How do you determine OAL and seating depth?

[Siggy Stardust]

Hey, Gang!

I've been out of shooting for a few years now after travelling and going to school, but I'm now back on track and looking to get back into many aspects of shooting once again.

I have several calibres that I reload for (.270, .303, 7mm-8) but no matter where I look I have not been able to find one simple answer that has eluded me for years...

"How do you determine what the exact OAL / seating depth should be for your particular bullet in your particular rifle?"

I found a couple different suggestions here and there, such as partly seating a bullet in a re-sized case, putting it in a rifle and using the action to seat it against the lands, or; blackening a seated dummy round in a candle then repeatedly chambering it in the rifle checking for marks from the lands until they no longer appear as you seat it a little deeper every succesive time.

I've also heard that ideally a bullet should be sitting .020" to .050" off the lands. But once again, how do I know where that magic sweet spot is?

This problem seems most relevant, or necessary if you will, for the 7mm-08 as I know there is a wide range of throat depths from manufactuer to manufacturer of rifles for this round...

I know there are millions of people out there that load their own ammo, so what is it everyone is doing that I am missing?

Any help or suggestions would be very much welcome and appreciated!


Signed,

Dazed and Confuzed

 

[350 Mag]

I have used the magic marker and once fired case method to good success.

I think the only way your going to find out is trial & error.

I usually seat .030 from the lands.

The Nosler manual reccomends .015-030 as long as the cartridge cylces properly and fits the magazine.

I think that if you have alot of free-bore in a rifle you get MORE velocity if you seat away from the lands.

If your talking about a run of the mill hunting rifle I don't think a few thous. of an inch difference in OAL is going to make alot of difference.

In a hunting rifle for 400 yards or less shots 1" or less groups @ 100 yards is quite sufficient.

I would focus more on the amount of powder and try and find the most accurate, fastest load(highest energy) then worrying about splitting hairs or 1-hole groups.

 

[SuperCub]

Another way is to close the bolt and insert a cleaning rod up against the bolt face after checking that gun is unloaded.

Mark that length on the rod at the crown.

Remove bolt.

Insert desired bullet into chamber and push and hold it againt the lands. I use a pencil.

Reinsert cleaning rod and push it up to the bullet tip. I put a plastic insert in the threaded end of the cleaning rod (for both measurements) so the bullet tip does not enter the open end of the rod and change measurement.

Again mark that length on the cleaning rod.

Measure between the marks and you now have the max OAL to the lands for that bullet. I usually back off by 0.020" for hunting loads.


.

 

[fisherking]

.15-030 is right.The easiest way I find to do it is take a piece of brass that has been fired in the rifle.Take a hack saw cut four slits in the case neck (X shape)seat a bullet in the case,a little longer than normal,put the round in the
chamber as far as it will go manually.Then close the bolt in one motion,when extracting be carefull that the round doesn't hit anything.I do this 3 times to make sure the measurements are the same,or as close as possible.Then I deduct .015"-.030" making sure that the rounds fit the magazine and cycle properly.

 

[Boomer]

The system I use is to seat a flat based bullet backwards in a resized unprimed case. When this round is chambered, the bullet will be pushed back into the neck and the resulting length is an accurate length to the lands. Next take the bullet you wish to load and push it firmly nose first into the muzzle of your rifle and twist it so that a line is etched on the bullet. This line shows the portion of the ogive that will first contact the lands. The OAL of your loads can now be easily determined by seating the bullet off the lands by what ever distance you choose.

The simple solution to OAL is to forget the whole thing. Choose bullets with cannelures and seat and crimp the bullet to the cannelure. The difference to field marksmanship is not discernible, and your ammo might actually be a bit better.

 

[stubblejumper]

I've also heard that ideally a bullet should be sitting .020" to .050" off the lands. But once again, how do I know where that magic sweet spot is?

The only way to know the best seating depths for your gun is by trial and error.And the best seating depth can change for every particular bullet.Even two similar looking bullets of the same weight may prefer two different seating depths.

The simple solution to OAL is to forget the whole thing. Choose bullets with cannelures and seat and crimp the bullet to the cannelure. The difference to field marksmanship is not discernible, and your ammo might actually be a bit better.

This is only for those people that really don't care about getting the best accuracy out of their guns.Changing the seating depth can cut groups in half with some gun/bullet combinations.Many bullets,including the majority of the premium bullets do not have cannelures,so you would be missing out on some of the best bullets available.Besides crimping is totally unecessary unless the gun has a tubular magazine or has extreme recoil,or in handguns.

 

[762shooter]

Another way is to close the bolt and insert a cleaning rod up against the bolt face after checking that gun is unloaded.

