Laser vs A-Tip Velocity?

[Taylorbok]

Curious to hear from others who have shot both.

I have a good load with 390 A-tips and picked up some 375gr Lasers for some testing, Thinking I might be able to make up the BC difference in velocity.
I tried some around the same powder charge I was shooting with the A-tips, they shot well but much to my surprise they were much slower, like 100fps slower using the same charge as 390gr A-tips.

I do know my throat is long for the A-tips so I am going to try seating some out far as I can to see if that makes a difference.

 

[Ledzep]

I can't speak for Lasers because I have no experience with them, but when it comes to monolithics like CX or Barnes what I've seen is that it's often not possible to get the same velocity as a same weight cup&core bullet at the same pressure. Two factors fighting you-- one is density. To get the same weight of bullet with solid copper/alloy construction you have to have more bullet volume, this volume robs case capacity. The 2nd thing is that the engraving forces are usually higher with monolithics because the bullet itself is harder to deform being a solid made of material considerably stronger than lead. There are ways around some of that (bore-rider, driving bands, etc..) but those usually come at a cost either in drag/BC or load length restrictions, etc..

There is definitely room for exceptions, but I think it's safe to say that's generally the case.

 

[Taylorbok]

I can't speak for Lasers because I have no experience with them, but when it comes to monolithics like CX or Barnes what I've seen is that it's often not possible to get the same velocity as a same weight cup&core bullet at the same pressure. Two factors fighting you-- one is density. To get the same weight of bullet with solid copper/alloy construction you have to have more bullet volume, this volume robs case capacity. The 2nd thing is that the engraving forces are usually higher with monolithics because the bullet itself is harder to deform being a solid made of material considerably stronger than lead. There are ways around some of that (bore-rider, driving bands, etc..) but those usually come at a cost either in drag/BC or load length restrictions, etc..

There is definitely room for exceptions, but I think it's safe to say that's generally the case.

I didn't think the engraving would be able to rob that much velocity but I don't know squat.

 

[Ledzep]

Oh yeah. If you lathe turn away the bulk of the bearing surface on a bullet and leave just enough to seal the bore you can easily remove upwards of 15-25% on peak pressure with all else the same (obviously very dependent on a lot of factors). Inertia (mass) is usually a bigger overall player but you can't ignore engraving forces as a contributor to the pressure rise.

You can look through various mfg. box ammo velocities and see the trend, though. In .308, 165 CX Outfitter is 2610fps MV, but 168gr Match is 2700fps.

 

[Sandow the Heretic]

I can't speak for Lasers because I have no experience with them, but when it comes to monolithics like CX or Barnes what I've seen is that it's often not possible to get the same velocity as a same weight cup&core bullet at the same pressure. Two factors fighting you-- one is density. To get the same weight of bullet with solid copper/alloy construction you have to have more bullet volume, this volume robs case capacity. The 2nd thing is that the engraving forces are usually higher with monolithics because the bullet itself is harder to deform being a solid made of material considerably stronger than lead. There are ways around some of that (bore-rider, driving bands, etc..) but those usually come at a cost either in drag/BC or load length restrictions, etc..

There is definitely room for exceptions, but I think it's safe to say that's generally the case.

Monolithics in larger calibers virtually always have lower engraving pressures than jacketed bullets. The length of the full bore diameter in a jacketed bullet is quite large and as you get to .510 you may have 5 times the surface area in an Amax then a monolithic. When you get to designs line bore riders, the amount of case capacity lost to the bullet is usually lower since you just seat the tail and the first .150".

Max safe speeds are also way lower in large jacketed bullets. In a BMG you can run a 750 solid up to 3000 fps with room to go but Amax is usually going to end up at 2650. As you get to smaller bullets, that effect evens out and it doesn't matter either way. Most light gun shooters are using jacketed bullets and most heavy gun shooters are using solids. Both shoot well though and predictability is essentially always more important than velocity.

