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Old September 14, 2020, 02:11 PM   #1
IdaSpud
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7mm rem mag bullet jump

Hi all, I need some advise. I'm loading 7mm rem mag, Hornady 175gr ELD-X. I measured the max overall length by starting a bullet into a fired case. I can push the bullet in with my fingers but it is still snug. I chambered the round to use the lands to push the bullet in. When I removed the round and measured it, it had a COAL of 3.448". The book call for a COAL of 3.290". This gives me a bullet jump of .158". I know this is not the most accurate way to measure, but I think it should be close. Is this is right, .158" seems like a long jump? what would be a better COAL? I'm thinking around 3.245". What say you experts?
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Old September 14, 2020, 02:35 PM   #2
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set it to book length and work up your powder charge. then you can start chasing the lands.
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Old September 14, 2020, 03:28 PM   #3
IdaSpud
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I did a work-up 55gr, 57gr, 59gr, and 61gr of H4831. Best group was 61gr and a best spread 1 3/8". Rifle is Remington 700 BDL. I bought it new in 1973 but I haven't fired it since 1978 until this year. The ammo I loaded back then still shot Quite well.
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Old September 14, 2020, 03:29 PM   #4
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Historically, the 7mm Remington Magnum has among the most diverse throating designs. SAAMI be darned, it seems every maker used his own dimensions. In the 1970s Bob Hagel (IIRC) made chamber casts of 8-10 different rifles chambered in the big 7 and discovered no two throats were the same. Some had very short throats, some had significant freebore. The ammunition makers and reloading manual folks had to make sure their loaded loa fits all rifles, so it is no wonder that some rifles have more jump than others.

Too many reloaders seem to focus on some magazine article they read which covers competition shooting and the vital importance of bullet jump. While this is a variable, very fine accuracy can be had with considerable freebore. Example, my Accumark in .257 Weatherby has just over 0.30” of freebore with my hunting load ( which fits safely in the magazine). That load aggs in the .6s and low .7s, better than plenty of rifles whose owners chase the lands. As stated above, there are more important things to worry about.



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Old September 14, 2020, 05:03 PM   #5
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Load rounds to fit in the magazine. SAAMI spec max or less.

Quote:
a best spread 1 3/8". Rifle is Remington 700 BDL.
Standard BDL sporting rifle? not heavy barrel, or match grade?

1 3/8" groups? It ain't broke, don't try to fix it.

Your rifle, try anything you want, but be prepared for doing a bunch of things for little or no significant improvement.
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Old September 14, 2020, 07:57 PM   #6
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Idaspud, I may be wrong but I get the impression that your measurement CAOL of 3.448 was from the tip of the bullet to the base, and the "book call of 3.290" was the same.

That is not accurate nor comparable. The "book call" was a measurement designed to fit all rifles that have chambers qualifying with SAAMI measurements.

You need to measurement your distance from the "ogive" of that bullet from the rifling using a "comparator" attached to your digital micrometer. Get the micrometer value of "0" based on the bullet touching the lands, then set it back 0.01, 0.015,0.02" and so on until you reach a satisfactory accuracy for THAT bullet in your rifle. If you buy another bullet of equal weight from another manufacturer, do not assume the same measurement will place that new bullet the same distance from the rifling. The "ogive" - or point on the bullet that engages the rifling- differs between manufacturers depending on the design of the bullet.
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Old September 14, 2020, 09:11 PM   #7
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Measuring from the ogive is key to getting any other information other than an answer to “will they fit in a magazine” bullets will vary in length, even the same lot and box. the ogive is all the rifling cares about. It could care less where the tip is


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Old September 14, 2020, 09:57 PM   #8
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My two cents

A friend got me interested in reloading. He owned a 7RM Interarms, changed the barrel and floated it. Then, he meticulously reloaded for it. I don't remember what his load was but more than once, I saw him print cloverleaf groups at 100 yards with that rifle.

