OAL or ogive to lands?

[ovenpaa]

QL is QuickLoad - software for computing internal ballistics, I use it mostly for start point load development with wildcat cartridges and find it very handy. It does not make up for range time but it sure does get me close.

[ColinR]

[/quote]
I think I need to spend some real time assessing the measurements and options because I think the 7.62 barrel (Walther I believe) has a long throat presumably to accommodate the dimensions of variable military cartridges with different weight bullets with different ogive position. I will take some measurements with different bullet types (155 Sierra and 170 Lock Base) and see where that takes me. Thanks for the input.[/quote]

Incidentally this barrel has only had about 500 rounds through it, so I do not expect that this throat dimension has anything to do with erosion

[ColinR]

QL is QuickLoad - software for computing internal ballistics, I use it mostly for start point load development with wildcat cartridges and find it very handy. It does not make up for range time but it sure does get me close.

Thanks. Does QL specifically list Hornady .338 HPBT for .338 Lap Mag? Hornady did give me some load data but for some weird and wonderful powders that I have rarely seen on sale, such as Retumbo. I'd certainly like to find a starting load for these bullets with Vit N560 or N165 as dimensioally they seem too good to be true. I'll get back to you with a provisional OAL with this bullet seated 20 thou off the lands which seems a good starting point; sometime tomorrow if thats OK. Thanks again, Colin

[ovenpaa]

QL lists it as .338, 285, Hornady BTHP 3339

Interesting you have a Walther barrel, both my 7,62x51 AI's have Border barrels fitted. Add the details to the post or PM me and I can give you a list of loads up to and including maximum for both the N160 and N560, if nothing else they are a good indicator of where to start.

[DaveT]

While on the subject of manufacturing accuracy I bought some Hornady 285 grain .338 HPBT AMP bullets the other day. I cannot believe the accuracy of these bullets in terms of dimension and weight. The ogives are accurate to less than 0001" and they have a BC up in the .700's. I have never seen bullets with such consistency and can't wait to try them. Only problem is I tend to use only Vit powder, either N165 or N560 for .338 LM, and can't find any load details for this combination.

QL suggests a maximum load of 82.5 grains of N560 with standard build dimensions, if you can give me your OAL to the meplat, case capacity and barrel length I can give a more accurate figure.

Regarding your original question measuring from the Ogive is always going to give more accurate results even with the Lockbase (Great bullets BTW!) The issue with using an OAL gauge and rimless brass is you are referencing from the shoulder to the ogive, not the head to ogive so a very short distance. Fine in principle though as it gives you a measurement in time. Better to measure from the bolt face to the ogive as the bolt face is a constant. I have built a couple of OAL gauges that emulate this but I am yet to come up with the definitive gauge due to the differences between rifle models.

In my opinion there is not an ideal solution on the market right now, certainly not one that takes throat erosion into account and that for me is an important factor.

I try to keep headspace 'tight' (couple of Thou) using the Hornady tool and headspace gauges to check for minimised shoulder bump in between pure neck sizing periods ..... so the Bullet comparator / Ogive method must be as close as you can practically get to a true measure without custom tools?

It can also 'chase' throat erosion if done periodically....within its own accuracy limits.

Magazine length is always a potential limiter to your maximum OAL unless you are prepared to single feed.

[ColinR]

QL lists it as .338, 285, Hornady BTHP 3339

Interesting you have a Walther barrel, both my 7,62x51 AI's have Border barrels fitted. Add the details to the post or PM me and I can give you a list of loads up to and including maximum for both the N160 and N560, if nothing else they are a good indicator of where to start.

That certainly sounds like the one - does QL update often as I understand this is quite a new bullet using Hornady's new AMP (Advanced Manufacturing Process).Sounds like a very useful program, but I am of that age that anything complex in terms of computing just goes right over my head.

I know that AI always used to use Border barrels but I am reliably informed that much of later manufacture uses Walther barrels. Apparently both my 7.62 and .338 have Walther barrels. Both these guns were purchased new during the last 18 months.

[ovenpaa]

Both AI's here are earlier, 2005 and 2007 from memory. I shot a prototype .50BMG last year and that had a Walther barrel, the company that built said they would not use any other barrel out of choice.

The data was from QL3.6, I have 3.3 and 3.0 and the Hornady I am looking at the moment is not on 3.3 so the bullet library must be updated with each revision. I know a few people running QL however it does take some mastering to fine tune it.

[ColinR]

Both AI's here are earlier, 2005 and 2007 from memory. I shot a prototype .50BMG last year and that had a Walther barrel, the company that built said they would not use any other barrel out of choice.

The data was from QL3.6, I have 3.3 and 3.0 and the Hornady I am looking at the moment is not on 3.3 so the bullet library must be updated with each revision. I know a few people running QL however it does take some mastering to fine tune it.

My AI's both shoot better than me, so I have no gripes with these barrels. My first AI .338 went back to AI because of a very rough chamber, they polished it and sent it back but there were other problems with the barrel and chassis being out of alignment, so eventually it was replaced with a new rifle.

Thank you very much for the help with the load data, I'll get back to you.

[ColinR]

Both AI's here are earlier, 2005 and 2007 from memory. I shot a prototype .50BMG last year and that had a Walther barrel, the company that built said they would not use any other barrel out of choice.

The data was from QL3.6, I have 3.3 and 3.0 and the Hornady I am looking at the moment is not on 3.3 so the bullet library must be updated with each revision. I know a few people running QL however it does take some mastering to fine tune it.

I thought I needed an avatar so this gives an idea of the size of the Hornady bullet, left to right, all .338, Hornady 285 HPBT, Lapua 250 Scenar HPBT , Lapua 250 LockBase FMJ. As you can see the Hornady is pretty long so OAL is going to be critical - will not fit AI magazine anyway, but seating depth could present a problem if too deep. I will check how the Hornady OAL stacks up when 20 thou off lands. Too late now so will do tomorrow and let you know.

[ColinR]

Both AI's here are earlier, 2005 and 2007 from memory. I shot a prototype .50BMG last year and that had a Walther barrel, the company that built said they would not use any other barrel out of choice.

The data was from QL3.6, I have 3.3 and 3.0 and the Hornady I am looking at the moment is not on 3.3 so the bullet library must be updated with each revision. I know a few people running QL however it does take some mastering to fine tune it.

I thought I needed an avatar so this gives an idea of the size of the Hornady bullet, left to right, all .338, Hornady 285 HPBT, Lapua 250 Scenar HPBT , Lapua 250 LockBase FMJ. As you can see the Hornady is pretty long so OAL is going to be critical - will not fit AI magazine anyway, but seating depth could present a problem if too deep. I will check how the Hornady OAL stacks up when 20 thou off lands. Too late now so will do tomorrow and let you know.

Hello again, Right the measurements are as follows using the Hornady tools to measure to lands and ogive position - from base of cartridge to tip of bullet = 3.705" - from base of cartridge to ogive is 2.959". These are for the ogive touching the lands, so no deduction has been factored in for stand off but as a starting point maybe .020" can be deducted from both values.

The OAL of the Hornady loaded round is 3.705" compared with 3.680" for a Sierra 250 HPBT, 3.681" for Lapua Scenar 250 HPBT and 3.602" for a Lapua 250 Lock Base. Only the latter will fit the AI magazine. Not having specific load data to check the case powder level experience suggests the Hornady may be, or be close to being, a compressed load at anything much over 80 grains due to the depth of seating. Thanks again for your help.