When loading 77 grain smk's or bergers over varget or 4895 to mag length my seating depths are all over the place. I've played around with it for a while and the variation is due to the powder being compressed. I've tried powder drop tubes and played around with different seating dies. Using anything over a minimum load in sierras manual leads to compression of the powder and variation in seating depth. I don't see anyone talking about this being an issue. What am I missing? How much neck tension are folks using to hold the bullet in place? Any other tricks out there to get some consistency?
Mag length 223 77gr seating depth variation
- Thread starter Jon D
- Start date
I'm assuming it's a compressed load? Check searing stem an concentricity. I switched to a Forster seating die which resolved a similar problem. I think other dies will work, bit you may need to chuck up a 77 with some valve grinding compound and polish the seater for better fit. Could be the meplat is hitting before the ogive.
jelenko
Gold $$ Contributor
Just to confirm, what variation in COAL are you seeing? The length of these bullets can vary by at least 10 thousandths within a lot and more from lot to lot.
Generally, that's not an issue as the seating depth that 'counts' is base to ogive - which is usually within a couple thousandths.
Generally, that's not an issue as the seating depth that 'counts' is base to ogive - which is usually within a couple thousandths.
Ned Ludd
Silver $$ Contributor
What brand of brass are you using and what is the average case volume? You could possibly buy yourself a little more case volume by switching to a brand of brass with larger internal capacity/volume. The idea there would be to prevent or minimize the compression issues. For example, I have gone through a lot of Lapua .223 Rem brass in my F-TR rifles, but recently gave Norma brass a try. The average volume for Lapua cases typically is somewhere around 30.7 to 30.8 gr. The Norma brass runs at around 31.3 to 31.4 gr volume, or a little over half a grain larger. I have been very pleased with the Norma brass so far. It requires a bit more effort up front with the flash holes (i.e. to remove "flashing" from the inside around the flash holes) than Lapua, but the precision has been every bit as good in my hands. The caveat to this approach is that using brass with larger capacity will require a little more powder to maintain the same velocity. Because of this, whether you would actually realize greater "effective" case volume by making such a change can only be known with certainty by testing and determining the "new" optimal charge weight in the larger capacity brass.
Another approach would be to use a vibrating device of some sort to settle the powder to a more compact volume. I have heard anecdotally that simply touching a vibrating hand massager to the edge of the loading tray can make the powder settle substantially. If you have a back massager (or similar) laying around, it'd be pretty easy to test whether this would help in your situation.
Jeff Porter
Gold $$ Contributor
Base to ogive variation is more concerning than the OAL variation. As Frank said, ogive to tip on quality HPBT 77’s can vary up to 0.010”. But your 0.008” BTO may be indicative of a cracked seating stem from running compressed loads. Forster micrometer seating stems are the worst about this. They do not warranty any damage from. compressed loads.
What type of seater are you using and how much H4895 are you stuffing I there ?
What type of seater are you using and how much H4895 are you stuffing I there ?
Im using a Redding competition seater. 23.0 to 23.6 is where I have been playing around at. I backed down to 23.0 in hopes of reducing the seating variation. I just had the seating stem out and didn't see any cracks, but I will take it to work and have it dye checked.
I'm really leaning towards neck tension. Right now I have about .002 when comparing outside neck diameter of a resized case to a load case. What are other folks using? How high can I can before damage to the bullet occurs and accuracy falls off?
I'm really leaning towards neck tension. Right now I have about .002 when comparing outside neck diameter of a resized case to a load case. What are other folks using? How high can I can before damage to the bullet occurs and accuracy falls off?
I never had a problem loading 77's on 24.3 Varget at mag length. Try .003 or .004 neck tension.
Elementary, my dear Watson.
.008 variation in cartridge base to bullet ogive is the problem, not overall length. The bullet base to ogive dimension on smk's or bergers rarely varies more than .001.
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Jeff Porter
Gold $$ Contributor
I run 23.4 of H4895 with Lapua 77’s and it is right at the edge of crunch in LC brass.
What overall length are you running and how are you dumping/tamping/vibrating the powder into the case? I get pretty good crunch at 23.4 with berger 77's and Lapua brass. I should check the capacity on some lake city then run it in GRT to see if there are any gains to be made.
I've loaded up a lot of Sierra 77s over the last year, and BTO spreads within 500-ct boxes have been nothing like as large as that. I would have expected that from Sierra some years ago, but my recent experience with MKs and TMKs has been very good - ~0.003" (and I batch them to 1 thou' too on the comparator).
