Reloading Question - OAL Measurements

[Steinmaster]

I just started reloading and am working up some loads for my Rem M700 .308 rifle. I used a Hornady Overall Length (OAL) gauge to measure the distance my bullets contact the lands and how far I should seat the bullets. I measured the length from the bullet ogive rather than from the bullet tip to get a more consistent measurement. What is a good starting point for "backing off" the bullet from the lands/rifling? I'm familiar with the fact that seating the bullet touching the lands will increase chamber pressure and I do not want this. Does anyone have some good load developed using this method? If so, how much "back off" is good.

[Ring]

this can be totally bullet dependent... and barrel dependent... and not always needed to get accuracy
being a 308, COL to tip of 2.80 to start, find a good load 1st, THEN try moving it out .01 to .02 at a time, 5 shot groups, to see if you notice get any better.. if you see no change then just just load them at 2.8

[markm]

What bullet EXACTLY???

If it's a tangent ogive bullet like an SMK, forget all that crap and load it to mag length. If it's a factory barrel and you're wanting to shoot a secant ogive like the VLDs....? You'll be loading way over mag length and single feeding.

[Steinmaster]

I'm reloading Hornady AMAX 168 gr and Sierra Match King 168gr BTHP (44 grains Varget). For the Sierra's, I backed off .030 inches from the distance where the bullet contacted the lands. I'm over the recommended OAL of 2.810 (per reloading manual). I tested the round in my Rem 700P. It chambered and feed from the magazine OK. Should there by any other thing I should be concerned about if the OAL is greater then 2.810? I think .030 allows enough "free travel" to prevent excess pressures. Any thoughts?

[Steinmaster]

What bullet EXACTLY???

If it's a tangent ogive bullet like an SMK, forget all that crap and load it to mag length. If it's a factory barrel and you're wanting to shoot a secant ogive like the VLDs....? You'll be loading way over mag length and single feeding.

I'm reloading Hornady AMAX 168 gr and Sierra Match King 168gr BTHP (44 grains Varget). For the Sierra's, I backed off .030 inches from the distance where the bullet contacted the lands. I'm over the recommended OAL of 2.810 (per reloading manual). I tested the round in my Rem 700P. It chambered and feed from the magazine OK. Should there by any other thing I should be concerned about if the OAL is greater then 2.810? I think .030 allows enough "free travel" to prevent excess pressures. Any thoughts?

[elephantrider]

I'm reloading Hornady AMAX 168 gr and Sierra Match King 168gr BTHP (44 grains Varget). For the Sierra's, I backed off .030 inches from the distance where the bullet contacted the lands. I'm over the recommended OAL of 2.810 (per reloading manual). I tested the round in my Rem 700P. It chambered and feed from the magazine OK. Should there by any other thing I should be concerned about if the OAL is greater then 2.810? I think .030 allows enough "free travel" to prevent excess pressures. Any thoughts?

You will not have any issues with excess pressure from not enough jump to the lands, 0.30" is plenty. It is only an issue if you are right up to, or into the lands. The Remington factory barrels have a very long throat, to prevent novice reloaders from seating a bullet too long, jamming it into the lands, and creating an overpressure situation. Typically if you are seating the bullet ogive anywhere near the lands on a Rem factory barrel, then the rounds become too long to feed through a magazine, and you are giving up case mouth bullet grip. Since you are so far away from the lands anyway I wouldn't focus on seating depth as it wont likely make much of a difference for you. Use a bullet that is more tolerant to the long jump like you are already doing (tangent ogive), and make sure the rounds feed reliably.

[Steinmaster]

You will not have any issues with excess pressure from not enough jump to the lands, 0.30" is plenty. It is only an issue if you are right up to, or into the lands. The Remington factory barrels have a very long throat, to prevent novice reloaders from seating a bullet too long, jamming it into the lands, and creating an overpressure situation. Typically if you are seating the bullet ogive anywhere near the lands on a Rem factory barrel, then the rounds become too long to feed through a magazine, and you are giving up case mouth bullet grip. Since you are so far away from the lands anyway I wouldn't focus on seating depth as it wont likely make much of a difference for you. Use a bullet that is more tolerant to the long jump like you are already doing (tangent ogive), and make sure the rounds feed reliably.

