Problems figuring out freebore and seating depth?

[Personofinterest99]

What am I doing wrong???

I use a Hornady Lock-n-Load OAL gauge to measure the run out for several Sierra, Nosler, and Barnes bullets I'm working up for a new Sako bolt gun. I very gently run several of each type of bullets into the chamber until they stop on the Ls&Gs with an ounce or so of pressure, then remove the gauge. Usually the bullet is still in the chamber so I take a duster can and give it a quick shot of air from the muzzle end which pushes the bullet back out of the chamber. Using a .308 comparator on my micrometer I measure and document the results for 6 of each type of bullet and average them. Then I seat the bullets .005-.01 shorter than the max measured length. Afterwards I clean up the freshly loaded bullet with 0000 steal wool and spin the bullet shiny with very fine concentric striations. Makes it easy to see if when I reinsert them if they touch the Ls&Gs. The Ls&Gs are perpendicular to the fine marks from the steel wool so they are easier to see. I prefer this to using a black dry erase marker. Anyway, after all the measuring and seating is done, using my fingers I push the bullets fully into the chamber and seat them where I think should be just short of the Ls&Gs. However, when I remove the bullets and look at them, they clearly have L&G marks on the bullets, usually on 1/2 to 2/3 the circumference of the bullet at a depth of .08-.15 deeper than where the OAL tool measurements suggest they should be. And my practice of using a shot of compressed are to back the bullet out of the chamber doesn't work. I have to push it out with a cleaning rod. I can barely feel any resistance when I push the rod in, but it is enough to feel when the cleaning rod actually makes contact with the bullet and pushes it out. No problem when I run resized but unloaded brass into the chamber. It easily pops out with a quick shot of air.

Where am I going wrong? Could it be a matter of concentricity, as suggested by L&G marks on just 1/2-2/3 the circumference of the bullets? The brass (once fired FC and RP) maybe not concentric with the bullets? I shot the rifle, a Sako 30-06, right out of the box and did a break in with generic reloads and it had no probs holding just over 1" groups, so I don't think there's anything serious wrong with the rifle. No pressure signs or anything odd on the brass. So what should I go with, what my OAL tool and measurements are telling me, or what the L&G marks on the bullets are telling me?

 

[taliv]

it is highly likely that the start of the rifling is not perfectly square. very few gunsmiths get that right consistently. so even if the bullet is perfectly concentric with the case and neck, when you insert it into the lands, it will touch lands on one side before the other.

i'm also pretty skeptical about those OAL tools, as you usually get a different result every time you measure

 

[Bart B.]

Taliv's right about chamber squareness. When the 'smith uses a reamer with a fixed, under size pilot, it wobbles around reaming a hole that's out of round. If he uses a reamer with a floating pilot .0001" smaller than bore diameter, the chamber will be much more square and much less out of round.

The chamber's freebore is a constant diameter section starting at the chamber mouth then forward to where the rifling angles down from that diameter to the bore diameter. It stays the same forever and never changes. On some rifles, such as the .30-06 and .300 Win Mag, SAAMI specs for their chambers has zero freebore length. The rifling starts angling right at the chamber mouth down to bore diameter. Freebore got it name from the "bore" being "free" of rifling for some distance in front of the chamber mouth. It varies quite a bit across all 30 caliber cartridges; it's .090" for the .308 Win and .346" for the .300 Wby Mag. They all have different diameters a little larger than bullet diameter specs.

If the bullet's a bit crooked in the round, one side will show contact with the rifling before the other does. And all bullets in a given lot do not all have identical shaped ogives; they vary a tiny bit in their diameter at any given point forward from their base. So I don't think that's an issue at all.

Seat bullets to whatever cartridge OAL you want, then shoot the darned things. Change the seating depth if you so desire. A few thousandths spread in bullet jump to the rifling is normal with even the most accurate rifles known to man.

 

[Personofinterest99]

Very informative...very helpful, Bart and Taliv. Thanks!

Do you see any pressure or safety issues if parts of the bullet are clearly in contact with lands when the bullets are chambered and fired? Will it cause premature erosion of the metal?

POI99

 

[Bart B.]

I've not observed any change in throat erosion measure its advancement for the lives of several .308 Win barrels shooting all rounds without them touching the rifling compared to others when half the rounds shot were touching the rifling. Seating a given load so the bullet into the rifling will raise its peak pressure a little bit. Cut those loads charge a grain or so all is back to normal and no significant change in accuracy; it might be better in some instances.

 

[gamestalker]

I jam most all my bullets into the lands, just something that works for me when it concerns accuracy. Yes, you may lose a little velocity, but as long as you don't use fast burning powders and don't start to high on the charge table, the results can be rewarding.

As for how I like to locate zero distance to the lands. I start with a bullet seated long, then decrease until I can feel it just barely sticking to the lands when I chamber it by hand, not with the bolt. I measure from the top of the stem to the bottom of the die, then document that measurement as zero. Then I adjust the seating stem up or down to the desired distance jammed or off the lands, then document the die measurement for that bullet.

