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VarmLR

6.5 Creedmoor; Lapua case capacity & life

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Just for interest, and many of you are probably aware of Lapua's reduced case capacity:

This cal is listed as having a case capacity of 52.5gr H20.  I thought I'd check case capacities from once fired and FL resized, and 2F and F-L sized Lapua SR creedmoor brass..  I had some Hornady LR brass which was bang on 52.5 (1F) so I thought I'd measure the Lapua and the result was that it has a reduced (average) capacity of just 50.5gr H20 with a variance of +/- 0.1gr either side for the 10 samples measured.

I don't know what others are finding, but perhaps this explains why I'm getting compressed loads quicker than QL predicted although this doesn't seem to have unduly raised pressures judging by velocities and case condition.  

2 full grains less capacity must limit potential velocities compared to other brass makes, but the lower volume also means thicker brass, since outside dimensions will be the same for whatever brass is used.  This should hopefully prove positive for case life.   Testing by the "6.5 Guys" as noted over on Accurate Shooter, achieved 20 firings using quite a stiff load of H4350 under 140 bullets without any split necks or other signs of damage and with no annealing:

 

 

 

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Funny you should say that VarmLR, i picked out ten random ones last night with the intention of checking the case capacity, i will check new, then twice fired to see what the difference is. I see that you have a Tac A1 in 6.5CM how are you finding it, i have got one as well, just trying to develop a load for it so i am still in the experimenting stage.

 

Kevgun

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That's interesting, I will have to check mine now, I use resized Remington 22-250

so I expect them to be less, as the neck is slightly shorter, by a couple of thou.

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20 minutes ago, Kevgun said:

Funny you should say that VarmLR, i picked out ten random ones last night with the intention of checking the case capacity, i will check new, then twice fired to see what the difference is. I see that you have a Tac A1 in 6.5CM how are you finding it, i have got one as well, just trying to develop a load for it so i am still in the experimenting stage.

 

Kevgun

The Tac A1 is a fabulous rifle.  The only annoyance I've found is that it's a little too easy to short stroke and not load rounds properly but other than that it shoots like you'd expect any T3 to.  I'm now averaging sub third inch groups with a load so far developed.  It shoots the 139 Lapua Scenar very well (what rifle doesn't like those?) and the Hornady SSTs not quite as well, but still well sub moa.  I've pretty much settled on those two bullets to do everything I need out of the rifle.  It's still just about light enough (unlike the Sabatti) to take across the fields with me when on long range corvid control work and after the odd fox or muntjac, and is perfect as a range gun for long range work.  The 24 inch tube combined with the 139 Scenar is easily enough to load for 1200 yards or more.  Couldn't ask for any more out of a rifle.  It's very well put together too.

One thing to be aware of (and GMK are aware) is that Tikka, in their wisdom, chose not to undercut the muzzle thread so GMK have offered some washers which were purpose stamped for the job, FOC to any CTR/TAC A1 owners wishing to use "right for cal" mods to avoid any misalignment issues.  You need four of them.  Just request them off your dealer and they get them from GMK.  I had mine properly undercut in the end as I don't like bodges.

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19 minutes ago, treetop said:

That's interesting, I will have to check mine now, I use resized Remington 22-250

so I expect them to be less, as the neck is slightly shorter, by a couple of thou.

Yes, you could well see closer to the Hornady case capacity with those...be interested to find out once you've done them.

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Hi Varm,

My Lapua brass are 52.80gr H2O, while Federal (I got 20 factory rounds thrown in very cheap with the rifle) are 53.52gr.

Because you're measuring FL sized brass, you're really just making a measurement particular to your dies, and while this makes a comparison across your brass of sorts, the measurement will be relatively meaningless in comparisons with varied brands in various different states. (For instance, QuickLoad stipulates that for all its calculations it requires entry of the H2O volume of your fired cases because it's the only state in which measurements will remain constant across the world's different 6.5 Creedmoor brass and sizing regimes.)

Also worth bearing in mind that "Full" FL sizing is pretty brutal. My Redding FL die, set "correctly" as per its instructions, knocks headspace from a fired state of between 1.540 and 1.542 (depending on load stoutness), right back to 1.533. That's a whole 9 thou of brass working, along with corresponding case volume restriction. (My new Lapua brass headspace measured 1.538, incidently.)

