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Old November 9, 2011, 12:40 PM   #1
Sarge43
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Question for those chasing grouping sizes.....

I am a long time pistol shooter and have recently gotten into rifle shooting again. I am hooked on chasing group sizes. I have not reloaded rifle cartridges before, but have loaded pistol ammo in the past. The question is this:
How much can individual bullet weights be off before you see a difference on the paper? I am reloading .308 Win and using Nosler 165 grain ballistic tips. In weighing the individual bullets, most of them are within 0.2 grains of each other, but once in a while, you'll get one that is up to 0.5 grains heavier/lighter. In a perfect world, every round you load will be EXACTLY the same, I understand that, but in reality, what is an "acceptable" variance in bullet weight with all other factors being equal?
Also, as a follow up question - (I feel like the rifle noob that I am here asking this) What affect can poor/inconsistent primer seating have on accuracy? In pistols with ranges normally at 25 yards, this isn't a real factor, but out at 600 yards, can this drastically affect accuracy?
Thanks in advance for the help and answers!
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Old November 9, 2011, 12:58 PM   #2
243winxb
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Brass Prep with Match Grade Bullets & Primers, High Power Scopes = Small Groups

The weight of your bullet is not importent. Bearing surface, base & nose are. Use a match grade primer & seat to the bottom of the cup. Primer should be flush to .004" below the case head. Read this > http://findarticles.com/p/articles/m...8/ai_83483904/
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Old November 9, 2011, 02:14 PM   #3
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Sarge,

It depends on what you are loading to shoot? Since you mention 600 yards, I assume it is Service Rifle or Match Rifle NMC shooting that interests you. On the other hand, you are using Ballistic Tips meant for hunting, so maybe not. All I can offer is what a computer simulation says a half grain of difference would do.

So, in QuickLOAD, loading with Reloader 15 to 55,000 psi, if I increase the bullet weight 0.5 grains, the velocity drops from 2760 fps to 2758 fps, and pressure goes up 140 psi. This is less than the normal shot-to-shot variation pressure and velocity that is normal in loads due to other factors. So, as far as interior ballistics (what happens inside the gun barrel), this just isn't significant.

For exterior ballistics, assuming the same external dimensions, ballistic coefficient will vary directly with weight. So the starting velocity for the lighter case with a BC of .4750 at 2760 fps verses a BC of .4164 with a starting velocity of 2758 adds up to a drop difference at 600 yards of and increase of 0.1 inches for the heavier bullet. A 10 MPH crosswind will move the heavier, slower bullet about 0.1" less at 600 yards.

So, that's as close as my calculations can come. I expect you're probably not going to worry much about half a grain after that.

As to the primers, if you go to match primers (you typically want something harder in gas guns with floating firing pins, but they're often best in bolt guns) the Federal 210M is a good one that I've used for years. Federal recommends for a large rifle primer that you seat until the anvil touches the bottom of the primer pocket, then push it in 0.003" further to set the bridge. For a small rifle primer, such as in the Lapua Palma .308 cases, that number is 0.002". That typically winds you up with the primer 0.004" below flush with the case head. You can use the primer seater on the Forster Co-ax press to set that distance below flush. You can use the K&M priming tool with gauge to measure it for each case.

If you can't do either of the above, err on the side of seating rifle primers too hard rather than too light. Erring too hard risks a misfire from cracked mix, while erring too light risks misfire from the firing pin having to complete seating, which absorbs a lot of its energy. But seating too light has another possible consequence; it can produce delayed firing by tens of milliseconds, and that allows shooter muscle contraction and trigger overtravel slam and other odds and ends of vibration to abnormally influence the position of the muzzle at bullet exit. It can also lower peak pressure by giving the bullet a slower start. So the consequences of an under-seated high primer are worse than for a hard seated primer. One of the authors of the Precision Shooting Reloading Guide said seating hard was the only way he could consistently get rifles down to under 10 fps velocity spread. So it's not a bad thing. Just don't crush them dead.
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Old November 9, 2011, 02:37 PM   #4
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The old 173 FMJBT's, their weight difference was plus or minus 2 grains.

There was an article in the NRA Competitive Shooting magazine about the USMC rifle team and their reloading.

Their Ammo Techs loaded 600 and 1000 yard ammunition. Those guys weighed their Sierra match kings and discarded any that exceeded 0.1 grain.

There was a picture of a Marine next to a scale and a couple of boxes. One for the good bullets, the other for the discard.

( I would have killed for a bucket of their discards!)

Weight makes a difference but I am of the opinion that center of gravity is more important. And we can't measure that with a scale. If the center of gravity is off center the bullet will wobble.

