Seating Depth - Test Results

[Big Al]

It seems like an age since Ive been able to get the rifle out, wet fields, bad weather, never ending gales and Christmas all got in the way. What made it worse was I got a new rifle at the end of November and Ive barely been able to shoot it. The rifle was built by Dave Folwell of Bowtec who also built my last rifle, he gave me some load data but the COAL didn't look right with a jump of some 0.120" to the lands.

 

 

I got out this morning after making some loads at varying depths. I found it interesting that just touching the lands was accurate then things opened up as the bullet was seated further away then it looks like its coming back again as they get further out. At 0.080" away the best group was two shots through the same hole and another just out to make 1/4" group. Im going to try this test again and add a further 2 loads at 0.100" and finally 0.120" away which seems a crazy jump but Ive read these 55gr Bergers might just like it and the load data may now be making sense. A powder charge of 31.1gr of N550 is giving me a nice steady 3500fps and no signs of pressure.

 

I didn't realise seating depth made such a big difference and seeing these results I thought members might be interested.

 

 

I accept that some may not think 3 shot groups are enough but this type of rifle won't give me 3,000+ shots so Im trying to get the results I need without wasting good barrel life, and Im a greedy Geordie . The gun was shot from bags on the roof of my jeep, wind was 3-4mph from the right and the scope was never properly zero'd as I was just looking for group sizes. For scale the white inner square on the target is 5/8" across the flats

[dannywayoflife]

I've found seating depth makes a massive difference with some bullets. The 75 Amax in my old 223 was very very fussy and wouldn't shoot unless it was jammed 3thou. Any less or any more and it wouldn't shoot. But with that seating it was AWESOME and shot very well out to 1000.

[Big Al]

I've found seating depth makes a massive difference with some bullets. The 75 Amax in my old 223 was very very fussy and wouldn't shoot unless it was jammed 3thou. Any less or any more and it wouldn't shoot. But with that seating it was AWESOME and shot very well out to 1000.

 

That interesting Danny.

 

I would imagine many would find it difficult to even measure from bolt face to lands and get it as close as 0.003" never mind jammed by that much.

 

I don't use any gauges, I seat my bullet in a loose neck to start with and close the bolt on it. Then I mark up the bullet with permanent marker and keep on re-seating it deeper until the lands no longer make a mark on the ink, I would say Im within 0.002" or so at best so when I say touching it might not actually be exact to the thou but very close.

[Big Al]

The next question this raises is will this seating depth test need to be done again should I change the powder load?

 

When I see the difference its making here to group sizes its as significant as a 0.3gr-0.5gr charge weight jump.

 

I really expected that charge weight would be the significant factor in group sizes and seating depth might make a smaller difference but it appears to be quite a lot or at least with these billets it is.

[The Gun Pimp]

I think you need to repeat the test but shooting 5-shot groups to get a proper result. If you combined all of your five targets you would have a very acceptable 15 shot group.

[garyw]

shoot 5 shot as gun pimp suggest but i would suggest put all your targets in one row

ie-1-2-3-4-5-6 this will show you the best seating depth for 2 or 3 groups .they will/should be in the same position on each target relative to your point of aim the bad loads/seating will show up better either side of the good groups.

you can then take the good groups and tweak those to get the best one.

shouldnt be too hard with the start you have i would play around groups 1 and2

[Offroad Gary]

Perhaps take smaller jumps. Heres one i did

 

[Big Al]

Perhaps take smaller jumps. Heres one i did

 

 

Wow, Im amazed by those results.

 

Its so obvious where the sweet spot is but we are talking only 0.002" difference between a great group and mediocre either side. I would never have thought such small differences could be so critical. When I started loading last summer I asked the forum which was the most important, powder charge or seating depth and the general consensus was powder but this test would suggest seating depth is just as critical.

 

With my .223 I never looked at seating depth at all, I went for 0.010" off and found some great groups, none of which were bigger than 3/4" and found the best one very quickly in the 1/4" range. That was with 55gr SBK's, I then loaded 40gr Vmax the same 0.010" off and again found 1/4" within my first OCW test.

 

Looking at that lot Im astounded that such a good group could easily get lost if you were jumping up in 0.005" increments.

[Big Al]

shoot 5 shot as gun pimp suggest but i would suggest put all your targets in one row

ie-1-2-3-4-5-6 this will show you the best seating depth for 2 or 3 groups .they will/should be in the same position on each target relative to your point of aim the bad loads/seating will show up better either side of the good groups.

you can then take the good groups and tweak those to get the best one.

shouldnt be too hard with the start you have i would play around groups 1 and2

 

I can see why you would say number 1 but why 2 over 3, 4 & 5 which are all better?

 

Is it because Ive 2 through the same hole in number 2?

[Big Al]

Another question;

 

Based on my results do you think it would be wise to stay at 100yds or move to a longer range for this testing?

 

Would 200yds show things up any better or does other things come into it that might interfere with the results?

[garyw]

 

I can see why you would say number 1 but why 2 over 3, 4 & 5 which are all better?

 

Is it because Ive 2 through the same hole in number 2?

because the point of impact on the target in groups 1-2 is near identical

offroad gary has his best group @16th off his next group is 18th and point of impact is near ovelapping apart from some vertical.thats where his node ends as the groups open up, in his groups i would play around with loads between 14th and 17th -but his 16th gets the nod -your node starts to come back on target 5 again poi is near identical to 1-2.

now man up and shoot 5 shots

[gbal]

I can understand Al's surprise at (Offroad) Gary's groups,which aren't very typical,but interesting-sort of. One very pleasing (16),and the rest are really rather mediocre-I'm assuming this is a Tooley custom smithed 22/250 with a decent barrel?Maybe it just don't like these bullets?