Mark that length on the rod at the crown.

Remove bolt.

Insert desired bullet into chamber and push and hold it againt the lands. I use a pencil.

Reinsert cleaning rod and push it up to the bullet tip. I put a plastic insert in the threaded end of the cleaning rod (for both measurements) so the bullet tip does not enter the open end of the rod and change measurement.

Again mark that length on the cleaning rod.

Measure between the marks and you now have the max OAL to the lands for that bullet. I usually back off by 0.020" for hunting loads.


.

That is what I do as well. I work with the rifle vertical, I mark the length to the bolt face by wrapping a piece of masking tape at the muzzle. Then with a bullet gently tapped in to the rifling I rest the rod on the bullet and measure from the muzzle to the tape with a caliper to get max OAL. I usually seat the bullets about .015" less than this measurement but you also have to check the max length that will feed properly from your magazine.

 

[Boomer]

Stubblejumper, crimping the bullet into the case uniforms the bullet pull weight which serves the same purpose as reducing the jump to the rifling. My .375 shoots sub MOA when loaded in this fashion. Given the cartridges the original poster loads for, it is unlikely than any of them are bench rest guns.

 

[looch]

I use the method SuperCub describes. I tried fisherking's method, but my ejector spring is stiff enough to push the bullet into the case prior to the casehead being in contact with the bolt-face, thus giving me a much shorter MAX COL measurement.

 

[Eagleye]

I invested in the Stoney Point OAL device. The best money I have spent. I also acquired a tap drill and tap so I can make my own "dummy" cases for the wildcats and chamberings that are more obscure. I usually start at .020" off the lands, and work each way from there to establish what works best in MY rifle. In my experience, rifles are somewhat like fingerprints, each is different. Remember, the finished round has to fit the magazine, unless you are shooting a single shot, so that may be the limiting factor as to COL. Regards, Eagleye

 

[Eagleye]

I use the method SuperCub describes. I tried fisherking's method, but my ejector spring is stiff enough to push the bullet into the case prior to the casehead being in contact with the bolt-face, thus giving me a much shorter MAX COL measurement.

This should make little difference, since headspace should be determined by case spec/chamber spec. The case should not go further into the chamber than it's headspace limitations, whether you have a spring loaded ejector or not. The bullet is well ahead of the datum line, the rim or the belt. Eagleye

 

[stubblejumper]

Stubblejumper, crimping the bullet into the case uniforms the bullet pull weight which serves the same purpose as reducing the jump to the rifling. My .375 shoots sub MOA when loaded in this fashion. Given the cartridges the original poster loads for, it is unlikely than any of them are bench rest guns.

Crimping may improve the accuracy with your particular gun and load,but it will not improve the accuracy with all other gun/bullet combinations.In fact it could reduce the accuracy in some combinations.Changing the COL may,or may not change the uniformity of the "pull weight" as you call it.If crimping was really a good way to improve the accuracy,all target shooters would crimp,and that is obviously not the case.If crimping was proven to increase accuracy in general,why don't companies like Sierra and Nosler have cannelures on all of their bullets?The original poster may not be shooting benchrest guns,but many of the basic principles to obtaining better accuracy still apply.
Others may disagree,but I am not buying in to the theory that crimping is an equivalent alternative to finding the optimum seating depth as you suggest.

 

[Boomer]

Crimping may improve the accuracy with your particular gun and load,but it will not improve the accuracy with all other gun/bullet combinations.In fact it could reduce the accuracy in some combinations.Changing the COL may,or may not change the uniformity of the "pull weight" as you call it.If crimping was really a good way to improve the accuracy,all target shooters would crimp,and that is obviously not the case.If crimping was proven to increase accuracy in general,why don't companies like Sierra and Nosler have cannelures on all of their bullets?The original poster may not be shooting benchrest guns,but many of the basic principles to obtaining better accuracy still apply.
Others may disagree,but I am not buying in to the theory that crimping is an equivalent alternative to finding the optimum seating depth as you suggest.

Target shooters are reluctant to add another variable in their quest for the ultimate in accuracy. It is easier for them to seat the bullet firmly into the lands or slightly off. The hunter in contrast to the target shooter, benefits more from absolute dependability than he does to accuracy measured to 3 decimal points. Absolute dependability cannot be achieved if a bullet is seated so long that it pulls out of the neck when the round is withdrawn from the chamber to be replaced in the magazine because the bullet is stuck in the lead. Most folks recognize this and resolve that problem by seating a hunting bullet not less than I caliber length into the case neck. However, unless the bullet is crimped into place, a rifle with enthusiastic recoil can push a bullet deep into the case body when the round in the bottom of the magazine has a number of rounds fired over it. The result of this can be a misfeed or a pressure spike due to the reduced powder capacity and a stuck case. If the bullet has some measurable jump due to a long lead, accuracy is improved through crimping, and reliability of the round is enhanced.

