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Posted: 6/30/2008 2:26:03 PM EDT
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Hey folks, another noob question for you all. I am loading up several batches of test rounds to take to the range later this week. All of my rounds are using mixed brass, CCI 450 primers and Hornady 55 gn FMJBT bullets. My test loads are consisting of H335, IMR 4198 and Varget powders. The load data for this bullet type with these powders calls for a COL of 2.200. I have been seating my bullets to mid cannelure for a COL of 2.240-2.243. Should I adjust my seating depth a little deeper to match the load data or will my slightly higher seating depth work ok? My thoughts were that the higher seating depth should work since I am using 450 magnum instead of 400 standard primers, even though I reduced the starting load by .5 grain to compensate for the expected higher pressures from the magnum primers. As always, thanks to all who give their input 
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There's NO GUARANTEES on how YOU preformed on the "other" aspects of your re-loading. So, I'll assume that you're just asking for an opinion. Not asking about giving you a 100% SAFETY.........."GTG, approval." Especially, since you didn't state the drop weight or powder used (H335 or IMR4198 or Varget) with your FMJ 55 gr. bullets. You only said, that it was .5 gr down from a "starting load." Note: that some book(s) will state a "starting load" and some will just state the "max load." And, "compensation" for a, mag primer vs. standard primer, is NOT always equal to a .5 gr. drop in powder weight. So, in the end.........you loaded it, you know the RISK(s) involved. So, IF, you're OK with it.........so be it. IF you're NOT.........pull it down and start over. Though, in the future, you might consider: What the book says vs. your own RISK TOLERANCE LEVEL for a safe starting load. Re-loading is a little bit of "experimentation" and you're talking about a seating difference of .04" (you said 2.240" vs. 2.200" from the book). BTW, the standard M193 (with 55 gr. FMJ) is reported to be 2.26" COAL. But, of course bullet(s) shape, construction, etc.... and mfn recommendations, vary. So, ASSUMING that you were thinking safety during the re-loading process. It doesn't SOUND LIKE you've crossed over some "magical line"...........that will be the difference between a "Ka-Boom" and a round going down range. Have a safe and productive day at the range. Remember to take notes. Aloha, Mark |
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Not so fast. Dropping ½ grain when switching from standard to magnum rifle primers is a prudent approach and doesn't make the load dangerous even if it ½ grain off of max charge. Remember, the reloading books are written by companies who employ lots of lawyers to ensure that they don't expose themselves to excess liabilities. Its a known fact that recent reloading books have lowered their 'max' charger weights from their recommended loads in years past. While seating depth and pressure spikes is not as critical in rifle ammo as in pistol ammo, you are loading the bullets long (avoiding excess pressure) but no where near long enough to worry about increased case pressure from you bullet being in contact with the lands. Now to your question. I've loaded my 55grn FMJBT at 2.60", 2.50", 2.40", 2.30", and 2.20" with the same charge to see if it accuracy is affected with absolutely no ill effects. I prefer longer loaded bullets over the recommended 2.20" and so I load mine at 2.40 with good results. You need to experiment with different OALs not for pressure issues, but rather to find you particular rifles best accuracy load length. |
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As COSteve says what you set bullet seating to affects both safety and accuracy. The safety issue has been covered. However, unless you have a good method to measure your barrel's leade you cannot know where to set bullet seating for accuracy. A good start are the Hornady and RCBS devices for measuring the leade and then setting the seating to meet the bullet jump you desire. Limiting factors are max OAL to achieve magazine function and min OAL to observe pressure issues. |
A load for an AR must be short enough to run in the magazine. Use 2.26 as the maximum. The chances are extraordinarily small that a rack grade AR has a barrel chambered with a leade short enough to contact the rifling with a 55 grain bullet. Or an 80 grain bullet. You might find a custom barreled R rifle intended for use with a light weight bullet; I'm not going to hold my breath, but I'm confident someone out there has assembled a rifle this way for whatever odd reasons they hold. Seat to the cannelure or not, it's not mandatory. If you want to seat off the cannelure yet crimp, use a taper crimp die. The next batch of similar bullets you buy will most likely have the cannelure in a different location. Deeper seating in a bottleneck case displaces a tiny percentage of the total case volume. Seating out permits a tiny bit more powder for more speed, but you'd best test with incremental charges on the way. Gaging the distance from the case head to the ogive of a magazine length load is a foolish waste of time for use in rifles with long throats. The magazine and the longest bullet are the controlling factors to work around. |
| So, with all this great info on safety and accuracy with respect to seating depth, what is the spread on the seating depth of a cartridge against the loading manual that you're using. Assuming the recommended COL is 2.20, and assuming that we all try to get it spot-on 2.20, there are some rounds that are a little over and others a little under the COL for the bullet and powder in use. What is the safe spread on either side of 2.20 before you pull the bullet and start over? |
