A question on seating depth for varmint rifles.

M

murphy

Guest
Some folks believe that seating a bullet close to the lands improves accuracy, and certainly if a load is developed with a bullet seated out it can be made to shoot but does it really help. Most of my rifles seem to find an accuracy node 50 to 75thou off the lands. If I am getting any flyers due to lack of concentricity I can not find them so I am thinking that the concentricity aspect may be a bit over rated. Is anyone brave enough to agree with me?:confused:
 
I seat bullets for my .222 and .220 Swift from .006 to .010 longer than touch, as measured with one of the Sinclair guages that uses a rod and collars. What sort of accuracy is typical for your rifles?
 
For my .223's and 6mm's I seat uncoated bullets .015" jump, except Barnes VG which seem to like .010" jump, unless I need to load shorter for magazine length. Coated bullets seem to work better with .010-.020" jam. In my 1:12 twist .223 I load 40 gr Nosler BT's .060" jump for magazine length. I think you can 'tune' for whatever seating depth you use and crimping (shudder... I said the 'C' word) may even help. - nhk
 
i guess i dont quite get where your jumping from how far to seat the bullets, and then making it into a comparison with concentricity!!?!?!? for what its worth, i have varmint guns where i jam them hard into the lands, and some that i seat way off. it depends on the rifle, and load.
 
Determining depth

lefty o said:
i guess i dont quite get where your jumping from
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I use the Hornady (Stoney Point) modified cases (or make my own) and bullet comparators and find the point that a bullet will touch the lands and then back off (jump) or advance (jam) the bullet. When I jam a bullet I make sure I haven't jammed it too far to be able to extract the round without pulling a bullet and dumping the powder. Since these are factory rifles with blind magazines I stay within the magazine length unless I'm going to single load.

I have several factory rifles and the throats are not symmetrical (confirmed with a bore scope). Accuracy seems better jumping than jamming in that situation. - nhk
 
To lefty o, I make the comparison to concentricity because I am of the understanding that the practice of seating on of close to the lands is to stop the bullet from cocking sideways as it enters the bore proper. My go to rifle is a stock Ruger MK11 .220 Swift with 6.5-20x40 VX111 Leupold, rifle has had a bedding job and trigger worked. My reloading gear is ordinary RCBS reloading dies an ancient powder scale and a $70 set of vernier calipers. Now people ask me how does it shoot, and that is a tough one as there is so much BS on these forums that it is difficult to get credebility. About the best I can do is to say that it is a sub.5 minute of angle preformer with Hornady 52g match pills. My reloading method is a little unorthodox but for what it is worth, this is how I go about it. I find the speed I require with a chronograph, seat the bullets out till they touch the rifeling and move back in 25 thou jumps and 3 shot groups till I find accuracy. With 36.5g of Varget and Rem91/2 primer Initial load development went like this. Touching lands 3 shots .471" 25thou off .805" 50thou off .351" 75thou off .301". Next time out rifle shot a .45" 5 shot group off a clean cold barrel with no warmers and has been giving that sort of accuracy for the last year or so. Do not wish to be disrespectful, and I know you people get good results but I like fine tolerences like the devil likes holy water but that does not stop me from being interested in what you do or how you go about it.
 
hang on while I put on my fire proof underwear,,,,while I do have a couple of jam rifles, MOST of the time (but NOT all the tiime)I can keep working until I find a load/tune that works jumping, the problem with jamming is sometimes you'll get a pressure spike and miss a chance to go hotter(ie:faster/flatter) because of this spike,,,,,,,,, the main thing IMHO is that a rifle is like a woman, ya got to feed her what she likes and not two are just alike,,,,,,,,,,,,,,,,

the wind is my friend,,,,,,,,,,,,,,,,,

DD
 
Thanks David, I always enjoy your posts. My undies are pretty right but my ears are burning a bit, so someone must be talking about me. Don't want to go into the rifle and women analagy too far but when you get one with a fetish it makes them very easy to please. I too have a jam rifle, a 22 Hornet of all things.
 
After sticking bullets in the rifling out in prairie dog towns I don't load my live varmint rifles to jam anymore. Most are 5 to 10 thou off the rifling and any difference in accuracy couldn't be proved by the prairie dogs. I've got one rifle that has a longish throat so bullets can't be seated close anyway, and it likes them a ways off anyway. A local gunsmith who looked at the bore with his borescope commented that the leade angle has a lot to do with how far bullets like to be seated. If it's fairly abrupt bullets seem to like to be seated back, otherwise close works best. Can't argue with him since he's forgotten more than I'll ever know.
 
To Larry Elliot, Read your post carefully and it makes a lot of sense. When I put up this post,I was not trying to stir up trouble, just trying to point out that all rifles are not happy seated right on the lands and a few dislike it intensely. I have a CZ550 sporter in .308 winchester that shoots 2" groups with bullets seated on or close to rifeling. Move it 50thou off and it will shoot a .35 "3 shot group. Also a lot of people do not have the right gear to make small repeatable seating depth moves and when they try they just get into trouble. The coarse changes I make to seating depth suit my gear and while my grouping may not be of benchrest standard, my results are extremely repeatable and as you say, the crows can't tell the difference between a .1" and a .3".
 