GS

 

[fguffey]

And I make transfers, I transfer the dimension of the chamber to the seating die. I have never encountered a chamber that was not centered by the reamer. When I push a bullet out of the case and into the rifling I always get an imprint that runs completely around the bullet.

I only use cases with bullet hold, I want all the bullet hold I can get.

F. Guffey

 

[Personofinterest99]

Something that happened today is preliminary but sort of supports what gamestalker said about pushing the bullet into the lands. When I first shot this particular rifle, I didn't have a lot of time to get ready. I loaded some Sierra and Nosler bullets and set them to the OAL in one of the reloading manuals that I used. They chambered and cycled okay. Those bullets shot very well, with both grouping a little more than an inch. I thought it would be easier to tighten things up the next time I loaded. So that's what I did, all the measurements and loading as described in my earlier post. And given some of the land marks on my bullets even after adjusting things a bit lower based on the OAL gauge measurements, I went ahead and seated the bullets quite a bit lower. Went to the range today. Really poor results compared to the "long" bullets last week. So maybe this particular rifle, and the bullets I'm loading, like to have a very tight connection. The same Sierra HPBTs that shot 1.25 inch last week shot 2+ this afternoon. Only real differences: I took extra time to do every step of the reloading process on the latest batch to exacting details, AND I seated them a lot deeper. So the seating seems to be the only factor that changed in a meaningful way. Back to the range next week with "longer" bullets. I'll watch for signs of possible pressure spikes. But interestingly my fired brass from last week, although I didn't look at it real close, had no flat primers, stretched pockets, etc. So probably no pressure spikes.

Thanks for all the info.

 

[gamestalker]

And I'm also a fan of transfer, but identifying the marks on the bullet have always been an issue for me. I don't know if the chambers I've loaded for are just so smooth at the lands that they don't leave a good identifiable mark, or what, but it just doesn't consistently work for me. I've tried smoking the bullet, using a sharpie, and just about anything that would leave a mark, but it's never been consistent enough to suit my need for positive identification of first contact. Where as hand chambering has always told me when I'm touching the lands, and has yet to fail for me. And once I'm sure I'm touching, I always follow up by closing the bolt on one to confirm I'm not reading things incorrectly, or too long as it were.

And all B.S. aside, no fish stories here, I have attained 1/2 groups with bone stock production rifles time and time again, with standard grade hunting bullets, not expensive match grade or BR quality projectiles. I do jowever do some dIY tuning jobs, trigger adjustment, floating the barrels, bedding the actions, hand lapping the lugs and barrels, good glass and hardware. But other than that, bone stock production rifles.

I some how think that Fguffey might think I use decreased neck tension when I'm landing the bullet, I don't, I seat the bullet in a fully resized neck, thus I want full neck tension, other wise I could get a false result due to the bullet getting pulled up when the cartridge is removed from the chamber.

As for what produces best accuracy, I'm only relating what works for me, which with just about every rifle, Weatherby being a definite exception, jamming has always been a major winner.

Regarding high pressure spikes, I have yet to experience the long rumored high pressure spikes when jamming. But I also think that using slow burning powders is key. Those who I know that have had some pressure issues were using faster burning powders, which in my opinion peak too quickly to correlate with the slight delay as the bullet engraves. Speer's older books made mention of this fact, in that seating as close to the lands often produces better accuracy, that is what initiated things for me. I've also noticed that Speer's tables, even some newer data, seems to range from starting charges to max with longer tables, and with significantly higher max charges than other publishers, as if to accommodate both those who prefer the running start, and those who jam.

And something else I think to be key in this respect. is to make sure that when jamming, that the chosen starting charge isn't too light, as that too could cause pressure to build to slowly, to get the bullet engraving quick enough, which IMO could result in a pressure spike due to pressures peaking prior to the bullet getting started. So there's a balance, an art to it, but I feel it leans toward making sure one starts off using enough slow burning powder, rather than too little IMO and experience. But every rifle is different, and each demands a proper development approach in order to identify what works best for that rifle.

GS

 

[Bart B.]

I don't think any human can accurately resolve a 5,000 to 10,000 psi or cup pressure spike between round A's bullet being .020" off the lands to round B with its bullet jammed into the lands by visual inspection of the cases and/or their primers. Having shot several hundred 7.62 NATO proof loads at 67,500 cup with a 172-gr. bullet and normal 7.62 service loads at 52,000 cup with a 149-gr. bullet, both with the same case, powder charge and primer, several people seeing both fired cases types all though the pressure in both were equal for all practical purposes.

If a 30 caliber bullet needs 50 pounds of force to push it out of the case neck, how many pounds per square inch of pressure inside the case is needed to do that?

