Talk:.300 Lapua Magnum

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[edit] Ballistic performance and test barrel length

Due to this cartridge very large case capacity in relation to its bore size a 24 in (609.6 mm) long barrel as used in the “info box - ballistic performance” section gives not the most realistic examples of the .300 Lapua Magnum or its ballistic twins ballistic potential, though the stated performance figures in this article are very credible. Barrels that are too short in relation to the employed cartridge will produce sub standard muzzle velocities, unnecessary recoil and lots of muzzle flash, smoke and report. The main cause for these effects is unburned propellant. The Lapua/VihtaVuori reloading guide 2006 states some (conservative) loads obtained with a 690 mm (27.165 in) long test barrel. This test barrel length is still relatively short for a .300 Lapua Magnum chambered rifle. Custom made rifles for these kind of super magnum cartridges generally sport 762 mm (30 in) or longer barrels to take advantage of the ballistic potential of these overbore cartridges. Francis Flinch 13:03, 3 September 2007 (UTC)

If you have a source with longer barrel lengths please feel free to update the ballistics to use that instead. None of my reloading manuals had this cartridge so I had to resort to AccuLoad. While it's some great software, I'd still prefer to use a loading manual or factory ballistics as a reference whenever possible. So have at it, it'll make it a better article. Arthurrh 17:57, 7 September 2007 (UTC)
The Italian website Reloading data for the .300 Lapua Magnum cartridge mentions several loads out of a 690 mm (27.165 in) long test barrel. These loads where copied out of the Lapua/VihtaVuori reloading guide 2002 (no longer online). The loads in these guides do vary a bit through the years. This probably has to do with variations between VihtaVuori propellant batches and maybe even legal stuff. The rather unusual test barrel length makes me suspect a Sako TRG-42 based test rifle chambered for this “CIP datasheet” cartridge was used.
Since I also do not have many sources to (re)check loads for this rare cartridge I checked it with the QuickLOAD ballistic software suite. QuickLOAD deemed the loads from the reloading guide as very fast and pressures as very low. I had to use significantly more powder in the virtual QuickLOAD world to replicate the muzzle velocities from the guide at computer predicted maximum piezo pressures around 400 to 430 MPa. QuickLOAD even deemed some loads from the guide as irresponsibly low in the cartridge filling ratio department. I also checked your 24 in barrel length AccuLoad predictions with QuickLOAD. The calculated muzzle velocities from the 2 programs were very similar. A possible guide could be the fact that the .300 Lapua Magnum and its ballistic sister cartridges must perform rather similar, since they are all overbore designs which makes them inefficient internal ballistic designs. When I did check the Wikipedia loads for the .30-378 Wby. Mag and .300 RUM and compared them to QuickLOAD predictions for the .300 Lap. Mag. I could get very close to them at around 430 MPa pressure.
It is dangerous not to properly fill up rifle cartridge cases with propellant. A (counterintuitive) catastrophic detonation instead of a controlled powder burn can occur when too much space in rifle cartridge cases is left empty! Francis Flinch 20:24, 7 September 2007 (UTC)

So I'd recommend we stick with the existing data until we can find another reliable source. Arthurrh 20:36, 7 September 2007 (UTC)

I found a reload guide online that uses a 27" barrel length. But I had to calculate the energy myself. Some my cite WP:OR, but it's just math. Math isn't subjective. Is this better than before? —Thernlund (Talk | Contribs) 21:29, 7 September 2007 (UTC)

You found an imperial version of the VihtaVuori reloading guide 2002 online. I have this guide in its metric version. The problem still remains that the loads in the VihtaVuori reloading guides 2002, 2004 and 2006 do not match up well with the AccuLoad and/or QuickLOAD predictions. If all data is entered correctly in such programs the predictions are normally expected to be remarkably close to reality. Since The .300 Lap. Mag. lies case capacity wise between the .300 RUM and .30-378 Wby. Mag. its performance has to in between those cartridges everything else being equal. I concur with Arthurrh to stick to his AccuLoad data. Maybe he will be so kind to recalculate those loads with a somewhat longer barrel. Chambering overbore cartridges in short barrelled rifles might be fashionable and commercially attractive, but they need long barrels to convert copious amounts of propellant into muzzle velocity. Francis Flinch 07:57, 8 September 2007 (UTC)

