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 Seating Depth On 7mm RM Loads
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Bang4TheBuck
Starting Member

USA
5 Posts

Posted - Oct 22 2016 :  09:46:11  Show Profile Send Bang4TheBuck a Private Message  Reply with Quote
I am now to the forum, and glad to be part of it. I have been loading intermittently for about 20 years. I started initially for economy, and have now been working on more precision loads. I appear to have made a rookie mistake in my load development. I loaded 35 carteridges with Winchester cases, CCI Large rilfe Magnum primers, and H1000 charges varied in 1 grain increments from 63 grains to 69 grains. I seated all of the 168 gr. Berger Match Hunting bullets at Spec COAL (3.290") I went to the range and tested all, by simply shooting 4 shot groups of each load with cool down between groups. 66 grains produced the smallest group (sub 3/4"). I was intending on then fine tuning from there by adjusting seating depth. I am now realizing that I might have make a mistake by not setting to longest COAL (.010 to ..015 off the lands), and working down (reducing the COAL) in small increments until I find the tightest group. So, my question is, do I need to start over with charge weights and longer cartridges, or can I use what I learned from the tests done at the spec COAL? Thanks in advance for the help.

Ireload2
Senior Member

USA
286 Posts

Posted - Oct 22 2016 :  11:08:35  Show Profile Send Ireload2 a Private Message  Reply with Quote
I usually start long because the pressures are probably the highest when touching the rifling. I can always make them shorter - even at the range if I take a seating die and some sort of press.
I concentrate on making my ammo as straight as possible and I usually find a decent load when touching the rifling.
However I have a 6mm Rem and I cannot load such ammo in the magazine so it was worked up with a long jump. That rifle is very accurate too.
If you have a bolt gun make sure the bullet is seated deep enough so that it does not fall out of the case or get knocked crooked during feeding.
Beware of boat tails when extended because you will loose grip length on the bullet due to the boat tail.

Since you are learning you might as well start another set of loads at the extended length and work up. You may find that it makes no difference or it might even make it worse.
If you are happy with the load you have, you can lengthen or shorten it a little if you still want to play with it.

Save your existing data so you don't have to reshoot it.
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Shastaboat
Advanced Member



USA
9124 Posts

Posted - Oct 22 2016 :  11:41:08  Show Profile Send Shastaboat a Private Message  Reply with Quote
I would start out where you left off however it is doubtful you will see much improvement. I am not a proponent of loading close to the lands especially in a hunting rifle. 7MM Rem Mag...right? Many times I just seat the base of the bullet to the base of the neck and call it good. Lets say you are chasing the lands and something happens, like "recoil" to move your bullet out and you chamber that round. You might experience a high pressure load if you shoot it or if you extract it you might pull the bullet and leave it in the bore and dump powder all through your action. Now you just ruined your hunt and are miles from having the tools to clear your bore and action.

Leave "chasing the lands" to someone who is just bench-rest shooting and loading one cartridge at a time.
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woods
Advanced Member

USA
2132 Posts

Posted - Oct 22 2016 :  12:17:42  Show Profile Send woods a Private Message  Reply with Quote
I start like you did and work up because I like to find the velocity that I want. IOW you don't want to shoot your 7 mag at 280 velocities, you want to utilize the increased velocity that the 7 mag is intended for. Once I find the velocity that is just under max for my rifle then I work with seating depth to fine tune accuracy.

Keep in mind that seating closer to the lands increases pressure and velocity while seating deeper decrease pressure and velocity. At least in all my rifles it does.

Normally I will start off at .030" off the lands for the velocity tests and then do a seating depth test at .015", .030"., .045", .060", .075" & .090". For me what I am looking for is accuracy but also Extreme Spread and Standard Deviation of velocities. The thought being that the load with the lowest ES & SD will show greater tolerance to minor changes in loading, temperature, elevation etc.



At what distance from the lands did you do your powder charge test?


When someone shares something of value with you and you benefit from it, you have a moral obligation to share it with others.

After Tuesday, even the calendar says WTF!