I will agree that both of my target rifles show superior accuracy when the bullets are seated into the lands, but I can't make use of the difference in accuracy between my hunting loads and my accuracy loads in the field. But, in the field I do benefit from the superior reliability of my hunting loads compared to my target loads.

 

[stubblejumper]

Target shooters are reluctant to add another variable in their quest for the ultimate in accuracy.

Reluctant yes,but most will do what it takes to win,and crimping has certainly not caught on with target shooters.

The hunter in contrast to the target shooter, benefits more from absolute dependability than he does to accuracy measured to 3 decimal points. Absolute dependability cannot be achieved if a bullet is seated so long that it pulls out of the neck when the round is withdrawn from the chamber to be replaced in the magazine because the bullet is stuck in the lead. Most folks recognize this and resolve that problem by seating a hunting bullet not less than I caliber length into the case neck. However, unless the bullet is crimped into place, a rifle with enthusiastic recoil can push a bullet deep into the case body when the round in the bottom of the magazine has a number of rounds fired over it.

I for one have never had to seat into the lands,or crimp,yet I am often able to obtain sub moa ,and usually much better with all of my current rifles.In fact not all of my rifles shoot best when seated even close to the lands.In fact I seat the barnes tsx and mrx .050" to .070" off the lands because that is where they shoot best in my rifles.I am able to consistently obtain 5/8 moa groups with three different rifles at these seating depths.I have hunted with two 300ultramags,two 7mmstws,one 375 h&h,one 300wby,one 8mmremmag,one 338x8mmremmag,most of which provide more recoil than the average hunting cartridge in use today,as well as other smaller capacity magnums,and I have never had an issue with bullets being pushed back into the case.
I would crimp for use in tubular magazines,or larger bore handguns or rifles,but it just isn't necessary for the vast majority of cartridges/rifles now being used by hunters.And I am certainly not severely limiting my choice of bullets or seating depths to use only bullets with a cannelure.

 

[Hotwheels81]

neck size a few cases and seat a shallow bullet, stuff em in and close the bolt...
back off .020...
this wont always work on older rifle's due to throat issues... a 150gr sierra in a well used .303 has about 1/8" of its tail in the case and i am not the only one who's had issues that i know of...

ya... i have taken a few hundred reloads with me hunting and bombing around the country... after a few hundred k's of washboard standing uprite in a MTM case you could see with your own 2 naked eye's the variance in OAL from round to round... i dont argue with people about crimping round's anymore... i just laugh at em when they find out the same way i did...

 

[looch]

This should make little difference, since headspace should be determined by case spec/chamber spec. The case should not go further into the chamber than it's headspace limitations, whether you have a spring loaded ejector or not. The bullet is well ahead of the datum line, the rim or the belt. Eagleye

You're hurting my brain. My cartridges come out about .100" shorter when using this method. Please explain what you think might be happening.

 

[stubblejumper]

ya... i have taken a few hundred reloads with me hunting and bombing around the country... after a few hundred k's of washboard standing uprite in a MTM case you could see with your own 2 naked eye's the variance in OAL from round to round..

neck size a few cases and seat a shallow bullet, stuff em in and close the bolt...
back off .020...

If you can fully seat the bullet in a neck sized case just by closing the bolt with your fingers,either your bullets are undersized,or the neck expander is too large.

 

[Hotwheels81]

thank's i read that and coffee came out my nose... you owe me a keyboard!

maybe your bullets are too large or your expander is too small? lmao...

no i'm quite sure all my kit is in top shape thank's... if you cant close your bolt and force the bullet farther into the case once its started then you have too much neck tension or a very small bolt handle.. i'm sure everyone here know's that the bullet sizes the case in the end anyway but more then a few thou neck tension after sizeing is just bad design by the die maker...

 

[stubblejumper]

Below are two 7mmstw cases with 162gr hornady bullets seated so that the amount of jacket extending from the neck to the base of the lead tip is identical.I held one cartridge in my hand and struck the bullet with a steel hammer until the lead was flattened as you can see.I remeasured the amount of bullet jacket from the case to the base of the lead tip,and it has not changed.

 

[stubblejumper]

if you cant close your bolt and force the bullet farther into the case once its started then you have too much neck tension or a very small bolt handle..

Apparently you missed:

by closing the bolt with your fingers

My rifles are remington 700s.I do not pound on my bolts or force them excessively.