If others agree that the AccuLoad data is likely the most reliable, and we find determine some choice that we believe is a barrel length reasonably likely to be in normal use, I can easily rework the load data. I really don't know what length would be in "normal" use. To use a longer barrel simply because it would be a better choice is not a good decision, IMO. It would mean that we should go through other cartridges and do the same to them. I'd prefer to go with a barrel length that one is likely to find in a .300 Lapua rifle. Maybe the 27" is the choice since that's whay Lapua used in their loading guide. I can also look at the predicted pressure to see what comes out. Arthurrh 08:29, 8 September 2007 (UTC)
Sure. Good by me. —Thernlund (Talk | Contribs) 12:22, 8 September 2007 (UTC)
I can also live with Lapua’s 27" as example barrel length. By the way, CIP rules 65,000 psi (448.16 MPa) Pmax for the .300 RUM and 63,816 psi (440 MPa) Pmax for the .30-378 Wby. Mag. Francis Flinch 12:55, 8 September 2007 (UTC)
I'm not sure what the source is for the CIP data. I used the AccuLoad pressure limit that they got from Lapua of 60,900 PSI. Anyway, most of the loads were with Accurate 8700 and stayed well below the limit, typically no more than 55,000 PSI. Barrel length of 27". Numbers are in the article. Arthurrh 08:05, 9 September 2007 (UTC)
The CIP data is CIP’s own data and verified with the QuickLOAD database (which is German software that can be set to English and imperial values if the software user wishes so). CIP rules 65,000 psi (448.16 MPa) Pmax for the .300 RUM and other RUM’s and 63,816 psi (440 MPa) Pmax for the .30-378 Wby. Mag. and other x-378 Wby. Mag’s. For the .300 Lap. Mag. CIP and QuickLOAD rule a rather stellar 470 MPa (68167 psi) and for its parent case the .338 Lap. Mag. “only” 420 MPa (60915 psi). This is a remarkable difference for what is essentially the same cartridge case family. The German guntool maker Triebel (Triebel has a good professional reputation) rates the .338 Lap. Mag. at the same very high Pmax level as the .300 Lap. Mag. QuickLOAD deemed your examples comftabley under 470 MPa and advised Norma MRP 2 propellent for the lighter bullets and ADI AR 2218 propellant for the heavier bullets.
The Lap. Mag. and 8 x 68 S offer the sturdiest brass I am aware of to be found in European cartridge designs. .338 Lap. Mag. and 8 x 68 S rifles are sometimes voluntary professionally proofed at CIP Pmax + 50%. For the .338 Lap. Mag. that means 630 MPa / 91373 psi and for the 8 x 68 S that means 660 MPa / 95725 psi. These 150% proof tests result normally in a pass mark. Since these cases can tolerate ludicrously high pressure levels Lap. Mag. and 8 x 68 S based wildcats (CIP does not rule wildcats) are reloaded up to 500 MPa / 72519 psi. Francis Flinch 10:52, 9 September 2007 (UTC)

[edit] Pressure sources

Ok, well my concern is that we have an increasing number of articles that are relying on CIP data but don't give a source for it. This is problematic for WP:VER. I can't validate the CIP data at all, and other readers will have the same problem. Does anyone know of a reference we can use for these CIP numbers? Arthurrh 19:30, 9 September 2007 (UTC)

I tried to find some non copyrighted information on CIP pressures. You can look at Cartridge Pressure Standards to find information on CIP Pmax levels that might help somewhat. CIP does however rule more cartridges then you can find there and I did only a few random checks on the table. I also added some new information at the Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives article that points out that SAAMI and CIP do measure piezo pressures differently which also results in different results. The source text is rather puzzling in the positioning of 40 mm+ length cases. I assume that the text has gotten garbled and the CIP measurement of all 30 mm+ cases is measured at the 25 mm point mentioned in the source text. Francis Flinch 18:41, 10 September 2007 (UTC)

I don't mind buying a book from Europe that lists CIP if you can recommend one. It would make a nice addition to my collection and fill a missing gap for me. I'm somewhat concerned about using kwk.us as a source, since it's not clear how accurate it is. Arthurrh 18:51, 10 September 2007 (UTC)

If you are a native English speaker I would advise to contact the Birmingham Gun Barrel Proof House (England is a CIP member state). I guess they can help you and have a CIP CD (CD-ROM?) for GBP 55 mentioned in their price list. Francis Flinch 19:55, 10 September 2007 (UTC)

Nice. I left an email for them to see how to arrange a US purchase. Thanks. Arthurrh 20:05, 10 September 2007 (UTC)