Problem with .338 Scenars

[ColinR]

I had a box of .338 Lapua Scenar 250 grain sitting in the cupboard for a couple of years and this afternoon I thought I'd load some to try in my AI .338LM. I measured the COL to the lands with a Hornady gauge (yes I know David at The Shed sells a far better bit of kit but this is what I have on hand at the moment) Anyway the base to meplat measures between 3.584" and 3.594" across a selection of 5 bullets. I reckoned to start 0.020" off the lands so measured the base to ogive and got 2.916" +/-. I set the seater to give me a consistent 2.896" base to ogive and loaded half a dozen cartridges with 83 grains of N165. Measuring the base to meplat of the loaded cartridges I had +/- 3.567" which seemed to coincide with the COL measurement to the lands (avg. 3.588")

The problem! The Vihtavouri data for the 250 grain Scenar in .338 LM gives a COL of 3.681" which is nearly 0.100" longer than my measurement base to lands and would ram the bullet into the lands. The max load for N165 is 86.6 grains, but seating the bullet nearly 0.100" deeper will obviously have an effect on pressure, so I have stopped loading needing a second or more opinions.

Am I going wrong somewhere I can't see. The base to lands measurement has been made several times and comes in just a few thou variation with different bullets. I even scrubbed out the chamber in case there was any fouling. I am at a loss to understand the difference between my chamber dimensions and presumably the SAAMI dimensions for this cartridge/bullet combination. Help!!

[M99]

Look for another source of data. I use both of those in that combination buyt not at that charge. (But I do seat long as I have TRG)

[zanes]

I'd hope that the designing companies of the calibre (Lapua and AI) and bullets in question would put out load data that is correct and compatible! :P

[ColinR]

Look for another source of data. I use both of those in that combination buyt not at that charge. (But I do seat long as I have TRG)

Hi Mike, I would have thought that the Vihtavouri data would be the most accurate given I am using Lapua brass and Lapua bullets with Vit. N165, which I think all come under the Nammo umbrella. What other data do you suggest in this case? As it stands a cartridge loaded to 3.681" as given in the Vihtavouri data will clearly not fit this chamber which in any case will be manufactured to loose military dimensions. Tomorrow I will make up a dummy cartridge to a COL of 3.681" just to check in reality rather than just measurement; although I can't see how that could change the outcome other than to confirm the measurements. Colin

[ColinR]

Confirmed!! Just made up a dummy cartridge to 3.681" and tried to chamber it - would not go. Bullet was forced into the rifling with some slight deformation and forced back into the case. Resulting COL base to meplat was 3.624". The difference between the gauge measurement and this measurement is probably due to a combination of the bullet being driven into the rifling and possibly being slightly pulled.

However, conclusively proves there is an anomaly in Vihtavouri's data (latest from website) or the chamber of this rifle is not to spec - I suspect the former as no problems with other bullet combinations.

What sort of adjustment in powder percentage should be made for seating 0.114" (0.020" off lands) lower than recommended - a ball park will do as I will now start 10% below max from Vihtavouri data. Will this be a reasonable margin given the revised seating depth?

Has anyone else encountered this problem with Scenars in .338 LM AI rifles?

[Alpha1]

I have encountered this problem before I have rifle chambered in 6.5x55. It will not chamber factory ammunition. Its fitted with a heavy Shilen barrel with a tight chamber. It will only chamber hand loaded ammunition. You just need to work out your cartridge over all length that it will accept and build your ammunition to suit.

[Laurie]

338 LM dimensions are CIP, not SAAMI, but the principle is unchanged. This situation is not at all unusual with the exception of many US mass manufactured sporting and LE rifles in common or garden chamberings such as 308 win where the chamber throating is such that people run 200 and even 215gn Hybrids in the Remy 700 PSS rifles and similar at near optimum bullet seating positions before they reach the lands. In this case, it's all about fear of litigation by some careless handloader who injures himself and overly long freebores reduce pressures and provide a huge safety net to cover the manufacturer's a*se.

It is a very common situation for many cartridges especially where custom rifles are involved. Lapua / CIP say the COAL for 6.5X47 Lapua is 2.800", but if you have a typical X47L built and don't tell the gunsmith you want to run 140s at this ovcerall length you'll find a worse mismatch than you're suffering from as most gunsmiths' reamers are geared to 123gn bullets and COALs of ~2.650". The answer is simply to load ammunition to suit the rifle and work up loads accordingly - that's what starting loads and working up charges in around 1% of max charge weight steps is for. It takes account of that rifle's individualities.

The 0.1" COAL variance in a 250gn Scenar / N165 load in 338LM changes PMax by ~3,000 psi according to QuickLOAD which may or may not be precise depending on factors such as actual as opposed to default fireformed case capacity and barrel internal dimensions. QL shows both COALs as over CIP PMax actually at 86.6gn, but with the longer COAL only marginally. With the shorter COAL that you have to use, your starting load of 83.0gn is computed to produce 56,100 psi PMax compared to the CIP allowed 60,916 psi maximum so you should have 4,800 psi leeway, but in practice might have none at all!

My personal opinion FWIW is that Lapua's recommended starting load of 76.4gn is a little on the low side at over 12% reduction from maximum, dropping 7.5-10% is usually more than enough. (For many, many years Hodgdon only ever quoted maxima and told users to reduce them by 6% to get starting loads with the exception of H110 magnum revolver powder where the recommendation was 3% reduction at most.) Your 4.2% reduction to get to 83gn is too little even if you were loading to the full CIP COAL.

As to whether your chamber is 'out of spec' in some way - that depends on what factory ammunition the rifle was built to handle and what its COALs actually run at which are often very different from the SAAMI or CIP nominals. It may well be the rifle is designed to handle 200 and 250gn factory ammunition all of which is loaded to a considerably shorter COAL than the CIP maximum. There is likely nothing wrong with your rifle and almost certainly nothing wrong with your bullet seating methodology expecially as the 'real world' check of actually seating the bullet at the longer COAL proved it's too long for the chamber.

[ColinR]

Laurie, Thank you for a most informative post. With your caution I will start 10% below the N165 max for this load and increase in 1% increments. As the AI .338lm is fundamentally a military rifle I believe the chamber is reamed for factory 250 grain Lapua Lockbase, which are loaded quite short to fit the magazine and which I normally handload for this rifle.

If this exercise has proven one thing it is not to handload anything relying on manufacturers dimensional data without measuring the chamber dimensions of the specific rifle first. I'm glad to say something I do religiously and which in future I intend to do with more precision by investing in one of The Shed's excellent gauges.

Clearly don't rely on anything when reloading, check and check again and if something does not seem right check again and ask for help if still confused. I realise no matter how long you have been reloading there is always something to learn. I always assumed manufacturers COL dimensions were sacrosanct and to date they have coincided with my own measurements, which can build complacency. However, this has been an example of an accident waiting to happen and unfortunately I know too many reloaders who rarely dimensionally measure a load to their specific rifle.

Again my thanks for providing the background and detail to my own basic findings.