So I’m new to reloading for precision center fire rifle and am wondering what the more experienced Reloader’s/ pro shooter types think about what standard to obey for maximum cartridge length. I know Saami spec is considered outdated when developing a load for precision rifle, and I have also heard of the rule of thumb that we should not load less than the caliber measurement deep on the bearing surface of the bullet inside the neck of the brass. So for .308 there should be at least .308 inches of bearing surface of bullet inside the case neck. In my particular rifle I am limited to a 2.95 coal by the magazine, (Tikka CTR) and my rifle allows a COAL of about 2.940 before jamming in the lands, but with the 168 grain SMK that I have chosen to load, if I start 10-15 thou off the lands, I have definitely broken the rule of minimum of caliber bullet depth, so what’s the consensus on right and wrong here and any guidance in this regard will be greatly appreciated.
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Limits of COAL beyond Saami
- Thread starter Rimfire77
- Start date
First SAAMI is not outdated. Read the purpose of the SAAMI standards. As a reloader you are not limited to interchangeability with other firearms.
The one caliber minimum seating in the neck is a generalization. You are not bound to maintaining that but you must understand the implication of reducing bearing surface in contact with the neck.
Cartridge length (COAL) and base to ogive (CBTO) have differing effects on the ammunition. COAL is a limitation that depends on magazine accommodation and it can be an issue depending on the feed ramps and bullet shape with the bullet being set back or the round jamming..
Cartridge Base to Ogive affects the engagement distance between the lands and the bullet. It also affects the case volume and hence pressure. That is, it will reduce pressure for a given charge until the bullet is near/into the lands where the pressure will increase.
You should also understand that it is likely your rifle chamber exceeds the SaAMI minimum chamber dimensions. In you r case you mention the 168 SMK. Your chamber likely has a longer freebore than the SAAMI minimum. In the case of my Remington 700 308 a 168SMK touching the lands has only the boattail in the case neck.
The one caliber minimum seating in the neck is a generalization. You are not bound to maintaining that but you must understand the implication of reducing bearing surface in contact with the neck.
Cartridge length (COAL) and base to ogive (CBTO) have differing effects on the ammunition. COAL is a limitation that depends on magazine accommodation and it can be an issue depending on the feed ramps and bullet shape with the bullet being set back or the round jamming..
Cartridge Base to Ogive affects the engagement distance between the lands and the bullet. It also affects the case volume and hence pressure. That is, it will reduce pressure for a given charge until the bullet is near/into the lands where the pressure will increase.
You should also understand that it is likely your rifle chamber exceeds the SaAMI minimum chamber dimensions. In you r case you mention the 168 SMK. Your chamber likely has a longer freebore than the SAAMI minimum. In the case of my Remington 700 308 a 168SMK touching the lands has only the boattail in the case neck.
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+1 on Doom's comments.
If you choose to go into non-standard territory, you take the responsibility for the work.
There is nothing new about seating a 308 long. How sturdy the results are is a matter of your specific rifle and context.
If you seat far out and run from a magazine, you have to test to find the limits of how sturdy your ammo is compared to what your action needs. Finding a good seating depth that results in ammo that is too delicate and suffers damage, is cold comfort.
You won't find a crisp black-white line, but more likely a grey zone transition. You should plan to test the limits to find where rounds will not tolerate magazine feed, or when they are too long to chamber, and then decide if those lengths are worth your trouble or if your best performance is found there or not. The results will be sensitive to brass prep, so your prep discipline will need to be held tight to keep the margins in your favor.
Good Luck and in for the range reports.
If you choose to go into non-standard territory, you take the responsibility for the work.
There is nothing new about seating a 308 long. How sturdy the results are is a matter of your specific rifle and context.
If you seat far out and run from a magazine, you have to test to find the limits of how sturdy your ammo is compared to what your action needs. Finding a good seating depth that results in ammo that is too delicate and suffers damage, is cold comfort.
You won't find a crisp black-white line, but more likely a grey zone transition. You should plan to test the limits to find where rounds will not tolerate magazine feed, or when they are too long to chamber, and then decide if those lengths are worth your trouble or if your best performance is found there or not. The results will be sensitive to brass prep, so your prep discipline will need to be held tight to keep the margins in your favor.
Good Luck and in for the range reports.
Develop your SMK load at around 2.800” coal. It will be very accurate in that coal area. Don’t worry about having to be close to the lands. It’s not necessary.
