OAL

[mrat]

I've been reloading for a few years, mostly just for deer hunting and related practicing. I've always stayed with the recommended OAL specs for each load. Now I want to go for a little more accuracy for target and varmint shooting. I know how to check for land distance. Other shooters gave bullet jump distance for specific loads,etc. My two questions are how much past reloading data lengths can you go (keeping about .035-.015 jump)? And what do you try first: jump distance tweaking or powder load tweaking? The stated "bullet seating=bullet diameter" doesn't even come out right with chart data. This is for a .270 with 90gr Sierra Varminters and 130gr Sierra boattail spitzers. I could just experiment but would like to hear from somebody who has actual knowledge on the subject.

[daschnoz]

I'm not sure about the actual jump/accuracy thing, but I can help with the OAL from an internal ballistics standpoint.

It's all about internal case volume. Since there is no direct way to measure the internal case volume, the OAL is used as an indirect measurement.

- shorter OAL = more of the bullet that is taking up internal case volume

- more volume taken up by the bullet = less volume for combustion gases

- too large of a powder charge for the available case volume = bad day at the range

Now, if you're not at the bottom end of the powder charge range, you can lengthen the OAL safely. You are increasing the internal case volume - giving the combustion gases more space to occupy. Lower pressures will result.


.

[dk99358]

In a large case like the 270, volume is not an issue like it is in small handgun cases. You mention deer hunting, that means your rounds must cycle through the magazine, that will most likely be the limiting factor.

I used to chase the length by seating a bullet in a dummy case (no powder or primer) and smoking the bullet with a match. Chamber it and look for marks from the rifling. Change depth as needed.

I gave that up, now I start at listed maximum length, play with the powder charge until I get the best accuracy at the velocity I want then try a few small adjustments to length. Quarter turn or two on the seater stem both in and out (if the mag will handle it).

A buddy of mine got caught on opening morning with rounds that would not go in his magazine even though they chambered fine. He hunted with a single shot that day. Lesson learned.

Dale

[mrat]

I did the dummy bullet thing,have that figured out. Mag length is fine.I'm checking all the bullet,case,depth,etc dimensions with a digital caliper. And I'm not going to be running any ground scorchers, just want to pull the group a little tighter.Thanks for the input.

[Delkal]

The OAL printed in reloading books is mostly worthless. It is probably at SAMMI minimum but most manufactures put a longer throat (sometimes MUCH longer) throat on their firearms. I have one rifle that won't touch the lands till the bullet leaves the cartrige (terrible accuracy). While the printed OAL will fit in all guns, usually you can get better accuracy if you can seat the bullet 25 thousandth from the lands (where the rifling starts).

NOTE: if you put a long bullet in another rifle with a short throat you might get into trouble pressure wise.

My way to determine bullet seating is to get a sized case, cut the neck twice with a dremel and slip your bullet in (longer than usual). Take a dry erase marker and blacken the bullet. Then put it into your chamber and close it. Carefully remove it and measure.

Sometimes the bullet will slightly stick on the rifling (thats why you marked the bullet). Reseat the bullet to the dry erase line and measure.

Its a good idea to do this 3-5 times with different bullets to determine your distance to lands. Then subtract 0.025 and seat to there.

While your at it......it is a good idea to make 5-10 rounds each at book OAL, lands -25 and lands -50. Shoot them accurately and see which gives the best group.

[mrat]

At .025 off lands, they are .035 and .085 longer than load chart specs. I have .185 and .120 bullet to case neck contact (depth). I guess as long as the bullet doesn't fall out of the case, they're good. All cases are FL resized and I don't crimp. I'm going to start with 80% max charge and come up 2gr at a time to 90% and find the best charge. Then I'll try .040 to .030 to .020 jump to lands and see what it likes. Does that seem right or is there a better way? You guys have helped a lot,thanks.

[Delkal]

At .025 off lands, they are .035 and .085 longer than load chart specs. I have .185 and .120 bullet to case neck contact (depth). I guess as long as the bullet doesn't fall out of the case, they're good. All cases are FL resized and I don't crimp. I'm going to start with 80% max charge and come up 2gr at a time to 90% and find the best charge. Then I'll try .040 to .030 to .020 jump to lands and see what it likes. Does that seem right or is there a better way? You guys have helped a lot,thanks.

Thats not much seating depth. Usually you want at least on caliber. I did see your using light bullets with a 90 grain for a .270 but the 130 grain should be deeper. Depending on your barrel twist you might want to consider a heavier bullet (especially for deer).

My advise applies if everything else works too (magazine length, functioning in an autoloader and actually being able to touch the lands). It sounds like with the light bullet you will be forced to have a big jump to the lands. Hope your rifle isn't long throated too. If you measure the distance to the lands and find the bullet won't be in the case your out of luck. Usually not a recipe for accuracy.

Untill you know exactly how your load is preforming I wouldn't seat closer that 0.025. This is just a rule ot thumb and some target shooters actually seat to the lands. But pressures can spike fast and until you get a lot of experience reloading I wouldn't try it.

[SteveWag]

I usually load to touch the rifling. SAMMI length for .223 is 2.25 inches, my OAL is 2.7 inches. I have found that 5 or ten thou. back keeps the rifling from “keeping” the bullet if I extract an unfired case. Start 10 thou. back (or max mag length), at min load and work your way up. Watch the primer and bolt lift. The best way is to shoot 3 or 5 rounds at each load through a chronograph and then graph velocity, extreme spread and standard deviation v/s load.
See:

http://www.gswagner.com/6.5matchrifl...tchrifle6.html

The link shows three powder tests, six graphs. See that 4895 has several sweet spots, 2520 only one and Spec. Ball has none. The $100 chronograph can’t be beat. A 25, 50 yard range is fine, no targets needed and hold, trigger pull. Etc are not an effect, unless you hit the ‘graph.
Steve

[mrat]

The 90gr were only .035 short of.025 set back. The 130gr actually had to be pulled out farther. Probably different ogive on the bullet profile. The reason the 130s don't have as much touching the case neck is due to the boattail design.There's almost .150 loss due to the angled boattail. I was going to try them just because of a better ballistic coeffient over the 90s. I wanted to do the 90's because of lighter bullet/lighter recoil plus I have a couple hundred. They got great reviews for accuracy, which I was surprised at because they are shorter. For deer loads I have about six boxes of factory core-lokts which should last the rest of my lifetime, also it's not my only caliber for deer. The rifle is a '73 Rem 700 BDL I bought new as a teenager. I don't think it even has 200rds down it. Was thinking of retiring it to varmint/bench gun status and wanted to squeeze a tighter group out of it. Got it originally with the thought of western hunting: antelope mt goat,etc. Never had a shot at deer over 100yds here in Pa or WV.