I have a good load with 390 A-tips and picked up some 375gr Lasers for some testing, Thinking I might be able to make up the BC difference in velocity.
I tried some around the same powder charge I was shooting with the A-tips, they shot well but much to my surprise they were much slower, like 100fps slower using the same charge as 390gr A-tips.

The lower engraving pressure will change how the powder ignites. My guess is that if you went looking for your Max load you'd find that the CE is probably faster but may well need more or a faster powder.

-Alex

 

[Taylorbok]

The lower engraving pressure will change how the powder ignites. My guess is that if you went looking for your Max load you'd find that the CE is probably faster but may well need more or a faster powder.

-Alex

I haven't tried to find pressure with the laser yet but I was surprised to see the lighter bullet have a much lower velocity with the same charge.
Ko2M Canada is coming here so I'll stick with the load that works.
I'll play with the lasers a bit more when I've got time, add more powder, try a faster powder. see what happens.

 

[Taylorbok]

Monolithics in larger calibers virtually always have lower engraving pressures than jacketed bullets. The length of the full bore diameter in a jacketed bullet is quite large and as you get to .510 you may have 5 times the surface area in an Amax then a monolithic. When you get to designs line bore riders, the amount of case capacity lost to the bullet is usually lower since you just seat the tail and the first .150".

If the engraving force is actually less what's the cause of large loss in velocity?
I seated some out another .200 to see if that makes any difference

 

[Bandit320]

Could it be loss of pressure due to a combination of more empty space in the case, lower engraving force, or less friction while pushed through the bore?

 

[Taylorbok]

Could it be loss of pressure due to a combination of more empty space in the case, lower engraving force, or less friction while pushed through the bore?

The way I had them seated I'd say they were maybe taking up slightly more space in the case. If the engraving pressure is less that would mean it should get out of the way faster (I would think anyways)
The only thing I can come up with is it's bleeding a lot of pressure because the band is so far off the rifling

 

[GIXXER2000]

What is your twist rate?? What is you seating depth?
Mine is 1-7.5 twist which is too fast for the 390 A-TIPS
I run 400gr Lazer at 5 thousand off the lands with 130.5 of N570 Giving me 3065 AVGFPS.
I have found you want the seal tight band just out of the case month for best seal.

 

[Taylorbok]

What is your twist rate?? What is you seating depth?
Mine is 1-7.5 twist which is too fast for the 390 A-TIPS
I run 400gr Lazer at 5 thousand off the lands with 130.5 of N570 Giving me 3065 AVGFPS.
I have found you want the seal tight band just out of the case month for best seal.

1:9 twist.

I’m not to sure how far off the lands they were honestly, I put the band near the case mouth but obviously the time it takes to seal is dependant on how far away from the lands it is which is dependant on the chamber so you might have a really short FB for solids and I know I’m throated for A-tips

 

[Geno C.]

If you’re throated for atips. It’s going to be a pretty big jump for lazers. They’re for sure going to be quite a bit faster

 

[GIXXER2000]

The 1-9 is perfect for the 390's just a bit to slow for the Lazer being a solid.

 

[Taylorbok]

If you’re throated for atips. It’s going to be a pretty big jump for lazers. They’re for sure going to be quite a bit faster

You agree the velocity drop is due to pressure loss due to the band being so far from the lands?

The 1-9 is perfect for the 390's just a bit to slow for the Lazer being a solid.

Mmmm, they recommend a 1:10 or faster for the 375gr, or 1” faster if ur going through trans.

 

[GIXXER2000]

Well i shoot 400's sooo

 

[Geno C.]

You agree the velocity drop is due to pressure loss due to the band being so far from the lands?


Mmmm, they recommend a 1:10 or faster for the 375gr, or 1” faster if ur going through trans.

No, the atip has a really long bearing surface

 

[Taylorbok]

Well i shoot 400's sooo

That’s very relevant to the question at hand.

 

[Taylorbok]

No, the atip has a really long bearing surface

I thought you were making a correlation between the jump and the velocity.