The way he taught me to determine my COL was to use a black magic marker and started to chamber then seating the bullet into a sized case until the rifling started to wear through the ink and the metal was just starting to show. I added more ink every time it was rubbed off. Then, that bullet was hard crimped and was the dummy load. Any future loads was the standard to seat one's test loads from. Than having a box of dummy loads, I bought a Sinclair comparator tool that looks like a nut with holes of various calibers in it. I use a Harbor freight outside caliper to measure the distance from the case to the end of the nut. If your cartridge won't fit into your magazine, you have two choices; always load them individually or load them by the the magazine box dimensions. My Arisaka throat is waaay too long so I just reload my 7.7 x 58 cartridges to fit the magazine. There is a lot of freebore so I don't care about seating the bullet in any more than what it is.

With 175gr bullets, you might want to consider experimenting with R22. H4831 is great and that's what I'm using for lighter bullets but I've read that you'll get more velocity and better accuracy with R22 with 160gr or up. The pressure climbs more per velocity increase compared to R22 . I have both for my 7RM but haven't done the tests yet. That's from what I've read but have not experienced. If you look at the Nosler website, they list R22 and not H4831 at this bullet weight range.

I hope this helps.
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Old September 14, 2020, 09:58 PM   #9
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Quote:
The "ogive" - or point on the bullet that engages the rifling- differs between manufacturers depending on the design of the bullet.
This is not correct. The ogive is NOT the point where the rifling contacts the bullet. That point is ON the ogive of the bullet. The ogive is the ENTIRE curved/sloped portion of the bullet from the most forward part of the bore diameter section all the way to the tip.

The point rifling contacts the bullet has, as far as I know, no specific name, and it has no fixed location. The point will vary with every different rifle and bullet combination. It will be somewhere on the bullet's ogive, but stating that ogive means the point of rifling contact is incorrect.
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Old September 15, 2020, 02:16 AM   #10
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The 3.290" of SAAMI is to ensure chambering for every rifle.
I'd be willing to bet Hornady has a different COAL for their 175gr ELDX.
The ELDX has proven very tollerant of jump.

How long can you load for your magazine length?
This seems to be more the limiting factor for COAL in the 7mm Rem Mag.
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Old September 15, 2020, 10:40 AM   #11
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I purchased Hornady OAL guides for several calibers, including 7RM. Outstanding because I've owned 4 7mmRM over the years and they are always short throated. The longest 284 I load is the 154 Interbond.
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Old September 15, 2020, 12:37 PM   #12
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Thanks for all the replies. I just thought it seemed like a large jump. Maybe not. Hornady's book calls for 3.290 COAL. At 3.448 it still fits in my mag. I think I'll just try tweaking my powder charge and see if I can improve my group. I may also try another powder if I can find it. I find a moa of 1.35 to be unacceptable. with this rifle, I used to shoot .5 moa and I don't think 40+ years in storage would diminish it's accuracy. Thanks for the input.
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Old September 16, 2020, 03:40 AM   #13
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Powder charge generally isn't going to have as much affect on group size as the distance from the lands.
Typically you start low & work up in powder charge looking for a "node" where your shots aren't differing vertically. This tells you a velocity range that the barrel likes.

Then play with seating depth looking for smallest group. This tells you what that bullet likes.

Then there is action tuning....
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Old September 16, 2020, 07:24 AM   #14
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When the 7mm Rem Mag was popular for long range matches in the 1970's, best accuracy typically happened with new cases and bullets seated to touch the throat.

The cartridge dimension from case head to bullet touch point diameter on the bullet increases about .001" for every 10 to 12 rounds fired. Barrel life was about 800 rounds.to test sub MOA extreme spread at 1000 yards for 25 shots.
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Old September 16, 2020, 11:07 AM   #15
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What steps do you take and have your read to develop your load? I have set my first set of test loads so the ogive is just off the rifling. Then, I start low and work my way up until it's not fun to shoot anymore. My bold isn't sticking yet. Then, I look for the closest node. The friend I mentioned earlier use to shoot test loads up to where his primers were flat and when the pocket was coming lose, then back off until he found his node. Then, he would test load by seating depth until he found his petload. I suppose that for what has been said, it's best to find the best node with a seating depth not touching the rifling unless (maybe) the chosen petload is not the maximum long-range load.
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Old September 17, 2020, 12:54 PM   #16
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Eld and Amax bullets almost require a much longer OAL than factory. My 162 AMax loads are about .33 of an inch longer.
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Old September 17, 2020, 02:08 PM   #17
Bart B.
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Quote:
Originally Posted by std7mag View Post
The 3.290" of SAAMI is to ensure chambering for every rifle.
I disagree. It's the length standard they used in their pressure and velocity tests.