I’m grateful for the feedback. I have been reading a great deal and it’s always good to have multiple perspectives to reflect upon when arriving at a good starting point for load development. Many experienced reloaders have suggested starting 10-15 thou off the lands and working out, or in for that matter in small increments to find a bullet to lands relationship that provides repeatable gains in accuracy downrange on target. Some have suggested that getting the bullet closer to the lands than factory match ammo is the one thing they have done that has given them the biggest payout in demonstrable results on accuracy. I’m sure every rifle being different and having its own harmonics can lead to diverse outcomes and there is no set standard for what will work for everyone, but as Erik Cortina says, believe the target, so we must test. Also I should add that in my original post I mentioned SAAMI being outdated, I guess I worded it wrong. I was referring to the article published on Berger’s website by Bryan Litz on measuring from base to ogive where he mentioned that some aspects of saami spec can be seen as outdated when pertaining to modern accuracy loading. I wouldn’t make such a seeeping statement on my own with so little experience! Main thing is this stuff is super fun and interesting and I’m excited to be a part of this community and appreciate all the wisdom and experience out there! Thanks guys! I’ll follow up with some range data once I find something worth reporting.
The internet is a terrible place to get advice because you will seldom get the whole story. When Brian discusses seating depth his frame of reference is in a custom barrel chambered with a reamer that is likely tailored to a specific bullet or range of bullets. When you see someone state they have a standard deviation of 5 fps you don't usually know if it's over 3, 5 or 20 shots. It matters. Stating a muzzle velocity with load data and no barrel length will likely mislead you until you find its from a 30" barrel and you are shooting a 24" barrel.
You mentioned Erik. He is a very good entertainer and I personally don't care for a lot of what he does but "believe the target" is one thing that he and I agree upon. You have to remember also he is a professional shooter. He has the best equipment/componants money can buy.
It's also important to remember in the case of competitive shooters what discipline they shoot in. A bencrh rest shooter shooting a less than caliber 3 shot group at 100yds is vastly different than an F-Class shooter doing the same or a Palma shooter doing it.
In your original post you mentioned your were new to precision centerfire shooting. The rifle you mentioned is a commercial factory rifle. It is a good product but it is far from a precision rifle in the sense of what the typical competitive shooter is discussing. Your rifle weighs in at 7-8 lbs and maybe 10-1/2 lbs with scope and bipod. F-Class weighs in at up to 22 lbs, F-TR at up to 18 lbs. Unlimited Rifle Bench rest has no limit that I'm aware of. You probably have a 1/2 MOA rifle at best. Some of the effects Eric or Brian mention may not even be detectable with your rifle.
I have a tendency to deep dive and overthink things usually. I am aware that my Tikka CTR is in no way on par with the custom barrels and actions the F class and bench rest shooters are using, and obviously my skill set has only just begun to take shape. I’m also aware that .308 is limited in its application compared to the hot rod calibers most long range competitors are shooting. I just want to do the best I can to extract every bit of ability from both myself and my equipment/ammo. I will probably just be an avid shooter/reloader and may never even compete in a PRS match, but I’m not ruling it out. So should I just load to 2.8 inches and find a charge that gives me consistent low ES and SD? I really just want to find a load that shoots better than factory match ammo and get lots of reps at various distances while mixing up positions. I appreciate the thought put into the replies, I’m all ears and open to anything that will make me a better shooter/reloader. —Rimfire77
OP listen to these guys...You really need to be careful at this stage, since you know enough to get in trouble, but not necessarily enough to stay out of trouble. Most good ideas right now--it seems to me-- will work in a saami spec configuration, even if that wasn't true 30 or 50 years ago.
With a new 308? I'd just buy FGMM and try to replicate it...Exactly... see, eg
SAKOs TRGs IIRC tend to like 168/169 alot of the time since they are 1:11 twist and when they were designed, that was .mil spec wt class. The Sako TRG bbl is the basic blueprint design adopted by the Tikka Tactical and later, modified into the CTR.
You probably won't bebefit from trying to re-invent the wheel... unless there is a very specific engineering-related thing you need to achieve. As a new shooter, making "engineering improvements" to match grade ammo is a bit ambitious right out of the gate.
I refer you do the .mil copying FGMM, despite working in-house on 308 sniper ammo for the previous 30 years.
Try to find a load around 2.8” , not necessarily at 2.800” but whatever gives you the best accuracy in that coal range. Could be 2.795”, 2.810”, etc.
Sierra BTO numbers vary wildly from lot to lot. I have two lots right now whoss bto is different by .055”. If you work up a load with a short bto lot at 20 thou off, then the next lot could jam you hard in the lands. Or it could put you farther away. SMK is just not consistent enough lot to lot for loading that close to the lands.
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