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Loading a Sierra 140 gr. Gameking SBT with a recommended O.A.L. of 3.300 according to the Sierra manual. Did an improvised chamber length check in my new Remington 700 with an empty brass and a loosely-fitted bullet- chambered it, took it out and measured it at 3.4735 where it touched the rifling. Brass is once-fired and trimmed. 1. Is that a big difference in seating depth? 2. What would be a good O.A.L. to try with this rifle and cartridge? 3. What effect would the adjusted O.A.L. have on the powder charge? <---- Yes, that's five shots, no keyholing. LOVE my .270! | ||
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seat .05 off the lands | |||
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Shibumi .050" off the lands is a lot. I'd start .005" off and then experiment with deeper seating in .005" increments until you find the best (most accurate) seating depth. But first, make sure what OAL your magazine will accomodate. Your final OAL may be determined by your magazine in which case you have little choice. Also, depending on your particular bullet you want to be sure that it is seated sufficiently in the case to ensure a good grip. The exact purpose of your rifle and loads will determine a lot also. What will be OK for a single-loading target cartridge may or may not be best for a big-game hunting cartridge loading from the magazine. Seating depth will have some effect on maximum loads and external ballistics but we're talking about small increments here. If you follow the usual caveat and work up, you'll be OK. Ray Arizona Mountains | |||
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Even .05 off the lands is 3.4235, on a bullet that Sierra says should be 3.300 finished length. At 3.4235 there is only about 1/8th of the bullet seated in the cartridge neck, that CAN'T be right. Is my chamber longer than normal???  <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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My experience with run of the mill factory Remingtons is that the free bore is long. Bullets seated to the lengths needed to get close to the rifling will result in cartrdiges longer than stardard OAL. As long as they fit in the magazine, you should be fine. But it doesn't sound like you have much bullet in the case neck. Somewhere there is a formula but I can't find it. Something about a minimum of 1 calibre of bullet length in the neck, ie for a .308 cal bullet, .308" of bullet in beyond the mouth of the case. This is all hearsay as I can't find a reference. Someone here, I'm sure, knows the answer. How many rounds through the rifle? You might have a significant amount of throat erosion. Is the rifle new or "new to you"? | |||
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BRAND new. I'll search for that formula, because even the extended length still fits in the magazine. <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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Shi Welcome to the world of factory chambers.  Here's a good way to see if your bullets are being held tight enough in the case: Load up 6 rounds. Put a round in the magazine and then put another on top of it. Load and fire the top one. Do this 5 times, always with the same round in the magazine. At the end of the exercise, measure the bottom round one last time. If it hasn't changed OAL then you're OK to go. On the other hand, if the bullet has tended to creep out of the case then you need to either seat it deeper or go to more neck tension. Or both.  Ray Arizona Mountains | |||
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In regard to powder charge, do I need to adjust it when going from 3.30 OAL to 3.42 OAL seating depth adjustment? Won't the depth of seating lower pressure in the case? Can you trim the cases longer to put the bullet closer to the lands? <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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When your bullet is at, in, or close to the lands, your pressure will be higher, so that is why I always start load development with the bullet touching the lands. The answer to your question is that you need to lower your powder charge when getting the bullet closer to the lands or at the lands, to start, then add powder and check for pressure. I only jam bullets into the lands if they are match type bullets, like a Berger. When your bullet is seated deaper, with the same powder charge, your pressue will be reduced. I'm not following the question about trimming a case longer and putting a bullet closer to the lands. Your chamber will have a max length when the bullet touches the lands. That is why you measure a loaded round from base of brass to ogive of bullet. It won't matter if your trim only .001 of the case neck or .010. The base to ogive length will not change in your chamber.
Well, be careful on your interpretation of this. Sierra is putting in print what THEY tested in terms of seating depth, for the chamber/rifle that THEY used. I don't think they are implying that this bullet SHOULD be seated to that depth. Seating depth is based on the individual rifle/chamber, not bullet make and weight. I always try to make sure of 2 things. 1) Put together a dummy round based on the bullet touching the rifling. See if that dummy round fits into the magazine. 2) Make sure there is plenty of bearing surface seated into the case mouth. With Remington rifles, I can recall only one occassion where a dummy round that touched the lands would fit the magazine but there was very little bullet bearing surface seated. This was the case with the 185 VLD Berger and my 300 RUM. At best, there was maybe 2mm of bullet seated. This is hardly enough to ensure some sort of consistent neck tension, let alone, you need the tension to be enough so that the primer doesn't blow out of its pocket. Ted Kennedy's car has killed more people than my guns | |||
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I always thought that the published OAL was a "standard" for a particular cartridge. It is the recommended overall length that all chambers would accomodate. It is measured from the tip of the bullet to the baseof the brass. The measurement from the base to the ogive is something different. I disagree that "seating depth should not be based on bullet type and weight" as different bullets have different shapes which results in the different bullets hitting the lands at different OALs. If you are trying to seat bullets a specific distance from the lands, you need to measure the OAL for each type of bullet you use (and sometimes between different lot #'s of bullets) If Shibumi were to use a different type of bullet, his measurement of OAL at which the bullet touched the lands would change. | |||
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It is. But we're not talking about the same value. The STANDARD COAL FOR ANY 270 is 3.34 maximum. What Shibumi was concerned about is that Sierra has a "published length" for the exact bullet he is testing, and that tested length by Sierra is 3.30, but, as I stated, that is what Sierra's test length was for their equipment. Shibumi's does not have to match that, and obviously, by his posts, he has demonstrated that the OAL for HIS rifle is different.