These are the two reasons I bump my brass back to a whisker over 1.539 (an average of around 1.5 thou)... thereby holding brass work to a minimum while maintaining the highest possible capacity along with case & neck uniformity and ease of chambering. In regard to Lapua's smaller capacity relative to other manufacturers brass, then a grain of so less (0.7 in my case) is two thirds of chuff all (as a quick fiddle with QL quickly reveals) and is more than off-set by its proven strength and pressure tolerance.

 

Glad you mentioned the muzzle thread issue. I never had any problems with my Wildcat Predator, however, when I became aware of the issue (through this forum), I dismantled the mod then fitted and tightened only its front portion to the rifle. On careful inspection I did actually notice a tiny gap and I found I could just squeeze a 2 thou feeler gauge between the mod rear and the barrel front face. I guess it never presented a problem as its already slightly rebated thread allowed as close to true alignment as made any difference. Anyway, I simply rebated the mod thread a further millimetre and the job was a good'n. Like you, I didn't much like GMK's Heath Robinson solution.

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So, I did a bit of measuring & had some interesting results.

my 22-250 cases - necked up but NOT fire-formed = 48.34 gr H2o

22-250 cases after fire-forming to my chamber = 53.30 gr H2o

 

 

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44 minutes ago, treetop said:

So, I did a bit of measuring & had some interesting results.

my 22-250 cases - necked up but NOT fire-formed = 48.34 gr H2o

22-250 cases after fire-forming to my chamber = 53.30 gr H2o

 

Sounds pretty good to me... :)

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I measured both fire formed and after FL sizing mactavish.  There simply wasn't the difference there that you suggest.  The FL resized were not anything like as reduced.  I'll measure some new, unfired examples tomorrow and see what they're like but fwiw,   my dies are set only to hold fire formed or FF minus 1 thou on headspace and no more, besides which you fire what you size to so that's the only case capacity that matters.  Isn't the idea of FL sizing to return cases to SAAMI outside dimensions?  Lapua was certainly thicker than the Hornady that I fired and that measured to 52.5, so something, somewhere isn't stacking up here.

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For what it's worth I measured case capacity in 60 Lapua 22-250 brass (large rifle) that I've converted to 6.5 Creedmore. Cases were blown-out using semolina and a small charge of Unique, neck-sized to 6.5mm and twice fired as 6.5 CM in my RPR.

Generally the average water capacity was 52.6 with a range of 52.2 to 52.9. There were two cases below and one above this range which I scrapped

However I mainly did the measurement to establish any relationship between case weight and case capacity. Basically there wasn't any, so to me batching cases based on their weight is a bit of a waste of time.

Triffid

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Perhaps we've just talked past each other, because it seems you're just bumping the shoulders back as opposed to "Full" Length sizing, which as you say, will bring a case back within SAAMI specs (and it appears well within, if die manufacturer setup instructions are followed to the letter).

"...besides which you fire what you size to so that's the only case capacity that matters."

No, not really. Load development really needs repeatable baselines and case volume measurement is an important one (as categorically required by QL for example).

So, given you're essentially bumping back only 1 thou, I can't imagine why your measured case volumes are coming out so relatively low, considering my findings tie very closely with both Treetop's & Trifid's above when our brass is compared like for like (ie fired case volumes). (Incidentally, my Lapua brass fired case volume of 52.8gr was gleaned from an average of 3 fired cases being measured.)

Perhaps it has something to do with your relatively mild loads in such sturdy brass? However, I still don't see that accounting for the large discrepancy between your Lapua results and those of both Trifid and me.

 

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From an internal ballistics perspective, the key factor isn't how a case has been sized, but what its internal capacity or volume is when it has obturated within the chamber under firing pressure.

That is why QuickLOAD says use a fired unsized case from that rifle's chamber  to obtain the case 'overflow water capacity' in order to produce more accurate results compared to the default value. The case expands in the chamber to grip its walls (thank goodness or we'd be in big trouble and/or need bolts built like downsized artillery pieces ) and its internal capacity is then at its maximum. That amount of space plus the volume of freebore ahead of the case that applies when the bullet has moved out of the case-mouth and has been stopped or checked in the rifling gives us and QL's equations the key initial combustion chamber volume, one of the primary metrics affecting peak pressure alongside powder grade / weight and bullet characteristics / weight.

