Seating Depth, Cannelure and Hornady Manual Data

[Late4Dinner]

This is my first post (both here and anywhere) so please go easy on me if I dont get it exactly right.

I searched for my answer, but couldn't find it so, here is my question:

I have been reloading for about a year, and generally do ok with it. I have all of the right gear for case prep, measuring, loading, etc. And even though I have the AP, I generally load the 308Win one round at a time, as repeatable accuracy is my goal.

My question is specifically about the COL specs for 308 Win in the Hornady 7th edition.

The Setup:
I am using a Hornady LnL AP with Hornady dies, loading 308Win with LC-93 Match brass (trimmed to 2.005" as per Hornady's 7th), Remington 9.5 primer, RL-15 powder (46.1gr), and Hornady #3037 150gr BT-FMJ bullet.

The Question:
The 7th Edition (page 447) advises that COL with this bullet should be 2.780".

However the 3037 bullet is a cannelure boat tail design FMJ. When seating the bullet to the depth required for the 2.780" COL, the cannelure is well outside of the case mouth.

In order to seat the cannelure properly, I must seat to a COL of 2.720 (a full .06" shorter than recommended the COL), and that is to the bottom of the cannelure.

Even at this significantly shorter than recommended COL, the 2.720" COL cartridge results in a stiff bolt closing, and appears to seat the ogive into the lands, leaving the tell-tale spiral scratches on the bullet when closing the bolt.

My gut/experience tells me that I need to back the COL even further, down to probably 2.715", to give proper ogive clearance and avoid excessive pressure upon firing - but that is taking me even further from the recommended COL for this round.

Case deminsions for headspace are within spec.

So, is the Hornady 7th Edition just wrong for this (Hornady) round, or am I doing something wrong, or I am just putting way too much thought into this?

Your advice please, and thank you.

[Slow Go]

"The Question:
The 7th Edition (page 447) advises that COL with this bullet should be 2.780". "

Your question is a common one, seems book OAL figures are meant to help but often cause more agonizing than it cures.

Truth is, book OAL is not what it "should be", it's only what the book makers used to develop their listed data, chosen in the belief it will work okay in most firearms. But the correct OAL is what works best in YOUR firearm, not theirs.

So - seat a dummy cartridge to the cannalure or seat to the book OAL as you are most comfortable with. Confirm that it will feed and chamber smoothly for your use. If it works, fine, it probably will. If not, change it as needed.

Then, with a functional OAL, load a series of cartridges about a half grain apart and test fire them. Start low, increase charges until you reach book max. Fire them in that order until you get to the top loads OR until you see signs of excess pressure - if you do, back off maybe 10-15% and say that's YOUR max. Believe me, some guns DO show high pressure signs well before reaching book max so don't assume that because a load is book listed it will certainly be safe for all weapons.

Once you know your max charge, you can start to expermenting for groups. Then, after you find your best charge, do another series while vary seating depth in and out until you find the best point for accuracy. For factory sporters that will rarely be with the bullet touching the lands so avoid going that far out.

Contrary to some "conventonal wisdom", seating deeper in rifles does not increase peak pressure as it does in handgun loads. Allowing the bullet a running start actually decreases the peak pressure in rifles. And the best seating depth is (usually) a range several thousanths wide, it is VERY unlikely to be at a specific point, plus or minus nothing. So, the various ways of taking OAL readings with some special ogive gage/tool is largely useless for most of us. Meaning that in the real world, you can do quite well just reading the OAL as what it is, meplat (bullet tip) to base with a common dial caliper reading in thousanths.

[bobvonb]

I'm having a 6.5x53r conversion done on a Steyr 95. That's going well enough. I know that historically 140 gr solids were used in this cartridge. However, when I look at the 140gr bullet they are quite long and if I were to crimp on the channelure they would sit quite a ways back into the case. How far back behind the neck is OK?

Or do I need to go to a lighter, and therefore shorter, bullet?

[Late4Dinner]

Originally Posted by Slow Go

Your question is a common one

Thank you Slow Go. Your advice is just what I was hoping for.

I should have included in my original, I am shooting a Remington 700P (SA/BDL), with HS-Precision stock and varmit profile heavy 26" (1:12) barrel.

I am aiming for .5 MOA performance (bench), and am attempting to take ammunition out of the equation. I am using the 150gr 3037s because I only have access to about a 100yd max shot, and well frankly, Hornady gave me 1,300 of them for free.