What does vary though is the BTO between cartons, up to 20 thou', so COAL may need adjusting on starting a new lot. Can't speak for standard 100-ct box to box variations.
Sound advice. There is a lot of difference between makes of 223 case. If you're loading a limited capacity model, switching to a roomier one will help considerably.
I've not looked at the relevant webpages for a while, but Redding used to state that its Competition Seater dies must NOT Be used on compressed loads. I certainly screwed up a 223 Rem Comp seater in short order loading 69gn MKs onto compressed charges of Viht powders many years ago. It's the ultra close fit of the small O/D seating stem in the collar. It's so close that when part pulled out upwards, the stem will only slowly and smoothly drop under its own weight. If you load bullets onto heavily compressed loads, it comes under too much pressure and both binds and ultimately distorts. Either way, the die stops working as it should. So check the stem's fit and free movement before anything else.
From Redding's Tech Line & Tips re this die:
https://www.redding-reloading.com/t...168-working-with-your-competition-seating-die
the relevant words being:
To hold the bullet concentrically, the Bullet Alignment Bore and the Seating Stem have been honed and ground to virtually the same diameter as a jacketed bullet. As a result, the seating stem walls are relatively thin and not as inherently robust as the Seating Plug in a standard Seating Die. Though the Stem is heat treated to make it as strong as possible, it will not endure the excess seating pressure of Compressed Charges. This excess seating pressure will crack the Seating Stem which will, in turn, damage the other internal parts of the Die. Please be mindful because replacement parts are costly and NOT covered under Warranty. Please remember that your Competition Seating Die is a precision instrument and should be used and treated as such. A handloader using this Die to compress powder is tantamount to a machinist using a Micrometer as a C-Clamp.
Although, Redding says it will crack the seater stem, that's not what happened to mine, or to some other owners' dies. They either distort or bell-out marginally towards the open end in which case they also no longer fit and move properly.
Otherwise if the die is OK and you're using a roomy case, then it's back to increasing neck tension. (Even so, you might want to consider using another make if you continue to load compressed charges.
I was loading 77SMK to 2.257 COAL in 223. I was checking random samples after seating
for COAL when one measures 1.274, I then start checking other rounds and find others
at 1.270, 1.265 COAL.
The odd thing is that when the few long outliers were measured the CBTO was the same as the
CBTO of all the normal rounds.
for COAL when one measures 1.274, I then start checking other rounds and find others
at 1.270, 1.265 COAL.
The odd thing is that when the few long outliers were measured the CBTO was the same as the
CBTO of all the normal rounds.
Jeff Porter
Gold $$ Contributor
Yes the LC brass is a slight bit roomier than the Lapua. 2.250” is my OAL for L-77’s.
That's not at all unusual. It's a result of bullet neck length variations between the meplat and that point on the ogive that where lands diameter is reached. Or, perhaps given uniform cartridge-head to ogive measurements after seating, between the meplat and the point on the bullet that the seating die stem bears upon.
Answers are to 1) change bullet make to one that's more consistently made; 2) trim bullets; 3) the simple answer - seat all bullets deep enough to stay within a COAL that functions reliably in the magazine. That of course will a) increase bullet jump which may be a problem with some designs, but rarely with the 77s as they're so jump-tolerant, and b) if charge compression is an issue will make the problem worse.
Although bullet ogive position (to use a not necessarily precise shorthand for the point on the shoulder that approximates to lands diameter assuming the comparator is reasonably accurately made) may be consistent whilst COAL isn't, I had an unusual case of linkage some years back when I had an AR rebuilt to 6.8mm Rem SPC. To run it in and get started, I bought a couple of hundred plastic bagged FMJ bullets sold under the UK distributor's 'RELCOM' name, probably Remington-made. Setting up the seater die to produce 20 thou' jump and/or just fit the magazine on a randomly chosen bullet was done as usual and a 50-ct box loaded. I soon found that COALs were all over the place and a significant percentage were over-length for the magazine. Shot single-loaded off a sled, these rounds were fine for barrel run-in and trying a couple of recommended powders, but not much more. 100 yard 5-round groups were 2.5-inches and up to ~4-inches. Checking bullet BTOs on the comparator found a very large measurement range, so cheap bullets or not, they were batched. This transformed COAL consistency and reduced group sizes dramatically to <1.5-inches, under the inch in some. It's the only time I've seen such a link, but as I normally load far more expensive match bullets, I'd certainly never expect to find this degree of variations.
I asked earlier to clarify and got ignored so would assume AR mags as the AICS wouldn’t have issues seating.
If that's the case, all the above advice is a moot point
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