Thanks for the useful information. I didn't realize that about Remington rifles. I did not notice when I was seating close to the lands, there was not much case mouth bullet grip. I reseated the bullets to the recommended COAL (2.800). Are the Sierra Match BTHP and Hornady AMAX considered tangent ogive bullets?

[elephantrider]

Thanks for the useful information. I didn't realize that about Remington rifles. I did not notice when I was seating close to the lands, there was not much case mouth bullet grip. I reseated the bullets to the recommended COAL (2.800). Are the Sierra Match BTHP and Hornady AMAX considered tangent ogive bullets?

Case mouth grip isn't the hugest deal, but something to think about when you start seating the bullets way out. Pretty sure both the SMKs and AMAXs you are using are tangent ogive. Here is an explanation of the two types.
http://bulletin.accurateshooter.com/2007/07/283/

[darr3239]

I discussed this with my gunsmith sometime back. He always loads to mag. length on .308s, and isn't concerning about the jump. He explained the bearing surface on a 30 cal. bullet is long enough for the bullet to stabilize in the barrel. A smaller bullet, such as the .22 to 6mm area, is a different story.

[opsoff1]

I just started reloading and am working up some loads for my Rem M700 .308 rifle. I used a Hornady Overall Length (OAL) gauge to measure the distance my bullets contact the lands and how far I should seat the bullets. I measured the length from the bullet ogive rather than from the bullet tip to get a more consistent measurement. What is a good starting point for "backing off" the bullet from the lands/rifling? I'm familiar with the fact that seating the bullet touching the lands will increase chamber pressure and I do not want this. Does anyone have some good load developed using this method? If so, how much "back off" is good.

Steinmaster,
I would submit that you pause for a moment and consider what your goal is. If it is hunting - different set of circumstances. If it's shooting small groups off a bench - again - different set of reloading rules. If it is a duty gun / tactical employment, then yes - again another set of issues to consider.
Based on bullet choices - I will venture a guess that you are looking for small groups. If that is the case - then I would strongly suggest you consider this.
1. Before you ever touch off a round - find the lands in your throat. Determine where the bullet of choice touches the lands. It will vary from bullet type to bullet type and mfr to mfr - all different.
2. This seating depth should be your start point - yes, ON the lands. let me be really clear - OAL/COL is utterly meaningless when viewed as a measurement of land engagement - far too many manufacturing variances for that dimension to have a place for precision/accuracy hand load development. HOWEVER (there's always a but...) The OAL / COL is meaningful IF...
a) you must feed through a magazine or
b) the throat is so long, that you can't seat the bullet in the neck.
If neither of those conditions exist, then drive on.
3. Your starting loads should be reduced about 6% from max. i.e. 42.0 gr of IMR 4895 - 5% = 2.4gr or 39.5gr. The reason you start on the lands with reduced loads to to create the high pressure node upfront. Pay careful attention to pressure signs - primer appearance is only a small indicator. Case head expansion just above the extractor groove is a better one.
4. I am strong advocate of the ILD method of load development. Incremental Load Development. It is basically a ladder system that will get you the right charge very quickly and without a lot of wasted powder, bullets, primers and barrel life. VERY simply, you are shooting incremental loads (in the 308, .3 increments work well) one round at a time - looking for clusters of shots that don't show vertical stringing. i.e. using some IMR4985 data, lets say you load in .3 increments from 39.5 up to 42.5. The loads at 41.6, 41.9 and 42.2 show a group that is less than 1/2" in vertical. This is one of your sweet spots or "accuracy nodes" (there are others at different velocities) Your initial conclusion should be that that your rough accurate load is in the middle of that group or at 41.9gr. This gives you leeway for slight over throws and slight underthrows of powder.
5. This load: 41.9 with the bullet on the lands is now established as your starting point for the "tuning phase." You have determined that you do not have pressure issues with the bullet on the lands at that charge weight, that it shows a sweet spot of higher & lower charges and if you are running over a chrono, you'd see the desired velocity.
6. In tuning - this is where you should be evaluating smaller changes in loads and seating depths. From the 41.9 baseline - you can try loads at .2, .1 above and below the original 41.9gr load. This will tighten the sweet spot. This also where you should now be loading/shooting 5 shot groups of the same charge. Look for nice round groups. Regarding the seating depth; since you've started on the lands, the logical movement will be away from the lands - I personally do this in .005 increments. So - to recap - fine tune the load THEN fine tune your seating depth.
GENERALLY speaking, SMK's - speciffically the 168's shoot well at about .010" off the lands to just touching. AMax's tend to shoot well about .020" off. And yes - both are tangent ogive bullets. Both are very tolerant of jump.
As you fine tune the load - you should see your groups shrink OR reduce the tendency for a flier. Finding the sweet spot also builds in a tolerance to keep the load accurate with respect to temperature changes. i.e. if it gets hot out - you have already proven that a higher charge is still going to go into the group without pressure issues. Increased ambient temps are going to have the same effect as an increase in powder charges.
If you find your throat is too long, then load to the longest length you can that provides enough neck support (in a 308 = 1 caliber or .3 of bearing surface should be in the neck - minimum)
This is all very simplified - but it is a proven sysytem and has provided an exponential increase in efficiency for load development. I have used it for 20+ years with refinements and have won on a national level utilizing it.
If you want more information - PM me and I can send you a comprehensive how to.