I've heard that conventional wisdom says the heavier 175gr shoots more accurate in this caliber, but I suspect that the lighter bullet will do OK given the short range and 2 full turns in the barrel.

Any thoughts? Again, your insight, experience and advice is greatly appreciated.

[Slow Go]

I have enough experiece to tell you that anyone who tells you what will shoot "best" in any rifle is kidding himself as well as you. Like women, each rifle is a law unto itself. There is hardly any happy "average" rule that can be applied with any consistancy, it just isn't that simple!

That said, the slow twist and velocity - comparitively - of a .308 lends itself to better accuracy with mid to light .30 cal bullets; your 150 Hornadys should do you good. But setting your sights on .5 moa at this point will likely lead to disappointment, at least initially...maybe later? And, in general terms, Sierras win more matches than any other off-the-shelf bullets but Hornady's do well.

Something few of us appreciate is how hard it is to get groups much under an inch, far more such are done on the web than in the field! Getting a 1" group to a 1/2" group isn't twice as hard, it's 4 times as hard! Getting to a 1/4" group is 16 times as hard, because it's a square law thing, not linerar.

It's much more difficult to see errors that small than may seem to think. Tiny changes in grip, cheek contact, trigger pull, sand bag bounce, slight wind, mirage, etc. makes consistant sub-minute groups VERY hard to accomplish. And that's assuming the rifle's action, barrel and your cleaning methods, stock bediding and the ammunition itself are up to the task. What I suggest is, take it easy on yourself, challange but don't defeat yourself with overly demanding goals at this point. Allow for time to develop your skills; learn to load better, practice shooting and in time you are likely to get where you hope to go without being discouraged.

It may require a new custom barrel on that rig to get to the accuracy level you seek, but work on what you have until you KNOW it's limits! And have fun in the effort, good luck!

[deadzero]

if your goal is accuracy you need to know what that rifle is going to use as a max OAL to adjust your OAL to best performance. if you switch brands or weights of bullets this will change. if you do not use a OAL gage then your blindly working every new load.
Hornady makes a OAL gage that is used with a modified case (sold seperately). the modified case is threaded in the primer pocket area to accept the gage. a rod telescopes inside the case. set the bullet you will be using in the case, insert it into the chamber, push the rod forward lightly until the round touches the rifling. lock down the adjustment. use a cleaning rod in the muzzle end to push the bullet, case, and gage back out of the chamber. now, measure the OAL of this bullet and case.
this is you Max. OAL for this style and weight of bullet in this chamber. write this number down. reduce this length by .010". this will now let you know you have an OAL for this cartridge that is going to allow .010" free run in your gun. adjust seating depth in or out to find best accuracy, and this way you will know exactly how much jump (free run) you are giving the bullet. also measure OAL with a bullet comparator so your measuring off the ogive through the production run. measuring to the bullet tip is not going to give you the best comparisons through the lot to judge the consistancy of your production run.

and you don't have to find max pressure on a load to find best accuracy. the best accuracy will be somewhere around 60% to 70% of max. generally.

[Late4Dinner]

Originally Posted by deadzero

if your goal is accuracy you need...

Thank you DeadZero.

I have the Hornady (straight) OAL gage, the modified case for 308Win, and the bullet comparator, as well as headspace guage and micrometer.

I thought I knew what my rifle was asking for in an OAL, and I thank you and Slow Go for taking the time to set me straight. I was seriously confounded by the Hornady data in their 7th RL Manual.

Truth is, to use an analogy and put words in your mouth, the books are kinda like speed limit signs - they are informed 'suggestions', and while they are not calibrated for every person's specific needs, completely disregarding them could cost you :-)

This site is a great source for info because of guys like you. Thanks again.

[jimkim]

Originally Posted by bobvonb

I'm having a 6.5x53r conversion done on a Steyr 95. That's going well enough. I know that historically 140 gr solids were used in this cartridge. However, when I look at the 140gr bullet they are quite long and if I were to crimp on the channelure they would sit quite a ways back into the case. How far back behind the neck is OK?

Or do I need to go to a lighter, and therefore shorter, bullet?