You have overinterpreted the meaning of my post. You are correct in pointing out that seating depth should also be based on bullet type and weight, but my intention was that these 2 factors are for YOUR rifle, not just what Sierra published for their test length. i.e., just b/c Sierra tested a length with the bullet in question at 3.30, does not mean we all must use that same OAL. You are generalizing for more than one bullet type and weight. I was specifically addressing the bullet mentioned and tried to focus on the original poster's concerns. This is all true, but we're not discussing other bullets. We're specifically talking about the 140 grain Sierra bullet and that Shibumi has noticed that he can seat THAT bullet longer for HIS rifle compared to what is published by Sierra. Ted Kennedy's car has killed more people than my guns | |||
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Doc, thanks for taking the time to share all this. I'm still confused on some things-
So the same explosion, in a SMALLER volume, creates LESS pressure?? I'm new to this, how does the physics work out on that?
See below-
Aren't they correlating this particular seating depth with the powder charge/FPS results they achieved? In other words, regardless of chamber dimensions if seated to the listed depth, results in FPS/powder delta should be similar in a different rifle with approximately the same barrel length/dimensions?
This is why I was asking about the trim length- my dummy round will fit in the magazine, but has precious little neck support when touching the lands. I was wondering if I could use a previously-fired round with longer case length than standard to give the bullet more support and seat it on the lands. <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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Shibumi, let me give you an example to work with here, a "control" if you will: Let's say you loaded up 12 test loads in your rifle with the 140 Gameking and your COAL was 3.30 just like the manual states. You find that the maximum powder charge shoots best in your rifle. And now you want to play with seating depth to fine tune accuracy. If you were to now load 5 test rounds at a max charge but you decided to seat your bullet at or very near the lands, (with little to no bullet jump), you may have excessive pressure. That is the reason you should start load development, beginning with the lowest powder charge with the bullet seated as long as possible, but making sure that you do have enough neck tension. Then add powder by .4 or .5 grain increments. Does that make sense? If you start with your bullets seated as long as they can go, and still fit in the magazine, and still have plenty of contact with the case mouth, then you only have one direction to go when fine tuning, and that is deeper. I now understand what you were asking about a case that has been fired and not trimmed, so as to gain a longer neck to grab the bullet. I do not subscribe to this myself. You should trim all brass to the same length and just seat your bullet a little deeper than where it is to touch your lands. Your chamber simply will not allow the bullet (140 gameking) to be seated out that much and still have enough neck tension/bearing surface contact with case mouth.
Well, of course, they can be similar, but your exact chamber and your exact bore diameter may be vastly different (in thousandths) compared to the test barrel by Sierra. That said, even though your bbl lengths may be the same, you can get less or more velocity than they did. Your speculation is right, however. Seems like your wanting to simply know if you duplicate the exact Sierra published data, then you should have very similar results. This can be true, but when talking about accuracy in your rifle, you are not bound to the test OAL they publish. You may find that if you seat to 3.40 with all else the same, you may get a little higher pressure and possibly higher velocity. Ted Kennedy's car has killed more people than my guns | |||
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Okay, so what I've learned-
Am I on track at this point? (Just call me Grasshopper) Edit: Okay, the Vicodin is starting to kick in (dentist earlier)- better toddle off to bed! <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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GREAT information! Thanks for the help Doc! <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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Correct. The "tested" OAL, not the "standard" max OAL, which is a SAAMI spec. In the case of the 270, the standard is 3.34 for every loaded round, so it must fit in any factory rifle.
Correct.
Correct.
You got it grasshoppah Ted Kennedy's car has killed more people than my guns | |||
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Cool! But I'm not grabbing no red-hot iron kettle with my forearms...  <---- Yes, that's five shots, no keyholing. LOVE my .270! | |||
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That's good. It really hurts. But they made me drag it b/w my frickin thighs.   Ted Kennedy's car has killed more people than my guns | |||
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