Most of my varmint rifles like a hard touch or just barely touching. With VLD bullets, I jam .005. I have never had an issue with bullets being pulled out of the cases with a .005 jam, then again, I have a good squeeze on the neck.
 
To keithcandler, Do you ever use Winchester ball powders, as I have observed in my experiments that they don't respond well to big seating depth changes? Most 220Swift owners would never have a problem with cartridges spilling their contents as the projectiles won't even come out with an inertia bullet puller.
 
For two varmint cartridges I currently reload for(223 & 6br), I ended up 8thou and 15thou off as best, which doesn't really mean anything for you I guess.
I arrived at this with what amounts to a ladder test for seating, starting at 5thou off and working in 5thou increments outward(using a medium pressure load). Then I return and refine a seating node. Then I move on to traditional ladder tests for powder adjustments.
I do not mess with 'just touching', but run an additional jammed ladder test to either keep or discard as a viable seating potential.

How's that for contrast over everything you've ever heard of?
Well, keep in mind that nobody KNOWS what you should do..
 
To mikecr, You are doing a very similar thing to what I do, but I move in 25thou increments. Do you find that 5thou is enough to get a big change in harmonics? 25thou makes an enormous difference but maybe my groups are going out and coming in 5 times in that distance and I don't know about it.
 
When I tune a load I change seating depth in .003" increments and powder in 1% (usually .3-.4 grain) increments to find nodes and finally to the nearest .1 grain with all charges weighed. My .308 F-Class load has an ES of 7 fps. A change of .025" in seating depth can actually be a significant pressure change on smaller volume cases when near maximum. - nhk
 
It doesn't hurt to go big initially for ruling out much of it, espescially with a magazine fed gun, or with VLDs. Everything I shoot is either single shot or I make it so, and 50thou off is as far as I've ever gone. With mine, a helluvalot happens in 25thou, plenty in 5thou, and then as much happens in +/-2-3thou(as nhkuehl adjusts). The only way I know to measure results here is on paper ~300yds.
I don't concern myself with, or measure velocity with seating checks. That's addressed with primer ignition, powder, pressure, neck tension, etc.
I find the best seating and move on using it.
 
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To nhkuehl, To my way of thinking a spread of 7 fps is remarkable for a 308 as plenty of 308 loads give a 100 fps spread and I consider that I have a good load if it does better than 40fps. Have never noticed any significant change in pressure even with quite large changes in seating depth, though I would be wary if working close to jam and I do tighten up my tolerences when working with a 22 Hornet. Did blow the extractor off a 270WIN. once when working very close to jam and with very light neck tension. People on this forum have assured me that what happened was not a fair dinkum blow up and would have nothing to do with seating depth or neck tension though it does make one wary, especially when you have had little blood spots all over your face.
 
I would suspect your blow-up had more to do with the powder charge or a defective case, or a long case neck. Usually jam (or crimping) compensates for too little neck tension. I watch primers very closely and how much they flatten out and crater and occasionally run into detectable bolt lift. I've purposely seated deeper just to see what happens with pressure and have gone from a flat primer to bolt lift in .060" increase in seating depth. When working up a load I graph group sizes to find my node(s) and velocity to see if I reach a velocity plateau. I enter velocity into a spreadsheet that calculates ES and standard deviation as well as average velocity. That's not the only load I've had with a single digit ES. The combination of components is really important and that takes some trial and error. - nhk
 
Murphy
I've never owned a 22 centerfire that liked any bullet near the lands or just off the lands.Mine like the bullet engraving the lands or about 0.22 off the lands.I am guessing everybody here uses a different method to determine there just touching length.

With the vld's you can jump them in the 0.025 increments you have mentioned but once you find a seating depth uising that method you need to measure your loaded rounds with a comparator.
If the seating depth shows alot of variance when using the comparator your groups will always be larger than they should be.I have seen as much as 0.013 seating depth variation out of the same box of vld bullets when using a comparator.If you reduce that variation to no more than 0.003 total variation your rifle will tend to shoot much more consistently ie no more 3 and 2 groups.
Lynn
 
murphy said:
Most 220Swift owners would never have a problem with cartridges spilling their contents as the projectiles won't even come out with an inertia bullet puller.
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I have several 220 Swifts and use Redding Competition dies (neck bushing resizer) and size necks ony a couple of thosandths--there's not a lot of neck tension and I have to be careful about sticking bullets in the throat when seating them very far out.

Maybe it's my equipment but I have carefully measured OAL using a Sinclair comparator and find that there is often 3-5 thousandths variation depending on case neck thickness and the amount of force necessary to seat bullets, and also some variation in bullet ogive (I use mainy Sierra 53 gr. Match bullets). Cases with thinner necks require less force to seat and have shorter OAL than thicker necks and more force. It doesn't take much difference in case neck thickness to get this effect. So I am always skeptical when I read about seating only 3-5 thousandths off the lands or accuracy trials changing seating depth in 3-5 thousandths increments. Maybe I'm wrong, but I think there is always variation in OAL and that it's very difficult to keep it less than 3-5 thousandths using equipment most varmint hunters have and the case preparation methods they use.
 
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