Just because the bullet is seated below the shoulder doesn't mean it will be less accurate. Most of the time it will be, but as was mentioned before every gun is different. You can always load a few and see how they shoot. If your still uneasy about doing this, try another bullet. Another option would be to ream the throat to extend the lead so you can load to a longer OAL. One more thing, buy a Lee FCD and you can crimp anywhere, not just in the cannelure. You should be able to machine(remove 2mm) the 6.5x55mm Lee FCD collet to 6.5x53R specs.

[bobvonb]

Originally Posted by jimkim

Just because the bullet is seated below the shoulder doesn't mean it will be less accurate. Most of the time it will be, but as was mentioned before every gun is different. You can always load a few and see how they shoot. If your still uneasy about doing this, try another bullet. Another option would be to ream the throat to extend the lead so you can load to a longer OAL. One more thing, buy a Lee FCD and you can crimp anywhere, not just in the cannelure. You should be able to machine(remove 2mm) the 6.5x55mm Lee FCD collet to 6.5x53R specs.

It is having that much bullet sticking back into the case that worries me, not the OAL. Indeed, at this point I'm not even concerned with accuracy, just safety. I could imaging all those hot gases squeezing in on the rear end of the bullet and not just getting behind the end and pushing it out, with an attendent pressure buildup. Is this a valid concern?

I paid good bucks for RCBS custom dies in 6.5x53R (aka 6.5x53.5R) so I should be good to go with seating at whatever depth I need.

Thank you.

[pathdoc]

Originally Posted by bobvonb

I could imaging all those hot gases squeezing in on the rear end of the bullet and not just getting behind the end and pushing it out, with an attendent pressure buildup.

I don't think so. I can see what you're getting at - that there would be some sort of "pinch" effect - but ultimately what you're dealing with is a movable object that has about 20 TONS per square inch behind it and only 15 POUNDS per sq.in. in front of it. Other shooters, please correct me if I'm wrong, but as I see it - ignition beginning as it does at the primer, the pressure wave is going to move from the back of the case to the front. That thing is going to get a move on long before radial pressures can "pinch" it into place.

[Slow Go]

"...you don't have to find max pressure on a load to find best accuracy. the best accuracy will be somewhere around 60% to 70% of max. generally."

That's "common knowledge" but I've never found it to be true.

Powders, or at least most of them will burn most consistantly in the design pressure range. Dropping much below that pressure seems to give varing pressure and accuracy.

[deadzero]

Originally Posted by Slow Go

"...you don't have to find max pressure on a load to find best accuracy. the best accuracy will be somewhere around 60% to 70% of max. generally."

That's "common knowledge" but I've never found it to be true.

Powders, or at least most of them will burn most consistantly in the design pressure range. Dropping much below that pressure seems to give varing pressure and accuracy.

do what works for you.

5 rounds of 308 in 1 single hole measuring .531" at 100 yds works for me.

powder burn rates and case fill volume are far more important to accuracy than top end speed and pressure. thats why my accuracy loads are generally with powders that max out as compressed charges. when I back down to the 70% mark i'm at max fill capacity, uncompressed.

[Late4Dinner]

Originally Posted by deadzero

...5 rounds of 308 in 1 single hole measuring .531" at 100 yds works for me.

What load configuration is that? What Powder/weight, primer, and bullet?

Thx,

[Slow Go]

"do what works for you. 5 rounds of 308 in 1 single hole measuring .531" at 100 yds works for me.z

.531" from a sporter? Nice shooting, that pretty well works for anyone! But it's not what I meant.

Firearms being what they are - individuals - there are unpredictible exceptions to anything. What I meant is it's more common for best accuracy to come at normal cartridge design pressures, not very often at lower ones, simply because the burn rate is somewhat erratic at lower pressures.

Repeatablity is the thing in accuracy, not the occasional, isolated group. So, since that's your 100 yard group, I wonder how consistanly you obtain that level of accuracy? I mean, was that .531" an average of a dozen or so consecutive groups or a random one-time, "wallet" keeper, group? I also wonder what your reduced velocity load's exteme spread/standard deviation is and how it might affect groups at 200-300 yards, plus?

[deadzero]

Originally Posted by Late4Dinner

What load configuration is that? What Powder/weight, primer, and bullet?

Thx,

I don't want to give actual OAL dimensions because this load is running with .004" of free run in my chamber. Hornady wants it at 2.800", im a bit longer but still at magazine length.

remington cases (same lot), annealed, once fired, trimmed to within .0005" of each other, partial neck resized, with minimal taper crimp.

