Seating Depth Testing

Jud96

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From what I've seen and read here and in other posts/forums - in all of the information, given freely, is this.
Bullet jump, powder, brass, primers, technique, posture, range shot, weather at time of the year - can have varying degrees of effect.
Just one thing I don't see mentioned here, is the freebore of the 243.
I'm guessing it maybe a custom barrel?
Jud96 - there's a lot of CBTO change from touching lands to 0.090"-0.100" off the lands and preserving powder space in the case.
Can you enlighten me please, as the process sounds well reasoned and has some barrel accuracy life challenges made easier to live with. TIA.

PS - I load AR2208/Varget in 308W/7.62x51, and find (for 155gn VLD type bullets), that any jump greater than 0.050", starts seriously compressing the powder column. To the point that CBTO becomes quite variable. Using 45.5gns powder in Lapua once fired to chamber brass (originally virgin at first loading).
This is a factory Remington 700. With the bullet seated .100 off the lands, the bearing surface/boat tail junction is seated .050 below the case neck. My powder still has a lot of room and my old load was .060ish off the lands and with 44.3gr of powder I still had room to go before being compressed. I have no clue what the Freebore is on this rifle. I just know when touching the lands the bullet is about 3/4 of the way down the neck.
 

LongBomber

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But at what stage does it affect accuracy?

Also does anyone have a link to this PRB article Id like to read
Link

And the answer to your question would come from testing seating depths in your rifle. But typically that window of accuracy is fairly narrow. When testing seating depth how fine of steps did you test? It seems most guys hear test at .005” steps and run with the depth that gave the best absolute accuracy.

The prb guys are concerned with PRS matches, shooting 150ish rounds a weekend. They also do not need the highest levels of accuracy as the targets are fairly large. More accuracy is always better, but this isnt benchrest either. They are willing to live with a group .1” larger to have a seating depth that will hit the same poi with no vertical shift for 150+ rounds and not come out of tune.
 

74honker

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Good info Jud96. I think some are maybe misunderstanding the point you are trying to make. I've read the series on PRB and found it very informative. To those with question marks all I can say is read the articles and think about it for a minute and I think the bulb will come on for you. I have done similar work with a 7mmRM with similar results also. Yes the gun will tell you what it likes best regardless the variable and regardless what you think it should or shouldn't do. The wrong thing is not to at least try something different until you do find that "sweet spot". As with anything in life do what works for you and that's what makes the world go round. It really is ok if someone does things different from prior conventional thinking.
 

kiwi49

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This is a factory Remington 700. With the bullet seated .100 off the lands, the bearing surface/boat tail junction is seated .050 below the case neck. My powder still has a lot of room and my old load was .060ish off the lands and with 44.3gr of powder I still had room to go before being compressed. I have no clue what the Freebore is on this rifle. I just know when touching the lands the bullet is about 3/4 of the way down the neck.

Wow - plenty of room to play with then.
The Omark 44B action and chamber are throated for 144/147gn FMJ NATO bullets.
So don't have much freebore room to play with there.
Have another Omark which is chambered for longer, heavier bullets. Will try your system out on that baby.
Cheers
Wally
 

MLN1963

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I think a good place to start load development might be with the Wheeler test for different bullets in your rifle before doing any reloading or shooting. If the bullet ends up sitting too deep or exceeds your mag length, it might just be better to pick a different bullet to work with from the start.
Remind me, what is the Wheeler test?
 

CaptnC

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Been reloading and shooting for a long time where MOA of dead deer was good enough, but recently got in fine tuning a loads for accuracy.

So far I've not done a seating depth test...
 

MLN1963

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I thought he was talking about a wheeler bullet seating method. I have seen this video and use the method.
 

antelopedundee

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I use an unprimed dummy case sized and given a minimum amount of neck tension. I seat the bullet long and ease it into the chamber. Generally it extracts without sticking in the lands. I now have a dummy round seated to touch. I've been using micrometer controlled seating dies or Redding competition seat dies. Use the dummy round to set the seater die to touch and then test fire a few. Very easy to screw the seater plug down by any amount that you want to. With the dummy you can always return the seat die to the touch position if you lost or forgot to write down the micrometer reading. Range pick up brass is good for this. I make a seater dummy for each type of bullet I use. Of course any loaded round must fit in the magazine.
 

Coldfinger

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Hey all. I just finished up doing some seating depth testing on my Remington 700 .243 Varmint rifle and figured it would be a good idea to post my methods and my findings on here. I like to do a lot of testing and I also like to help and share whatever I find and experience with others. I often recommend to others to test their seating depth. It can very much change your group size and your results as you will see below.

Before I get into my results, I’d like to explain my methodology and how I go about this test. First, I’d like to say every bullet is going to have preferences to bullet jump. There’s the thought that certain bullets are less sensitive than others, and that may be true, but in my testing and experience it seems they all can be tweaked to shoot their best. I highly recommend everyone to go over to the Precision Rifle Blog and read their latest articles on bullet jump and the results that Mark Gordon of Short Action Customs and other top shooters have found and tested. That is a very good read and it really opened my eyes up to test seating bullets even further from the lands than I ever did in the past. I’d also like to say, this is for guys who want to shoot at 100 yards or may only have access to 100 yard ranges most of the time. I have to travel an hour or longer to get to places that I’m able to shoot 300+ yards. I use this method to find good results at 100 yards where I’m able to shoot year round and is only 5 minutes from home.

When I go about doing seating depth, I first find my lands by using the Wheeler method. There’s a video on YouTube of Alex Wheeler demonstrating and explaining it. I will then load rounds up in .010 increments from say .020 off to .100 off. I like to load 3 at each length to shoot a group of 3 to better represent what they’ll actually shoot like. I have tried this with two shots and have seen others do it with one, but 3 gives you an average and a true group. For the test I did today, I just started 3gr below max in my new Peterson brass and shot the seating depth test. In my experience and the experience of others, if you have the right bullet jump, you can shoot any powder charge and your sweet spot in bullet jump will stay the same. I have experienced this in multiple rifles of my own and friends, and have seen the data from others to back this up.

There are also ways to fine tune your seating depth when you’re closer to the lands by adjusting in .002-.003 increments. The problem with having a load close to the lands is that it can be very sensitive to change. If you have a hot magnum you may erode the throat .005-.010 in 100 rounds. Then you have to keep chasing the lands. Finding a more forgiving bullet jump “node” like I show below will result in good groups even with some throat erosion. There may be a sensitive seating depth that shoots even better, but I find it annoying to have to chase the lands. So this is why I look for a window in seating depths that give good results and are not as sensitive.

Today I shot groups from .030 off the lands to .100 off. These were all shot with virgin Peterson .243 brass, 87gr VMAXs, 41.0gr IMR 4451, and Winchester Match primers. I took a few minute break between each group to let the barrel cool and to not get uncomfortable or fatigued behind the rifle. I started with a clean barrel and fired 3 rounds from my previous load on the bottom right target. That group was very good, but this load has some pressure signs in warmer weather and the ES is a little higher than I’d like. I then adjusted my scope down and put one in the center just to return to zero. Today’s test was mainly looking to see if I could improve on anything and to just do some more testing for fun and for data.

Here are my results. Starting from top left is .030 off and ending with .100 off on the third target on the bottom row. My conclusion is .090-.100 off looks really good and will be where I do some further testing. I will say I feel like I pulled one shot today and that was the lower impact on the .090 off group. I’m very happy with that .100 off group and the couple other good ones I shot today. This rifle sure hammers for a factory Remington with some bedding and handloads!View attachment 193964View attachment 193963View attachment 193962
Very interesting awesome info
 
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