If you're working loads up, there's no real "spread". Set a length to meet the requirements of the gun and the bullet, and start with a load about 10% below the maximum published. The overall length will be strongly influenced by the bullet length. Some will be fairly uniform, others, particularly HPBT bullets, vary a surprising degree, 0.030 inches and more. With respect to seating depth, that variation of length doesn't matter as the seater is pushing the bullet on the ogive; the distance between a reference datum on the ogive and the cartridge base will be identical (within a couple of thousandths or less, depending on the bullet quality) for bullets from the same lot. Often the bullet design determines the seating depth; too much and the bullet falls inside the case mouth, too little and the bullet engagement with the case neck is too little for good neck tension. Part of the answer to your question is that we have to sit at the press seating bullets and taking measurements to understand the limits of the equipment, and details such as too little neck tension to hold a bullet against a compressed charge of gunpowder. |
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AeroE, I suppose that for plinkers who are not interested in the ultimate accuracy of their rifle they do not need to seat to a known bullet jump distance. However, to seat to the ultimate accuracy you need to know how much jump the bullet is being set to and test loads with different jump distances. My opinion is that benchrest shooters that are shooting for the best grouping and accuracy are not being foolish and they carefully seat base to ogive not OAL. After all, it is the ogive of the bullet which first contacts the rifling, not the meplat. |
I understand that. It's out of context for a rack grade AR type rifle, and damn near every factory bolt gun I've picked up. The chambers are throated so long that you're wasting your time worrying about the jump to the rifling, it's huge, an 80 grain bullet will fall out of the case before touching the rifling. Magazine length cartridges are even farther out. Once the jump to rifling is more than 0.040 or so, there's no point in the pursuit of that factor. If you're shooting bona fide benchrest guns, the story is different, and it's not necessarily what some members here think. Neck tension practices are different, cases are sized full length by most shooters now, and the bullets are jammed 0.000 to 0.010 (and probably more by some shooters) into the lands, for starters. Setting the seating depth by the length to the ogive is not the same thing as setting it for a particular dimension off the rifling lands. |
It is if you use a gauge such as the Hornady which allows you, in your rifle's chamber, to position the bullet in a brass at the point the bullet ogive makes contact with the rifling. Then, when you measure the resulting OAL with that bullet and brass, and seat that bullet in your brass to that OAL. you can with a gauge (such as the RCBS Precision Mic) measure the base to ogive for that bullet just touching the rifling. Then adjust seating for either positive or negative jump. This way you are always seating to the point on the bullet, the ogive, which first touches the rifling. As you pointed out, the variation of bullet length does not allow this level of seating accuracy when seating only to OAL. |
Don't take this personal........... It's meant in the sprit of those in general............ _______________________________________________ I figure it's more a matter of what YOU are willing to accept as a variance. Same, with your powder drop or when trimming cases. We all try, to get it exact but, sometimes it just ain't working out. So, at what point do you call it GTG? Hey, sometimes, it's part experimentation, too. Anyway.......YOU DECIDE. IF that's too hard for you to decide........perhaps, you need a different hobby?  Sorry, that was harsh. But, I hope there is some "reality message" in it.______________________________________________ Things VARY. YMWV. With this hobby, don't always expect to see/find an exact "magic line," between failure (Ka-Boom) and success (.001 accuracy). Take heed of the Mfns warnings. Start with what the book recommends. Subsitutions are not (usually) recommended by the book. IF, you subsitute components, KNOW that it can change things and even be dangerous. When, you start.........."Start low and work your way up." Aloha, Mark |
You don't get my point. Setting the seater to produce a head to ogive length is a fine way to eliminate the problem with the variation of bullet length. That practice produces cartridges with bullets seated to uniform depths into the case, which is important. It also produces cartridges that are guaranteed to have bullets all the same distance from the lands. Those are good things. However, it doesn't mean squat for tuning a load when the jump to the lands is very long. The damage is done, and you're wasting your time tweaking the bullets when they're out 0.030 or 0.040 inches or more. In this case, the best you can do is to seat the bullets as long as possible to reduce the jump to the shortest distance possible (consistent with magazine function), plus take advantage of some added case volume for a little more push. |
I agree and we may have been saying the same things. An example is that today I am measuring my Wilson 20" barrel with Wylde chamber for a new bullet. Normally I would want to start at 0.003 jump to test my loads. However, to get that jump in this barrel with the Speer 52gr MatchKing bullets the OAL would need to be 2.300. Too long for magazine function by 0.040. This is exactly your point. To shoot with 0.003 jump I must manually load one at a time into the chamber, which is exactly what benchrest shooters do. |
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