its mechanism for accepting interchangeable barrels. The bolt actually bolts into the barrel rather than the receiver. Seems to me this will make bedding even less of an issue. I'm eager to see how it shoots.

I'm planning to start sorting rounds by case weight too. Is it reasonable to expect a 1/10MOA improvement in accuracy with more uniform case weights?

Thanks again for your help.

 

[dakotasin]

peak accuracy comes from consistency. the more consistently uniform everything is across the board, the more accurate your rifle will be. and, my philosophy is that accuracy starts w/ the case, so case prep is important to me, too.

but in a hunting rifle, especially w/ factory barrel and chamber, you are unlikely to notice any significant improvement over what you are already doing. if you weigh cases for a sporter gun, and eliminate the extreme heavy and extreme light, you'll probably account for the occasional flier.

your decision to switch to sierra bullets will probably account for a lot more accuracy than using the speers. in a non-deer hunting 223, i highly reccomend sierra matchkings... my prairie dog guns use matchkings. in small game, you'll notice no difference in killing effectiveness between the matchkings and a bullet designed for hunting, but you will likely be more accurate.

if you get the rifle down to one hole groups for 5 shots at 100 yards, you need to get into benchrest competition, and teach them fellers a thing or two about shooting! in seriousness, the one or two wonder groups are gratifying, but true accuracy is to do it every time you are out...

might also put hornady a-max's on your list of bullets to try. by far the most accurate bullet i've run thru my 308 (long range prairie dog gun).

 

[30Cal]

I'm curious what case trimmer you're using. You may just need to be more sensitive to putting the same amount of pressure on it each time to get it to cut more uniformly from case to case.

FWIW, I have a Lee hand trimmer that I chuck in my drill press. It's very accurate and very fast--also works with a cordless screwdriver in front of a television.

Culling cases by weight would help to eliminate some fliers. Not sure if it will actually bring the groups in tighter unless you are ready to reject a lot of brass.

Ty

 

[Significent]

dakotasin: Thanks for the info. I may need to try the Hornady .308 a-max in my 30-06.

30Cal: I have a Forster trimmer and I've been very careful to apply the same amount of pressure each time. The only thing I can imagine could account for the variance is some sort of case deformity. The trimmer sets up relative to the case head around the perimiter. My calipers measure straight across the center of the case head. If some case heads are slightly convex and some are slightly concave, I could understand the disparity. I may have to try figuring out a way to measure the flatness of the case head.

 

[labgrade]

FWIW, I decided to play around with an "average load" to make it all work in 3X .30-06 rifles I own.

A 165 gr Hornady bullet (I like having the "game-getting" capability) .....

In any event, I loaded up a nominal charge/no case prep whatsoever/yada.

I fired 'em from 2X bolts & one pump-gun & in each instance, they turned in either 1 MOA, or less = very satisfactory.

No "tuning" to each rifle (which I have done), but this load did a very fine job for everything I could have wished for.

Realy, a "wish list," & turned out that this load did everything I wanted.

No case prep, no nothing other than a standard laoding which turnedout to e very satisfactoryj=in all three rifles.

YMMV