 

[Geno C.]

The atips will be slower, all things being equal because they have a long bearing surface. The added jump that you’re going to get using the cutting edge in the atip chamber is only going to add to the increase in speed. That, along with the reduced weight

 

[Taylorbok]

The atips will be slower, all things being equal because they have a long bearing surface. The added jump that you’re going to get using the cutting edge in the atip chamber is only going to add to the increase in speed. That, along with the reduced weight

That’s the exact opposite of what’s happening.

The Lasers are slower

 

[Geno C.]

Recover a bullet. You might have a tight bore

 

[Taylorbok]

Recover a bullet. You might have a tight bore

Any tips on that? Just go fish around near the target?

 

[Geno C.]

Yeah it shoot into some jugs of water

 

[SIDS01]

What's the round count on the barrel? Is the free bore dimension available?

I think decreasing the jump is heading the right direction, but you might not get the results you're after until you actually jam it 5 or 10. The jam is where the most pronounced increase in pressure happens. 10 usually gives enough jam to set the bullet back on chambering a few thou without sticking the bullet if you have to eject a loaded round. Play with a couple dummies before you load up 100 like that.....

STH gave the reply that's the most consistent with my experience. An occasional poster that does deep dives into bullet design named Boatright told me to check my 6 and provided some QL coaching after I posted some irrationally exuberant 33XC results. I'll try to pay it forward here. The QL coaching was run the Start Pressure up until the modeled velocity matches the chronoed velocity. The insights that provided from my earlier data produced a serious step up in my ELR game. You won't win any internet velocity contests with that method though.

The start pressure is a short event, it's not friction down the entire length of the barrel. It's over after the bearing surface is engraved. Velocities increase with increases in start pressure because it starts more of the powder burning sooner. Peak pressure increases pretty much in step with start pressure so that velocity increase isn't free.

It takes more pressure to get a solid to obturate. The Seal Tite Band will only cover so much throat wear and I don't think it was intended to be the only seal. Just the final seal for maximum consistency. That barrel might be in a catch 22 situation. It doesn't build enough pressure to seal because it doesn't seal soon or well enough. A lead core bullet could still expand enough that a seal is generated quickly. I'd check the OAL it takes to touch the lands with the Lazers. If there isn't enough bearing surface left in the neck, test the next faster powder. Don't be too disappointed if it can't be fixed. Throats die really quickly after leaking at peak pressure starts. It'd be a good idea to figure this out or bail with as few shots as possible.

 

[Taylorbok]

What's the round count on the barrel? Is the free bore dimension available?

I think decreasing the jump is heading the right direction, but you might not get the results you're after until you actually jam it 5 or 10. The jam is where the most pronounced increase in pressure happens. 10 usually gives enough jam to set the bullet back on chambering a few thou without sticking the bullet if you have to eject a loaded round. Play with a couple dummies before you load up 100 like that.....

STH gave the reply that's the most consistent with my experience. An occasional poster that does deep dives into bullet design named Boatright told me to check my 6 and provided some QL coaching after I posted some irrationally exuberant 33XC results. I'll try to pay it forward here. The QL coaching was run the Start Pressure up until the modeled velocity matches the chronoed velocity. The insights that provided from my earlier data produced a serious step up in my ELR game. You won't win any internet velocity contests with that method though.

The start pressure is a short event, it's not friction down the entire length of the barrel. It's over after the bearing surface is engraved. Velocities increase with increases in start pressure because it starts more of the powder burning sooner. Peak pressure increases pretty much in step with start pressure so that velocity increase isn't free.

It takes more pressure to get a solid to obturate. The Seal Tite Band will only cover so much throat wear and I don't think it was intended to be the only seal. Just the final seal for maximum consistency. That barrel might be in a catch 22 situation. It doesn't build enough pressure to seal because it doesn't seal soon or well enough. A lead core bullet could still expand enough that a seal is generated quickly. I'd check the OAL it takes to touch the lands with the Lazers. If there isn't enough bearing surface left in the neck, test the next faster powder. Don't be too disappointed if it can't be fixed. Throats die really quickly after leaking at peak pressure starts. It'd be a good idea to figure this out or bail with as few shots as possible.