The fireformed and unsized case's capacity isn't quite that of the case in its obturated in-chamber form as the case shrinks slightly once pressure goes (again, thank goodness or we'd never extract it), but is so close as to make no difference. FL sizing can reduce the case overflow water weight reading considerably to produce a false value and reduce QL's accuracy.

What this also means is that there are two factors at play in this issue - 1) the case's capacity as a result of how it has been made, wall and web thickness etc; and 2) the rifle chamber size. There may be a considerable difference in the capacity of a given make of fireformed case taken from a mass produced cheap sporting rifle and that of the same case fired in a custom build whose barrel has been chambered with a reamer made to 'minimum SAAMi / CIP' spec.

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I've just measured a fired but unsized case and it had an internal capacity of 51.3gr, with a new, unfired case being 50.3.  As you say Laurie, it won't be up to the obiturated case internal volume but it still seems low to some other brass out there.  Just an interesting exercise to compare with what I started using (Hornady).

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It is low! Fired in an industry  standard PT&G chamber, I got 52.5gn for what I regarded as the heavy case weight Norma and two batches of early Hornady brass gave 53.4 and 53.7gn, all fireformed.

At 51.3gn, this version of the Creedmoor case isn't offering much more capacity than the 6.5X47mm Lapua whose fireformed brass gave me 48.8gn when I shot that number, an increase of a shade over 5%. As case capacity % change gives an MV % change of capacity variance in % divided by 4, that's only 1.25% or 35 fps improvement on a 2,800 fps load. (That assumes both cartridges are loaded to the same pressure and fired in the same barrel length.)

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4 hours ago, Triffid said:

For what it's worth I measured case capacity in 60 Lapua 22-250 brass (large rifle) that I've converted to 6.5 Creedmore. Cases were blown-out using semolina and a small charge of Unique, neck-sized to 6.5mm and twice fired as 6.5 CM in my RPR.

Generally the average water capacity was 52.6 with a range of 52.2 to 52.9. There were two cases below and one above this range which I scrapped

However I mainly did the measurement to establish any relationship between case weight and case capacity. Basically there wasn't any, so to me batching cases based on their weight is a bit of a waste of time.

Triffid

 

 

Yes, there is much less interest in weight batching brass these days, especially if one of the better makes is used. Some people still do it, but many precision shooters have decided it is a complete waste of time. I still weigh Norma and Lapua brass out of the box, but purely now to identify the very occasional rogue individual that is way outside the curve.

However, I've just bought 100 new PPU 243 Win cases for an upcoming project and a sample of maybe 30-40 cases ranged from 171.3 to 177.0gn a variance of 5.7gn on a median weight of 174.2 or 3.3%. In the days when people religiously weighed and batched brass (properly done after trimming and any other preparation such as neck-turning, uniforming primer pockets etc) the target was everything within 1% or 1.5% tops. Today, people speak of 2% being acceptable if not good ............ but based on what criteria?

Out of interest, I'll see how many of the 100 pieces I can batch within 1.5% (2.6gn) and see if there is any noticeable difference in groups and/or ES and SD in a reasonable quality factory 'varmint' model rifle between the batched and the all-over-the-place weight lots.

ALSO .... some time back, Edgar Bothers pressed a couple of 50-ct bubble packs of prepared ready to use 'Top Brass' cases onto me in 223 and 308. These are recycled military cases, cleaned, resized, trimmed, primer crimp rings removed etc - but goodness knows how many makes and year headstamps. I did explain that using brass like this in my FTR rifles is against my religious beliefs, but Edgars was insistent. So, I'll do a test of them at the same time for an eventual write-up in Target Shooter. I imagine, that they'll work fine for the short distance plinker and even fox or deer shooter.

Here's a Gun Mart review of this brass by Pete Moore to let people see just what I'm blathering about.

https://www.gunmart.net/ammunition/reloading/cases/top-brass-once-fired-cases

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48 minutes ago, Laurie said:

It is low! Fired in an industry  standard PT&G chamber, I got 52.5gn for what I regarded as the heavy case weight Norma and two batches of early Hornady brass gave 53.4 and 53.7gn, all fireformed.