[Steinmaster]

Very good information. Thank you for taking the time to explain this. I measured my Remington 700P OAL to the lands and I do not have enough room to seat the bullet (SMKs and AMAX). Looks like the throat length is pretty long. Looks like I will seat the bullet to .308 minimum and go from there.

[opsoff1]

Steinmaster
Out of curiosity, with say a 168 SMK touching the lands - how long is the OAL of the loaded cartridge?

[Steinmaster]

Steinmaster
Out of curiosity, with say a 168 SMK touching the lands - how long is the OAL of the loaded cartridge?

Using the Hornady OAL gauge, I measured 2.339 off the ogive. If I were to use this minus .020 inches, there is not enough bullet left to adequately seat (.308), so I just used COAL from reloading manual. I'm getting superb accuracy from the SMK by the way.

[opsoff1]

What is the total overall length of the loaded cartridge? (Base of case to tip of bullet?)

[Steinmaster]

What is the total overall length of the loaded cartridge? (Base of case to tip of bullet?)

2.919

[opsoff1]

Wow and that is new factory barrel?

[Steinmaster]

Wow and that is new factory barrel?

Yeah. Brand new. I've had some other forum members say Remingtons have longer throats. I was surprised when I measured to the lands. The gun shoots 0.5 MOA at 100 hundred years so I'm not going to do anything to it.

[opsoff1]

Thats stunning - I use an Obermeyer 308 reamer in most of my 308/762 bolt guns and to give you an idea / comparison - with a 180 SMK (old style) .005 into the lands - my aprox OAL is 2.840". My son has a Remy 700 SPS in .223 and it has an astoundingly short throat (probably a straight .223 Remington) - I'd love to figure out what goes through the minds of Remy engineers when they spec a reamer for consumer guns.

[Steinmaster]

Thats stunning - I use an Obermeyer 308 reamer in most of my 308/762 bolt guns and to give you an idea / comparison - with a 180 SMK (old style) .005 into the lands - my aprox OAL is 2.840". My son has a Remy 700 SPS in .223 and it has an astoundingly short throat (probably a straight .223 Remington) - I'd love to figure out what goes through the minds of Remy engineers when they spec a reamer for consumer guns.

I'm waiting for my GA Precision .308 bolt gun. Should be interesting to see what the measurement is and whether I can play with the OAL.

[HD1911]

in general, SMK and Amax are usually very jump tolerant. It's not unheard of for them to jump .110+ and still group very well.