Barrel has like 80 rounds on it.
.290" FB
I seated some out as far as I could so we'll see where that gets me. I don't think I can get the ring to the lands but this will get me much closer.
I also bumped up the powder to see where I can get to.
I also loaded some with the next faster powder to see what that does. Hopefully I'll get to shoot them tonight and report back.

I've never played with QL.

Thanks for the input

 

[Taylorbok]

The long ones didn’t gain any speed but they sure shoot well. By my math they are still roughly .150 off the lands.
I did bump the charge up until I found pressure and I got them going faster than the A-tips but not as much as I'd have liked.

Faster powder didn’t help, over pressure before I found good velocity.

 

[Taylorbok]

Forgot I have some 400gr lazers also. I’ll have to try them. At this point I suppose there’s a chance I can move them the same speed as the 375gr. I’m not gonna test them now because I don’t wanna throw another wrench in the system lol.
Ko2M Canada is coming up quick

 

[JB.IC]

That’s the exact opposite of what’s happening.

The Lasers are slower

My experience is the same as yours. Farther jumps reduce MV. Here is an example with a 6.5CM. The two jump factors have an average difference of 13.6 FPS with just an 0.08” difference in jump. One is a 0.02” jump and the other is a 0.1” jump. I rarely jump past 0.03” so I cannot reason to test farther jumps than this. This experiment has a 90% power to detect a 3 FPS difference or ~100% to detect a 4 FPS difference.

 

[Taylorbok]

My experience is the same as yours. Farther jumps reduce MV. Here is an example with a 6.5CM. The two jump factors have an average difference of 13.6 FPS with just an 0.08” difference in jump. One is a 0.02” jump and the other is a 0.1” jump. I rarely jump past 0.03” so I cannot reason to test farther jumps than this. This experiment has a 90% power to detect a 3 FPS difference or ~100% to detect a 4 FPS difference.

View attachment 8484267

I can’t find the correlation to seating depth and velocity but I’m still .150 ish off.
I’m able to run more powder with the 375gr and get close to where I’d like to be velocity wise. I tossed some 400’s in to see how those do, hopefully try them tomorrow and see what hapoens

I talked with another buddy and his EnAbelr is slow with the lasers also.

 

[JB.IC]

I can’t find the correlation to seating depth and velocity but I’m still .150 ish off.
I’m able to run more powder with the 375gr and get close to where I’d like to be velocity wise. I tossed some 400’s in to see how those do, hopefully try them tomorrow and see what hapoens

I talked with another buddy and his EnAbelr is slow with the lasers also.

I am pretty sure based off my experience with my three 300NMs, larger cartridges are more robust to changes. Meaning, it takes more of a change to produce a noticeable response.

My EnABELR was slow with the 377 MTACs. I bought them for practice bullets since they were cheaper than the Lazers. I got ~2875 FPS with a 32” barrel. 2950 FPS is where I got pressure signs. I think a few guys were getting in the 2900s with 400gn Berger solids but my memory is fuzzy because I sold that rifle a few years ago.

 

[Geno C.]

The linger jump decreases pressure, and therefore speed. But, the increased jump, decreasing pressure, will allow for more powder before reaching the same pressure, therefore increasing speed. That’s my experience anyway. And the way weatherby worked their stuff way back in the day

 

[Taylorbok]

The linger jump decreases pressure, and therefore speed. But, the increased jump, decreasing pressure, will allow for more powder before reaching the same pressure, therefore increasing speed. That’s my experience anyway. And the way weatherby worked their stuff way back in the day

I can’t help but wonder what the results would be if it had a short throat.