Some 308 chambers have freebore shorter or throat angles steeper for match rifles using bullet weights about 150 grains. There's no mandate that all chambers for a given cartridge be the same dimensionally. Same for bore and groove diameters. Tolerances and preferences rule.
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Old September 17, 2020, 02:45 PM   #18
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Compliance with SAAMI standards is voluntary, NOT required. The point is to ensure commonality of fit and safety of ammo in everything made to meet the standard.

Some people don't agreed with SAAMI specs. SAAMI specs are not Holy Writ, and some people don't follow them.
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Old September 17, 2020, 03:43 PM   #19
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IdaSpud,

The way you measured jump in post #1 is best done by removing the extractor from your bolt and then, after seating the round, gently pushing it out from the bore with a cleaning rod. The reason is the bullet offten sticks a little in the lands of the rifle at contact, resulting in it being pulled back out of the case a little when you extract it. Pushing it out with the cleaning rod avoids this issue.
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Old September 21, 2020, 05:03 PM   #20
IdaSpud
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Hi all. Just an update. I loaded up some more test rounds and tried them out.
I loaded the same amount of H4831 in test 2 that I used in test 1. Only difference was the COL. BOY did it make a difference in spread and SD. Didn't do anything for accuracy but the velocity was about the same for the same powder charge and the longer COL.
5 shot groups.

Test 1
175gr ELD-X
59gr H4831
COL 3.290
avg. 2663 fps
ES 107
SD47.6


Test 2
175gr ELD-X
59gr H4831
COL 3.416
avg. 2657 fps
ES 35
SD 13.7


Test1
175gr ELD-X
57gr H4831
COL 3.290
avg. 2540
ES 56
SD 25.4

Test2
175gr ELD-X
57gr H4831
COL 3.416
avg. 2542
ES 18
SD 8.1
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Old September 22, 2020, 01:56 PM   #21
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.158" is the distance to the lands. Like sako2 says, work up the load, first. Then, if you feel like it, you can fiddle with the off-the-lands thing. Said thing being a load tweaking technique that is 100% trial and error.
59 grains of H4831 is a full grain over current max.
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Old September 22, 2020, 03:49 PM   #22
burbank_jung
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I don't have a current reloading manual but Ken Waters' Petloads book lists 62-63gr H4831 and one was close to max for the 175gr bullets he used ( Hornady and Speer ). To me, a reloading manual is a guideline to take seriously. A sticking bolt, flatten primer, and tender shoulder are my indicators for an excessive load.
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Old September 23, 2020, 06:54 PM   #23
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Burbank said: "To me, a reloading manual is a guideline to take seriously."

It's true, but it depends on YOUR rifle and degree of comfort experimenting. MY 7mm Rem Mag Browning A-Bolt with a BOSS shoots great groups with 175 gr Nosler Partition, and has taken 2 Elk in the past. The load is 73.0gr of H-1000, graphed at 2985 fps.

Max manual Loads: Nosler: 65.5gr; Lyman 70.0gr; Hodgdon (with the partition) 64.5gr.

Higher velocity is not always more accurate, as we all know. But in my case, in this situation, climbing to 73.0 gr without "side effects" and better accuracy, disproves that.
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Old September 23, 2020, 08:42 PM   #24
burbank_jung
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Exactly. When I started reloading, I had a friend who load way off the chart where his primer primers were flat and his primer pockets became loose. He knew this wasn't his accuracy load. Then he backed down to find his node. Any shooter should look at such loads with caution, start within the guidelines, and work up. Of course, if a shooters prefers a lighter load or a load that matches his bullet, he/she may opt for a lower charge within the guidelines. An example might be Sierra SMP bullets. I've read and heard so many stories of them not holding up, I'm thinking they they are possibly designed for lower charges.
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Old September 25, 2020, 08:59 AM   #25
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I shoot 162gr ELD-X in 280AI and the 175gr ELD-X is just little longer 1.567" vs 1.478" 162gr.

I'm little over 3.400" and use VLD seater stem. They do rec 1/8.5 or faster twist for that 175gr ELD-X.

You may do better change bullets.
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