Hornady 168 gr. A-Max .308 #305026

Wolf Larger Rifle Mag Primers.

Winchester 760 powder ( I highly recommend this load be worked up with a chronograph since no load data exists that I have found for Mag Primers) this powder works good with 180 gr bullets, for the 168 gr. I used the hotter Mag primer ignition. best accuracy was at 47.5 gr. in my gun.* (2635 fps with diviation numbers < 10 fps) this is max case fill just before compression, but bullet is running over length.

Rifle is Savage Model 10 FCPXP, 1:10 twist, with NightForce 12-42X56 benchrest.


* Hornady 7th edition does not list this powder/bullet weight.
Hornady 3rd edition lists 43.3 gr. to 50.3 gr. of win. 760
Lyman 46th edition lists 43.8 gr. to 49.0 gr. compressed charge. of Win. 760.

**** these loads are with standard large rifle primers.****

3 shots thru one hole is pretty consistant, 4 in one is pretty common, 5 in one is up to my skill level, repeatable, usually only once or twice in a session (usually 50 rounds per rifle). .531" was the tightest so far. thats a deviation of .253" on the spread. off the bench on a bipod. the combination can do it, just some days I'm not up to it.

[Slow Go]

" thats a deviation of .253" on the spread."

Most BR matches include both 100 and 200 yard group shooting. Few serious competitive shooters use the same load in the same rifle at both ranges, for a variaty of reasons but velocity variation is one of them.

[Late4Dinner]

Thanks guys. I did some more experimenting today, and found that 2.7175 works really well for OAL out of the lands for my particular 700 action. Pretty steep deviation from the book's 2.8, and even more so from DZ's >2.8, but now I am confident that it is what is right for mine. Who would've thought that there would be THAT much deviation in action specs?

I'll be playing with different load work-ups in the up-coming weeks, but wanted your opinons on RL-15 powder. Have you used it? Is there an alternative powder that you swear by, and if so, why? I read Win760 above, and I'll give that a try too if I can find some locally. What else is worth trying?

BTW, I will be shooting from a secured bench/gun vice with remote trigger actuator, pretty much taking me completely out of the equation, so this really will be a working test of rifle and load compatibility. Once I nail down what really works for this rifle, then I'll see what "I" can do with it :-)

[deadzero]

thats why the OAL gage is important. your using a FMJ and I'm using the A-Max. even in my chamber the OAL for the 2 bullets will be different, due to different variations in design of the ogive. if the gun is new, you may notice the OAL gage will give you a different reading after a couple hundred rounds have gone thru the barrel. when re-checking OAL with the gage, make sure the bore has been well cleaned with a brush and solvent to give you the most accurate readings possible.
I have a 700 SPS Varmint in 223 that acted like that when new, the chamber gage OAL was right at Hornady's recommended OAL with 0.0" free bore. after a good break in the gage showed I now had room to "play". I would not have thought it could make that much difference, but it did.

I've never used a bench gun vise. I've seen them used in gun magazines and often wondered how good they work and what the cost of one might be. but as it is now, I already haul enough equipment to the range as it is. (a whole locker full of stuff. from sand bags, Chrony with tripod, spotting scope, range finder, brass catchers, targets, cleaning kits, and assorted goodies.)

[Late4Dinner]

Originally Posted by deadzero

I've never used a bench gun vise. I've seen them used in gun magazines and often wondered how good they work and what the cost of one might be.

I paid about 3 bills for mine; it really is a sweet setup (if it works, of course) which is what I will find out shortly. I haven't used it for live fire yet, but have set it up on my workbench. Seems very stable and secure, with hydraulic recoil dampeners, etc. It will be mounted (bolted) to the shooting bench, so, if it works as designed, it should bring it down to a question of rifle and ammo, and not at all about Point of Aim. We'll see.

Originally Posted by deadzero

...but as it is now, I already haul enough equipment to the range as it is. (a whole locker full of stuff. from sand bags, Chrony with tripod, spotting scope, range finder, brass catchers, targets, cleaning kits, and assorted goodies.)

Heard that! :-) Hey, brass catchers? what do you use? Not so much a problem for my 700, but my ARs, AKs and M1A have me chasing down brass all over the place. Been wondering if there was any solution to that problem...

[samuel]

Good read!What a breath of fresh air!Someone actually realises that all "out of the box" rifles don't shoot .5" and under.This is a very informative thread. ,,,sam.