 

[JB.IC]

The linger jump decreases pressure, and therefore speed. But, the increased jump, decreasing pressure, will allow for more powder before reaching the same pressure, therefore increasing speed. That’s my experience anyway. And the way weatherby worked their stuff way back in the day

If I had a pressure measuring device to constrain where the maximum charge would be and a range of representative cartridges I would test this myself. But I have to wonder what kind of increase velocity delta could be achieved. Because if the average across these hypothetical cartridges is like 20-50 FPS difference, I wouldn’t even bother with testing it. If the average difference for say a specific cartridge was say 200 FPS, then maybe it would be a consideration.

If MV average is the only response we care about, then maybe it’s worth it. But we know bullet, barrel, and powder combinations can have a mind of their own. If the dispersion pattern turns out to be horrible at larger jumps required to lower pressure to achieve a higher MV, then it might be all for nothing. The problem is we don’t know until we do all the work.

 

[Taylorbok]

375gr and 400gr Lasers shoot the exact same speed with the same charge weight.
I’m gonna try and bump the charge weight of the 400 a bit and see where I hit pressure. The one load I tried shot very well

 

[JB.IC]

How are you defining pressure since you’ll be using a proxy as an estimate? Different categories of bolt lift resistance?

I was trying to imagine how I would estimate pressure but some of my rifles just do not have the same bolt lift. My AIs for example could be mistaken for heavy bolt lift whereas my TAC Driver action would be more sensitive to bolt lift changes.

 

[Taylorbok]

How are you defining pressure since you’ll be using a proxy as an estimate? Different categories of bolt lift resistance?

I was trying to imagine how I would estimate pressure but some of my rifles just do not have the same bolt lift. My AIs for example could be mistaken for heavy bolt lift whereas my TAC Driver action would be more sensitive to bolt lift changes.

If I'm unsure on the pressure I'll measure near the 200 line to make sure there was no case growth there. I'll also punch the primer and make sure its not mushrooming out, I'll usually accept around .001" as safe, when they get really hot and flat they really mushroom.
I've also completely stripped the bolt and put fired cases back in the chamber, I've found acceptable pressure loads the bolt will drop closed, once you get to hot there will be resistance.

With this action I've found the bolt lift (clicker) shows up just before any other major pressure signs so I've started mainly relying on that.

 

[SIDS01]

On the short throat solid/jacketed velocity question, I tested the 285 Flatline against the 285 ELDm in a 33XC years ago. The chamber was set up for solids. The Warner/Hornady comparison was pretty unique because almost all of the length difference showed up ahead of the ogive. The bullet weight, starting case capacity and jam were very similar leaving differences in the starting pressure as the largest determinant of differences in velocity.

Charge Weight, Vel, ELDm, Vel, Flatline
117, 3049, 3026
119, 3100, 3069
121, 3168, 3137
123, 3231, 3202

Not 375, not Lazers, but a really clean comparison between solids and jacketed with a solids freebore.

 

[SIDS01]

On the jump/velocity questions, I read something about longer jumps giving lower velocity spreads in a fleet of PRS guns. I was working on a 7/300PRC set up for 190s at the time. Those results were:

Jump, Avg Vel, ES, SD
10 Jam, 3025, 11, 4.9
25 Jump, 3002, 10, 4.3
50 Jump, 2999, 14, 5.2
75 Jump, 2998, 15, 5.5

5 shot strings, shot in the order presented. The most likely source of noise was the air heating up about 5 degrees during the test.

The assertion was jumps beyond 50 gave better velocity spreads on the whole. I decided that might be the case if you were loading for several PRS rifles but the first cut at it didn't look that promising with relatively overbore cartridges and an individual rifle.

 

[JB.IC]

On the short throat solid/jacketed velocity question, I tested the 285 Flatline against the 285 ELDm in a 33XC years ago. The chamber was set up for solids. The Warner/Hornady comparison was pretty unique because almost all of the length difference showed up ahead of the ogive. The bullet weight, starting case capacity and jam were very similar leaving differences in the starting pressure as the largest determinant of differences in velocity.