At 51.3gn, this version of the Creedmoor case isn't offering much more capacity than the 6.5X47mm Lapua whose fireformed brass gave me 48.8gn when I shot that number, an increase of a shade over 5%. As case capacity % change gives an MV % change of capacity variance in % divided by 4, that's only 1.25% or 35 fps improvement on a 2,800 fps load. (That assumes both cartridges are loaded to the same pressure and fired in the same barrel length.)

That's the confusing thing.  I filled the case to the top with water until overflowing and wiped the top so the meniscus dipped in the centre a little (ie as full as I could get the case) and then tipped out the water onto a scale.  It could well be that a drop or two remained inside the case, and it would only take a drop or two to make that difference between 52.5 and 51.3.

I'll repeat I think with some other fire formed cases and see what I get, but this batch of brass does seem to be a little on the low side.  I checked my .308 brass and that was on the money (also Lapua).

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As a sanity check, I took a more representative sample of some twice fired cases which had been full length sized prior to firing and the average over quite a number of cases (primers left in) was 51.8gr so still very much on the light side.

 

This makes me wonder if

1) it's taking more than a few firings to get the brass to spec;

2)  the cases in this batch are just a little on the beefy side and;

3)  whether my chamber is a little on the tight side.

I weighed a selection of the empty cases (de-primed) and the average +/- 0.1gr was 156.5gr

I'd be interested what others are getting for case weight as this might be a clue (ie if others are less than this then it could just point to a batch with slightly more wall thickness?) 

 

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1 hour ago, VarmLR said:

That's the confusing thing.  I filled the case to the top with water until overflowing and wiped the top so the meniscus dipped in the centre a little (ie as full as I could get the case) and then tipped out the water onto a scale.  It could well be that a drop or two remained inside the case, and it would only take a drop or two to make that difference between 52.5 and 51.3.

I first weigh the case, then add water until it’s level at the neck, wipe off any droplets on the case and finally weigh the filled case in total to determine the increase. You may first wish to deprime and clean fired cases, but the residual volume of water inside the emptied case could vary somewhat and result in unnecessary fliers if you tip out the water for weighing.

If you need to compare different states such as fired/cleaned, cleaned/various types resized with new cases, I would consider using some type of putty to consistently fill and seal the primer pockets of the deprimed cases before proceeding. 

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Yes, all fair comment Bianchi.  The cases were cleaned but not de-primed nor sized.

Update edit:

One case weighed first then weighed with water left inside case and capacity resulted in 52.1gr.  That's more like it but still a little low.  It would indeed appear that trying to tip water out of each case leaves enough wetting the insides to make accurate weighing impossible.  I didn't weigh more but would expect the average to be in the low to mid 52's which is fine.

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For what it's worth, my Lapua small primer 6.5CM brass capacity is 51.2.

This is an average of 10 twice fired cases (in a Howa chassis rifle).

Using 41.5gr H4350, 140 ELD-M's giving just under 2700fps and tiny groups.

I'm not going to worry about the case capacity :-)

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I'm loading RS62...44gr for 2650fps in once fired (2633fps fresh brass).  Very accurate load.  I took the time to check more cases this evening weighing case plus water then deducting case.  Average turned out to be 52.2gr.

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For reference, interest and what it's worth, I've just cracked a brand new box of Lapua S/R Primer brass and the first one I picked out and weighed was 166.84gr (with a spot of blue-tack up its pocket). With water it was 218.44gr, giving a case volume of 51.60gr. The second out was 167.02gr, going up to 218.46gr, giving 51.44gr.

It's probably fair to say virgin Lapua CM case volume is around 51.5gr of your finest H2Os.

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27 minutes ago, No i deer said:

All this seems a lot of messing about for what....?

 

The main reason we might want to know an accurate figure for case water volume is to help calculate accurate pressure and MV data in load development software like QuickLoad. Also, no reason it should entail too much messing about. At least not beyond taking a few simple measurements.

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+1

Far from "messing about", it's taking the time and trouble to refine our understanding of what we are doing.  No messing about involved.  It's not mandatory to be interested :D

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