Gary,did the superb group (16) get repeated on further testing?I'd have done a straight repeat with that bughole load/seating... .02 either side have lost it,opened up too much.

 

Al,5 shots better than 3 of course-but here's a thought-if your first two shots are "too far apart" (for what you wish) then there isn't any point in shooting any more-the group can't get any smaller,and you save 3 shots wear...for now anyhow.Persevere with all 5 if the shots so far are 'in your sweet group',and shoot 5 more (or 3,3,3 etc...whatever-just more of any very good group for a decent sample,and yes,200+ shows it better,and is closer to 'modal' real shooting distances.It's possible this load/rifle doesn't much like jump at all-the more jump the more dispersal.I would not jam into lands (fear is spilled powder,if have to unload),but a 'firm touch' might be worth a couple of shots....as well as,of course,a tad more seating out to see if another node come in,as you say.(More the 'expected' pattern of things...).

g

[Big Al]

I must say George I was quite shocked to be honest seeing Gary's results, it also deflated me a bit as if seating depth and such small increments are so critical then God help me. I can barely hold 0.002" tolerance in base to ogive with my cheap Lee loading turret press.

 

A few of these different seating depths seem to show promise so Im wondering if I should pick a couple of the better ones and use much smaller increments around those lengths?

 

 

[Offroad Gary]

The rifle was a tooley 22-250, blueprinted remmy, hart 26" fluted barrel. Bought it from dave ryan, sold it a few years ago to grumpy gary. Once i found that load i just kept on shooting it, very rarely missed. It was so accurate it became my go-to rifle, hence it had to go not being deer legal. I think baldie has painted it since i sold it and i believe its still shooting very well. Someone once commented on that picture that it looked like a fussy rifle. All i know is it shot well, very well with that load.

[Offroad Gary]

Loading was with wilson dies

[gbal]

Thanks (Offroad) Gary.Just seemed an odd 'non-pattern' in the tests. Glad it continued to shoot sweet with that good load.One 1/4 moa is worth a dozen 1/2 moa loads!

 

Bottom line,one good load is all that is needed.

 

g

[onehole]

Don,t play with seating depth just stick to 5 thou off,,seems to work with a lot of cals and rifles I,ve had mind you other than powder load each round is anally built exactly the same,,,absolutely concentric through neck turning and heads sorted for size.Sometimes I struggle at 100yds to confirm a best load,,,,,only tried the 29.5 at 200 so far,,,do I need to stress the rifle any more?don,t think so.Nice window to play with though!!!!

[Finman]

I've found seating depth the final and critical detail for an accurate round (i.e. establish which powder suits the round/bullet best, then test the maximum load, change primers and decide on the most suitable and then play with seating depth). Tested this in my 6mmBR, my .308 and my 6.5x55 as well as the 7x57.

 

Each bullet has its own seating depth and once found it remains the same independent on the change in powders, primers etc. Perhaps one reason to re-examine this would be throat errosion.

 

Interestingly, in my 6.5x55 I have had two variations on seating depth: one 20thou off and the other at SAAMI OALs (which is something like 90thou off). These two gave identical groups and the best of the lot, any other combination giving significant spread. I suspect that this may also be dependent on the barrel as well (i.e. if I change the barrel I may find that the seating depths that worked previously don't work any more...)

 

best wishes

 

Finman

[foxyloxy]

Don,t play with seating depth just stick to 5 thou off......

I assume OH that either you are dropping your rounds in one at a time or your magazine is capable of taking the longer rounds. I don't remember the figures off hand but the magazine in my 308 holds the SAAMI spec rounds and nothing more (168 gr Amax in a Howa 1500).

For me to play with seating depth, I would need to forget about mag loading which isn't an option really.

[jcampbellsmith]

...

For me to play with seating depth, I would need to forget about mag loading which isn't an option really.

Seat deeper into the case, 5 thou at a time and test carefully. Regards JCS

[onehole]

I assume OH that either you are dropping your rounds in one at a time or your magazine is capable of taking the longer rounds. I don't remember the figures off hand but the magazine in my 308 holds the SAAMI spec rounds and nothing more (168 gr Amax in a Howa 1500).

For me to play with seating depth, I would need to forget about mag loading which isn't an option really.

Apologies,,,yes one at a time for my purpose and use and forgetting mag users have limited space and sometimes long freebores.I also didn,t mean do not play with seating depth its just that I don't any more,,,,,,regds ,,,O

[AckImp]

We've just been testing a 7mm-08 and had 168 Berger VLDs and some 160 Sierra HP on the shelf. Knowing that the VLDs have a reputation for being finicky we decided to try the Sierras first. We always start with charge weight and got nowhere this time, so we picked the best (least bad!) charge and started playing with the seating depth. No joy. Onto the notoriously length intolerant Bergers, some at mag length, the others loaded out to the lands and we were instantly rewarded with 1/2" groups with both combinations!

 

This was a real eye opener for us as what we "knew" about the Bergers turned out to be wrong. We've also had a think about how long we should persevere with a combination before ruling it out. In hindsight, the first couple of groups with the 160s should've been enough for us to change to the Bergers in the first place!