 

[fguffey]

I some how think that Fguffey might think I use decreased neck tension when I'm landing the bullet

I do not know what methods and or techniques you use. I choose to use all the bullet hold I can get. Then there is that other part, that would be the part where I explain 'why'. Also, I try to explain why I do not use other methods and or techniques. After determining the distance from the lands to the bolt face I do not want the bullet to move because I am going to use the transfer to adjust the seating die to zero off the lands.

No Sinclair tool, no Hornady tool, no spacer from Low's, Ace Hardware or Home Depot. Basically I am using an understanding of the concept 'ZERO'. Then there are of those variations? When 'measuring from' I use a sharp edge, I know, the radius is user friendly.

You should not worry about what I think, it is OK to ask.

F. Guffey

 

[fguffey]

If a 30 caliber bullet needs 50 pounds of force to push it out of the case neck, how many pounds per square inch of pressure inside the case is needed to do that?
__________________

Do you have R. Lee's book on modern reloading? He has a section covering crimping. There are factors, he does not include the .7854 factor.

F. Guffey

I don't think any human can accurately resolve a 5,000 to 10,000 psi or cup pressure spike between round A's bullet being .020" off the lands to round B with its bullet jammed into the lands by visual inspection of the cases and/or their primers. Having shot several hundred 7.62 NATO proof loads at 67,500 cup with a 172-gr. bullet and normal 7.62 service loads at 52,000 cup with a 149-gr. bullet, both with the same case, powder charge and primer, several people seeing both fired cases types all though the pressure in both were equal for all practical purposes.

Then there is that part where reloaders have to be convinced measuring the diameter of the case head before and again after firing can be done. Normal case head expansion would be considered .00025" for factory loaded ammo. A case head expansion of .001" for the first firing would be considered excessive.

F. Guffey

 

[Jim Watson]

Are you a slow fire target shooter going from ammo box to chamber and back to box?
Then you can frotz around with short jump - contact - jam on bullet seating.
But if you are hunting or otherwise need the magazine, you will likely be well off the lands with magazine length cartridges.

 

[spitballer]

Anything other than a fire-formed case for that particular chamber may not give an accurate reading when it's pushed forward. I always load about .010" over for my long gun and let the lands seat the bullets, keeping the neck fairly loose so they have consistent tension when they're chambered, but I use soft bullets and a slow powder. Fast powder and hard bullets (esp monolithic) may require seating off the lands, and for that I still use the old-fashioned method of chambering an empty case with a bullet and measuring with a caliper. You'll still need to use a fire formed case, though.

 

[merrill]

If 50lbs of force is required to push a .308 diameter bullet out of the neck of the case, then the pressure required would be in the neighborhood of 672 to 675lbs/in. squared

 

[gamestalker]

Spitballer, I've been hearing for almost my entire reloading life that production rifle magazines, won't accommodate landed or jammed cartridge lengths. But honestly, I've yet to encounter a rifle that the magazine limits how long I seat them?

That said, my hunting cartridges are the same landed / jammed oal, as what I shoot at the range, and they always fit and feed just fine. And also interesting, a lot of the chambers I load for are too short to accommodate published oal's.

Maybe I've just been lucky, in that, the last few dozen rifles I've loaded for have short throats.

GS

 

[Walkalong]

But honestly, I've yet to encounter a rifle that the magazine limits how long I seat them?

Your a lucky man.

 

[sage5907]

I have five 30-06 rifles with a magazine box length of 3.400. The OAL cartridge for the longest throated rifle that I have touches the lands at a length slightly longer than 3.300. I can reduce the OAL length from 3.300 to 3.280 and shoot the bullets in all of the rifles without touching the lands in any one of the rifles. I have older pre 64 Winchester rifles and the tolerances for these rifles may have been tighter than in some of the newer rifles. This supports what gamestalker says about being able to seat to the lands and never having a round that won't feed through the magazine box. This was using Berger Classic 168 grain bullets.

 

[spitballer]

GS the only time I've ever had a .224 bullet that was too long to fit in the magazine was 64gr Berger, and even those I managed to get two of them in on top of the follower. That was the original 700 ADL Varmint barrel. My current barrel has a little less freebore than the original and I'm actually able to load 40gr boattails into the lands, but I stick with the Nosler 55gr BT's for consistency.

I've long since converted to a single-shot so OAL is a non-issue

 

[Personofinterest99]

With regard to jamming bullets, I loaded for a friend of mine who shoots a Model 70 in 300 WM. I used his once fired factory brass and set the OAL where he wanted it: Max length to fit in the mag AND be firmly seated on the lands. I seem to recall he gave me Nosler 180gr BTs and RE 22 to use. Hand loading went fine. Neck tension was firm. Bullet to neck contact length was adequate. Then he cycled the first bullet through his rifle. The brass ejected, the bullet remained seated in the barrel, and powder went everywhere. After that I reseated all of his bullets quite a bit lower. Didn't want to chance anything on an elk hunt. I'm fine with slightly bumping into the lands but I stop at that.