Big bore load development process

[nksmfamjp]

What are we planning to hunt with the Lott?

Cape buffalo have a heart that's about 12" in diameter. As long as you can group your Lott at 3-4 MOA, you're golden.

For ele, you're shooting maybe 40-50 yards max. Never been after ele, but sure looks like a lot of shots are 25-30 yards. Even 10 MOA at that distance turns into a 2.5-3" group.

Paper for now.....buffalo some day...

 

[sgt_zim]

to keep your practice inexpensive, or at least less expensive, check out Beartooth Bullets dot com (they have a chat board there, so I can't directly link here).

I shoot 525 gr lead alloy out of my 45-70 at about 1625 fps. You don't need published loads - any 525 gr jacketed bullet with a published load for your Lott will be safe with BTB 525 gr Piledrivers. The 525s are gas-checked, so you can push them pretty hard without having to worry about obturating the base. Counting shipping, those bullets run about 58 cents each. They also make 425 gr with the same nose profile as the 525.

 

[nksmfamjp]

Also Speer makes some reasonably priced 400gr bullets for practice.

 

[Forrest Halley]

Paper? Shoot steel with it and behold the energy transfer! I like to shoot my .375 at my swinger...it's quite activated by it.

 

[tarbe]

Also Speer makes some reasonably priced 400gr bullets for practice.

Yes, they do! And if you shop around you can get them for under 35 cents each.

 

[nksmfamjp]

Just asking....why not h4895? I think the issue is the anemic data from Hornady!

I found 2224 FPS at 79.0gr of h4895 with minimal pressure signs. I think I’ll stick there until I can try it in warmer weather.

 

[fourfive8]

Yes! Good appropriate powder and you're in a good place at 2224! Try the hot weather test with the chronograph by letting the ammo and rifle get reasonably warm to hot in the sun and if no pressure signs you'll be golden if the accuracy is good.

 

[nksmfamjp]

Will a big bore straight wall ever show bolt lift? I have a model 70.....with the safety on, bolt lift is near zero. With a new, sized case, it has zero bolt lift. With 79gr of h4895 and 500gr bullets, it still has no bolt lift.....

 

[fourfive8]

Oh yes. And every gun is different. It may not be a gradual thing either and you may have to exceed max working pressure by quite a bit before it shows. But you'll know it when it happens. Several things are indictors of too much pressure. Without pressure testing equipment, which few of us have, one of the best is excess case head expansion were the head does not shrink back after peak pressure. Unfortunately it is one of the most difficult to measure correctly. So that leaves such indicators as primer flattening and bolt lift as the most commonly used. Once you get into the zone of acceptable velocity where you are nearing your predetermined "target" velocity, it is time to go very slow and not make large increases in charge weights... if any at all. I'd say you are very close to being in that velocity target zone right now with the 500 gr bullet. After all, pushing up against the ragged edge of too much pressure just to gain an extra 50-75 fps has very little upside and a lot of downside potential when it comes to a DG load that will be used in the field. I'll go with the conservative, near 100% reliable type conservative load every time!

 

[nksmfamjp]

I’d still like to find max so I can avoid it as a choice.

 

[fourfive8]

Exactly, but finding it in a controlled way and correctly calling it max is the secret. Kinda of a moving target with every nuance of differences in ammo components, rifle specs and conditions all playing a role. Probably best you can do is to carefully nudge up to it, recognize the signs you are close then back off a little to allow for all the variables that can enter the equation. I don't know if that is the best method but until someone convince me otherwise, I'll continue to do it that way for working up my hunting loads.

Nudge carefully up to max pressure, recognize the signs, test in hot conditions, use a chronograph as an objective measuring tool, back off a little to account for ANY variable likely encountered- label it as "Hunting Load" in the load log.

 

[Forrest Halley]

Try to find the accurate load above 2200 and end the quest there.

 

[nksmfamjp]

Well, I’m at 84.4 gr of H-4895...2340 fps(22”)...and little to no bolt lift feeling. I would NOT call this load safe. It is above all data I can find for 458 Lott.

I really can’t put anymore powder in the case. This load pushes the bullet back out pretty hard.

I measured cases with a micrometer and will check them again. I’ll post expansion numbers, but 2340fps is really more rifle than I need.

 

[fourfive8]

Yes, I'd say you are there at 2340! so back off a little maybe to 2250 and do a high temp test when available.

 

[nksmfamjp]

Well, got the micrometer out. I’m getting 0.005” case head expansion at 2340.....that is a no go for me. Probably scrap that brass.

I’m backing off to 2291fps and 0.0031” case head expansion....still seems high to me. I might even go down a couple from there.....btw, this is all with minimal pressure signs.

I wonder if this is just the wrong powder??

I wonder if I should try something faster like H332??

Does anybody have any factory 458 Lott that they can measure case head, or belt diameter on?

 

[Forrest Halley]

Well, got the micrometer out. I’m getting 0.005” case head expansion at 2340.....that is a no go for me. Probably scrap that brass.

I’m backing off to 2291fps and 0.0031” case head expansion....still seems high to me. I might even go down a couple from there.....btw, this is all with minimal pressure signs.

I wonder if this is just the wrong powder??

I wonder if I should try something faster like H332??

Does anybody have any factory 458 Lott that they can measure case head, or belt diameter on?

I measured just before the belt and found the following:
Once fired Nosler: 0.511- 0.512"
Loaded New Nosler: 0.508-0.509"
So I'm getting .003 expansion on first firing.
Maybe that guy will stop charging an arm and a leg for that collet die and you could save the brass...

 

[nksmfamjp]

Well, that gives me a data point....thanks

 

[nksmfamjp]

Maybe that guy will stop charging an arm and a leg for that collet die and you could save the brass...

why would I need that? The cases rechamber fine. Also, that die won’t fix head thinning ahead of the belt.

 

[bruce moulds]

just before the belt is not case head expansion.
this is measured on the belt.
you will often get quite big expansion on first firing a new belted case, then none on subsequent loads.
a thing you have to come to grips with when loading belted.
bruce.

 

[fourfive8]

I've found that about .002-.003" expansion at the belt, comparing new brass to once fired brass at full pressure, is fairly normal. From then on that expansion usually stabilizes to a very slow, shot to shot increase over several shots- likely causing no issues for the life of the brass. If it is much more than that, maybe in the .006-.008" range expansion after the first shot, I would think pressure is way too high. The less likely possibility for a large first shot expansion at the belt would be that you have a maximum dimensioned chamber and started with minimum dimensioned brass that also could be a bit soft.

A different but related area of concern is just in front of the belt, a zone regular dies can't fully resize. That area will expand and not spring back enough for completely friction free chambering after some number of full pressure firings. If you are not feeling ANY friction in chambering after a couple of reloadings, sooner or later you will and a regular sizing die may not address it. Then the only die that will resize that area enough for friction free chambering will be a collet die. A collet sizing die may extend the useful life of belted cases by two or a few more loadings, hard to say exactly. But sooner or later their safe and reliable life span will be reached and it would be time to pitch them.