Look, if your bullets only vary by 0.5 grain, be happy. They are great. Load them and shoot them and concentrate on your sight alignment and trigger pull. Errors in aiming are measured in yards, sometimes continents. I have a few that might have made orbit.
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Old November 9, 2011, 03:33 PM   #5
Sarge43
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Gentlemen,
Thank you so much for the in depth answers you have provided! Great information that I will put to use in the very near future.
I truly appreciate your help!
Sarge
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Old November 9, 2011, 03:53 PM   #6
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At one time, the Sierra match bullets in .30 caliber dominated rifle competitions (it may still, I do not know). However, at one time I weighed their 155 Palma match bullets that I use in my .308 Ruger M77 Target/Varmint rifle. There was that variation as you describe. It did not have an apparent negative effect on the accuracy.

Additionally, I worked up loads with Speer and Hornady match bullets and they all produced excellent accuracy, albeit with different powder charges. It would seem that all three manufacturers produce good shooting match bullets.
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Old November 9, 2011, 04:09 PM   #7
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Interesting. I don't think I've ever noticed more than 0.1 grains difference in two SMK's unless you went to different lots.

Slamfire brings up a good point. The reason the military teams would toss a bullet for a small weight difference is concern it might indicate a lead shaving or something that wasn't symmetrical around the center of mass. Not likely, but could happen, and at 600 a bullet wobbling from mass asymmetry would, indeed, be less accurate than normal. If you don't have a bullet spinner or other method of determining mass symmetry it becomes a form of precaution to do that, just in case.

If you want to see if your bullets have an issue like that, just segregate out the extra heavy and light ones and load and shoot them separately to see if your groups change size. Most likely they won't, but what the heck. This is a hobby, after all and you may as well have fun trying things out.


Slamfire,

I think it was ±1.5 grains; i.e., 174.5 grains +0/-3 grains. Saw the spec somewhere, but don't recall where off the top of my head. Despite that range, when Frankford Arsenal rolled the NM ammo, they used set aside lots of those bullets that had proven extra accurate, so they were probably more consistent in weight than that 3 grain spread in any given year. I heard that at some point after LC took over rolling NM ammunition, though, their management put a stop to that extra testing and sorting, so mixed, non-select lots began to be used and NM ammunition was never as good again. Don't know what year though.
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Old November 9, 2011, 04:54 PM   #8
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A lot of the fussiness of handloading for competition is going to depend upon what kind of competition and how small a group you want to "chase." There are at least 3 or 5 types of competition conducted at 600 yards and all stress varying skills, which is why they are different matches.

Depending upon which type of competitor you talk to and at what level that person competes, you will get varying answers to your questions. As mentioned, many BR, F-class and other serious competitors will consider a weight variance in bullets, brass, powder and primers to be indicative of other defects. This is why they use components geared toward competition, and will choose among them to further refine the quality to the point which they require. As an example, Sierra rightly claims the lion's share of use by serious competitors in service rifle and across the course competitions, possibly the newer 3 gun as well. That being said, almost no BR short range, and few long range shooters serious, about competing, list Sierra as bullet of choice in the NBRSA or IBS equipment lists which accompany match results in the newsletters. These folks are using custom made bullets, made one at a time individually inspected and virtually guaranteed to have no difference in weight, base to ogive length, jacket thickness and concentricity. F-class shooters are beginning to plump for these very expensive bullets, too. There are varying levels of quality in components from there on down. If the groups you are chasing are not normally measured in tenths of an inch, you will not need to explore the wonderful (addictive and expensive) world of premium components.

As for primers, there can be a big difference in downrange results if you are chasing those tenths of an inch. This is why there are favored brands and types of primers listed in those equipment lists. This is also why various super precise primer seaters are sold, including at least one that actually allows you to measure the depth of the primer pocket, the height of the primer cup, and will tell you how many thousandths of an inch you have "crushed" the primer. Again, depending upon your obsession, you may also want to buy things like primer pocket uniformers and flash hole reamers.

Many experienced rifle handloader/competitors/hunters will tell you all this stuff is a waste of time--they are right--from their perspective. There are also folks with vast experience in the BR/long range varmint/f-class world who will tell you it is required to win or even finish in the pack and not behind it.

A friend of mine had some good advice for my son when he started to get serious about rifle accuracy: if you shoot it off a rest listen to Tony Boyer. If you shoot it offhand listen to David Tubb. These days you can read their books too.
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Old November 9, 2011, 05:02 PM   #9
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Quote:
I heard that at some point after LC took over rolling NM ammunition, though, their management put a stop to that extra testing and sorting, so mixed, non-select lots began to be used and NM ammunition was never as good again. Don't know what year though
Early 60' NM was better than late 60's or 70's. You can look at the data in American Rifleman.

McNamara contracted out the Arsenals and any organic capability in the Government. He started it and it just has got worse over time. The whole Government is contracted out. LC today is a “Government owned, Contractor Operated" facility.

The old Government Arsenals were interested in getting the best product out the door that they could. Contractors are interested in making the maximum profit. When you have LC up for bid, the current contractor runs the facility into the ground to make the most he can because winning the next bid is not guaranteed.

By the time you get into the 80’s LC bullets were so bad that the Government bought Sierra Match kings for the 308 NM ammunition.
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