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Bang4TheBuck
Starting Member

USA
5 Posts

Posted - Oct 22 2016 :  19:33:31  Show Profile Send Bang4TheBuck a Private Message  Reply with Quote
I didn't measure the distance off the lands, I simply loaded to the spec length. I don' have an effective tool to measure the length. Im considering getting one. But have not yet.
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ligonierbill
Senior Member

USA
202 Posts

Posted - Oct 22 2016 :  20:21:22  Show Profile Send ligonierbill a Private Message  Reply with Quote
Sub 3/4" group. No pressure signs. "In spec" loads. Me, I'm done.
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Ireload2
Senior Member

USA
286 Posts

Posted - Oct 22 2016 :  22:45:43  Show Profile Send Ireload2 a Private Message  Reply with Quote
If you have worked up the loads starting at the lands your >> like "recoil" to move your bullet out<< scenario is not logical since the load has already been tried and found safe at that length. All that might happen is the bolt or breech block has to seat the round. However if you are really a prudent loader you always use enough neck and bullet shank so that your rounds never move. I have 45 years of hunting experience with loads set up just like that with zero problems. That includes rounds with 500 grain bullets that are much easier to move due to the greater inertia of the heavy bullets.


quote:
Originally posted by Shastaboat

I would start out where you left off however it is doubtful you will see much improvement. I am not a proponent of loading close to the lands especially in a hunting rifle. 7MM Rem Mag...right? Many times I just seat the base of the bullet to the base of the neck and call it good. Lets say you are chasing the lands and something happens, like "recoil" to move your bullet out and you chamber that round. You might experience a high pressure load if you shoot it or if you extract it you might pull the bullet and leave it in the bore and dump powder all through your action. Now you just ruined your hunt and are miles from having the tools to clear your bore and action.

Leave "chasing the lands" to someone who is just bench-rest shooting and loading one cartridge at a time.

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chig78
Average Member



USA
164 Posts

Posted - Oct 22 2016 :  23:58:53  Show Profile Send chig78 a Private Message  Reply with Quote
Bang for the Buck,
An easy way to measure OAL is with a wooden dowl rod. First close your action with an empty chamber. Insert a dowl rod down the barrel tight against the bolt face and hold it there. Make sure you are up against the face and not any other part of the bolt. Using a gun vise or cleaning stand really helps to hold the rifle and it doesn't hurt to have a buddy help out if needed. Once your have the dowl up against the bolt face take a utility knife blade and very carefully lay it horizontally flat on the end of the muzzzle and scribe a mark on the wooden dowl. Then remove the dowl from your barrel. A sharpie works great to help identify the scribe mark. Next remove the bolt from the rifle, take one of the bullets you want to load and drop it into the bore on the action end. Use a second dowl rod to hold the bullet against the lands of your chamber. This is where a buddy is a big help. Hold the dowl securely to the bullet, DON'T PUSH REAL HARD, Just enough to seat it against the lands. Now take the same dowl rod that has your first mark on it, (while holding the other dowl securely) and insert it in the barrel again. Slide it down the barrel very gently just to you feel it touch the tip of the bullet. Don't press it into the bullet as it will give a false measurement due to the bullet piercing the end of the dowl rod. Once touching the bullet take your blade and make a second mark on the dowl the exact way you made the first. remove everything from both ends and the distance between the two marks will be your chambers OAL for that specific bullet. You can then use that as a baseline and make your adjustments to seating depth from there. .010 to .015 of the lands is a good place to start with minimum powder charges. With higher powder charges I would start from .030 to .035 off the lands just to be safe from pressure spikes. The procedure that Woods explains above is probably the most effective, Efficient and safe method to use in load development. I personally use this method for finding OAL for all of my rifles and it works great and is very inexpensive. Hope this helps and Welcome to the NEst!

Chig78
I your gonna be dumb, Ya better be tough

Edited by - chig78 on Oct 23 2016 00:24:39
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Bang4TheBuck
Starting Member

USA
5 Posts

Posted - Oct 23 2016 :  08:04:46  Show Profile Send Bang4TheBuck a Private Message  Reply with Quote
Chig, your answer is exactly what i was looking for. My Charges are in the middle of the spectrum, so I will start with them .035 off the lands, and go from there. Without other advice, I would work up groups in .010" increments from there. Make sense?
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woods
Advanced Member

USA
2132 Posts

Posted - Oct 23 2016 :  10:08:18  Show Profile Send woods a Private Message  Reply with Quote
chig's method is great. I do the same thing except with a $25.00 tool that makes it easier to get exact measurements



But I would start at .020", then .035" and then deeper by .015" increments. In my experience (some good some bad ) you need to go a little more than .010" as your seating depth can vary by +-.005" depending upon case prep, press linkages, seating pressure, bullet tip variance (if you are not using an ogive comparator) etc. etc.