Charge Weight, Vel, ELDm, Vel, Flatline
117, 3049, 3026
119, 3100, 3069
121, 3168, 3137
123, 3231, 3202

Not 375, not Lazers, but a really clean comparison between solids and jacketed with a solids freebore.

Are those MV averages or single shot?

 

[Taylorbok]

As I went up in charge the gap widened between the 400 and 375gr Lazers.
I'm going to test at distance between the 390 and 400 next week. The A-tip should be a bit better in the wind but it's not a huge difference.
This is based on 5 shot sample.

Charge wt.	390 A-tip	375 Lazer	400 Lazer
108​	2871​	2791​	2789​
109​	2890​	2802​	2808​
110​	2915​	2882​	2828​
111​		2918​	2842​

​

 

[SIDS01]

Are those MV averages or single shot?

5 shot averages. They weren't great, between 20 and 30 fps on the ES.

 

[JB.IC]

5 shot averages. They weren't great, between 20 and 30 fps on the ES.

Based on those ES, it’s assumed the SD is around 10 FPS. We would see approximate distributions like the figure below. We can see there are some of overlap.

 

[SIDS01]

A bit of trivia is for cartridges with ELR overbore ratios, 100 fps takes about 10,000 psi.
PRS stuff is closer to 150 fps for 10,000 psi.

Another STH gem that's being ignored is jacketed bullets won't take whatever pressure you decide to operate them at. Lapua or boutique brass will operate at higher pressures for multiple reloads than jacketed bullets will give optimum performance at.

After noticing, probably after it happened a few times, that lower pressure fire forming loads were out scoring full house loads beyond 2000 yards, it occurred to me to test lower pressures with seasoned cases. That was after I chased case prep around for awhile. Sure enough, by the time you're shooting at distances far enough for BC variations to matter, beyond a certain pressure you lose more in BC spread than you gain from dropping TOF. It shows up as more vertical.

I've burst my share of bullets and thought anything short of that was OK. It's not.

After that, barrel wear needs to be dealt with. Barrels speed up because the start pressures go up. You can convince yourself on that with case expansion measurements. I prefer the extractor groove of fresh cases. In order to keep the peak pressure in line, the charge weight needs to drop. Even with the same peak pressure, the lower charge weight gives a lower average pressure and the velocity drops. It's not a lot, maybe 30-40 fps over the useful life of the barrel.

If you wait to replace the barrel until the velocity noses over or groups open up, you'll have spent a lot of money on components that never had a chance for scoring at distance. Over the last 4-5 years, the component/barrel cost balance has really shifted towards earlier barrel replacements. Everybody hangs on to their first barrel too long.

 

[SIDS01]

Based on those ES, it’s assumed the SD is around 10 FPS. We would see approximate distributions like the figure below. We can see there are some of overlap.

View attachment 8485701

That's some serious navel gazing.....

 

[SIDS01]

predictability is essentially always more important than velocity.

This is the final bit that's being ignored and it's the most important.

The full error budget includes velocity and BC spread components. The relative importance of each component changes with distance.

At 100 yards, the differences in the individual shot velocities and BCs won't be seen.

By a mile, all 3 have significance at the levels attained with reasonable effort.

At 3000 yards, BC variations start to dominate because they're also significantly affecting the average velocity. This is where the Lazers can be exploited, but only if the velocity spread is also tightly controlled. It's easy to find bullets with better BCs than the Lazers, it's not easy to find bullets that will out score them at 3000 yards. Just buying the box won't do it though. You'll need a chamber that's set up for them. If the freebore is too long, the bore rider section of the bullet isn't used to full effect.



This is what 20 fps ES and 2% on the BC for 10 shots looks like at 3300 yards. 2950 fps with a 0.45 G7, pretty similar to 375 Cheytac with Lazers. With a properly chambered fresh barrel and top notch loading, the BC spread can be 1% and 10 fps on the velocity. The vertical will be a little over half of what's in this video. After the similarities to 375CT ballistics, the next thing I like about this test is the wind is obviously up there but vertical is clearly the larger problem.