Also some bullets/rifles like bullets seated +-.020" off so if you start at .035" you may miss an opportunity


When someone shares something of value with you and you benefit from it, you have a moral obligation to share it with others.

After Tuesday, even the calendar says WTF!

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chig78
Average Member



USA
164 Posts

Posted - Oct 23 2016 :  15:16:55  Show Profile Send chig78 a Private Message  Reply with Quote
Woods,
Can't agree more. OAL guage and an Ogive comparator are definatly the most accurate way to obtain your OAL measurement. Just never got around to gettin one yet....lol. The 7mm Mag that i shoot loves the bullet seated .025 off the lands and my 264 Win Mag loves them at .015. For some reason they just don't like alot of jump. Every gun is different though.

Bang for the Buck,
Glad to be able to help out. This is an excellent site for research due to the broad spectrum of knowledge and perspectives. I usually learn something every time I read through the posts here on the Nest!

Chig78
I your gonna be dumb, Ya better be tough
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Bang4TheBuck
Starting Member

USA
5 Posts

Posted - Oct 23 2016 :  18:50:17  Show Profile Send Bang4TheBuck a Private Message  Reply with Quote
So , I went and got two 1/4' oak dowels and a couple of electrical ground lug clamps and made a tool. I closed the bolt and fed the dowel into the muzzle and and clamped one of the clamps against the end of the muzzle. I then fed the 168 Grain Berger Hunting VLD into the chamber and gently pushed it until it it kissed the lands. I inserted the other rod to into the muzzle again and manipulated the bullet from both ends until it was just kissing the lands again. I Clamped the other clamp down and took my measurement. 3.420". I'll now seat a bullet into an empty case to the dimension I decide on, based on the advice above and then check it with the bullet comparator, and I should be good to go!!! Thanks for the help. I'll let you know how it goes at the range. Thanks to all that contributed.
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Zero333
Advanced Member



Canada
811 Posts

Posted - Oct 23 2016 :  21:44:59  Show Profile Send Zero333 a Private Message  Reply with Quote
If you worked up to 69gr with out pressure issues and lets assume it was a long jump to the rifling. You will have no problems with pressure loading close to the rifling with a 66gr charge weight since it's a full 3gr less than 69gr.

I have not found "much" pressure difference between a very long jump (say 0.250" away from the rifling) and 0.020" away from the rifling.

Once you start to touch the rifling with the bullet or jam the bullet in the rifling, the pressure goes up.


Treat that trigger like it’s your first date, not like you’ve been married to it for 20 years.
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Bang4TheBuck
Starting Member

USA
5 Posts

Posted - Oct 30 2016 :  14:45:58  Show Profile Send Bang4TheBuck a Private Message  Reply with Quote
I went to the range today and shot 7 different groups varying the seating depth in .010" increments. I had two groups that looked decent. One had a vertical spread of .176, the other .192". Both groups had some horizontal dispersion that opened the groups up to ~.651 and .690" respectively. The last shot of each group was always the one that opened the group up. As much as I tried to wait between shots, the mirage off of the barrel had the target dancing through the scope. The one thing that is didn't have time for was to shoot through the chronograph. Can one of you guys with that fancy software help me with calculating my velocity? Here are the specs: 7mm Remington Magnum , Winchester cases, cci large rifle magnum primers, 66 grains of H1000 powder, 168 grain Berger VLD Hunting .020" off the lands. I intend on trying to shoot one more time and use POI at extended ranges to back-calculate the velocity, but I would like to have some decent Idea where I am. Thanks
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Shastaboat
Advanced Member



USA
9124 Posts

Posted - Oct 31 2016 :  09:00:34  Show Profile Send Shastaboat a Private Message  Reply with Quote
Quick load or any other computer program is not reliable for quoting velocity figures. Figure a +-10% error rate.
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chig78
Average Member



USA
164 Posts

Posted - Nov 10 2016 :  18:39:19  Show Profile Send chig78 a Private Message  Reply with Quote
quote:
Originally posted by Shastaboat

Quick load or any other computer program is not reliable for quoting velocity figures. Figure a +-10% error rate.



+1. Chrony is the only way to go.

Chig78
I your gonna be dumb, Ya better be tough
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