With a jacketed bullet freebore, the payoff at distance is a lot less likely to be there.

 

[SIDS01]

Twist rate is another problem.

The internet has latched on to Sg>1.5 is gtg. Maybe for PRS. With smaller bores, high velocities and barrel twists can skate into RPM problems.

With jacketed bullets, below 1.5 is where more serious losses in BC and BC variation often start. The BC will increase and the BC variation decreases up to about Sg = 2.0. An Sg of about 1.7-1.8 at sea level will be above 2.0 at the altitudes ELR is often shot at. That's where the ATip is with the 1:11 Hornady recommends. 1:9 might cause problems late in the barrel's life, but I've seen guys running them with 1:8 to 2600 yards.

The 1:7 to 1:8 the 375CT guys run the 400 Lazers at is to help the BC spread. Sg>2.25 for solids is the general recommendation. The point is even if you succeed in getting them to shoot at 100 yards and your solver tells you some elevation came out of the turret, your score won't increase.

Many will experiment like crazy when they start ELR. After a barrel or two they settle on a load and move forward. Now they can start to learn the barrel life cycle characteristics and how to deal with them.

 

[JB.IC]

That's some serious navel gazing.....

Says the guy who just wrote us a novel lol

 

[Taylorbok]

@SIDS01 thats all good info that I’ll have to process a bit. This is my second tube in this chambering, (first one was just a test on another rifle and had minimal rounds) I had full intention of just feeding it the old A-Tip load. I did and it loved it but I acquired these Lazers and as the saying goes. “Curiosity killed the cat, satisfaction brought it back”

I’m very happy with both loads. I’m gonna test them both out to 2k next week. I don’t really have the proper twist for the 400’s so we’ll see what happens I’ll likely stick with A-tips for now.

I might order another barrel with faster twist and possibly another reamer with a short throat to experiment with.

 

[Taylorbok]

FWIW my twist is actually a 1:8.
I was cleaning last night and decided to double check. and came up with 8. then I went and checked my invoice and sure enough I ordered an 8 so that's a bonus for the 400 Lazers

 

[SIDS01]

You're heading the right direction. Figuring out how solid primary extraction screws up bolt lift as a pressure estimate was insightful. Most just want to convince themselves they're not over pressure and whatever problems they're having are not self inflicted injuries. I also thought the primer measurements were interesting. I use the extractor groove expansion but after I've done a 5x5 pressure ladder the cases have different pressure histories and the results get fuzzy.

Many of the concepts I've presented won't be internalized until you've tested them yourself. They shouldn't be. Testing them far enough to convince yourself it's a dead end might go faster than session after session of pounding your head on the shooting mat trying to force something to work.

Yea, 1:8 changes the story. Some altitude and you might be on to something. Especially while the barrel is fresh.

My thoughts on the key points that make the Lazers so good for BC spread are first they're a conservative design aerodynamically, solids are much stiffer than lead core so they're less likely to bend or engrave unevenly and the bore rider section provides better starting alignment. They work well with short versions of standard 1.5 degree target throats. The load will need to have SDs consistently in the 3-4 fps for 10 shots range or the velocity spread will dominate the ELR vertical and eat some of the BC spread benefit.

On cleaning....

You may have already recognized this, but showing up to a match, or even a test session with a clean barrel puts you in a hole. It'll take a few rounds for the velocities to settle down. Long range cold bore hits become a lot less likely. You can't unsee them, so they stay in your brain even after the chrono tells you they were 20-40 fps slow. I keep a box of foulers loaded from the remnants of those experiments that went nowhere.

Another reason to settle on a load or two early is to figure out their temperature dependence. I use a Harbor Freight infrared thermometer to check the primer temperature and save it in my data book. Wide temperature spreads in the same box of ammo are what you're after to generate that perspective. A couple hundred rounds apart and the barrel wear starts affecting the results. Having a better idea of what that the velocity average is going to be on the first target is huge.